Pharmacokinetics of intravenous cefetamet and oral cefetamet pivoxil in patients with hepatic cirrhosis

Pharmacokinetics and pharmacodynamics of oral and intravenous cefetamet in dog

The pharmacokinetic (PK) and pharmacodynamic (PD) properties of intravenously (IV) administered cefetamet-Na and per os (PO) administered cefetamet pivoxil were investigated in eighteen healthy dogs at three different dose levels. The three doses for IV cefetamet-Na were 95, 190 and 380 mg, while those for oral cefetamet pivoxil were 125, 250 and 500 mg (both equivalent to 90, 180 and 360 mg of cefetamet). An efficacy predictor, measured as the ratios of the time that the concentration of the free drug is over the MIC90 (T > MIC90) and the dosing interval (f% T > MIC90) of IV and PO administration were calculated. The PK parameters' maximum concentration (C max), half-life (t 1/2) and area under the curve (AUC0-t ) after three IV doses were 42.85 ± 11.79 μg/mL, 1.66 ± 0.36 h and 80.10 ± 28.92 mg h/L (95 mg); 93.50 ± 30.51 μg/mL, 1.47 ± 0.13 h and 1.47 ± 0.13 mg h/L (190 mg); 185.74 ± 113.83 μg/mL, 1.60 ± 0.38 h and 263.20 ± 73.27 mg h/L (380 mg). After PO administration, the C max, t 1/2 and AUC0-t at three doses were 9.25 ± 1.02 μg/mL, 1.79 ± 0.50 h and 31.90 ± 4.76 mg h/L (125 mg); 9.75 ± 1.77 μg/mL, 1.93 ± 0.65 h and 42.69 ± 8.93 mg h/L (250 mg); 15.55 ± 6.65 μg/mL, 2.02 ± 0.54 h, and 68.72 ± 24.11 mg h/L (500 mg). The IV f% T > MIC90 was greater than PO f% T > MIC90 when MIC90 was within the range of 0.25-256 mg/L.

Clinical pharmacokinetics of newer cephalosporins

Several new cephalosporins have been developed in recent years. These agents include several oral and parenteral agents with extended activity against Gram-negative pathogens. The pharmacokinetic literature for these agents is quite extensive; therefore, we have summarised this information and presented it in tabular form for critical comparison. With a few exceptions, the newer cephalosporins share similar pharmacokinetic properties. Cefixime, cefetamet pivoxil and ceftibuten differ from the others in that they exhibit nonlinear pharmacokinetic properties. The nonlinear nature of these agents is reflected by decreasing maximal concentrations with escalating doses of cefixime and cefetamet pivoxil, decreasing area under the serum concentration-time curve with increasing doses for cefixime, and a reduced bioavailability with large doses of ceftibuten. Attention to such characteristics aid the clinician in selecting appropriate dosage regimens that will optimise drug absorption. The majority of agents are primarily renally eliminated; however, renal elimination accounts for only 20% of cefixime elimination. The pharmacokinetic parameters noted for the newer cephalosporins are not influenced by multiple-dose administration, suggesting lack of drug accumulation over time. The pharmacodynamics of antimicrobials should be considered when extrapolating pharmacokinetic information into the clinical arena. In the case of the beta-lactams, the time which drug concentrations remain above some critical threshold, such as the minimal inhibitory concentration, appears to have the greatest influence on bactericidal activity. Therefore, it is important to select dosage regimens that will optimise the time serum concentrations remain above this threshold. We present an evaluation of these agents with respect to their activity against a variety of pathogens in an effort to demonstrate a pharmacokinetically-based process of antimicrobial selection.

