Here, the patient seems to be intolerant to standard metformin. In such cases, modified-release preparations is considered as the most appropriate next step.
There is some evidence that these produce fewer gastrointestinal side-effects in patients intolerant of standard-release metformin.

Metformin is a biguanide and reduces blood glucose levels by decreasing the production of glucose in the liver, decreasing intestinal absorption and increasing insulin sensitivity.
Metformin decreases both the basal and postprandial blood glucose.
Other uses: In Polycystic Ovarian Syndrome (PCOS), Metformin decreases insulin levels, which then decreases luteinizing hormone and androgen levels. Thus acting to normalize the menstruation cycle.

Note:
Metformin is contraindicated in patients with severe renal dysfunction, which is defined as a glomerular filtration rate (GFR) less than 30 ml/min/1.732m2.
Metformin overdose has been associated with hypoglycaemia and lactic acidosis, for this reason, it has a black box warning for lactic acidosis.

Among the above statements, gastric lavage and normal saline IV infusion are the two appropriate interventions for a patient of acute lithium toxicity.

Activated charcoal is not effective after lithium overdose, although gastric lavage should be considered if patients present within 6–8 h.
Where levels are above 3 mmol/l, the use of normal saline to induce diuresis should be considered, although careful monitoring of fluid balance is necessary.
Where levels of lithium are above 4 mmol/l, dialysis is often required. Haemodialysis is preferred, but in a facility where haemodialysis is not possible, peritoneal dialysis may be considered.
Patients should not be discharged until they are asymptomatic and have a serum lithium level less than 1.5 mEq/L.

Loss of vision after consumption of antifreeze is a characteristic presentation of methanol poisoning.

Pathophysiology of methanol toxicity:
When ingested, methanol is absorbed rapidly via the gastrointestinal tract in less than 10 minutes. Methanol is not protein-bound and is absorbed directly into the total body water compartment.
Metabolism occurs mainly in the liver through serial oxidation via alcohol dehydrogenase and aldehyde dehydrogenase but begins with alcohol dehydrogenase present in the gastric mucosa.
Alcohol dehydrogenase oxidizes methanol to formaldehyde, and aldehyde dehydrogenase subsequently oxidizes formaldehyde to formic acid.
Formic acid is the primary toxic metabolite that accounts for the associated anion gap metabolic acidosis and end-organ damage.

Clinical presentation:
Patients who present within the first 12 to 24 hours following ingestion may appear normal, and this is described as the latent period.
Nausea, vomiting, and abdominal pain subsequently ensue, followed by CNS depression and hyperventilation due to metabolic acidosis.
Ocular symptoms associated with retinal toxicity are often evident in the form of blurry vision, decreased visual acuity, photophobia, and “halo vision.”

Treatment:
Treatment options for methanol toxicity include supportive care, fomepizole (Antizole, 4-Methylpyrazole or 4MP), ethanol, dialysis, and folate.

The symptoms of ataxia, slurred speech and blurred vision are all suggestive of phenytoin toxicity. Cimetidine increases the efficacy of phenytoin by reducing its hepatic metabolism.

Phenytoin has a narrow therapeutic index (10-20 mg/L) and its levels are monitored by measuring the total phenytoin concentration.
Cimetidine is an H2 receptor antagonist used in the treatment of peptic ulcers. It acts by decreasing gastric acid secretion.
Cimetidine also has an inhibitory effect on several isoforms of the cytochrome enzyme system including the CYP450 enzymatic pathway. Phenytoin is metabolized by the same cytochrome P450 enzyme system in the liver.
Thus, the simultaneous administration of both these medications leads to an inhibition of phenytoin metabolism and thus increases its circulating levels leading to phenytoin toxicity.

The given clinical scenario is suggestive of myo-neuropathy and is most likely to be caused by colchicine toxicity.
It gives rise to subacute proximal muscle weakness and on occasions can lead to an acute necrotizing myopathy. Creatine phosphokinase may be normal or may be elevated.
Weakness resolves when the drug is discontinued but the neuropathic features remain.
Death is usually a result of respiratory depression and cardiovascular collapse.
Treatment is symptomatic and supportive, and the treatment for colchicine poisoning includes lavage and measures to prevent shock.

Tacrolimus is a calcineurin inhibitor used as an immunosuppressive agent used for prophylaxis of organ rejection post-transplant.

Pharmacology: Calcineurin inhibition leads to reduced T-lymphocyte signal transduction and IL-2 expression. It has a half-life of 12 hours (average).

Other off-label indications for the use of tacrolimus include Crohn disease, graft-versus-host disease (GVHD), myasthenia gravis, rheumatoid arthritis.

Adverse effects of tacrolimus includes:
Cardiovascular: Angina pectoris, cardiac arrhythmias, hypertension
Central nervous system: Abnormal dreams, headaches, insomnia, tremors.
Dermatologic: Acne vulgaris, alopecia, pruritis, rash
Endocrine and metabolic: Decreased serum bicarbonate, decreased serum iron, new-onset diabetes mellitus after transplant (NODAT), electrolyte disturbances.
Gastrointestinal: Abdominal pain, nausea, vomiting, diarrhoea
Genitourinary: Urinary tract infection
Hepatic: Abnormal hepatic function tests
Neuromuscular and skeletal: Arthralgia, muscle cramps
Ophthalmic: Blurred vision, visual disturbance
Otic: Otalgia, otitis media, tinnitus
Renal: Acute renal failure

Other options:
Sirolimus (a macrolide) is an mTOR inhibitor that blocks the response to IL-2 and has a half-life of 12–15 hours.
Azathioprine inhibits purine synthesis, an essential step in the proliferation of white cells and has a half-life of around 5 hours.

