Formulary
Phenobarbital: Indications, Dosing, Side Effects and Interactions
Phenobarbital clinical drug profile including indications, dosing, side effects, cautions and interactions.
MedNext Academy | 3 min read
Phenobarbital: Indications, Dosing, Side Effects and Interactions
Phenobarbital clinical drug profile including indications, dosing, side effects, cautions and interactions.
Indications and dose
**All forms of epilepsy except typical absence seizures for phenobarbital**
- **Child 1 month-11 years** (By mouth): Initially 1-1.5 mg/kg twice daily, then increased in steps of 2 mg/kg daily as required; maintenance 2.5-4 mg/kg 1-2 times a day.
- **Child 12-17 years** (By mouth): 60-180 mg once daily.
- **Neonate** (Initially by slow intravenous injection): Initially 20 mg/kg, then (by slow intravenous injection or by mouth) 2.5-5 mg/kg once daily, adjusted according to response.
**Status epilepticus for phenobarbital**
- **Neonate** (By slow intravenous injection): Initially 20 mg/kg, then 2.5-5 mg/kg 1-2 times a day.
- **Child 1 month-11 years** (By slow intravenous injection): Initially 20 mg/kg, then 2.5-5 mg/kg 1-2 times a day.
- **Child 12-17 years** (By slow intravenous injection): Initially 20 mg/kg (max. per dose 1 g), then 300 mg twice daily.
Interactions
**Severe interactions:**
- Concomitant administration of strong or moderate CYP3A inducers, (such as rifampicin, rifabutin, carbamazepine, phenobarbital, phenytoin, efavirenz and St John's wort), is expected to significantly...
- John's wort ( Hypericum perforatum ), rifampicin, carbamazepine, phenobarbital, and phenytoin may result in significantly decreased cobicistat and elvitegravir plasma concentrations, which may...
- The plasma concentrations of carbamazepine, phenobarbital, and sodium valproate have also been monitored during controlled clinical trials and no clinically significant interactions have been...
- Contraindications of concomitant use Primidone and its main metabolite phenobarbital are strong inducers of cytochrome P450 and thus lead to life-threatening situations due to the risk of decreased...
- Possible toxicity with phenytoin on stopping primidone); stiripentol, tiagabine, valproic acid, zonisamide.
- Anticonvulsants Carbamazepine and longacting barbiturates (including but not limited to: phenobarbital, mephobarbital) [potent CYP450 inducers] Although not studied, carbamazepine and long-acting...
- John's wort ( Hypericum perforatum ), phenobarbital, phenytoin, and primidone) could significantly decrease glecaprevir or pibrentasvir plasma concentrations and may lead to reduced therapeutic...
**Other interactions (139):**
- Co-administration with other potent inducers of P-gp and CYP3A4, such as carbamazepine, phenobarbital and phenytoin, has not been studied.
- Medicinal products that cause strong CYP3A4 and/or P-gp induction, such as anticonvulsants (e.g.
- CYP enzyme inducers: The metabolism of estrogens and progestogens may be increased by concomitant use of substances known to induce drug-metabolising enzymes, specifically cytochrome P450 enzymes,...
- ANTICONVULSANTS Carbamazepine Oxcarbazepine Phenobarbital Phenytoin Not studied.
- Similar effects may be observed with e.g., phenytoin and phenobarbital which also induce CYP3A4 hepatic enzyme, as well as P-glycoprotein.
- The impact of other strong inducers of drug metabolizing enzymes, such as phenytoin and phenobarbital, on UGT1A1 is unknown; therefore, co-administration with raltegravir 1,200 mg once daily is not...
Clinical governance
**Author:** MedNext Clinical Team. **Clinical reviewer:** Dr Shameer Deen, MBBS, MS, MRCS. **Sources:** BNF, Indian Pharmacopoeia, CIMS India. **Correction:** Report errors at support@mednext.academy.
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