Pyridoxine (Vitamin B6)

How it works

Isoniazid depletes the active form of pyridoxine needed to synthesise the inhibitory neurotransmitter GABA; high-dose pyridoxine replenishes this cofactor and restores GABA production, terminating the seizures.

Prescribing in practice

• In isoniazid-induced seizures, give pyridoxine intravenously as the specific antidote, as standard anticonvulsants alone are often ineffective.
• The antidotal dose is matched to the amount of isoniazid ingested where known, and is guided by UK poisons information advice.
• Benzodiazepines are used as adjunctive seizure control alongside pyridoxine.

Monitoring

Monitor seizure control, conscious level, acid-base status and overall neurological recovery during treatment.

Counselling the patient

• Explain to the team that high-dose vitamin B6 specifically counteracts isoniazid-induced seizures.
• Note that it is used together with benzodiazepines for seizure management.
• Advise that the dose is informed by the quantity of isoniazid taken and poisons-centre guidance.

Evidence & guidelines

Pyridoxine is the established specific antidote for isoniazid toxicity and refractory seizures, with dosing guided by UK poisons information (TOXBASE).