In addition, most laboratories do not rou- tinely perform serum streptomycin assays and may not have access to a clinical pharmacist to assist in dosing adjustments. Streptomycin use should be avoided in patients with creati- nine clearance <50 mL/min. If the strain of enterococcus is susceptible to both gentamicin and streptomycin, it is reason- able to use gentamicin rather than streptomycin for therapy. When gentamicin therapy is not an option, then a double - lactam regimen (see later section) is reasonable. Short-Course ( 2-Week) Gentamicin Therapy Olaison and Schadewitz189 in Sweden reported a 5-year pro- spective study of 78 cases of enterococcal IE treated with a -lactam and an aminoglycoside. The older age of these patients was a factor in their inability to tolerate prolonged aminoglycoside therapy. The median duration of aminogly- coside therapy was 15 days, and the microbiological cure and survival rates were similar to those for patients who received longer courses of gentamicin therapy. The major advantage of short-course aminoglycoside therapy is reduced risk of aminoglycoside-associated nephrotoxicity. The disadvan- tage is that this is a single nonrandomized, noncomparative study. The results of a Danish pilot study185 that represented a before and after study, which was based on 2007 guidelines that recommended a 2-week treatment course of gentamicin for enterococcal IE in combination with -lactam therapy for 4 to 6 weeks, confirmed the results seen in the Swedish Double -Lactam Regimens for E faecalis IE Most strains of E faecalis are inhibited but not killed in vitro by penicillin or ampicillin, with MICs usually 2 to 4 g/ mL penicillin; ampicillin MICs are usually 1 dilution lower. Cephalosporins and antistaphylococcal penicillins (oxacillin, nafcillin) have minimal or no in vitro activity against entero- cocci. The in vitro activity of carbapenems is variable, with imipenem being most active. 