Synergistic action of ampicillin and nafcillin against ampicillin-resistant Haemophilus influenzae

Comparative in vitro and in vivo activity of temocillin (BRL 17421) and ampicillin against Haemophilus influenzae type b

A total of 42 strains of Haemophilus influenzae type b isolated from pediatric patients were sensitive in vitro to temocillin (90% minimal inhibitory concentration = 0.25 microgram/ml). No difference in mean minimal inhibitory concentration between beta-lactamase producer (0.25 microgram/ml) and nonproducer (0.23 microgram/ml) strains was found. Various dosages of ampicillin or temocillin for the treatment of infant rats with ampicillin-resistant H. influenzae bacteremia and meningitis yielded no difference in cure rates. These results suggest that temocillin may not be as effective as other new cephalosporins for the treatment of H. influenzae type b infections.

In vitro and in vivo synergism between amoxicillin and clavulanic acid against ampicillin-resistant Haemophilus influenzae type b

Eight strans of ampicillin-resistant beta-lactamase-producing Haemophilus influenzae type b were studied in vitro for synergy between amoxicillin and clavulanic acid. The minimal inhibitory concentrations for amoxicillin alone were 6.25 to 12.5 microgram/ml, and for clavulanic acid alone they were 12.5 to 25 microgram/ml. However, seven of eight strains were inhibited by a combination of 0.36 microgram of amoxicillin and 0.36 microgram of clavulanic acid per ml. Infant rat models of bacteremia and meningitis were used to test the efficacy of amoxicillin and clavulanic acid alone and in combination upon four strains of ampicillin-resistant H. influenzae. Neither amoxicillin alone (27 animals) nor clavulanic acid alone (20 animals) sterilized the blood or cerebrospinal fluid of the animals. In contrast, 30 of 33 blood cultures and 29 of 33 cerebrospinal fluid cultures were sterile when a combination of the two drugs in the same dosages was used. The observed in vitro and in vivo synergism between amoxicillin and clavulanic acid suggests that the combination may be effective therapy for invasive infections in humans caused by ampicillin-resistant H. influenzae type b.

Synergistic action of nafcillin and ampicillin against ampicillin-resistant Haemophilus influenzae type b bacteremia and meningitis in infant rats

Infant rats with bacteremia and meningitis induced by ampicillin-resistant Haemophilus influenzae type b were treated with ampicillin and nafcillin, alone or in combination. Neither ampicillin alone (in 19 animals) nor nafcillin alone (in 20 animals) sterilized the blood or cerebrospinal fluid of any treated infant rat. When the combination of ampicillin and nafcillin was used, blood cultures were negative in 18 of 19 infant rats, and cerebrospinal fluid cultures were sterile in 15 of 19 when cultured 30 h after initiation of treatment. In vitro results demonstrated definite synergism between ampicillin and nafcillin against ampicillin-resistant H. influenzae type b. The study suggests that such synergism also exists in vivo.