Comparative Effects of Amoxycillin and Ampicillin in the Treatment of Experimental Mouse Infections

Summary

Amoxycillin was significantly more effective than ampicillin in the parenteral treatment of intraperitoneal mouse infections. After subcutaneous injection, antibiotic blood concentrations were the same for both compounds, but amoxycillin was more effective than ampicillin in reducing bacterial counts in the peritoneal cavity and in the blood of infected mice. Amoxycillin also produced greater bactericidal effects than ampicillin in vivo after intraperitoneal injection and consequently was more effective by this route in the treatment of infection. The results of these studies show that the superior activity of amoxycillin in the mouse when given by injection was due to its higher level of bactericidal activity in vivo compared with ampicillin and to differences in the distribution of the two penicillins in the infected animal.

Amoxycillin shows a spectrum and general level of antibacterial activity in vitro similar to that of ampicillin (Sutherland and Rolinson, 1971) but initial chemotherapeutic studies showed that amoxycillin was significantly more effective than ampicillin in the treatment of a variety of experimental mouse infections (Acred et al, 1971). The superior activity of amoxycillin by the oral route was attributed to the higher blood concentrations produced by amoxycillin in mice by this route, but this was not the case for parenteral administration where the serum concentrations produced by amoxycillin in experimental animals were no greater than those of ampicillin (Acred et al, 1971). Similar findings were reported by Hunter et al (1973) who concluded that amoxycillin produced greater bactericidal effects in vivo than did ampicillin.

In the studies reported here the effects of amoxycillin and ampicillin given by injection in the treatment of intraperitoneal mouse infections have been compared by measurement of levels and bacterial growth in the blood and peritoneal cavity of infected mice and correlation of these data with effectiveness of treatment, (Comber et al, 1975).