Some Pharmacodynamic Aspects of Cefepime

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.


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][2][3][4][5].
Expanded information concerning the pharmacodynamic effects of cefepime will be of bene�ts to both physicians and their patients. erefore, 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.

Materials
2.1.1. Cefepime. Cefepime is a new semisynthetic, broad spectrum, fourth generation cephalosporin antibiotic formu-lated 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.

Laboratory Animals.
Guinea pigs of both sexes and different weights (300-450 g) were used for investigating the effect of cefepime on the isolated ileum, auricles, and tracheal strips. Rabbits of both sexes and different weights (1500-2000 kg) were used for studying the effect of cefepime on isolated small intestines, heart, and electrocardiograph changes. Rats of both sexes and different weights (150-220 g) were used for studying the effects of cefepime on isolated colon, fundic strip, and uterine muscle in different stages of sex cycle and phrenic nerve hemidiaphragm. Egyptian toads were used for studying the effect of cefepime on isolated rectus abdominis muscle and sciatic nerve gastrocnemius muscle preparations. Mongrel dogs of both sexes weighing (15-20 kg) were employed for studying the effects of cefepime on blood pressure and rate of respiration. All animals were 2 Journal of Pharmaceutics maintained on feed and water ad libitum and were kept in a good ventilation room at 25 ∘ C.

2.2.
Methods. e method explained by Valeri et al. [6] was used for studying the effect of cefepime on the isolated ileum of guinea pigs. e method described elsewhere [7] was used for studying the effect of cefepime on isolated rabbit's duodenum, rat's colon, and uterine muscle of rats at various stages of sex cycle. e effect of cefepime on isolated rat's fundic strip was investigated according to the method described by �ilenov and �al�n [8]. e effect of cefepime on isolated guinea pig tracheal smooth muscle was studied using the glass jar bath apparatus [9]. e method described by Barlow et al. [10] was used for investigating the effect of cefepime on frog's gastrocnemius muscle-sciatic nerve preparation. e effect of cefepime on the isolated frog's rectus abdominis muscle was investigated [7]. e effect of cefepime on the isolated rat's phrenic nerve hemidiaphragm was studied by using the method described by Bulbring [11]. e glass jar bath was used for studying the effect of cefepime on isolated guinea pig's auricles [12]. e method using Gunn's apparatus (heart infusion assembly) was used for studying the effect of cefepime on rabbit's heart [13]. e effect of intravenous injection of cefepime on blood pressure and rate of respiration in an anaesthetized dog and the electrocardiographic changes in conscious rabbits aer intramuscular injection of cefepime were performed using the method described by Jackson [14].

Results
e effect of cefepime on isolated guinea pig's ileum, rabbit's duodenum, rat's colon, and rat's fundic strip and uterine motility of female rats at various stages of sex cycle have been recorded and presented in Table 1. Action of cefepime on the rabbit duodenal motility is shown in Figure 1. e rat's fundic strip was depressed by cefepime in a dose-dependent manner and histamine was not able to produce its stimulant effect in presence of cefepime ( Figure 2) so cefepime might appear to have an antihistaminic-like effect. Cefepime stimulated the uterine motility during estrus and nonestrus stages and depressed it during early and late pregnancy and these �ndings might be attributed to the direct effect of cefepime (Figures 3(a) and 3(b) and Figures 4(a) and 4(b)). Cefepime had no effect on the resting tonus of the isolated guinea pig's tracheal chain but histamine (60 g/mL bath) was not able to produce its contractile effect in the presence of cefepime (400 g/mL bath) as shown in Figure 5. is indicated that cefepime might have an antihistaminic like effect on this tissue.
Cefepime at concentrations of 200 and 400 g/mL bath induced marked inhibition in the force of muscular twitches of frog's gastrocnemius muscle which was less potent than that induced by procaine hydrochloride 2% ( Figure 6). Concentrations of 20 g/mL bath caused marked decrease in the contracture of frog's rectus abdominis muscles while complete blockade was produced in the presence of 40 g/mL bath of cefepime ( Figure 7). e concentrations of 80 g/mL bath produced marked inhibition in the force of rat's phrenic nerve hemidiaphragm which was reversed by 2.5 g acetylcholine/mL bath (Figure 8(a)) or 25 g neostigmine/mL bath (Figure 8(b)). is indicated that cefepime might act directly to induce neuromuscular blockade. e effect of gradually increased concentrations of cefepime on isolated guinea pig's auricles, rabbit's heart, and aortic strip has been demonstrated in Table 2. Cefepime depressed the isolated perfused rabbit's heart and this depression might be attributed to the direct effect of cefepime ( Figure 9).
Intravenous injection of cefepime in doses of 13.33, 26.67, and 53.33 mg/kg body weight had no effect on blood pressure and rate of respiration in anesthetized dogs ( Figure 10). Single intramuscular injection of 23.33, 46.67, and 93.33 mg/kg body weight induced no effects on the ECG parameters along period of 8 hours in conscious rabbits as shown in Table 3.

