Isoniazid is an antituberculous drug. It can cause peripheral neuropathy and rarely convulsions by decreasing the availability of pyridoxine (vitamin B6). Isoniazid binds to pyridoxal-5-phosphate, the active form of pyridoxine to form isoniazid-pyridoxal hydrazone. Pyridoxal-5-phosphate is necessary for the functioning of the enzymes glutamic acid decarboxylase and GABA transaminase which function in the GABA synthesis pathway. Thus isoniazid decreases the synthesis of GABA. Since GABA is an inhibitory neurotransmitter, deficiency of GABA can lead to increased excitatory action and siezures.
Pyridoxine 10 mg per day can be used to prevent peripheral neuropathy. In established isoniazid induced peripheral neuropathy, pyridoxine 100 mg per day is given.