The presentation of the patient is typical of chronic lithium toxicity (due to the presence of mainly neurological manifestations). Additional to the blood investigations mentioned, urine analysis, electrolyte levels, and renal function should also be performed. A low urine Anion gap and a low urine specific gravity are highly suggestive of lithium toxicity.
ECG obtained in this patient is likely to show: nonspecific, diffuse ST segment depression with T wave inversion.
Acute lithium toxicity presents with more GI manifestations while, the clinical features of chronic lithium toxicity are mainly neurological and can include:
Coarse tremors (fine tremors are seen in therapeutic levels), hyperreflexia, acute confusion, seizures, and coma.
The management of lithium toxicity is as follows:
Immediate GI decontamination with gastric lavage (in case of acute intoxication)
Saline Administrations: the goal of saline administration is to restore GFR, normalize urine output and enhance lithium clearance.
Haemodialysis remains the mainstay treatment for lithium toxicity as lithium is readily dialyzed because of water solubility, low volume of distribution, and lack of protein binding.
The Extracorporeal Treatments in Poisoning Workgroup (EXTRIP Workgroup) recommendations for dialysis (extracorporeal treatment) in lithium toxicity include:
• Impaired kidney function and lithium levels > 4.0 mEq/L
• Decreased consciousness, seizures, or life-threatening dysrhythmias, regardless of lithium levels
• Levels are > 5.0 mEq/L, significant confusion is noted, or the expected time to reduce levels to < 1.0 mEq/L is more than 36 hours
As post-dialysis rebound elevations in lithium levels have been documented, continuous veno-venous hemofiltration (CVVH) has been advocated.

Different Oral Hypoglycaemic Agents (OHAs) and their respective mechanism(s) of action include:
• Sulfonylureas (such as, glipizide, gliclazide, glimepiride) – bind to ATP sensitive Potassium channels (K – ATP channels) in the ? cells of the islets of the pancreas. Inhibition of these channels lead to an altered resting membrane potential in these cells causing an influx of calcium which increases insulin secretion.
• Meglitinides (like Repaglinide) through a different receptor, they similarly regulate K – ATP channels thereby causing an increase in insulin secretion.
• Biguanides (e.g., Metformin) increase the hepatic AMP-activated protein kinase activity leading to reduced gluconeogenesis and lipogenesis and increased insulin-mediated uptake of glucose in muscles. (it doesn’t increase insulin secretion)
• Thiazolidinediones (rosiglitazone, pioglitazone) bind to PPAR-? and increase peripheral uptake of glucose and decrease hepatic glucose production.
• α-Glucosidase inhibitors (such as acarbose, miglitol, voglibose) competitively inhibit α-glucosidase enzymes in the intestine that digest the dietary starch thus, inhibiting the polysaccharide reabsorption as well as metabolism of sucrose to glucose and fructose.
• DPP-4 inhibitors (sitagliptin, saxagliptin, vildagliptin, linagliptin, alogliptin) prolong the action of glucagon-like peptide. This leads to inhibition of glucagon release, increase in insulin secretion and a decrease in gastric emptying leading to a decrease in blood glucose levels.
• SGLT2 inhibitors (dapagliflozin and canagliflozin) inhibit glucose reabsorption in the proximal tubules of the renal glomeruli leading to glycosuria which in-turn reduces blood glucose levels.
Note: Side effects of pioglitazone are weight gain, pedal oedema, bone loss and precipitation of congestive cardiac failure.

Cyanide poisoning:
Aetiology:
Smoke inhalation, suicidal ingestion, and industrial exposure (specific industrial processes involving cyanide include metal cleaning, reclaiming, or hardening; fumigation; electroplating; and photo processing) are the most frequent sources of cyanide poisoning. Treatment with sodium nitroprusside or long-term consumption of cyanide-containing foods is a possible source.
Cyanide exposure most often occurs via inhalation or ingestion, but liquid cyanide can be absorbed through the skin or eyes. Once absorbed, cyanide enters the blood stream and is distributed rapidly to all organs and tissues in the body. 

Pathophysiology:
Inside cells, cyanide attaches itself to ubiquitous metalloenzymes, rendering them inactive. Its principal toxicity results from inactivation of cytochrome oxidase (at cytochrome a3), thus uncoupling mitochondrial oxidative phosphorylation and inhibiting cellular respiration, even in the presence of adequate oxygen stores.

Presentation:
• ‘Classical’ features: brick-red skin, smell of bitter almonds
• Acute: hypoxia, hypotension, headache, confusion
• Chronic: ataxia, peripheral neuropathy, dermatitis

Management:
• Supportive measures: 100% oxygen, ventilatory assistance in the form of intubation if required.
• Definitive: Hydroxocobalamin (iv) is considered the drug of choice and is approved by the FDA for treating known or suspected cyanide poisoning.
• Coadministration of sodium thiosulfate (through a separate line or sequentially) has been suggested to have a synergistic effect on detoxification.
Mechanism of action of hydroxocobalamin:
• Hydroxocobalamin combines with cyanide to form cyanocobalamin (vitamin B-12), which is renally cleared.
• Alternatively, cyanocobalamin may dissociate from cyanide at a slow enough rate to allow for cyanide detoxification by the mitochondrial enzyme rhodanese.

Lidocaine is an example of class IB antiarrhythmics.

The Vaughan-Williams classification of antiarrhythmics
I: Membrane stabilizing agents
IA: Quinidine, Procainamide, Disopyramide
IB: Lidocaine, Mexiletine
IC: Propafenone, Flecainide
II: β blockers – Propranolol, Esmolol
III: Agents widening AP – Amiodarone, Dronedarone, Dofetilide, Ibutilide, Sotalol
IV: Calcium channel blockers – Verapamil, Diltiazem
V: Miscellaneous – Digoxin, adenosine, magnesium

The next step in managing this patient is to give 10 mg and continue administering in 10 mg increments each hour until symptoms are under control.

