phenobarbital: prescribing and clinical use
Focused clinical detail for use alongside current product information, local policy and patient-specific assessment.
phenobarbital: clinical details
Prescribing considerations
- Avoid abrupt withdrawal because of dependence, withdrawal symptoms and rebound seizures.
- Review depression, suicidal thoughts, substance-use history, respiratory disease and factors increasing sedation risk.
- Phenobarbital is a strong enzyme inducer; perform a broad interaction review before initiation, discontinuation or adding other treatments.
- Long-term treatment is associated with altered vitamin D and bone metabolism; assess relevant risk factors.
- Pregnancy potential requires documented risk discussion, contraception review and specialist pre-conception planning.
Contraindications and cautions
- Hypersensitivity to barbiturates or an elixir ingredient
- Severe respiratory depression
- Severely impaired hepatic or renal function
- Acute intermittent porphyria
- Hyperkinetic children
Monitoring
- Seizure control, adherence, sedation, coordination, cognition and behaviour
- Suicidal ideation or significant mood change
- Respiratory status in susceptible patients or when combined with other depressants
- Interaction-sensitive treatments when phenobarbital is introduced, withdrawn or changed
- Serum phenobarbital where toxicity, adherence, interactions or loss of seizure control are concerns
- Bone-health and vitamin D risk during long-term treatment
Clinical pharmacology
Oral absorption is slow but complete. Phenobarbital has a long elimination half-life, induces hepatic drug-metabolising enzymes and is cleared through both hepatic metabolism and pH-dependent renal excretion; exposure may be prolonged in older people and hepatic or renal disease.
Formulation and product differences
- The selected elixir contains substantial ethanol plus glycerol, benzyl alcohol and azo colourings.
- A licensed ethanol-free oral suspension is available; liquid products may have different concentrations and must not be interchanged volume-for-volume.
- Phenobarbital is a category 1 antiseizure treatment for which continuity of a specific manufacturer’s product is generally important.
- The selected ethanol-containing elixir is not suitable for children according to current SPS medication-safety guidance.
phenobarbital interactions
Phenobarbital induces hepatic enzymes and can lower the effectiveness of many medicines. Sedating combinations can also intensify central nervous system and respiratory depression.
Alcohol, opioids, sedatives and sedating antihistamines
May cause additive drowsiness and potentially serious respiratory depression; alcohol should be avoided.
Oestrogen- or progestogen-containing contraception
Accelerated hormone metabolism may cause contraceptive failure or breakthrough bleeding; alternative contraception requires professional discussion.
Coumarin anticoagulants such as warfarin
Accelerated metabolism may reduce anticoagulant effect, requiring clinical and laboratory review.
Sources
These sources were used to prepare and review this medicine page.
Prepared and reviewed by the iatroX editorial team.