A sensitive urine-test method for monitoring the ingestion of isoniazid.

A method is described for monitoring the ingestion of isoniazid based on detecting its metabolites, isonicotinic acid, and isonicotinylglycine in the urine. The sensitivity of the method is high so that reliably positive results were obtained up to about 24 hours after the ingestion of 100 mg isoniazid. The method should facilitate monitoring the taking of isoniazid by tuberculosis patients and the use of isoniazid as a marker for assessing the regularity with which other drugs prescribed for self-administration are actually ingested.