A defectiva and Granulicatella Species and VGS With a Penicillin MIC 0.5 g/mL The determination of antimicrobial susceptibilities of A defec- tiva and Granulicatella species (both formerly known as nutri- tionally variant streptococci) is often technically difficult, and the results may not be accurate. Moreover, IE caused by these microorganisms is uncommon and has been more difficult to cure microbiologically compared with IE caused by a strain of For these reasons, in patients with IE caused by A defectiva and Granulicatella species, it is reasonable to administer a combination regimen that includes ampicillin (12 g/d in divided doses) or penicillin (18 30 mil- lion U/D in divided doses or by continuous infusion) plus gen- in 2 3 divided doses) with infectious diseases consultation to determine length of therapy. Findings from an animal model of experimental endocarditis suggest that if vancomycin is chosen for use in patients intolerant of penicillin or ampicillin, then the addition of gentamicin is not Ceftriaxone combined with gentamicin may be a reasonable alternative treatment option125,126 for VGS isolates that are susceptible to ceftriaxone on the basis of the Clinical and Laboratory Standards Institute definition and are resistant to penicillin (MIC 0.5 g/mL, as defined in this statement). Currently, there is no reported clinical experience with the combination of ampicillin plus ceftriaxone for IE caused by these organisms. Table 7. Therapy of NVE Caused by Highly Penicillin-Susceptible VGS and Streptococcus gallolyticus (bovis) Regimen Dose* and Route Duration, wk Strength of Recommendation Comments Aqueous crystalline penicillin G sodium 12 18 million U/24 h IV either continuously or in 4 or 6 equally divided doses 4 Class IIa; Level of Evidence B Preferred in most patients >65 y or patients with impairment of eighth cranial nerve function or renal function. 