isoniazid + rifampicin: clinical use

Prescribing considerations

• Prescribe under respiratory or other suitably qualified specialist supervision.
• Review prescribed, non-prescription and herbal products when starting or stopping treatment.
• Assess hepatic and renal disease, alcohol use, nutritional status, diabetes, HIV, epilepsy, psychiatric history and existing peripheral neuropathy.
• Consider pyridoxine for patients at increased risk of isoniazid-related neuropathy.

Contraindications and cautions

• Hypersensitivity to isoniazid, rifamycins or product excipients
• Current jaundice
• Concurrent saquinavir with ritonavir
• Concurrent lurasidone, sofosbuvir, daclatasvir, telaprevir, cabotegravir, fostemsavir or lenacapavir

Monitoring

• Before treatment: hepatic enzymes, bilirubin, serum creatinine, full blood count and platelet count.
• Review adherence, adverse reactions and symptoms of hepatitis, neuropathy, blood disorders, renal injury and paradoxical deterioration.
• Repeat liver tests according to risk and clinical findings, with closer monitoring for people aged over 35 or with hepatic risk factors.
• Monitor relevant co-medication concentrations, effects or laboratory markers where enzyme induction may alter exposure.

Clinical pharmacology

Both components are bactericidal antituberculosis agents. Rifampicin inhibits bacterial DNA-dependent RNA polymerase and acts against rapidly, slowly and intermittently growing organisms. Isoniazid acts mainly against actively growing bacilli. Food can reduce absorption of both; isoniazid clearance varies with acetylator status.

Formulation and product differences

• The selected product is an orange, capsule-shaped, sugar-coated tablet containing rifampicin 300 mg and isoniazid 150 mg.
• It contains sucrose and sunset yellow (E110), which can cause allergic reactions.
• The selected product is not recommended for children or adolescents.
• A lower-strength Rifinah tablet is a separate marketed product.

Tablet

Route: Oral

Strengths: 150 mg + 100 mg, 300 mg + 150 mg