Isoniazid (brand name INH) is primarily used to treat tuberculosis (TB), including both active and latent forms. For active tuberculosis, isoniazid is typically combined with other antibiotics such as rifampin, pyrazinamide, and ethambutol to effectively kill the bacteria and prevent the development of drug-resistant strains. In the case of latent TB, where the bacteria remain dormant in the body without causing symptoms, isoniazid helps prevent the progression to active TB, especially in individuals with weakened immune systems, such as those living with HIV. Additionally, isoniazid is used as a preventive therapy for people who have been exposed to TB or are at high risk of developing it, such as those in close contact with active TB patients or individuals with compromised immune systems. By treating latent infections and preventing new cases, isoniazid plays a crucial role in TB control and management.
Common side effects include nausea, vomiting, and loss of appetite. More serious side effects can include liver damage, neuropathy (numbness, tingling, or pain in the hands or feet), and allergic reactions. Vitamin B6 (pyridoxine) is often prescribed alongside isoniazid to prevent neuropathy.
Isoniazid can cause liver damage (hepatotoxicity), so liver function should be monitored regularly. People with existing liver problems, heavy alcohol users, or those over 35 should be monitored closely. It can also cause peripheral neuropathy, especially in people with diabetes or HIV, so vitamin B6 is often given to prevent this. Isoniazid should not be used during pregnancy unless the benefits outweigh the risks, and it is excreted in breast milk, so caution is advised for breastfeeding mothers.