Antimycobacterials

Question 1

Treatment of M. tuberculosis

Answer 1

PPx: Isoniazid

Tx (“RIPE”): Rifampin, Isoniazid, Pyrazinamide, Ethambutol

Question 2

Treatment of M. avium-intracellulare

Answer 2

Ppx: Azithromycin, Rifabutin

Tx: Azithromycin or clarithromycin + ethambutol

Question 3

Treatment of M. leprae

Answer 3

PPx: N/A

Tx: Dapsone and rifampin (for tuberculoid form). Add clofaximine (for lepromatous form)

Question 4

Isoniazid (INH)

Answer 4

Decreases synthesis of mycolic acids. Bacterial catalase-peroxidase required to convert INH to active metabolite.

PPx and Tx of M. tuberculosis

“INH”: Injures Neurons and Hepatocytes. INH competes with pyridoxine (vitamin B6) binding sites and increases its urinary excretion. Pyridoxine supplementation can prevent neurotoxicity and lupus.

Question 5

Rifamycins (rifampin, rifabutin)

Answer 5

Inhibit DNA-dependent RNA polymerase

Treat M. tuberculosis (delays resistance to dapson when used concurrently for leprosy)

Meningococcal prophylaxis

Chemprophylaxis in children exposed to HiB

“Four R’s”: RNA polymerase inhibitor, Ramps up P-450 (rifAMPin only), Red/orange body fluids, Rapid resistance if used alone

Question 6

Pyrazinamide

Answer 6

Effective in acidic pH of phagolysosomes, where it inhibits growth of M. tuberculosis. Requires activation by mycobacterial enzyme pyrazinamidase.

Only TB drug that affects intracellular TB.

Question 7

Ethambutol

Answer 7

Blocks arabinosyltransferase, which decreases carbohydrate polymerization of the mycobacterial cell wall.

Treats M. tuberculosis.

Optic neuropathy (red-green color blindness)

Question 8

Streptomycin

Answer 8

Aminoglycoside antibiotic that inhibits mycobacterial protein synthesis by disabling the 30S subunit.