Methadone alleviates opioid withdrawal symptoms and reduces cravings. Methadone is useful for detoxification from longer-acting opioids such as morphine or methadone itself.
Methadone should be used with caution if the patient has:
Respiratory deficiency
Acute alcohol dependence
Head injury
Treatment with monoamine oxidase inhibitors (MAOIs)
Ulcerating colitis or Crohn’s disease
Severe hepatic impairment
The dose must be reviewed on a daily basis and adjusted based upon how well the symptoms are controlled and the presence of side effects. The greater the dose of opioids used by the patient, the greater the dose of methadone required to control withdrawal symptoms.

To avoid the risk of overdose in the first days of treatment The recommended dosing of methadone is 30mg in two doses of 15mg morning and evening.

It is important to note that a methadone dose equivalent to what the patient reports they are taking should never be given.
It is rare to need more than 40 mg per 24 hours: beware of overdosing which can lead to respiratory arrest.

Cefalexin should be avoided in this patient.
This patient is known to have a severe penicillin allergy. None of the above antibiotics are penicillin based. However, 0.5 – 6.5% of patients who are proven to have an IgE mediated penicillin allergy will also be allergic to cephalosporins, including cefalexin.

Penicillin, cephalosporins, and carbapenems are all members of the beta-lactam group of antibiotics and share a common beta-lactam ring. There is, therefore, a small risk of allergy cross-over between all these antibiotics. The rates of allergy cross-over are lower with second and third-generation cephalosporins than first-generation cephalosporins such as cefalexin.

It is important to question the patient carefully to ascertain what symptoms they had on exposure to penicillin. Symptoms such as an urticarial rash or itching make it more likely that they have an IgE mediated allergy.

Agitation, hypomania and suicidal intent within a few days after initiating corticosteroid therapy is highly suggestive of a diagnosis of corticosteroid-induced psychosis.

In some patients corticosteroid related psychosis has been diagnosed up to 12 weeks or more after commencing therapy.

Euphoria and hypomania are considered to be the most common psychiatric symptoms reported during short courses of steroids.
During long-term treatment, depressive symptoms were the most common.
Higher steroid doses appear to carry an increased risk for such adverse effects; however, there is no significant relationship between dose and time to onset, duration, and severity of symptoms.

Management: Reduction or cessation of corticosteroids is the mainstay of treatment for steroid psychosis. For those patients who cannot tolerate this reduction/cessation of steroids, mood stabilizers may be of some benefit.

The principal mechanism by which strontium inhibits osteoclast activity is by enhancing the secretion of osteoprotegerin (OPG) and by reducing the expression of the receptor activator of nuclear factor κB ligand (RANKL) in osteoblasts.

Osteoporosis is defined as low bone mineral density caused by altered bone microstructure ultimately predisposing patients to low-impact, fragility fractures.

Management:
Vitamin D and calcium supplementation should be offered to all women unless the clinician is confident they have adequate calcium intake and are vitamin D replete
Alendronate is the first-line treatment. Around 25% of patients cannot tolerate alendronate, usually due to upper gastrointestinal problems. These patients should be offered risedronate or etidronate.
Strontium ranelate and raloxifene are recommended if patients cannot tolerate bisphosphonates.
Other medications that are useful in the treatment of osteoporosis are denosumab, teriparatide, raloxifene, etc.

The use of nitrates and nicorandil concomitantly with sildenafil citrate is contraindicated.

Sildenafil (Viagra) is a phosphodiesterase type V inhibitor used in the treatment of impotence.

Contraindications
– Patients taking nitrates and related drugs such as nicorandil
– Hypotension
– Recent stroke or myocardial infarction (NICE recommend waiting 6 months)

Side-effects:
Visual disturbances e.g. cyanopsia, non-arthritic anterior ischaemic Neuropathy
Nasal congestion
Flushing
Gastrointestinal side-effects
Headache

Renal elimination of a drug has no role in altering the bioavailability of a drug.
The bioavailability of a drug is the proportion of the drug which reaches systemic circulation.
Mathematically, bioavailability is the AUCoral/AUCiv x 100%, where AUC = area under the concentration-time curve following a single (oral or iv) dose.

Other options are true:
By definition, the bioavailability of a drug given intravenously is 100%.
Drugs given orally that undergo high pre-systemic (first-pass) metabolism in the liver or gut wall have a low bioavailability e.g. lidocaine.
Bioavailability is also affected by the degree of absorption from the gut and this can change depending on gut motility and administration of other drugs.

The cytochrome p450 3A4 enzyme system in the liver is affected by grapefruit juice.

Patients taking antihistamines should be advised to avoid drinking grapefruit juice. This is because constituents of grapefruit juice such as naringin and bergamottin inhibit CYP3A4 in the liver, particularly at high doses, leading to decreased drug elimination via hepatic metabolism and can increase potential drug toxicities.

Inhibition of this enzyme system leads to reduced metabolism of antihistamines leading to an increased incidence of side effects like excessive drowsiness and nausea as in this patient.

The most appropriate intervention in this patient is intravenous hydroxocobalamin.
The clinical scenario provided is suggestive of acute cyanide toxicity secondary to burning plastics in the house fire.
Cyanide ions inhibit mitochondrial cytochrome oxidase, preventing aerobic respiration. This manifests in normal oxygen saturations, a high pO2 and flushing (or ‘brick red’ skin) brought on by the excess oxygenation of venous blood. In the question above it is important to note that the blood gas sample given is venous rather than arterial. His blood gas also demonstrates an increased anion gap, consistent with his high lactate (generated by anaerobic respiration due to the inability to use available oxygen).

The recommended treatment for moderate cyanide toxicity in the UK is one of three options: sodium thiosulfate, hydroxocobalamin or dicobalt edetate.

Among the options given is hydroxocobalamin and this is, therefore, the correct answer. Hydroxocobalamin additionally has the best side-effect profile and speed of onset compared with other treatments for cyanide poisoning.

