The in vitro susceptibility of human isolates of Pasteurella multocida to oral antimicrobial agents from our current study and from a review of the literature suggests that dicloxacillin (oxacillin), erythromycin, clindamycin, cephalexin, cefaclor, and cefadroxil should not be used for empiric therapy of animal bite wounds. Agents that were consistently active against P. multocida were penicillin, ampicillin, amoxicillinclavulanic acid, tetracycline, minocycline, chloramphenicol, trimethoprim-sulfamethoxazole, and cefuroxime. Possible reasons for the confusion regarding the activity of oral cephalosporins are addressed.Pasteurella multocida is an important pathogen in human infections due to dog and cat bites (2,9,10,12,14,15,17,23). These wounds account for approximately 1% of emergency room visits (6) and over $30 million in health care costs annually (7). Many of these patients are given oral antimicrobial therapy and are followed as outpatients.While penicillin is considered to be the drug of choice, alternative therapy must be considered when Staphylococcus aureus either is suspected to be or is present in the wound or when the patient gives a history of penicillin allergy. In these situations, the selection of alternative therapy has been varied. The use of penicillinase-resistant penicillins such as oxacillin or dicloxacillin has been advocated (3,7,8,16). In the penicillin-allergic patient either oral cephalosporins or erythromycin is often used.To clarify the potential utility of oral agents for empiric therapy, we report the comparative activities of some commonly used oral antimicrobial agents against strains of P. multocida recently isolated (1986) from humans with infected animal bite wounds, and we also review the published English-language data on P. multocida susceptibility. Strains were taken from frozen cultures and transferred twice to ensure purity and good growth. Mueller-Hinton agar supplemented with hemin (10 ,ug/ml) was used as the basal medium. Plates for testing the activity of SXT were supplemented with 5% laked horse blood. Freshly prepared solu-* Corresponding author. MATERIALS AND METHODStions of twofold dilutions of antimicrobial agents were incorporated into the media described to yield final concentrations of 64 to 0.06 jxg/ml. SXT was prepared in a sulfamethoxazole-to-trimethoprim ratio of 19:1.The plates were inoculated with a Steers replicator (Craft Machine Inc., Chester, Pa.) using a standard inoculum corresponding to a 0.5 McFarland standard no. 1 and were further diluted 1:10 (104 CFU/ml, final concentration). Control plates without antimicrobial agents were inoculated before and after each series of drug-containing plates. Plates were incubated at 35°C in an aerobic environment for 24 h and then examined. The control strain (S. aureus ATCC 25923) was tested simultaneously. The MIC was defined as the lowest concentration of an agent that yielded no growth or one discrete colony. RESULTS Eighty-five references were cited in the literature search, of which three described th...

Serum and milk concentrations of aztreonam were studied in 12 lactating, healthy subjects over the 8 h period after the administration of a single intramuscular or intravenous 1 g dose. Milk concentrations of aztreonam were found to be much lower than serum concentrations at all time points after both routes of injection. Peak milk concentrations of aztreonam averaged less than 1% of peak serum concentrations. Times to peak concentrations averaged 6 and 10 times longer in milk than in serum after intramuscular and intravenous injections, respectively. The low milk levels, as well as the previously determined poor oral absorption of aztreonam, suggest a low risk of untoward effects in the nursing infant.