rifamicinas

Rifamicinas, or rifamycins, are a group of antibiotics produced by the soil bacterium Amycolatopsis mediterranei. They are widely used in the treatment of mycobacterial infections and in various preventive strategies, as well as in some gut-directed indications for rifaximin.

Mechanism and spectrum: Rifamycins act by binding the beta subunit of bacterial DNA-dependent RNA polymerase, inhibiting transcription and proving bactericidal in many organisms. They have strong activity against Mycobacterium tuberculosis and other mycobacteria, as well as several Gram-positive bacteria. Their effectiveness against many Gram-negative bacteria is limited, and resistance can develop rapidly when used alone, so they are typically employed in combination regimens.

Common drugs and clinical use: The main rifamycins are rifampin (rifampicin), rifabutin, rifapentine, and rifaximin. Rifampin and rifapentine are core components of active tuberculosis regimens and are also used for latent TB infection in combination with other drugs (for example, rifapentine with isoniazid in a weekly regimen). Rifabutin is preferred over rifampin in some HIV coinfection scenarios because it has fewer drug interactions. Rifampin and rifabutin also serve as prophylaxis for close contacts of individuals with meningococcal or Haemophilus influenzae type b disease. Rifaximin is poorly absorbed from the gut and is used for traveler's diarrhea, hepatic encephalopathy, and certain irritable bowel syndrome cases; its limited systemic absorption reduces most systemic adverse effects and interactions.

Pharmacokinetics and safety: Rifamycins are generally well absorbed orally (with notable exceptions like rifaximin). They are potent inducers of cytochrome P450 enzymes and can reduce plasma levels of many drugs, including oral contraceptives and antiretrovirals. Adverse effects range from hepatotoxicity and hypersensitivity to dermatologic reactions and harmless orange-red discoloration of bodily fluids. Resistance typically arises with monotherapy, underscoring the importance of combination therapy.