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

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)

Excessive sweating points towards a morphine overdose.

Morphine is considered the classic opioid analgesic with which other painkillers are compared. Like other medications in this class, morphine has an affinity for delta, kappa, and mu-opioid receptors.
Most commonly used in pain management, morphine provides major relief to patients afflicted with pain.

Among the more common adverse effects of morphine use is constipation. Other side effects include nausea, vomiting, drowsiness, and confusion. Psychological and physical dependence may occur.

Other side effects include bronchospasm, angioedema, urinary retention, ureteric or biliary spasm, dry mouth, sweating, rash, facial flushing, vertigo, tachycardia, bradycardia, palpitations, orthostatic hypotension, hypothermia, restlessness, mood change, hallucinations, seizures (adults and children) and miosis, headache and allergic reactions (including anaphylaxis) and decreased libido or potency.

Raised intracranial pressure occurs in some patients. Muscle rigidity may occur with high doses. Elevated liver enzymes may occur due to biliary sphincter constriction. Large doses can lead to respiratory depression, circulatory failure, and coma.

Treatment of opioid overdose:
Initial treatment of overdose begins with supportive care.
Naloxone is a pure competitive antagonist of opiate receptors and has no agonistic activity. The drug is relatively safe and can be administered intravenous, intramuscular, subcutaneous or via the endotracheal tube.
Alternatively, nalmefene and naltrexone maybe considered.

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

Clozapine can cause neutropenia or agranulocytosis.

Clozapine is an atypical antipsychotic used in the treatment of schizophrenia, and in patients who are intolerant to, or unresponsive to other antipsychotics.

It is a weak D2-receptor and D1-receptor blocking activity, with noradrenolytic, anticholinergic, and antihistaminic properties.

Many antipsychotic drugs can occasionally cause bone marrow depression, but agranulocytosis is particularly associated with clozapine.

Other side effects include:
Hypotension, tachycardia
Fever, sedation, seizures (with high doses)
Appetite increase
Constipation
Heartburn
Weight gain
Extrapyramidal symptoms
Agranulocytosis
Neuroleptic malignant syndrome

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.

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)

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.

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

MDMA commonly known as ecstasy or molly, is a psychoactive drug primarily used as a recreational drug. The desired effects include altered sensations, increased energy, empathy, and pleasure. Features of MDMA abuse include hyponatraemia, tachycardia, hyperventilation, and hyperthermia.

Metabolic acidosis is associated with cocaine overdose.
In overdose, cocaine leads to agitation, tachycardia, hypertension, sweating, hallucinations, and finally convulsions.
Metabolic acidosis, hyperthermia, rhabdomyolysis, and ventricular arrhythmias also occur.
Chronic use may be associated with premature coronary artery disease, dilated cardiomyopathy, and increased risk of cerebral haemorrhage.
There are 3 stages for acute cocaine toxicity:
Stage I: CNS symptoms of headache, vertigo, pseudo hallucinations, hyperthermia, hypertension.
Stage II: increased deep tendon reflexes, tachypnoea, irregular breathing, hypertension.
Stage III: Areflexia, coma, fixed and dilated pupils, hypotension, ventricular fibrillation, apnoea, and respiratory failure.

Treatment:
– Airway, breathing, and circulation to be secured. The patient’s fever should be managed, and one should rule out hypoglycaemia as a cause of the neuropsychiatric symptoms.
– Cardiovascular toxicity and agitation are best-treated first-line with benzodiazepines to decrease CNS sympathetic outflow.
– The mixed beta/alpha blocker labetalol is safe and effective for treating concomitant cocaine-induced hypertension and tachycardia.
– Non-dihydropyridine calcium channels blockers such as diltiazem and verapamil have been shown to reduce hypertension reliably, but not tachycardia.
– Dihydropyridine agents such as nifedipine should be avoided, as reflex tachycardia may occur.
– The alpha-blocker phentolamine has been recommended but only treats alpha-mediated hypertension and not tachycardia.

Triptans are specific 5-HT1 agonists used in the acute treatment of migraine. They are generally used as first-line therapy in combination with an NSAID or paracetamol.

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

Among the following hypertensives, lisinopril (an ACE inhibitor) is contraindicated in patients who are planning for pregnancy.

Per the NICE guidelines, when treating the woman in question, she should be treated as if she were pregnant given the absence of effective contraception.
ACE inhibitors such as lisinopril are known teratogens and most be avoided.

Drugs contraindicated in pregnancy:
Antibiotics
Tetracyclines
Aminoglycosides
Sulphonamides and trimethoprim
Quinolones

Other drugs:
ACE inhibitors, angiotensin II receptor antagonists
Statins
Warfarin
Sulfonylureas
Retinoids (including topical)
Cytotoxic agents
The majority of antiepileptics including valproate, carbamazepine, and phenytoin are known to be potentially harmful.