Other options:
– Intubation would be appropriate treatment in the context of airway burns but this patient has no evidence of these, although close monitoring would be advised.
– High-flow oxygen is the treatment for carbon monoxide poisoning – a sensible differential, but this man’s very high lactate and high venous pO2 fit better with cyanide toxicity. Intravenous dexamethasone would be another treatment for airway oedema once an endotracheal tube had been placed.
– Intravenous sodium nitroprusside is a treatment for high blood pressure that can cause cyanide poisoning, and would, therefore, be inappropriate.

Note:

Cyanide may be used in insecticides, photograph development and the production of certain metals. Toxicity results from reversible inhibition of cellular oxidizing enzymes
Clinical presentation:
Classical features: brick-red skin, the smell of bitter almonds
Acute: hypoxia, hypotension, headache, confusion
Chronic: ataxia, peripheral neuropathy, dermatitis

Management:
Supportive measures: 100% oxygen
Definitive: hydroxocobalamin (intravenously), also a combination of amyl nitrite (inhaled), sodium nitrite (intravenously), and sodium thiosulfate (intravenously).

The most probable diagnosis for this patient is delirium tremens due to alcohol withdrawal, which should be treated as a medical emergency. 
Delirium tremens is a hyperadrenergic state and is often associated with tachycardia, hyperthermia, hypertension, tachypnoea, tremor, and mydriasis.
Treatment:
– The most common and validated treatment for alcohol withdrawal is benzodiazepine: first-line treatment includes oral lorazepam.
– If the symptoms persist, or the medication is refused, parenteral lorazepam, haloperidol or olanzapine should be given.
– Central-acting, alpha-2 agonists such as clonidine and dexmedetomidine should not be used alone for the treatment of alcohol withdrawal.
– It is also recommended to avoid using alcohol, antipsychotics, anticonvulsants, beta-adrenergic receptor blockers, and baclofen for the treatment of alcohol withdrawal as there are not enough studies to support the safety of these.

The total daily morphine dose is 30 x 2 = 60 mg. Therefore, the breakthrough dose should be one-sixth of this, 10 mg.

Among the options provided, hypothermia is not a symptom of opioid withdrawal.

Symptoms of opioid withdrawal include dysphoric mood, yawning, insomnia, muscle aches, lacrimation/rhinorrhoea, papillary dilatation, piloerection, fever, sweating, nausea/vomiting, diarrhoea.
If the patient is having an opioid withdrawal reaction, then give 10 mg of methadone syrup and wait about 60 min to determine its effect.

COWS (Clinical Opioid Withdrawal Scale) assessment for opioid withdrawal is commonly used to determine the severity of opioid withdrawal.

Tiotropium is a specific long-acting antimuscarinic agent indicated as maintenance therapy for patients with COPD (chronic obstructive pulmonary disease).
It should be used cautiously in patients with narrow-angle glaucoma, prostatic hyperplasia or bladder neck obstruction.
The most frequently encountered adverse effects of tiotropium include pharyngitis, bronchitis, sinusitis, dry mouth, cough, and headaches. Paradoxical bronchospasm may also occur as a rare side-effect.
Dry mouth occurs in up to 14% of patients taking tiotropium, in keeping with its anticholinergic profile.
Rarer side-effects include tachycardia, blurred vision, urinary retention, and constipation.

Tumour lysis syndrome (TLS) occurs most notably in patients with haematological malignancies including, Non-Hodgkin’s Lymphoma (NHL) and Acute Lymphocytic Leukaemia (ALL).
Risk factors for TLS include:
• Large tumour burden
• Sensitivity of the tumour to chemotherapy
• Rapid tumour growth rate
TLS is characterized by:
• Hyperuricemia
• Hyperkalaemia
• Hyperphosphatemia
• Hypocalcaemia
Treatment of TLS:
• Allopurinol: It is a xanthine oxidase inhibitor, it reduces the conversion of nucleic acid by-products to uric acid. Thus, it prevents urate nephropathy and subsequent oliguric renal failure. Note: dose reduction is essential in renal failure or if given along with mercaptopurine or azathioprine.
Alternatives to Allopurinol: Febuxostat; Rasburicase are useful in patients with hyperuricemia.
• Hydration
• Diuresis: Should be considered in well hydrated patients with insufficient urine output. Furosemide to be considered in normo-volemic patients with hyperkalaemia. Urine alkalization can be considered for promoting alkaline diuresis.
• Treatment of electrolyte imbalances including hyperkalaemia, hyperphosphatemia, and hypocalcaemia.
• Dialysis can be considered in refractory cases.

The most probable diagnosis in this patient is an oculogyric crisis, that is most appropriately managed with procyclidine or benztropine (antimuscarinic).

An oculogyric crisis is a dystonic reaction to certain drugs or medical conditions.

Features include:
Restlessness, agitation
Involuntary upward deviation of the eyes

Causes:
Phenothiazines
Haloperidol
Metoclopramide
Postencephalitic Parkinson’s disease

Management:
Intravenous antimuscarinic agents like benztropine or procyclidine, alternatively diphenhydramine or ethopropazine maybe used.

Digoxin acts by inhibiting the Na+/K+ ATPase pump.
Digoxin is a cardiac glycoside now mainly used for rate control in the management of atrial fibrillation. As it has positive inotropic properties it is sometimes used for improving symptoms (but not mortality) in patients with heart failure.

Mechanism of action:
It decreases the conduction through the atrioventricular node which slows the ventricular rate in atrial fibrillation and atrial flutter.
It increases the force of cardiac muscle contraction due to inhibition of the Na+/K+ ATPase pump. It also stimulates the vagus nerve.

