Active Ingredients

Isoniazid – Effect, Application & Risks


Isoniazid is an active substance from the class of antibiotics and assigned to the group of tuberculostatics. The drug is used to treat and prevent tuberculosis in infected people.

What is isoniazid?

Isoniazid is short for isonicotinic acid hydrazide . It is an antibiotic that is mainly used in combination with the antibiotic rifampicin to treat the infectious disease tuberculosis. In HIV patients , isoniazid is used in particular for tuberculosis prophylaxis. As a result, the number of tuberculosis cases and also the total number of deaths from tuberculosis in HIV patients has been greatly reduced.

The first synthesis of the drug took place in 1912 at the University of Prague and was carried out by Meyer and Malley. However, the antibiotic effect was first recognized around 30 years later. In the laboratories of the pharmaceutical companies Hoffman-La Roche and Bayer AG, the researchers and chemists Herbert Fox and Gerhard Domagk and their team further developed the substance until it was finally ready for the market.

Pharmacological action

The bactericidal active substance isoniazid is taken up by the bacterial cells. Inside the bacterial cell, the enzyme catalase or peroxidase (KatG) then converts isoniazid into isonicotinic acid. This isonicotinic acid is incorporated into the NAD coenzymes by the bacteria instead of nicotinic acid.

NAD play a crucial role in various metabolic processes and metabolic reactions. Due to the built-in isonicotinic acid, the coenzymes can no longer perform their function, so that the synthesis of nucleic acids and the synthesis of mycolic acid are disrupted. Mycolic acid is an important component of bacterial cell walls. This accounts for the resistance of the bacterium. When the cell wall is unstable due to the antibiotic, the bacteria perish.

Medical Application & Use

The main indication of isoniazid is the therapy of tuberculosis. The drug is also used to treat people who have been infected with tuberculosis but are not yet ill. Tuberculosis is an infectious disease that can be caused by various mycobacteria . However, the main pathogen is Mycobacterium tuberculosis . About 1.3 million people die from tuberculosis every year.

Basically, tuberculosis can be divided into different stages. Serious infections occur mainly in people with weakened immune systems. Therefore, the antibiotic isoniazid is also used to prevent tuberculosis in HIV patients. For this, the antibiotic is usually administered orally.

Isoniazid has a good bioavailability of around 90 percent . 75 percent of acetylation occurs in the liver . The drug and its metabolites are ultimately excreted through the kidneys .

Isoniazid is usually administered together with other tuberculostatic drugs. This is to avoid the development of resistance.

Risks & side effects

Medication with isoniazid can lead to gastrointestinal symptoms such as nausea , vomiting or diarrhea . Central nervous system disorders , allergies and peripheral neuropathies are also among the possible side effects . Furthermore, intrahepatic icterus ( jaundice ) can occur as a result of a certain degree of liver toxicity .

Due to the impaired liver, some patients also suffer from alcohol intolerance . Vitamin B6 deficiency can occur when taking antibiotics . As a result, polyneuritis can develop, which is accompanied by various neurological symptoms such as tingling , abnormal sensations or paralysis . In order to avoid such polyneuritis, the doctor treating you can also administer a vitamin B6 preparation.

Isoniazid shows interactions with various other preparations. Simultaneous administration of acetaminophen ( paracetamol ) increases the toxicity of this drug, which can lead to severe liver damage . There is also an interaction with the drug carbamazepine . Isoniazid decreases carbamazepine clearance, allowing the drug to stay in the blood longer . On the other hand, isoniazid lowers the levels of ketoconazole , a drug used to treat fungal infections . Isoniazid increases serum levels of theophylline and valproate. Theophylline is used to treat bronchial asthma and valproate to treat epilepsy .

In diseases of the liver, isoniazid is absolutely contraindicated. Intake should be avoided if possible in the case of acute hepatitis and liver failure . Taking the antibiotic isoniazid is also not recommended in the case of alcohol abuse and the metabolic disease diabetes mellitus .

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.