Gentamycin for prophylaxis of bacterial endocarditis: a review for the dentist

New guidelines have recommended that gentamicin in combination with ampicillin be used for prophylaxis of bacterial endocarditis in patients with prosthetic heart valves. This article reviews some of the important and practical considerations for its use by the dentist. Gentamicin is an aminoglycoside antibiotic most exclusively reserved for treatment of serious infections caused by gram-negative bacteria in which less toxic antibacterials are ineffective. It has also been shown to be impressive in combination with penicillin in treating high-risk endocarditis patients. All strains of enterococci that are resistant to penicillin plus streptomycin are almost always sensitive to penicillin plus gentamicin. There is minimal absorption into the bloodstream from the gastrointestinal tract after oral administration but rapid absorption after intramuscular injection. Peak serum concentrations appear 30 to 90 minutes after intramuscular injection. The T1/2 is 2 hours, and in normal kidneys 85% to 95% of the drug is excreted within 24 hours by glomerular filtration. Ototoxicity and nephrotoxicity are the most serious toxic effects resulting from gentamicin therapy. The incidence of ototoxicity is about 2%, with affected patients experiencing vestibular effects rather than hearing loss. Nephrotoxicity is usually not seen before the patient has had 5 to 7 days of frequent dosing for treatment of systemic infections; the incidence is 2% to 4%. There are no data to suggest that ototoxicity or nephrotoxicity will occur in the patient given a single intramuscular injection of gentamicin for the prophylaxis of bacterial endocarditis. A single intramuscular or intravenous injection each of ampicillin and gentamicin should provide adequate blood levels for protection in the endocarditis patient for at least 4 to 5 hours.(ABSTRACT TRUNCATED AT 250 WORDS)