Digoxin toxicity:
Plasma concentration alone does not determine whether a patient has developed digoxin toxicity. The likelihood of toxicity increases progressively from 1.5 to 3 mcg/l.
Clinical feature of digoxin toxicity include a general feeling of unwell, lethargy, nausea & vomiting, anorexia, confusion, xanthopsia, arrhythmias (e.g. AV block, bradycardia), and gynaecomastia

Precipitating factors:
Hypokalaemia
Increasing age
Renal failure
Myocardial ischemia
Hypomagnesaemia, hypercalcemia, hypernatremia, acidosis
Hypoalbuminemia
Hypothermia
Hypothyroidism
Drugs: amiodarone, quinidine, verapamil, diltiazem, spironolactone (competes for secretion in the distal convoluted tubule, therefore, reduce excretion), ciclosporin. Also, drugs that cause hypokalaemia e.g. thiazides and loop diuretics.

Management of digoxin toxicity:
Digibind
Correct arrhythmias
Monitor and maintain potassium levels within the normal limits.

Oxycodone is a safer opioid to use in patients with moderate to end-stage renal failure.
Active metabolites of morphine accumulate in renal failure which means that long-term use is contraindicated in patients with moderate/severe renal failure.
These toxic metabolites can accumulate causing toxicity and risk overdose.
Oxycodone is mainly metabolised in the liver and thus safer to use in patients with moderate to end-stage renal failure with dose reductions.
Adverse effects:
Constipation is the most common overall side effect. Others include: asthenia, dizziness, dry mouth, headache, nausea, pruritus, etc.

Medications in renal failure:
Drugs to be avoided in patients with renal failure
Antibiotics: tetracycline, nitrofurantoin
NSAIDs
Lithium
Metformin
Drugs that require dose adjustment:
Most antibiotics including penicillin, cephalosporins, vancomycin, gentamicin, streptomycin
Digoxin, atenolol
Methotrexate
Sulphonylureas
Furosemide
Opioids
Relatively safe drugs:
Antibiotics: erythromycin, rifampicin
Diazepam
Warfarin

The most probable diagnosis in this patient is serotonin syndrome.

The serotonin syndrome is a cluster of symptoms and signs (range from barely perceptible tremor to life-threatening hyperthermia and shock).
It may occur when SSRIs such as citalopram, escitalopram, fluoxetine, fluoxetine, paroxetine, and sertraline that impair the reuptake of serotonin from the synaptic cleft into the presynaptic neuron are taken in combination with monoamine oxidase inhibitors or tricyclic antidepressants. It has also been reported following an overdose of selective serotonin reuptake inhibitors (SSRIs) alone.

Treatment:
Most cases of serotonin syndrome are mild and will resolve with removal of the offending drug alone.
After stopping all serotonergic drugs, management is largely supportive and aimed at preventing complications.
Patients frequently require sedation, which is best facilitated with benzodiazepines.
Antipsychotics should be avoided because of their anticholinergic properties, which may inhibit sweating and heat dissipation.

The patient (known case of acromegaly) seems to have developed cholelithiasis (presenting with right upper quadrant pain) probably due to octreotide.

It is a long-acting analogue of somatostatin which is released from D cells of the pancreas and inhibits the release of growth hormone, glucagon, and insulin.

Uses
– Acute treatment of variceal haemorrhage
– Acromegaly
– Carcinoid syndrome
– Prevent complications following pancreatic surgery
– VIPomas
– Refractory diarrhoea

Adverse effects
Gallstones (secondary to biliary stasis)

Other options:
– Bromocriptine – a dopamine agonist with side effects arising from its stimulation of the brain vomiting centre.
– Desmopressin – predominantly used in patients with diabetes insipidus by increasing the presence of aquaporin channels in the distal collecting duct to increase water reabsorption from the kidneys. The main side effects include headache and facial flushing due to hypertension.
– Metformin – mainly reduces hepatic gluconeogenesis in patients with type 2 diabetes, common side effects include diarrhoea, vomiting, and lactic acidosis
– Levothyroxine – synthetic thyroxine used in patients with hypothyroidism, common side effects result from incorrect dosing and mimic the symptoms of hyperthyroidism.

Hormone replacement therapy (HRT) involves the use of a small dose of oestrogen, combined with a progestogen (in women with a uterus), to help alleviate menopausal symptoms. The main indication is the control of vasomotor symptoms. The other indications, such as reversal of vaginal atrophy and prevention of osteoporosis, should be treated with other agents as first-line therapies.

Drug metabolism can be broadly classified into:
Phase I (functionalization) reactions: also termed non-synthetic reactions, they include oxidation, reduction, hydrolysis, cyclization and de-cyclization. The most common and vital reactions are oxidation reactions. (Of the given enzymes only Alcohol dehydrogenase is involved in phase I drug metabolism. Succinate dehydrogenase, is a vital enzyme involved in the Kreb’s cycle and the mitochondrial electron transport chain). They are mainly catalysed by Cytochrome P-450 enzyme.

Phase II (conjugation) reactions: occur following phase I reactions, they include reactions: glucuronidation and sulphate conjugation, etc. They are mostly catalysed by UDP-glucuronosyltransferase enzyme. Other phase II enzymes include: sulfotransferases, N-acetyltransferases, glutathione S-transferases and methyltransferases.

Carbon monoxide (CO) poisoning:
It is considered as the great imitator of other diseases as the patients present with a myriad of symptoms. The carbon monoxide diffuses rapidly across the pulmonary capillary membrane binding to the haem molecule with a very high affinity (240 times that of oxygen) forming carboxy-haemoglobin (COHb). Non-smokers have a baseline COHb of ,3% while smokers have a baseline COHb of 10-15%.

