Rifapentine (RPT)

Rifapentine is a semisynthetic rifamycin antibiotic, that has been included in shortened tuberculosis (TB) treatment regimens, as adviced in latest WHO guidelines 2025. Its pharmacokinetic profile allows for less frequent dosing and shorter treatment durations compared to the traditional standard, Rifampin.

1. Mechanism of Action and Antimicrobial Spectrum

• Mechanism: Rifapentine inhibits mycobacterial DNA-dependent RNA polymerase. By binding to the β-subunit of the enzyme, it blocks RNA synthesis, leading to cell death.
• Spectrum: Potently bactericidal against Mycobacterium tuberculosis. It also has activity against Mycobacterium avium complex (MAC).
• Cross-Resistance: M. tuberculosis strains resistant to Rifampin are almost always cross-resistant to Rifapentine.

2. Pharmacokinetic Advantages (vs. Rifampin)

Rifapentine’s clinical utility stems directly from its superior pharmacokinetics:

• Half-Life: longer half-life (~15 hours) compared to Rifampin (~2–3 hours). This long duration of action allows for intermittent (weekly) or high-dose daily dosing.
• Potency: more active in vitro against M. tuberculosis than Rifampin.
• Absorption: Absorption is increased by food, particularly a high-fat meal. Patients are usually advised to take it with food to maximize bioavailability.

3. Adverse effects

Hepatotoxicity (DILI) - Baseline and monthly Liver Function Tests (LFTs). Risks increase with INH co-administration or daily high-dose RPT.

Gastrointestinal Effects - Nausea, vomiting, abdominal pain. Often mitigated by taking with food.

Hypersensitivity Reactions - Including "flu-like syndrome" (more common with intermittent dosing).

Body Fluid Discoloration: (not a side effect but should be communicated to patients) Turns urine, sweat, tears, and saliva an orange-red color. Can permanently stain contact lenses.

4. Interactions

Rifapentine is a potent inducer of the Cytochrome P450 system (especially CYP3A4), though generally less potent than Rifampin. It significantly reduces the plasma concentrations of many co-administered drugs. Key affected classes include:

• Antiretroviral Therapy (ART): Protease inhibitors, NNRTIs, and integrase inhibitors. Requires specialized consultation in HIV-positive patients.
• Oral Contraceptives: Patients must use barrier methods of birth control while on therapy.
• Warfarin
• Anticonvulsants