Multiple drug interactions and adverse effects may occur with all anticonvulsants. This table highlights the key areas of concern only. Seek further information if required.
| Type of epilepsy | Adverse effects | Interactions | Monitoring | Notes |
| Sodium valproate | ||||
All types of epilepsy First-line for generalised epilepsies |
Common – weight gain, tremor, GI disturbance and hair loss (usually mild) Thrombocytopenia Hepatic failure Pancreatitis Other blood dyscrasias |
Interacts with:
|
CBC, LFT, electrolytes at baseline, at three months and then annually Repeat tests if clinical suspicion of haematological or hepatic damage If warfarin commenced, check INR after 5–7 days (warfarin dose decrease may be required) |
Avoid in women of childbearing potential Regarded as less sedating than other anticonvulsants |
| Carbamazepine | ||||
Partial epilepsies (first-line), also in generalised or mixed epilepsies May worsen absence or myoclonic seizures |
Common - nausea and vomiting, sedation, dizziness and ataxia Allergic rash (may be severe) Leucopenia Hyponatraemia (action not required if sodium stable above 125 mmol/L) Hepatotoxicity Other blood dyscrasias |
Increased plasma concentration (increasing the risk of toxicity) if used with:
Induces hepatic enzymes and reduces the effect of some medications including:
|
CBC, LFT, electrolytes at baseline Repeat tests if clinical suspicion of haematological or hepatic damage If warfarin commenced, check INR after 5–7 days (warfarin dose increase may be required) |
Use slow release preparations Carbamazepine or lamotrigine are the anticonvulsant drugs of choice in pregnancy |
| Lamotrigine | ||||
Most forms of epilepsy Alternate first-line for partial epilepsies |
Common – allergic rash, headache, dizziness, blurred vision Serious allergic rash particularly:
|
Plasma concentration is increased by sodium valproate Plasma concentration is decreased by enzyme inducing anticonvulsants, oestrogens and progestogens |
Not routinely indicated |
Start low, go slow to avoid allergic rash Lamotrigine or carbamazepine are the anticonvulsant drugs of choice in pregnancy Avoid doses over 200 mg in women of childbearing potential |
| Phenytoin | ||||
Most forms of epilepsy May worsen absence or myoclonic seizures |
Common - headache, tiredness, nausea, dizziness, drowsiness and insomnia Allergic rash (may be severe) Hirsutism, coarsening of facial features, acne and gingival hyperplasia Hepatotoxicity Blood dyscrasias |
Induces hepatic enzymes and reduces the effect of some medications including:
|
CBC, LFT, electrolytes at baseline, at three months and then annually Repeat tests if clinical suspicion of haematological or hepatic damage If warfarin commenced, check INR after 5–7 days (warfarin dose increase may be required) |
Therapeutic drug monitoring is useful due to non-linear pharmacokinetics e.g. when adjusting dose or adding additional medications with potential for interaction No longer widely used (narrow therapeutic index, long term toxicity) |
| Gabapentin | ||||
Partial and secondarily generalised tonic-clonic seizures May worsen absence or myoclonic seizures |
Common – dizziness, tiredness and nausea Weight gain, peripheral oedema Allergic rash (may be severe) |
No clinically important drug interactions |
Not routinely indicated |
More widely used for neuropathic pain than epilepsy |
| Topiramate | ||||
Generalised seizures Partial epilepsy |
Common – ataxia, confusion, dizziness, tiredness Weight loss Acute angle closure glaucoma Kidney stones Cognitive impairment (up to 15%) particularly if used with sodium valproate |
Can decrease serum concentration of digoxin and oral contraceptives by about 30% |
Not routinely indicated |
Often used as adjunctive therapy Patients should be advised to have adequate fluid intake |
Phenobarbitone and primidone are effective in most forms of epilepsy except absence seizures. However they are no longer widely used due to multiple adverse effects particularly on the CNS and respiratory system. Their use is associated with tolerance, dependence and in elderly people, with falls, osteoporosis and fractures. Primidone can be effective for essential tremor.
Ethosuximide is only effective for absence seizures. It may worsen generalised tonic clonic seizures. It is not widely used.
Vigabatrin is used in treatment of epilepsy (via special authority) that is not well controlled with other anticonvulsants. It may worsen absence or myoclonic seizures. Its use has been limited by the risk of concentric irreversible visual field defects, which are seen in 30–40% of patients.9 These defects are usually initially asymptomatic and begin with bilateral nasal field loss. Refer for baseline visual field testing by perimetry with follow up tests every six months.10
Levetiracetam is only available by specialist application to the Special Access Panel. It is effective as adjunctive treatment of partial onset seizures with or without secondary generalisation.
Pregabalin is effective in the treatment of partial seizures with or without secondary generalisation. It is indicated in New Zealand as adjunctive therapy for patients with this type of epilepsy and also for neuropathic pain, however it is not subsidised.
Oxcarbazepine is not subsidised in New Zealand and therefore not widely used.