Mycobutin (Rifabutin)

Rifabutin is used to treat infections caused by mycobacterial species, particularly in immunocompromised patients.

• Mycobacterium avium complex (MAC) infection: prevents and treats MAC disease in HIV‑positive individuals.
• Active tuberculosis: contributes to bacterial clearance as part of multidrug therapy for pulmonary and extrapulmonary TB.

• Rifabutin binds to the β‑subunit of bacterial DNA‑dependent RNA polymerase, inhibiting the initiation of RNA synthesis. By blocking transcription, it suppresses the replication of mycobacteria, including Mycobacterium tuberculosis and Mycobacterium avium complex. The drug’s lipophilic nature facilitates intracellular penetration, allowing activity within macrophages where mycobacteria reside. The inhibition is concentration‑dependent and exhibits a post‑antibiotic effect, supporting once‑daily dosing in many regimens.

Rifabutin may cause a range of adverse reactions, varying from mild to severe.

Common Side Effects

• Nausea
• Vomiting
• Abdominal pain
• Rash

Serious or Rare Side Effects

• Hepatotoxicity (elevated liver enzymes)
• Severe neutropenia or agranulocytosis
• Hypersensitivity reactions (including Stevens‑Johnson syndrome)
• Thrombocytopenia

Before initiating Rifabutin therapy, clinicians should consider several precautionary measures to minimize risk.

• Assess liver function: obtain baseline hepatic enzymes and monitor periodically.
• Monitor complete blood count: watch for neutropenia or thrombocytopenia.
• Review concomitant medications: avoid drugs with known major interactions.
• Use caution in HIV‑positive patients: consider resistance development and drug‑drug interactions.
• Evaluate hypersensitivity history: discontinue if severe allergic reaction occurs.
• Store at ambient temperature: keep in original packaging, protect from moisture and light.

Rifabutin interacts with several medicines; some combinations should be avoided while others require close monitoring.

Major Interactions (Avoid)

• Protease inhibitors (e.g., ritonavir): markedly increase Rifabutin plasma concentrations.
• Macrolide antibiotics (e.g., clarithromycin, azithromycin): raise Rifabutin levels and risk toxicity.
• Antiretroviral agents (e.g., efavirenz): may reduce Rifabutin exposure, compromising efficacy.

Moderate Interactions (Monitor Closely)

• Warfarin: Rifabutin can enhance anticoagulant effect, requiring INR monitoring.
• Anticonvulsants (e.g., phenytoin, carbamazepine): may lower Rifabutin levels.
• Oral contraceptives: efficacy may be decreased, advise additional contraceptive measures.