VERBITAL 30
Phenobarbital BP 30mg
What it does
Phenobarbital is a medication used to help control seizures and manage certain types of epilepsy.
Commonly used for: seizures, epilepsy
Read more in plain English ↓Plain-language summary for general understanding - not medical advice. Always follow your pharmacist/doctor.
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Answers come only from this medicine's registration record, BNF monograph and interaction data - not medical advice.
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Sourcing - Kenya onlyRegistration & product details
Source: Rwanda Food and Drugs Authority · fetched 2026-03-11 22:07:15 · updated 2026-09-21 02:30:20
Drug Interactions
79Pharmacodynamic Warnings
Phenobarbital appears in TABLE 11: Drugs with CNS depressant effects
Severe (12)
Antiepileptics - decreases absorption
Iron chelators (dexrazoxane) might decrease the absorption of antiepileptics (fosphenytoin, phenytoin). Avoid.
Antiepileptics - decreases exposure
Lumacaftor is predicted to decrease the exposure to antiepileptics (carbamazepine, fosphenytoin, phenobarbital, phenytoin, primidone). Avoid.
Antiepileptics - decreases concentration
St John’s wort is predicted to decrease the concentration of antiepileptics (fosphenytoin, phenobarbital, phenytoin, primidone). Avoid.
Antiepileptics - increases risk of overheating and dehydration
Hydroxyzine potentially increases the risk of overheating and dehydration when given with antiepileptics (zonisamide). Avoid in children.
Antiepileptics - increases risk of overheating and dehydration
Haloperidol potentially increases the risk of overheating and dehydration when given with antiepileptics (zonisamide). Avoid in children.
Moderate (29)
Aminophylline - decreases exposure
Phenobarbital is predicted to decrease the exposure to aminophylline. Adjust dose.
Antiepileptics - increases concentration
Intravenous chloramphenicol increases the concentration of antiepileptics (fosphenytoin, phenytoin) and antiepileptics (fosphenytoin, phenytoin) affect the concentration of intravenous chloramphenicol
Antiepileptics - decreases concentration
Diazoxide decreases the concentration of antiepileptics (fosphenytoin, phenytoin) and antiepileptics (fosphenytoin, phenytoin) are predicted to decrease the effects of diazoxide. Monitor concentration
Antiepileptics - increases concentration
Disulfiramincreasestheconcentrationofantiepileptics (fosphenytoin,phenytoin).Monitorconcentrationandadjust dose.rStudy →AlsoseeTABLE12p.1520
Antiepileptics - increases concentration
Fluorouracilincreasestheconcentrationofantiepileptics (fosphenytoin,phenytoin).Monitorconcentrationandadjust dose.rAnecdotal 1xidneppA|snoitcaretnI A1 https://www.facebook.c (Books-Courses-Medic
Unknown (38)
Antiepileptics - increases risk of overheating and dehydration
Acetazolamide potentially increases the risk of overheating and dehydration when given with antiepileptics (zonisamide). Avoid in children.
Antiepileptics - increases risk of visual disturbances
Alcohol potentially increases the risk of visual disturbances when given with antiepileptics (retigabine).
Antiepileptics - decreases exposure
Enzalutamide is predicted to slightly decrease the exposure to antiepileptics (brivaracetam).
Antiepileptics - decreases exposure
Apalutamidepotentiallydecreasestheexposureto antiepileptics(valproate).nTheoretical
Antiepileptics - increases concentration
Capecitabine increases the concentration of antiepileptics (fosphenytoin, phenytoin).
Data from BNF 85 (British National Formulary). This is not a substitute for professional medical advice. Matched via: class
About this medicine
Phenobarbital is a medication used to help control seizures and manage certain types of epilepsy.
What it treats
- seizures
- epilepsy
How it works
Phenobarbital works by calming the brain and reducing the electrical activity that causes seizures.
Who it's for
This medication is typically prescribed for people who have seizure disorders or epilepsy.
Drug class
Antiepileptics
Cautions
- • Be cautious if taking other medications that can also make you feel sleepy or slow down your brain function.
AI-assisted summary grounded in BNF data - general information only, not medical advice. Always confirm with your pharmacist or doctor.
Clinical monograph: Phenobarbital
BNF-referencedPhenobarbital is a long-acting barbiturate primarily used as an anticonvulsant and sedative-hypnotic agent. It is effective in the management of various seizure disorders, with the exception of absence seizures. Its therapeutic effects are largely due to its action on GABAA receptors, which enhances inhibitory neurotransmission in the central nervous system. Phenobarbital also plays a role in lowering bilirubin levels in certain conditions. Despite its efficacy, caution is advised in its use due to potential for dependence and various drug interactions.
Indications
- Epilepsy
- Seizure disorders
- Status epilepticus
Dosage
Children: In children aged 1 month to 11 years, the initial dosage is 1–1.5 mg/kg twice daily, with increases of 2
Adults: For adults, the recommended dosing is 60–180 mg once daily, preferably taken at night. In cases of status epilepticus, an intravenous dose of 10 mg/kg (maximum per dose 1 g) is advised.