Effect of Cefepime on Smooth Muscle
Preparations. e present investigation showed that cefepime in vitro stimulated the contractility of guinea pig's ileum, rat's colon, and rabbit's duodenum. e stimulatory effect of cefepime was proportional to the graded tested concentrations. Presence of atropine sulphate as a muscarinic cholinergic receptor blocker and large dose of nicotine sulphate as ganglionic (nicotinic receptor) blocker did not inhibit the stimulatory effect of cefepime. In addition, the adrenaline as an adrenoceptor agonist produced its inhibitory effect in presence of cefepime. ese results proved that; the cefepime might directly stimulate the intestinal smooth muscles of rabbit's duodenum, guinea pig's ileum, and rat's colon. ese obtained results were similar to the fact that cefeperazone in vivo enhanced the ileal motility in guinea pigs at 62.5 and 125 mg/kg, respectively, and promoted gastrointestinal propulsion of barium sulfate meal in mice at 1000 mg/kg and in vitro enhanced slightly the motility of isolated rabbit's gastrointestinal tract at 0.001 g/mL [15]. Also these �ndings were similar to the fact that the spontaneous motility of smooth muscle in situ was temporarily increased with 800 mg/kg cefminox when administered intravenously and in upper doses [16,17]. In contrast, cefadroxil had no effects on the isolated smooth muscle organs and the passage of charcoal meal in mice [18]. In addition, ceizoxime sodium neither affected the spontaneous motility of isolated rabbit's and guinea pig's ileum at concentration equal to 10 −2 g/mL nor interacted with acetylcholine or histamine on the isolated guinea-pig's preparation [19]. e spontaneous movement and tone of isolated ileum, colon, and acetylcholine-, histamine-, nicotine-, or barium chloride-induced contraction of ileum were not affected following ceuperazone application [20]. Furthermore, cefprozil did not affect the isolated smooth muscles of rat's uterus, guinea pig's ileum, or rabbit's duodenum and did not in�uence ganglionic transmission in cats [21]. Cefepime had no effect on the intestinal smooth muscle and did not show any antagonism against some smooth muscle contracting drugs [22]. Cefamandole Journal of Pharmaceutics 3 T 1: e effect of cefepime on isolated guinea pig's ileum, rabbit's duodenum, rat's colon, rat's fundic strip, and uterine motility of female rats.     [23]. e maximum contractile responses to carbachol and histamine were signi�cantly reduced in response to the ceriaxone sodium [24]. Cefepime inhibited the contractility of the rat's fundic strip. is inhibitory effect was dose dependent. In presence of cefepime, histamine was unable to stimulate the fundic strip. is result indicated that cefepime had an antihistaminic like effect on the rat's fundic strip. e obtained results came in harmony with the dose-dependently suppressed effect of ceizoxime sodium aer intravenous dose of 320 to 1000 mg/kg of the spontaneous contraction of the pyloric antrum in morphine-urethane-anesthetized dogs [19], while Cefadroxil had no effects on the motility of the stomach in situ in rabbits [18]. On the other hand, cefotaxime, ceriaxone, and ceazidime produced concentration-dependent tonic contractions of rat's fundus [25] and cefamandole had stimulatory effect on the rat's fundic strips [23].