Clinical features of carbon monoxide toxicity:
Headache: 90% of cases (most common clinical feature)
Nausea and vomiting: 50%
Vertigo: 50%
Confusion: 30%
Subjective weakness: 20%
Severe toxicity: ‘pink’ skin and mucosa, hyperpyrexia, arrhythmias, extrapyramidal features, coma, death
Cherry red skin is a sign of severe toxicity and is usually a post-mortem finding.
Management
• 100% oxygen
• Hyperbaric oxygen therapy (HBOT)

The use of Hyperbaric oxygen therapy (HBOT) for treatment mild to moderate CO poisoning is not routine.
The selection criteria for HBOT in cases of CO poisoning include:
• COHb levels > 20-25%
• COHb levels > 20% in pregnant patient
• Loss of consciousness
• Severe metabolic acidosis (pH <7.1)
• Evidence of end-organ ischemia (e.g., ECG changes, chest pain, or altered mental status)

Bradycardia and miosis should be anticipated following the administration of anticholinesterases.

Anticholinesterase agents include the following medications:
– Pyridostigmine, neostigmine, and edrophonium which play a significant role in the diagnosis and the management of myasthenia gravis.
– Rivastigmine, galantamine and donepezil are cholinesterase inhibitors found to be significantly useful in the management of Alzheimer’s disease.

Mechanism of action and pharmacological effects:
Inhibition of cholinesterase increases the level and the duration of action of acetylcholine within the synaptic cleft.

Thus, cholinergic effects such as a reduction in heart rate (bradycardia), miosis (pupillary constriction), increased secretions, increased gastrointestinal motility and reduction in BP may occur with anticholinesterases.

Toxins such as organophosphates and carbamates also are primarily anticholinergic and cause the following typical SLUDGE symptoms:
– Salivation
– Lacrimation
– Urination
– Diaphoresis
– Gastrointestinal upset
– Emesis

Among the given options the most appropriate management in this patient would be ethanol and haemodialysis.

Ethanol competes with ethylene glycol for alcohol dehydrogenase and thus, helps manage a patient with ethylene glycol toxicity.

Ethylene glycol is a type of alcohol used as a coolant or antifreeze
Features of toxicity are divided into 3 stages:
Stage 1: (30 min to 12 hours after exposure) Symptoms similar to alcohol intoxication: confusion, slurred speech, dizziness (CNS depression)
Stage 2: (12 – 48 hours after exposure) Metabolic acidosis with a high anion gap and high osmolar gap. Also tachycardia, hypertension
Stage 3: (24 – 72 hours after exposure) Acute renal failure

Management has changed in recent times:
Fomepizole, an inhibitor of alcohol dehydrogenase, is now used first-line in preference to ethanol.
Ethanol has been used for many years works by competing with ethylene glycol for the enzyme alcohol dehydrogenase this limits the formation of toxic metabolites (e.g. glycolaldehyde and glycolic acid) which are responsible for the hemodynamic/metabolic features of poisoning.
Haemodialysis has a role in refractory cases.

The presence of tinnitus, fever and hyperventilation are clues for aspirin (salicylate) toxicity.
Clinical Presentation of salicylate toxicity can include:
• Pulmonary manifestations include: Hyperventilation, hyperpnea, severe dyspnoea due to noncardiogenic pulmonary oedema, fever and dyspnoea due to aspiration pneumonitis
• Auditory symptoms caused by the ototoxicity of salicylate poisoning include: Hard of hearing and deafness, and tinnitus (commonly encountered when serum salicylate concentrations exceed 30 mg/dL).
• Cardiovascular manifestations include: Tachycardia, hypotension, dysrhythmias – E.g., ventricular tachycardia, ventricular fibrillation, multiple premature ventricular contractions, asystole – with severe intoxication, Electrocardiogram (ECG) abnormalities – E.g., U waves, flattened T waves, QT prolongation may reflect hypokalaemia.
• Neurologic manifestations include: CNS depression, with manifestations ranging from somnolence and lethargy to seizures and coma, tremors, blurring of vision, seizures, cerebral oedema – With severe intoxication, encephalopathy
• GI manifestations include: Nausea and vomiting, which are very common with acute toxicity, epigastric pain, GI haemorrhage – More common with chronic intoxication, intestinal perforation, pancreatitis, hepatitis – Generally in chronic toxicity; rare in acute toxicity, Oesophageal strictures – Reported as a very rare delayed complication
• Genitourinary manifestations include: Acute kidney injury (NSAID induced Nephropathy) is an uncommon complication of salicylate toxicity, renal failure may be secondary to multisystem organ failure.
• Hematologic effects may include prolongation of the prothrombin and bleeding times and decreased platelet adhesiveness. Disseminated intravascular coagulation (DIC) may be noted with multisystem organ failure in association with chronic salicylate toxicity.
• Electrolyte imbalances like: Dehydration, hypocalcaemia, acidaemia, Syndrome of inappropriate antidiuretic hormone secretion (SIADH), hypokalaemia
Management of these patients should be done in the following manner:
• Secure Airway, Breathing, and Circulation
• Supportive therapy
• GI decontamination
• Urinary excretion and alkalization
• Haemodialysis

The rationale behind the use of sodium bicarbonate is that it increases the alkalinity of the urine promoting lithium excretion. The preferred treatment in severe cases would be haemodialysis.

Lithium is a mood-stabilizing drug used most commonly prophylactically in bipolar disorder but also as an adjunct in refractory depression. It has a very narrow therapeutic range (0.4-1.0 mmol/L) and a long plasma half-life being excreted primarily by the kidneys. Lithium toxicity generally occurs following concentrations > 1.5 mmol/L.

Toxicity may be precipitated by dehydration, renal failure, diuretics (especially Bendroflumethiazide), ACE inhibitors, NSAIDs and metronidazole.

Features of toxicity
Coarse tremor (a fine tremor is seen in therapeutic levels)
Hyperreflexia
Acute confusion
Seizure
Coma

Management
Mild-moderate toxicity may respond to volume resuscitation with normal saline
Haemodialysis may be needed in severe toxicity
Sodium bicarbonate is sometimes used but there is limited evidence to support this. By increasing the alkalinity of the urine it promotes lithium excretion.

