Final answer:
The tricuspid valve is most commonly affected by bacterial endocarditis in IV drug users, with treatments varying based on the type of endocarditis and bacteria involved, but generally including targeted intravenous antibiotics.
Step-by-step explanation:
The most common heart valve affected by bacterial endocarditis in IV drug users is the tricuspid valve. IV drug use can introduce bacteria such as Staphylococcus aureus directly into the bloodstream, potentially leading to acute endocarditis, which tends to develop rapidly and can be life-threatening if not treated promptly. In contrast, subacute bacterial endocarditis develops more slowly and generally involves different bacteria, such as the viridans group of streptococci. Treatment for both acute and subacute endocarditis involves high doses of intravenous antibiotics.
Acute bacterial endocarditis is often treated with a combination of ampicillin, nafcillin, and gentamicin for synergistic coverage. In individuals with prosthetic valves and those who develop prosthetic-valve endocarditis, treatment typically includes a combination of vancomycin, rifampin, and gentamicin. The additional use of rifampin is pivotal for its ability to penetrate the biofilm that can form on foreign materials within the body. It is important for healthcare providers to be aware of valvular disorders potentially caused by cardiac inflammation due to autoimmunity in response to certain bacteria, like Streptococcus pyogenes causing rheumatic or scarlet fever.