Isokin 300 Avoid using this medicine if you are allergic to it, if you have any liver disorders or if you have had hepatitis from any medicine. Tell your doctor if you have diabetes, a history of alcohol or other substance abuse, kidney problems, nerve problems, unsanitary injectable drug habits, HIV, a history of liver problems or if you are older than 35 years old, you have recently given birth, or you have previously taken isoniazid.