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Stop all drugs at the first sign of a hypersensitivity reaction. If isoniazid is reinstituted, it should be given in very small and gradually increasing doses to determine whether the manifestations are drug induced.
Use of isoniazid should be carefully monitored in patients with convulsive disorders (see Interactions), pre-existing hepatic diseases, or severe renal dysfunction.
Optic neuritis has been reported as a rare complication. Periodic ophthalmoscopic examinations during isoniazid therapy are recommended when visual symptoms occur.
It is believed that isoniazid competes with pyridoxyl phosphate for the enzyme apotryptophanase which may lead to symptoms of pyridoxine (vitamin B6) deficiency. Pyridoxine administration can prevent and reverse peripheral neuropathy complicating isoniazid use.
