Some pharmacodynamic effects of cefepime, a new injectable semisynthetic cephalosporin, were studied in laboratory animals and the following results were obtained. Cefepime maximally stimulated isolated guinea pig's ileum, rat's colon (80？μg/mL bath), and rabbit's duodenum (400？μg/mL bath). Contrarily, complete relaxation of isolated rat's fundic strip was produced by 80？μg/mL bath. Effects of cefepime on isolated rat's uterine muscle were different according to stage of sex cycle. Cefepime did not induce any effects on the resting tonus of isolated guinea pig's tracheal chain and rabbit's aortic strip. Concentrations of 200 and 400？μg/mL bath induced marked inhibition in the force of muscular twitches of the isolated frog's gastrocnemius muscle which was less potent than that induced by procaine hydrochloride 2%. Cefepime completely blocked the neuromuscular transmission of frog's rectus abdominis muscle (40？μg/mL bath) and rat's phrenic nerve hemidiaphragm preparation (200？μg/mL bath). This blockade was reversed by acetylcholine and neostigmine. Cefepime produced dose-dependent negative inotropic effect on isolated rabbit's heart and guinea pig's auricles. There were no changes in blood pressure and rate of respiration in anaesthetized dog after cefepime injection. These findings indicate that cefepime has a low potential to produce adverse reactions at therapeutic doses. 1. Introduction Cefepime, a parenteral fourth generation cephalosporin antibiotic, is an established and generally well tolerated drug with a broad spectrum of antibacterial activity. Cefepime has in vitro activity against Gram positive and Gram negative organisms and is stable against many of the common plasmid and chromosome mediated beta lactamases [1–5]. Expanded information concerning the pharmacodynamic effects of cefepime will be of benefits to both physicians and their patients. Therefore, the purpose of this study was to investigate some pharmacodynamic effects of cefepime on smooth, skeletal, and cardiac muscles, as well as on systemic blood pressure, respiration, and electrocardiographic changes in guinea pigs, rabbits, rats, frogs, and dogs. 2. Materials and Methods 2.1. Materials 2.1.1. Cefepime Cefepime is a new semisynthetic, broad spectrum, fourth generation cephalosporin antibiotic formulated for parenteral administration in strengths equivalent to 500？mg, 1？g, and 2？g of cefepime. It was produced by Bristol Myers Squibb Company (Egypt) and has the commercial name Maxipime. 2.1.2. Laboratory Animals Guinea pigs of both sexes and different weights (300–450？g) were
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