MSRA-2138

A 28-year-old man who has been on antiepileptic medication for several years presents with complaints of fatigue, weakness, bone pain, tingling and numbness in his lower limbs and swelling of his gums. Upon investigation, the following results were obtained:
Investigation Result Normal value
Haemoglobin 90 g/l 120-155 g/l
Mean corpuscular volume 110 fl/red cell 80-96 fl/red cell
White cell count 6.8 × 109/l 4.5-11 x 109/l
Platelets 180 × 109/l 150-450 x 109/l
Alkaline phosphatase 600 IU/l 44-147 IU/l
Parathyroid hormone 12.2 pmol/ml 10-55 pg/ml
Which of the following antiepileptic medications is most likely responsible for these symptoms?