Concentrations
Cefepime stimulated the uterine motility during estrus and nonestrus and inhibited the uterine motility during early and late pregnant stage. e effect was dose dependent. ese effects might be attributed to the direct action of the cefepime on the isolated uterus. During estrus and nonestrus, and in presence of atropine sulphate (0.25 g/mL bath), cefepime induced its stimulant effect and the adrenaline (0.5 g/mL bath) relaxed the uterus aer its stimulation with 800 g/mL bath cefepime. During the early and late pregnant stages, the addition of acetylcholine in a small concentration (0.25 g/mL bath) produced its stimulatory effect in the presence of cefepime (800 g/mL bath) and the cefepime in the same concentration relaxed the uterus aer its stimulation with 1 g propranolol/mL bath. e obtained results were consistent with the uterine stimulant effect of cefeperazone during estrus and nonestrus stages in four of six experiments and the uterine depressant effect of it in two of six experiments while during pregnancy, cefoperazone might not affected or depressed and/or stimulated the uterine motility [15]. Also the present results were similar to the effect of ceeram pivoxil during nonpregnancy. Ceeram pivoxil increased both the force and frequency of the uterine motility in four of six experiments and had no changes in four of another six experiments. During pregnancy it induced no changes in four of six experiments and increased in four of another six experiments [26]. e obtained results during estrus and nonestrus stages were agreeable also with the effect of cefamandole on uterine contractility; cefamandole concentrations of 2048 and 4096 micrograms cefamandole/mL bath caused marked stimulation in force and frequency of rat uterine muscle in all stages of sex cycle [23]. In another observation, cefepime had no effect on the delivery status of the offspring rats [27], and the spontaneous movement and tone of isolated uterus were not affected following ceuperazone application [20]. Effects of betalactam antibiotics on smooth muscle isolated preparations were tissue and species dependent, indicating selectivity of their action [25].
e guinea pig's tracheal smooth muscles seemed to be insensitive to the tested concentrations of cefepime. In presence of cefepime, histamine was not able to produce its stimulatory effect, thus cefepime blocked the action of histamine on the tracheal smooth muscles. e obtained results in this study were similar to the effect of cefprozil and cefamandole which had no effect on the tracheal smooth muscles in different graded concentrations. e two antibiotics blocked the stimulatory effect of histamine on the guinea pig's tracheal muscles in a dose-dependent manner [21,23]. On the other hand, ceizoxime and cefminox relaxed the resting tonus of the isolated guinea pig's tracheal chain preparation at a concentration of 10 − g/mL [16,19]. Cefoperazone and ceeram pivoxil caused slight stimulation of the isolated guinea pig's tracheal smooth muscles in a concentration as high as 10 −2 g/mL and 10 − g/mL, respectively [15,26]. ese results might be attributed to the high concentration of the used antibiotics than those used in this study.

Effect of Cefepime on the Skeletal Muscle Preparations.
e effect of cefepime on skeletal muscle preparations (frog's gastrocnemius muscle sciatic nerve, frog's rectus abdominis muscle, and rat's phrenic nerve hemidiaphragm) was investigated. e cefepime elicited a marked neuromuscular blocking activity in response to indirect muscle twitches; also cefepime exhibited a local anaesthetic like activity on frog's gastrocnemius sciatic nerve preparation. Cef.
Adr. Cef. min (b) 800 g/mL bath cefepime (Cef.) followed by 0.5 g/mL bath drenaline (Adr.).  Trials were performed to detect the site of action of cefepime on the skeletal muscle preparations. e results showed that cefepime did not impair the stimulatory effect of neostigmine and acetylcholine on rat's phrenic nerve hemidiaphragm preparation. erefore, the neuromuscular blocking effect of cefepime seemed to be attributed to two mechanisms� the �rst might be due to local anaesthetic effect of cefepime which is responsible for blocking of conduction through sciatic and phrenic nerve. e second mechanism might be attributed to calcium ions antagonistic effect of the cefepime. Calcium ions in�ux is necessary for acetylcholine release as well as other neurotransmitters and hormones [28].
e neuromuscular blocking activity of cefepime on skeletal muscle preparations in the present work was similar to the fact that the twitch tension of gastrocnemius muscle evoked by electrical stimulation of sciatic nerve was slightly reduced following administraton of cefminox and ceeram pivoxil, respectively [16,26]. Also the present effect was similar to the fact that cefepime reduced spontaneous locomotor activity in mice [22]. Cefamandole had a neuromuscular blocking effect on isolated frog's gastrocnemius muscle, frog's rectus abdominis muscle, and rat's phrenic nerve hemidiaphragm [23].
e obtained results were inconsistent with the fact that ceizoxime did not affect the contractile response of the isolated rat's diaphragm to electrical stimulation of the phrenic nerve at concentration of 10 −3 g/mL [19]. Cefoperazone enhanced slightly the twitch tension of musculus gastrocnemius induced by electrical stimulation in rats at 500 mg/kg body weight [15]. Ceuperazone had no effect on the neuromuscular junction [20].
From the present study it could be concluded that cefepime has depressant effect on the skeletal muscles in a manner similar to that of the local anesthetic effect of procaine hydrochloride.