The true statement among the given options is that she will still be protected against pregnancy if she takes amoxicillin for a lower respiratory tract infection while on the combined pill.

Other than enzyme-inducing antibiotics such as rifampicin, antibiotics do not reduce the efficacy of the combined oral contraceptive pill.

It was previously advised that barrier methods of contraception should be used if taking an antibiotic while using the contraceptive pill, due to concerns that antibiotics might reduce the absorption of the pill. This is now known to be untrue. However, if the absorptive ability of the gut is compromised for another reason, such as severe diarrhoea or vomiting, or bowel disease, this may affect the efficacy of the pill.

The exception to the antibiotic rule is that hepatic enzyme-inducing antibiotics such as rifampicin and rifaximin do reduce the efficacy of the pill. Other enzyme-inducing drugs, such as phenytoin, phenobarbital, carbamazepine or St John’s Wort can also reduce the effectiveness of the pill.

Other options:
The combined pill is often prescribed for women with heavy periods as it can make them lighter and less painful.
There is no evidence that women on the combined pill put on any significant weight, although they may experience bloating at certain times in the course.
Women on the pill require monitoring of their blood pressure.
There are multiple different types of combined pills.

Tricyclic compounds can’t be cleared by haemodialysis.

Drugs that can be cleared with haemodialysis include: (BLAST)
– Barbiturate
– Lithium
– Alcohol (inc methanol, ethylene glycol)
– Salicylates
– Theophyllines (charcoal hemoperfusion is preferable)

Drugs which cannot be cleared with haemodialysis include:
– Tricyclics
– Benzodiazepines
– Dextropropoxyphene (Co-proxamol)
– Digoxin
– Beta-blockers

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 likely complaint of this patient would be hot flushes.

Alopecia and cataracts are listed in the BNF as possible side-effects. They are however not as prevalent as hot flushes, which are very common in pre-menopausal women.

Tamoxifen is a Selective Oestrogen Receptor Modulator (SERM) which acts as an oestrogen receptor antagonist and partial agonist. It is used in the management of oestrogen receptor-positive breast cancer

Adverse effects:
Menstrual disturbance: vaginal bleeding, amenorrhoea
Hot flushes – 3% of patients stop taking tamoxifen due to climacteric side-effects.
Venous thromboembolism.
Endometrial cancer
Tamoxifen is typically used for 5 years following the removal of the tumour.

Raloxifene is a pure oestrogen receptor antagonist and carries a lower risk of endometrial cancer.

Although antagonistic with respects to breast tissue tamoxifen may serve as an agonist at other sites. Therefore the risk of endometrial cancer is increased cancer.

Carbon monoxide has high affinity for haemoglobin and myoglobin resulting in a left-shift of the oxygen dissociation curve and tissue hypoxia. There are approximately 50 deaths per year from accidental carbon monoxide poisoning in the UK. In these circumstances, antidotal therapy to block alcohol dehydrogenase with ethanol or 4-MP alone is insufficient to treat the poisoning. Data suggest that a severe lactic acidosis needs initial correction and in this patient the most appropriate treatment would be IV fluids with bicarbonate to correct the metabolic acidosis. Haemodialysis may be required thereafter.

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.

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.

Blue tinge of vision/cyanopsia is caused due to the intake of sildenafil citrate.

Sildenafil citrate (Viagra) is the first oral drug to be widely approved for the treatment of erectile dysfunction.
It is a potent and selective inhibitor of type-V phosphodiesterase, the primary form of the enzyme found in human penile erectile tissue, thereby preventing the breakdown of cyclic guanosine monophosphate (cGMP), the intracellular second messenger of nitric oxide.

Uses:
It is used for the treatment of erectile dysfunction, idiopathic pulmonary hypertension, premature ejaculation, high altitude illness, penile rehabilitation after radical prostatectomy, angina pectoris, and lower urinary tract symptoms.

Adverse effects:
Mild headache, flushing, dyspepsia, cyanopsia, back pain, and myalgias – due to a high concentration of PDE11 enzyme in skeletal muscle, which shows significant cross-reactivity with the use of tadalafil.
It can also cause hypotension, dizziness, and rhinitis.

Note: Xanthopsia (yellow-green vision) may occur secondary to treatment with digoxin.

Vestibular damage is a neurological side effect of streptomycin.

Streptomycin is an aminoglycoside bactericidal antibiotic. It is used in the treatment of tularaemia and resistant mycobacterial infections.
The most common neurological side-effect is vestibular damage leading to vertigo and vomiting.
Cochlear damage is less frequent and results in deafness.
Other side-effects include rashes, angioneurotic oedema, and nephrotoxicity.

