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Therapeutic action
- Antiseizure (antiepileptic)
Indications
- Epilepsy: generalised tonic-clonic seizures and focal (partial) seizures
Forms and strengths
- 100 mg tablet
Dosage
Start with a low dose then increase gradually based on patient's response and tolerance.
- Child 1 month to 11 years: start with 1.5 to 2.5 mg/kg 2 times daily; increase the daily dose by increments of 5 mg/kg every 3 to 4 weeks, up to 2.5 to 5 mg/kg 2 times daily if necessary (max. 7.5 mg/kg 2 times daily or 300 mg daily).
- Child 12 years and over: start with 75 to 150 mg 2 times daily; increase the daily dose by increments of 25 mg every 3 to 4 weeks, up to 150 to 200 mg 2 times daily if necessary (max. 300 mg 2 times daily).
- Adult: start with 150 to 300 mg once daily or 75 to 150 mg 2 times daily; increase the daily dose by increments of 50 mg every 3 to 4 weeks, up to 200 to 400 mg once daily or 100 to 250 mg 2 times daily if necessary (max. 400 mg once daily or 300 mg 2 times daily).
Duration
- As long as required. Do not stop treatment abruptly, even if changing treatment to another antiseizure medication.
Contra-indications, adverse effects, precautions
- Administer with caution to patients with hepatic impairment (reduce dosage), heart failure, atrioventricular block, cardiac rhythm disorders, hypotension.
- May cause:
- drowsiness (caution when driving/operating machinery), dizziness, headache, behavioural disturbances, insomnia;
- gastrointestinal disturbances (nausea, vomiting), vitamin D deficiency (consider supplementation), osteoporosis, hepatotoxicity and gingival hypertrophy;
- rarely: haematologic disorders (thrombocytopenia, agranulocytosis, anaemia), hypersensitivity reactions (including severe cutaneous reactions such as Stevens-Johnson, Lyell and DRESS syndromes). In these cases, stop treatment. Early symptoms such as fever, rash, mouth ulcers and bleeding require immediate medical attention.
- If possible, perform at least FBC and liver enzymes, at baseline then regularly during treatment.
- Avoid or monitor the combination with:
- rifampicin, mefloquine (reduced effect of PHT);
- sulfonamides, chloramphenicol, fluconazole, isoniazid, fluoxetine, omeprazole (increased PHT toxicity);
- drugs containing alcohol, benzodiazepines, opioid analgesics, antipsychotics, first-generation antihistamines (hydroxyzine, promethazine), antidepressants, other antiseizure medications, etc. (increased sedation).
- PHT may reduce the effect of many drugs:
- diazepam, midazolam, digoxin, corticosteroids, antimicrobials, some antiretrovirals, itraconazole, warfarin, etc. Adjust dosage if necessary.
- implants and oral contraceptives: use injectable medroxyprogesterone or an intrauterine device.
- Avoid alcohol during treatment (increased risk of adverse effects).
- Pregnancy: avoid (risk of cardiac malformations)
- In case of pregnancy during treatment, prefer a safer drug (levetiracetam). If PHT is the only option, provide counselling about the risks to the child; use the lowest effective dose.
- Administer folic acid high dose (5 mg daily) during the first trimester. Start as soon as possible, including during the preconception period in case of planned pregnancy.
- PHT plasma concentrations may decrease during pregnancy. Monitor clinical response; increase dose if needed then resume the usual dose after delivery. Monitor the child for a few days (risk of accumulation and drowsiness or withdrawal symptoms).
- Breast-feeding: administer with caution (excreted in milk); reduce the dose if increased during pregnancy.
Remarks
- PHT is not recommended for myoclonic and absence seizures (risk of worsening symptoms).
- Also comes in 30 mg/5 ml oral solution.