Estreptograminas

Estreptograminas, or streptogramins, are a class of antibiotics that inhibit bacterial protein synthesis by targeting the 50S ribosomal subunit. The class comprises two groups, streptogramin A and streptogramin B. In clinical practice, the main agent is the fixed combination of dalfopristin (streptogramin A) and quinupristin (streptogramin B), marketed in several countries under names such as Synercid.

Mechanism of action is synergistic when the two components are used together. Dalfopristin binds to the ribosome and alters the ribosomal structure to enhance the binding of quinupristin, which then blocks elongation during protein synthesis. The combination can be bactericidal for many organisms due to its dual blockade of protein synthesis.

The spectrum is limited to Gram-positive bacteria. The dalfopristin/quinupristin combination is active against many staphylococci (including some MRSA strains) and streptococci, and it has activity against Enterococcus faecium, including some vancomycin-resistant strains, but shows poor activity against Enterococcus faecalis. Activity against Gram-negative bacteria is negligible.

Clinical use is reserved for serious infections caused by resistant Gram-positive pathogens when alternative therapies are unsuitable or ineffective. Indications include certain MRSA infections, complicated skin and soft tissue infections, bacteremia, and some infections caused by VRE. The drug is administered exclusively by intravenous infusion and is not used orally.

Adverse effects and safety considerations include infusion-related pain and phlebitis, nausea, arthralgia, myalgia, and hepatotoxicity. It can inhibit certain drug-metabolizing enzymes (notably through CYP3A4 interactions), leading to possible drug interactions. Resistance mechanisms include target-site modification and efflux, which limit the utility of this class and underscore the need for susceptibility testing prior to use.