Mycobacterial Infections including Tuberculosis
Core concepts
Know TB regimens: RIPE (rifampin, isoniazid, pyrazinamide, ethambutol) for 2 months, then rifampin + isoniazid for 4 months for drug-susceptible pulmonary TB. Latent TB: 4R (rifampin 4 months), 3HP (isoniazid + rifapentine weekly x12), or 9H. Isoniazid causes peripheral neuropathy (give pyridoxine) and hepatitis; rifampin induces CYP450 and turns secretions orange; pyrazinamide causes hyperuricemia; ethambutol causes optic neuritis (check color vision).
Must-know syndromes
Miliary/disseminated TB, TB meningitis (prolonged steroids, longer duration), drug-resistant TB (MDR = R + H resistance; XDR = additional resistance), nontuberculous mycobacteria (MAC-azithromycin + ethambutol; M. abscessus-complex, often multidrug), and leprosy (dapsone + rifampin + clofazimine).
Traps
Don't miss TB in immunocompromised hosts with negative smears. Rifampin interactions with ART (use rifabutin with certain regimens). Isoniazid hepatotoxicity-stop if transaminases rise significantly with symptoms. Ethambutol is avoided in young children who can't report visual changes.
Worked rule of thumb
For a patient with suspected TB meningitis, start empiric RIPE + dexamethasone immediately; do not wait for culture. Add pyridoxine to isoniazid to prevent neuropathy, especially in pregnancy, diabetes, and HIV.