Zonisamide

How it works

It blocks voltage-gated sodium and T-type calcium channels to stabilise neuronal membranes, and has weak carbonic anhydrase inhibitory activity.

Prescribing in practice

• It is a sulfonamide and can cause serious hypersensitivity reactions including Stevens-Johnson syndrome and toxic epidermal necrolysis; stop immediately if a rash develops.
• It can reduce sweating and cause hyperthermia, particularly in children and in hot conditions, and may precipitate metabolic acidosis and renal stones.
• Antiepileptic treatment should not be stopped abruptly because of the risk of rebound seizures; withdraw gradually.

Monitoring

Monitor for signs of metabolic acidosis, hyperthermia, weight loss, and mood changes, and review renal function and bicarbonate as clinically indicated.

Counselling the patient

• Report any skin rash, fever, or mouth ulcers promptly as these may signal a serious reaction.
• Stay well hydrated and avoid overheating, especially in warm weather or during vigorous activity.
• Maintain good fluid intake to reduce the risk of kidney stones and report any new abdominal or flank pain.

Evidence & guidelines

Antiepileptic drugs carry an MHRA-recognised small increased risk of suicidal thoughts and behaviour, and patients should be monitored accordingly.