5-episisomicin (
Sch 22591) is a novel semisynthetic
aminoglycoside with a spectrum and potency similar to
gentamicin in its activity against susceptible bacterial strains, but with increased potency against Pseudomonas, Providencia, and Proteus rettgeri. It is also more active than
tobramycin and
amikacin against these last-mentioned species.Against resistant strains,
Sch 22591 is significantly more active than
gentamicin or
tobramycin. Against resistant gram-negative bacteria other than Pseudomonas,
Sch 22591 has activity similar to that of
amikacin, but
Sch 22591 is more potent. Against Pseudomonas strains, it is active against most
gentamicin- and
tobramycin-resistant strains and is more active than the other three
antibiotics. Some Pseudomonas strains are resistant to
Sch 22591, but susceptible to
amikacin. Against a selection of
aminoglycoside-resistant staphylococci,
Sch 22591 has very good activity against strains resistant to
tobramycin,
amikacin, and
gentamicin. The superior in vitro potency of
Sch 22591 against Pseudomonas has been confirmed in vivo in experimental
infections in mice. Absorption in dogs is similar to that of other
aminoglycoside antibiotics. The acute toxicity of
Sch 22591 in mice is greater than that of
gentamicin; its vestibular toxicity potential and nephrotoxicity potential in cats and rats appear to be similar to those of
gentamicin.