FOOD AND ISONIAZID

The absorption of isoniazid is reduced by food. Patients taking isoniazid who eat some foods, such as mature cheese and particularly fish from the scombroid family (e.g. tuna, mackerel, salmon) that are not fresh, may experience an exaggerated histamine poisoning reaction e.g. chills, diarrhoea, flushing and itching of the skin, headache, tachycardia, vomiting, wheeze.
For maximal absorption isoniazid should be taken without food, hence the manufacturer's guidance to take it at least 30 minutes before or 2 hours after food. There is no need to introduce general dietary restrictions, but if any of these reactions is experienced, examine the patient's diet and advise the avoidance of any probable offending foodstuffs.