Mechanism of action
Phenobarbital acts on GABAA receptors, increasing synaptic inhibition and elevating seizure threshold, thus reducing seizure activity. It may also inhibit calcium channels, decreasing excitatory neurotransmitter release. Its sedative-hypnotic effects stem from its action on the midbrain reticular formation, which regulates CNS arousal. Additionally, it induces glucuronyl transferase, aiding in the conjugation of bilirubin.
Pharmacodynamics
As the longest-acting barbiturate, phenobarbital exhibits anticonvulsant properties effective in managing all forms of epilepsy except for typical absence seizures. It possesses sedative-hypnotic qualities and is utilized for its ability to modulate central nervous system excitability.
Pharmacokinetics
Phenobarbital is well-absorbed orally and reaches peak plasma concentrations in approximately 2 to 8 hours. It has a long half-life of 79 to 120 hours, which can vary significantly among individuals. The drug is extensively metabolized in the liver, primarily through glucuronidation, and is eliminated mainly via urine. Monitoring of plasma concentrations is typically less useful due to the development of tolerance, although therapeutic ranges are between 15–40 mg/litre.
Contra-indications
- Severe hepatic impairment
- Hypersensitivity to phenobarbital or other barbiturates
- Porphyria
Adverse effects
- Drowsiness
- Dizziness
- Cognitive impairment
- Respiratory depression
- Hypotension
- Dependence
- Withdrawal seizures
- Dermatological reactions
Interactions
- Ketoconazole (decreases concentration)
- Posaconazole (decreases concentration)
- Cholic acid (decreases effects)
- Lumacaftor (decreases exposure)
- St. John's Wort (decreases concentration)
- Aminophylline (decreases exposure)
- Cenobamate (increases exposure)
- Folate supplements (decreases concentration)
- Rifamycins (decreases exposure)
- Antifungal azoles (unknown effect on concentration)
Precautions
- Use with caution in patients with hepatic impairment
- Monitor for signs of dependence and withdrawal
- Avoid abrupt withdrawal in patients with prolonged use
- Use with caution in patients with respiratory conditions
Pregnancy
Manufacturer advises caution; potential risks include intra-uterine growth restriction. Effective contraception is recommended during treatment.
Breast-feeding
Manufacturer advises avoidance if possible; monitor for drowsiness in infants.
Storage
Store in a cool, dry place away from light. Keep out of reach of children.
Formulations
- Oral tablets
- Oral suspension
- Injectable solution
AI-synthesized from BNF references - general information only, not a substitute for professional medical advice or the current BNF. Verify doses with a pharmacist.
Molecular reference: Phenobarbital
PubChem CID 4763Molecular formula: C12H12N2O3
Mechanism of action
Phenobarbital acts on GABAA receptors, increasing synaptic inhibition. This has the effect of elevating seizure threshold and reducing the spread of seizure activity from a seizure focus. Phenobarbital may also inhibit calcium channels, resulting in a decrease in excitatory transmitter release. The sedative-hypnotic effects of phenobarbital are likely the result of its effect on the polysynaptic midbrain reticular formation, which controls CNS arousal. /Phenobarbital/ produces anticonvulsant effects in subhypnotic doses. The drug lowers serum bilirubin concentrations in neonates and patients with congenital nonhemolytic unconjugated hyperbilirubinemia and patients with chronic intrahepatic cholestasis, presumably by induction of glucuronyl transferase, the enzyme which conjugates bilirubin. The exact mechanism(s) by which barbiturates exert their effect on the CNS, has not been fully elucidated. However, it is believed that such effects are related, at least partially, to the drugs' ability to enhance the activity of gamma-aminobutyric acid (GABA), the principal inhibitory neurotransmitter in the CNS, by altering inhibitory synaptic transmissions that are mediated by GABAA receptors. /Barbiturates General Statement/ Although the drugs act throughout the CNS, a site of particular sensitivity is the polysynaptic midbrain reticular formation which is concerned with the arousal mechanism. Barbiturates induce an imbalance in central inhibitory and facilitatory mechanisms influencing the cerebral cortex and the reticular formation. The significance of the effect of barbiturates on neurotransmitters is unclear. It appears that the drugs decrease the excitability of both presynaptic and postsynaptic membranes. It has not been determined which of the various actions of barbiturates at cellular and synaptic levels are responsible for their sedative and hypnotic effects. /Barbiturates General Statement/ Relatively low doses of the barbiturates depress the sensory cortex, decrease motor activity, and produce sedation and drowsiness. In some patients, however, drowsiness may be preceded by a period of transient elation, confusion, euphoria, or excitement, especially after subhypnotic doses of aprobarbital, pentobarbital, or secobarbital. /Barbiturates General Statement/ For more Mechanism of Action (Complete) data for Phenobarbital (12 total), please visit the HSDB record page.
Pharmacodynamics
Phenobarbital, the longest-acting barbiturate, is used for its anticonvulsant and sedative-hypnotic properties in the management of all seizure disorders except absence (petit mal).
Biological pathways
Source: PubChem (NCBI) · pathways from PathBank, Reactome, WikiPathways & PharmGKB.
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