Gentamicin combination therapy

Patients with PVE caused by penicillin-susceptible strains of viridans streptococci require treatment for 6 weeks with penicillin G or ceftriaxone with or without gentamicin during the initial 2 weeks of therapy. However, if the organism demonstrates less susceptibility to penicillin (MIC greater than 0.12 mcg/mL), a combination therapy with penicillin G or ceftriaxone plus gentamicin should be given for the entire 6 weeks. Vancomycin remains the primary alternative if the patient is allergic to (l-lactams (e.g., penicillins, cephalosporins, etc.). 

It is important to determine (1) whether the isolate is methicillin-susceptible or methicillin-resistant and (2) whether the patient has a prosthetic valve. For patients with no prosthetic material, methicillin-susceptible staphylococci treatment should consist of a penicillinase-resistant penicillin (e.g., nafcillin or oxacillin) with or without gentamicin, and for methicillin-resistant strains, therapy should consist of vancomycin (see Table 71-4). Combination therapy with aminoglycosides, when used in these patients, typically is given only during the first 3 to 5 days of therapy. In the absence of prosthetic material, some treatment guidelines do not recommend combination therapy against MRSA. However, many clinicians may combine either gentamicin or rifampin with vancomycin if the patient is unresponsive to monotherapy. 

Recommended therapy in the uncomplicated case caused by fully susceptible strains is 4 weeks of either high-dose penicillin G or ceftriaxone, or 2 weeks of combined therapy with high-dose penicillin G plus gentamicin (Table 37-3). 

Combination therapy is often used when dealing with infections caused by both aerobic and anaerobic bacteria [50,80]. Combination of metronidazole with either gentamicin or ciprofloxacin appeared to be effective in preventing infection of abdominal trauma [101] when combined with ciprofloxacin, metronidazole was affective as a preoperative antibiotic in colorectal surgery and appeared equal in efficacy to impipenem/cilastin for the treatment of complicated intraabdominal infections [103]. Combination therapy is not always indicated for the treatment of polymicrobial infections. New antibiotics, whose spectrum includes multiple classes of microorganisms (e.g., imipenem), may often preclude combination therapy. 

The recommended therapy for patients with left-sided IE caused by methicillin-sensitive S. aureus (MSSA) is 4 to 6 weeks of nafcillin or oxacillin, often combined with a short course of gentamicin (Table 37-6). 

Vancomycin is also an effective alternative therapy for the treatment of staphylococcal enterocolitis and endocarditis. The combination of vancomycin and either streptomycin or gentamicin acts synergisticaUy against enterococci and is used effectively for the treatment or... 

Bacterial endocarditis. An aminoglycoside, usually gentamicin, should comprise part of the antimicrobial combination for enterococcal, streptococcal or staphylococcal infection of the heart valves, and for the therapy of clinical endocarditis which fails to yield a positive blood culture. 

Love LJ, Schimpff SC, Hahn DM, Young VM, Standiford HC, Bender JF, Fortner CL, Wiernik PH. Randomized trial of empiric antibiotic therapy with ticar-cillin in combination with gentamicin, amikacin or netilmicin in febrile patients with granulocytopenia and cancer. Am J Med 1979 66(4) 603-10. 

Bailey RR. Renal failure in combined gentamicin and cephalothin therapy. BMJ 1973 2(5869) 776-7. 

Fortun J, Navas E, Martinez-Beltran J, Perez-Molina J, Martin-Davila P, Guerrero A, Moreno S. Short-course therapy for right-side endocarditis due to Staphylococcus aureus in drug abusers cloxacilhn versus glycopeptides in combination with gentamicin. Clin Infect Dis 2001 33(l) 120-5. 

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