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.

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.

Benign Prostatic Enlargement or Hyperplasia (BPE/BPH) is the most probable diagnosis of the patient in question. It is a histological diagnosis characterized by proliferation of the cellular elements of the prostate.
The initial treatment modality of choice is selective alpha 1 antagonists (such as Prazosin, Alfuzosin and Indoramin, and long acting agents like, Terazosin, Doxazosin, etc.) as they provide immediate relief from the bothersome lower urinary tract symptoms (LUTS).
Other treatment modalities include:
• Non-selective alpha blockers: no longer used due to severe adverse effects and the availability of selective alpha 1 blockers.
• 5 alpha reductase inhibitors: Finasteride and Dutasteride, they target the underlying disease process and reduce the overall prostate volume. Thus, reduce the urinary retention and the lower urinary tract symptoms. (They do not provide immediate relief from LUTS and thus are not preferred as first line drugs over alpha 1 antagonists)
• PDE-5 Inhibitors: The long-acting tadalafil has proven to be useful.
• Surgical Treatment modalities: TURP, Prostatectomy, etc.

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.

The most appropriate steps of initial management include iv glucagon and iv isoprenaline.

The most likely diagnosis in the above scenario (decreased conscious level, profound hypertension, and bradycardia) is β-blocker toxicity/overdose.
Bronchospasm rarely occurs in an overdose of β-blockers, except where there is a history of asthma.

Immediate management is to give iv glucagons (50–150μg/kg) followed by infusion to treat hypotension and isoprenaline or atropine to treat bradycardia.
Where patients fail to respond to these measures, temporary pacing may be required.
If the patient is seen within the first 4 hours of the overdose, gastric lavage may be of value.

Lead can be absorbed through the skin and by inhalation. It is associated with iron deficiency and a microcytic anaemia. The most common gastrointestinal symptoms are abdominal colic and constipation.

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 farmer has most likely ingested an organophosphate insecticide.
Organophosphorus compounds are used widely as:
• Insecticides – Malathion, parathion, diazinon, dichlorvos
• Nerve gases – Soman, sarin, tabun, VX
• Ophthalmic agents – Echothiophate
• Antihelmintics – Trichlorfon
• Herbicides – merphos
• Industrial chemical (plasticizer) – Tricresyl phosphate
Signs and symptoms of Organophosphorus Poisoning (OPP) can be classified as:
• Muscarinic effects:
o Cardiovascular – Bradycardia, hypotension
o Respiratory – Rhinorrhoea, bronchorrhea, bronchospasm, cough, severe respiratory distress
o Gastrointestinal – Hypersalivation, nausea and vomiting, abdominal pain, diarrhoea, faecal incontinence
o Genitourinary – Incontinence
o Ocular – Blurred vision, miosis
o Glands – Increased lacrimation, diaphoresis
• Nicotinic effects:
o Muscle fasciculation, weakness, cramping, diaphragmatic failure, and autonomic side effects include: hypertension, tachycardia, and mydriasis.
• Central nervous system (CNS) effects:
o Anxiety, emotional lability, restlessness, confusion, ataxia, tremors, seizures, coma, apnoea
Mainstay Treatment:
• Decontamination
• Securing Airway, Breathing and Circulation
• Atropine
• Pralidoxime
• Benzodiazepines

Desmopressin test (done to differentiate nephrogenic diabetes insipidus from central diabetes insipidus), and serum lithium levels can together confirm a diagnosis of lithium-induced nephrogenic diabetes insipidus.

Bipolar disease is most often managed with mood stabilizers like lithium. This patient develops gastrointestinal symptoms followed by an acute confusional state associated with polyuria and polydipsia. These symptoms are suggestive of diabetes insipidus.

In a case where these symptoms occur in a bipolar patient under treatment, lithium-induced nephrogenic diabetes insipidus should be considered as the most probable cause.

Lithium intoxication can present with symptoms of nausea, vomiting, mental dullness, action tremor, weakness, ataxia, slurred speech, blurred vision, dizziness, especially vertical nystagmus and stupor or coma. Diffuse myoclonic twitching and nephrogenic diabetes insipidus can also occur. Such a clinical syndrome occurs above the serum level of lithium of 1.5–2.0 mEq/L.

Management:
– Correcting electrolyte abnormalities in patients with acute disease is critical and often life-saving.
– Treatment should be initiated with parenteral fluids to replete hypovolemia (normal saline at 200-250 mL/h), followed by administration of hypotonic fluid (0.5% normal saline).
– On the restoration of the volume status of the patient forced diuresis should be initiated by the administration of parenteral furosemide or bumetanide accompanied by continued intravenous hypotonic fluid administration to maintain volume status.
– Polyuria is managed with hydrochlorothiazide combined with amiloride, acetazolamide.