Effect of Cefepime on the Cardiovascular Muscle Prepara-
tions. e obtained results in this study on the cardiovascular muscles proved that cefepime had a negative inotropic effect on the isolated guinea pig's auricles and rabbit's heart. Cefepime produced a direct and dose dependent depression of the myocardial contractility. is negative inotropic effect of cefepime was not referred to either ß1 adrenergic blocking effect or cholinergic stimulant effect, as adrenaline (2 g/mL canula) was able to produce its cardiac stimulatory effect in presence of cefepime (1200 g/mL canula) and aer addition of atropine sulphate (25 g/mL canula), cefepime (1200 g/mL canula) was able to produce its inhibitory effect.
Contraction of the cardiac cells is believed to be dependent upon the intracellular concentration of available calcium ions in the vicinity of the contractile apparatus [29] so the direct myocardial depressant effect of cefepime in the present work might be attributed to a modi�cation of calcium function.
e negative inotropic effect of cefepime on guinea pig's auricles and rabbit's heart in the present work was similar to the direct depressant effect of cefamandole on the contractility of isolated guinea pig's auricles and rabbit's heart min Hist. in a dose-dependent manner [23]. is obtained result was not consistent with that; cefadroxil and ceizoxime sodium in a dose of 10 −2 g/mL had no effects on the isolated hearts of rabbits and the spontaneous movement in isolated guinea pig's atrium, respectively [18,19]. e obtained results were also inconsistent with the fact that cefminox did not affect the spontaneous contraction of isolated guinea pig's atria and the blood vessels in perfused rabbit's ears [30].
It was observed that cefepime had no effect on the smooth muscle of aorta. In the presence of cefepime, noradrenaline was not able to produce its stimulatory effect, thus cefepime appeared to cause an alpha adrenergic blocking like effect on isolated rabbit's aortic strip. is result was consistent with the fact that ceuperazone, ceeram pivoxil, and cefamandole, respectively, did not affect the rabbit's descending aorta and the adrenaline and noradrenaline fail to produce its stimulatory effect in the presence of these antibiotics [20,23,26]. is was inconsistent with the fact that cefoperazone potentiated the presser response to adrenaline in dogs [15].

Effect of Cefepime on Blood Pressure and Respiration.
Aer intravenous injection of cefepime in doses of 13.33, 26.67, and 53.33 mg/kg body weight, no changes were induced in blood pressure and rate of respiration in an anaesthetized dog over a period of half hour aer each dose. is is supported by the lack of cefepime effects on the electrocardiographic parameters in this study. e depressant effects of cefepime on isolated heart and auricles and the alpha adrenoceptor blocking effects of cefepime on the isolated aortic strip in this study might be attributed to the higher doses of cefepime in the organ bath. e obtained results were consistent with the fact that cefadroxil induced no marked Ach. min Cef.

Cef.
Neost. changes in the respiration and blood pressure in anesthetized dogs [18]. e obtained �ndings were inconsistent with the fact that cefoperazone increased transiently the respiratory rate and potentiated the depressor response to acetyl choline at 125 mg/kg, increased femoral blood �ow, and potenti� ated the presser response to adrenaline in dogs [15]. Also, ceuperazone caused transient increase of respiratory rate, slight hypotension, and transient increase of femoral blood �ow in dogs at intravenous doses of 250�1000 mg/kg [20]. Moreover, cefminox slightly raised a level of blood pressure in dogs when intravenously given more than 400 mg/kg [30]. Ceeram caused a slight hypotension and increased both respiratory rate and femoral blood �ow [26]. e respiration and blood pressure were depressed by cefepime [22]. In the same direction, cefamandole in a dose of 53.2 mg/kg body weight in anaesthetized dogs caused very marked hypotensive effects and decrease in rate of respiration [23]. ese might be attributed to the higher doses used in these studies.

Effect of Cefepime on Electrocardiographic Changes.
Aer single intramuscular injection of the 23.33, 46.66, and 93, 32 mg/kg body weight of cefepime in conscious rabbits, no changes were observed in electrocardiographic parameters during a period of 8 hours aer injection. is result was consistent with those observed in rabbits [15,20,21] and dogs [26]. is result was inconsistent with the fact that the electrocardiogram was affected by cefepime and this might be attributed to the use of higher doses (1000 mg/kg body weight) of cefepime, a factor that might have caused modi�cation of calcium ions function [22].

Conclusion
From the present study it could be noticed that cefepime stimulates the smooth muscles of intestines and uterus during estrus and nonestrus and depresses those of stomach, uterus during early and late pregnancy as well as cardiac muscles. Cefepime also has depressant effect on the skeletal muscles in a manner similar to that of procaine hydrochloride. e study also showed that cefepime has no effect on blood pressure, respiration, and ECG. From the present results and previous reports, it is evident that cefepime has strong potential as highly safe and useful antibiotic agent in clinical use.