Sarin acts by inhibiting acetylcholinesterase.

Sarin gas is a highly toxic synthetic organophosphorus compound which causes inhibition of the enzyme acetylcholinesterase
Sarin gas is a highly toxic synthetic organophosphorus compound which causes inhibition of the enzyme acetylcholinesterase. This results in high levels of acetylcholine (ACh).

The effects of excessive ACh can be remembered by the mnemonic DUMBELLS:
Diarrhoea
Urination
Miosis/muscle weakness
Bronchorrhea/Bradycardia
Emesis
Lacrimation
Salivation/sweating

Organophosphate insecticide poisoning:
One of the effects of organophosphate poisoning is inhibition of acetylcholinesterase
Features can be predicted by the accumulation of acetylcholine (mnemonic = SLUD)
Salivation
Lacrimation
Urination
Defecation/diarrhoea
cardiovascular: hypotension, bradycardia
miosis, muscle fasciculation.

Organophosphate poisoning is treated with the anti-muscarinic atropine.

Confusion and pink mucosae are typical features of CO poisoning.
The patient often presents, most commonly with headaches, and other symptoms like malaise, nausea, and dizziness.

Carbon monoxide (CO) poisoning, considered as the great imitator of other diseases as the patients present with a myriad of symptoms. The carbon monoxide diffuses rapidly across the pulmonary capillary membrane binding to the haem molecule with a very high affinity (240 times that of oxygen) forming carboxy-haemoglobin (COHb). Non-smokers have a baseline COHb of ,3% while smokers have a baseline COHb of 10-15%.

Features of carbon monoxide toxicity
– Headache: 90% of cases
– Nausea and vomiting: 50%
– Vertigo: 50%
– Confusion: 30%
– Subjective weakness: 20%
– Severe toxicity: ‘pink’ skin and mucosae, hyperpyrexia, arrhythmias, extrapyramidal features, coma, death

Treatment:
Use of Hyperbaric oxygen therapy (HBOT) for treating mild to moderate CO poisoning is not routine.
The selection criteria for HBOT in cases of CO poisoning include:
• COHb levels > 20-25%
• COHb levels > 20% in pregnant patient
• Loss of consciousness
• Severe metabolic acidosis (pH <7.1)
• Evidence of end-organ ischemia (e.g., ECG changes, chest pain, or altered mental status)

Both fibrates and nicotinic acid have been associated with myositis, especially when combined with a statin. However, the Committee on Safety of Medicines has produced guidance which specifically warns about the concomitant prescription of fibrates with statins concerning muscle toxicity.

Bezafibrate: It is a fibric acid derivative (fibrate) that has been used as a class of agents known to decrease triglyceride levels while substantially increasing HDL-C levels.
Pharmacological effects:
– Increases VLDL catabolism by increasing lipoprotein and hepatic triglyceride lipase.
– Decreases triglyceride synthesis by inhibiting acetyl-CoA reductase.
– Decreases cholesterol synthesis by inhibiting HMG-CoA reductase.

Side effects:
– Hypersensitivity
– Primary biliary cirrhosis
– Pre-existing gallbladder disease
– Concurrent use with HMG-CoA inhibitors (statins) can produce myopathy
– Hepatic/renal impairment in a patient warrants dose adjustment as this drug is primarily excreted via the renal mechanism.

Contraindications: Concurrent use of MAO inhibitors, hypersensitivity, pre-existing cholestasis, and pregnancy.

Use: It can be used to treat Barth syndrome (characterized by dilated cardiomyopathy, neutropenia (presenting with recurrent infections), skeletal myopathy and short stature)

Ethanol competes with ethylene glycol for alcohol dehydrogenase and thus, helps manage a patient with ethylene glycol toxicity.

Ethylene glycol is a type of alcohol used as a coolant or antifreeze
Features of toxicity are divided into 3 stages:
Stage 1: (30 min to 12 hours after exposure) Symptoms similar to alcohol intoxication: confusion, slurred speech, dizziness (CNS depression)
Stage 2: (12 – 48 hours after exposure) Metabolic acidosis with a high anion gap and high osmolar gap. Also tachycardia, hypertension
Stage 3: (24 – 72 hours after exposure) Acute renal failure

Management has changed in recent times:
Fomepizole, an inhibitor of alcohol dehydrogenase, is now used first-line in preference to ethanol.
Ethanol has been used for many years works by competing with ethylene glycol for the enzyme alcohol dehydrogenase this limits the formation of toxic metabolites (e.g. glycolaldehyde and glycolic acid) which are responsible for the hemodynamic/metabolic features of poisoning.
Haemodialysis has a role in refractory cases.

N-acetylcysteine depletes glutathione reserves by providing cysteine, which is an essential precursor in glutathione production.

Glutathione within the liver can normally detoxify these minuscule quantities of NAPQI and prevent tissue damage.
N-acetylcysteine (NAC) is the mainstay of therapy for acetaminophen toxicity.

Paracetamol overdose:
The liver normally conjugates paracetamol with glucuronic acid/sulphate. During an overdose, the conjugation system becomes saturated leading to oxidation by cytochrome P450 (predominately CYP2E1) mixed-function oxidases. This produces a toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI).

Normally glutathione acts as a defence mechanism by conjugating with the toxin forming the non-toxic mercapturic acid. If glutathione stores run-out, the toxin forms covalent bonds with cell proteins, denaturing them and leading to cell death.

Other uses: In COPD, cystic fibrosis, and other lung conditions, nebulized NAC has mucolytic, anti-inflammatory, and antioxidant properties.

Moxonidine and alpha-methyl dopa are centrally acting antihypertensives and modify blood pressure through modifying sympathetic activity.

Other options:
Verapamil is a calcium antagonist.
Minoxidil and hydralazine are both vasodilators.
Phenoxybenzamine is an alpha-blocker.