Hyperthermia (Temperature 39.5 C) points towards the use of ecstasy.

MDMA (3,4 – methylenedioxymethamphetamine), or more commonly known as Molly or Ecstasy, is a synthetic psychoactive substance.
Patients who consumed MDMA may present in a tachycardic, hypertensive, hyperthermic, and agitated state.
Adverse effects, even at minor recreational doses, include increased muscle activity (such as bruxism, restless legs, and jaw clenching), hyperactivity, insomnia, difficulty concentrating and feelings of restlessness.

Treatment of MDMA overdose:
Emphasis should be on maintaining the airway along with the stabilization of breathing and circulation.
Patients may present obtunded due to hyponatremia requiring endotracheal intubation.
For the hyperthermic patient, evaporative cooling along with ice packs to the groin and axilla are beneficial.
Patients who present in severe toxicity within one hour of ingestion can receive activated charcoal PO or via an NG tube.
Antipyretics, such as acetaminophen, should be avoided as they have no role and can worsen an already compromised liver.

Among the give options, reactivation of tuberculosis may occur in a patient under treatment with etanercept.
Etanercept is a biological TNF inhibit commonly used to control ankylosing spondylitis, juvenile idiopathic arthritis, plaque psoriasis, psoriatic arthritis, and rheumatoid arthritis.
Etanercept is a soluble receptor that binds both TNF-alpha and TNF-beta to inhibit the inflammatory response in joints and skin that is characteristic of these autoimmune disorders.
The most common adverse effects include infections (viral, bacterial, and fungal – mostly upper respiratory tract infections) and injection site reaction (erythema, itching, pain, swelling, bleeding, bruising).
Rarely it can also cause, reactivation of hepatitis B and TB, pneumocystis pneumonia, congestive cardiac failure, Steven-Johnson syndrome, toxic epidermal necrolysis, etc.

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.

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.

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.

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.

Ezetimibe is a cholesterol-lowering agent that acts to prevent cholesterol absorption by directly inhibiting cholesterol receptors on enterocytes.
It does not affect the absorption of drugs (e.g. digoxin, thyroxine) or fat-soluble vitamins (A, D and K) as the anion-exchange resins do. It does not affect the cytochrome P450 enzyme system.
The increased risk of myositis associated with the statins is not seen with ezetimibe.
The most common adverse effects include headache, runny nose, and sore throat.
Less common reactions include body aches, back pain, chest pain, diarrhoea, joint pain, fatigue, and weakness.

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

Sildenafil citrate (Viagra) is the first oral drug to be widely approved for the treatment of erectile dysfunction.
It is a potent and selective inhibitor of type-V phosphodiesterase, the primary form of the enzyme found in human penile erectile tissue, thereby preventing the breakdown of cyclic guanosine monophosphate (cGMP), the intracellular second messenger of nitric oxide.

Uses:
It is used for the treatment of erectile dysfunction, idiopathic pulmonary hypertension, premature ejaculation, high altitude illness, penile rehabilitation after radical prostatectomy, angina pectoris, and lower urinary tract symptoms.

Adverse effects:
Mild headache, flushing, dyspepsia, cyanopsia, back pain, and myalgias – due to a high concentration of PDE11 enzyme in skeletal muscle, which shows significant cross-reactivity with the use of tadalafil.
It can also cause hypotension, dizziness, and rhinitis.

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 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.

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%.

Use of Hyperbaric oxygen therapy (HBOT) for treatment of 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)
Principle of HBOT:
Exposing patients to 100 percent oxygen under supra-atmospheric conditions results in a decrease in the half-life (t1/2) of COHb, from , 90 min in atmospheric air to , 30 minutes. The amount of oxygen dissolved in the blood also rises from , 0.3 to 6 mL/dL, increasing the delivery of non-haemoglobin-bound oxygen to the tissues.

1mg Prednisolone = 4mg hydrocortisone, so the actual equivalent daily dose is 7mg.

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.

Dilation of systemic veins is a beneficial effect of nitro-glycerine.

Administration of nitro-glycerine results in the dilation of systemic veins and decrease of myocardial wall tension and oxygen demand. Dilatation of systemic veins can cause reduced systemic vascular resistance leading to reduced cardiac workload thus reducing anginal symptoms secondary to demand ischemia.

This is accompanied by vasodilation of large and medium-sized coronary arteries with increased coronary blood flow to the sub endocardium.

Proton pump inhibitors can reduce gastric acid secretion by up to 99%. Acid production resumes following the normal renewal of gastric parietal cells.

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.