Isoniazid

How it works

Isoniazid inhibits synthesis of mycolic acids, essential components of the mycobacterial cell wall, exerting a bactericidal effect against replicating Mycobacterium tuberculosis.

Prescribing in practice

• Hepatotoxicity is the major risk — assess liver function before and during treatment and advise patients to stop and seek urgent review if they develop nausea, vomiting, jaundice or dark urine.
• Co-prescribe pyridoxine to prevent peripheral neuropathy, particularly in those at higher risk such as people with diabetes, alcohol dependence, malnutrition, HIV or pregnancy.
• Isoniazid inhibits several hepatic enzymes and interacts with multiple drugs, so review co-medication before starting.

Monitoring

Monitor liver function and clinical features of hepatitis throughout treatment, and review for symptoms of peripheral neuropathy.

Counselling the patient

• Stop the tablets and contact your TB team urgently if you develop yellowing of the skin or eyes, persistent nausea or dark urine.
• Take it as part of the full combination and complete the whole course to prevent resistance.

Evidence & guidelines

Isoniazid within multidrug regimens is standard of care for tuberculosis in NICE guidance and UK TB programmes.