Adverse effects:
Dry mouth and somnolence were the most frequently reported adverse events, followed by headache, dizziness, nausea and allergic skin reactions.

The most appropriate treatment in this patient would be to stop warfarin therapy and keep the patient under observation.

The drugs that lead to enhanced potency of warfarin include: disulfiram, trimethoprim-sulphamethoxazole, metronidazole, phenylbutazone, aspirin, heparin, and clofibrate.
Liver disease, thrombocytopenia, hyperthyroidism also increase the oral anticoagulant potency.
If the patient has minor bleeding and the international normalized ratio (INR) is >6.0, warfarin should be stopped; the INR should be rechecked daily and in addition to the stoppage of warfarin, vitamin K 2.5 mg oral or 0.5 mg intravenously should also be administered.
In a patient with INR of 2.0 or 3.0, it takes two or three times longer for that individual’s blood to clot than someone who is not taking any anticoagulants. Most patients on warfarin have an INR goal of 2 to 3.

If there is major bleeding then prothrombin complex concentrates 50 u/kg or fresh-frozen plasma 15 ml/kg may be considered.

Memantine is an antagonist of the NMDA (N-Methyl-D-Aspartate)-receptor subtype of glutamate receptor. It is used to slow the neurotoxicity thought to be involved in Alzheimer’s disease and other neurodegenerative diseases.

Drug interactions:
When given concomitantly with other NMDA-receptor antagonists (e.g., ketamine, amantadine) increase the risk of psychosis.
Dopamine agonists, L-dopa, and anticholinergics enhance effects of memantine.
Antispasmodics (e.g., baclofen)  enhance effects, as memantine has some antispasmodic effects.
Drugs excreted by cationic transporters in the kidney (e.g. quinine, cimetidine, ranitidine) reduce excretion.

Common adverse effects include dizziness, headache, confusion, diarrhoea, and constipation.

Androgen deprivation therapy (ADT) for prostate cancer:

Goserelin (Zoladex) is a synthetic gonadotropin-releasing hormone (GnRH) analogue; chronic stimulation of goserelin results in suppression of LH, FSH serum levels thereby preventing a rise in testosterone.

Dosage form: 3.6 mg/10.8mg implants.

Adverse effects include flushing, sweating, diarrhoea, erectile dysfunction, less commonly, rash, depression, hypersensitivity, etc.

The blood investigations in this patient reveal hyponatremia as well as hypokalaemia. Among the options provided, Bendroflumethiazide therapy can cause the above presentation with the electrolyte disturbances.
Note:
– Spironolactone is a potassium-sparing diuretic that is associated with hyperkalaemia.
– Enalapril therapy can cause side effects of dizziness, hypotension, cough, and rarely a rash.
– Felodipine therapy can cause side effects of dizziness, headache, cough, and palpitations.

Drug metabolism can be broadly classified into:
Phase I (functionalization) reactions: also termed non-synthetic reactions, they include oxidation, reduction, hydrolysis, cyclization and de-cyclization. The most common and vital reactions are oxidation reactions. (Of the given enzymes only Alcohol dehydrogenase is involved in phase I drug metabolism. Succinate dehydrogenase, is a vital enzyme involved in the Kreb’s cycle and the mitochondrial electron transport chain). They are mainly catalysed by Cytochrome P-450 enzyme.

Phase II (conjugation) reactions: occur following phase I reactions, they include reactions: glucuronidation and sulphate conjugation, etc. They are mostly catalysed by UDP-glucuronosyltransferase enzyme. Other phase II enzymes include: sulfotransferases, N-acetyltransferases, glutathione S-transferases and methyltransferases.

Carbimazole is used to treat hyperthyroidism. Carbimazole is a pro-drug as after absorption it is converted to the active form, methimazole. Methimazole prevents thyroid peroxidase enzyme from coupling and iodinating the tyrosine residues on thyroglobulin, hence reducing the production of the thyroid hormones T3 and T4 (thyroxine).

Temazepam is an orally available benzodiazepine used in the therapy of insomnia.
The soporific activity of the benzodiazepines is mediated by their ability to enhance gamma-aminobutyric acid (GABA) mediated inhibition of synaptic transmission through binding to the GABA-A receptor.
The recommended initial dose for insomnia is 7.5 mg before bedtime, increasing as needed to a maximum dose of 30 mg.

The most common side effects of temazepam are dose-related and include daytime drowsiness, lethargy, ataxia, dysarthria, and dizziness.
Tolerance develops to these side effects, but tolerance may also develop to the effects on insomnia.

The blood gas analysis provided above is suggestive of a mixed respiratory alkalosis and metabolic acidosis characteristic of salicylate overdose.

Pathophysiology:
The direct stimulation of the cerebral medulla causes hyperventilation and respiratory alkalosis.
As it is metabolized, it causes an uncoupling of oxidative phosphorylation in the mitochondria.
Lactate levels then increase due to the increase in anaerobic metabolism. This, along with a slight contribution from the salicylate metabolites result in metabolic acidosis.

Tinnitus is characteristic and salicylate ototoxicity may produce deafness. Other neurological sequelae include encephalopathy and agitation, seizures and CNS depression and coma. Cardiovascular complications include tachycardia, hypotension, and dysrhythmias (VT, VF, and asystole).

Sodium cromoglycate principally acts by inhibiting the degranulation of mast cells triggered by the interaction of antigen and IgE.
The inhibitory effect on mast cells appears to be cell-type specific since cromoglycate has little inhibitory effect on mediator release from human basophils.
Thus, it inhibits the release of histamine, leukotrienes, and slow-reacting substance of anaphylaxis from mast cells by inhibiting degranulation following exposure to reactive antigens.

Adverse effects include cough, flushing, palpitation, chest pain, nasal congestion, nausea, fatigue, migraine, etc.