Cefetamet pivoxil clinical pharmacokinetics

Cefetamet pivoxil is an orally absorbed prodrug ester of the microbiologically active cephalosporin, cefetamet. The prodrug ester is completely hydrolysed to the active compound cefetamet on its first pass through the gut wall, the liver or both. Cefetamet is classified as a third generation cephalosporin with excellent activity against streptococci, Enterobacteriaceae, Neisseria and Haemophilus species. It has enhanced stability against beta-lactamases compared with penicillins and first and second generation cephalosporins. The antibacterial spectrum is comparable with that of cefotaxime except for its poor activity against staphylococci. Following a 20-minute zero-order intravenous infusion, cefetamet had a rapid distribution phase followed by a monoexponential decline. The average pharmacokinetic parameters from 152 healthy volunteers were: total body clearance 136 ml/min (8.16 L/h); renal clearance 119 ml/min (7.14 L/h); nonrenal clearance 17 ml/min (1.02 L/h); volume of distribution at steady-state 0.29 L/kg; terminal elimination half-life 2.2 hours; 88% of the dose recovered in the urine. Cefetamet is not extensively bound to plasma proteins. Consequently, these data indicate that cefetamet is predominantly eliminated unchanged by the kidney via glomerular filtration with possibly a minor component of tubular secretion. Cefetamet has a relatively small apparent volume of distribution consistent with that of other beta-lactam antibiotics. Results following ascending intravenous doses of cefetamet in healthy young male volunteers demonstrated that the pharmacokinetics of intravenous cefetamet are independent of the dose. The absolute bioavailability of cefetamet tablets following oral cefetamet pivoxil administration is enhanced by the presence of food. Under fed conditions, 50 to 60% of the final oral dose is absorbed into the systemic circulation. This food effect is observed when cefetamet pivoxil is administered within 1 hour of a meal. Food also produces a slight delay in the time to reach peak plasma concentrations of this drug. Changes in fluid volume intake with cefetamet pivoxil administration have no effect on the bioavailability of this drug. Similar absorption characteristics have been observed for all of the tablet dosage formulations studied during clinical development. The absolute bioavailability of the final syrup dosage formulation was between 38 and 47%. Little improvement in the bioavailability of this preparation has been observed with food. The absorption and disposition of cefetamet in human subpopulations [i.e. children, elderly (< 75 years of age), renal impairment, liver disease and patients taking concomitant drugs] have been studied extensively. Only impaired renal function appears to significantly alter the elimination of this drug.(ABSTRACT TRUNCATED AT 400 WORDS)

Cefetamet pivoxil. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Cefetamet pivoxil is an oral third-generation cephalosporin which is hydrolysed to form the active agent, cefetamet. Cefetamet has excellent in vitro activity against the major respiratory pathogens Streptococcus pneumoniae, Haemophilus influenzae, Moraxella (Branhamella) catarrhalis and group A beta-haemolytic streptococci; it is active against beta-lactamase-producing strains of H. influenzae and M. catarrhalis, but has poor activity against penicillin-resistant S. pneumoniae. Cefetamet has marked activity against Neisseria gonorrhoeae and possesses a broad spectrum of activity against Enterobacteriaceae. Both staphylococci and Pseudomonas spp. are resistant to cefetamet. Cefetamet pivoxil has been investigated in the treatment of both upper and lower community-acquired respiratory tract infections and has demonstrated equivalent efficacy to a number of more established agents, namely cefaclor, amoxicillin and cefixime. In patients with group A beta-haemolytic streptococcal pharyngotonsillitis, a 7-day course of cefetamet pivoxil was as effective as a 10-day course of the standard agent, phenoxymethylpenicillin, in this indication. In complicated urinary tract infections, cefetamet pivoxil showed similar efficacy to cefadroxil, cefaclor and cefuroxime axetil. Cefetamet pivoxil was effective in the treatment of otitis media, pneumonia, pharyngotonsillitis and urinary tract infections in children. Preliminary data indicate that single dose cefetamet pivoxil can effectively eradicate N. gonorrhoeae from both men and women. Cefetamet pivoxil has a tolerability profile similar to that of other oral cephalosporins, with gastrointestinal effects being the most commonly reported adverse events. To date, no symptoms of carnitine deficiency have been reported with cefetamet pivoxil. Cefetamet pivoxil offers effective alternative oral therapy for outpatient treatment of community-acquired respiratory tract infections, with the advantage of improved activity against H. influenzae and increased beta-lactamase stability. However, its use in areas with a high incidence of penicillin-resistant S. pneumoniae is likely to be limited. Cefetamet pivoxil is also effective in the treatment of urinary tract infections, although further trials are required to define any comparative advantages over other oral agents.

Clinical pharmacokinetics of newer antibacterial agents in liver disease

Liver disease may produce significant, albeit highly variable, effects on the pharmacokinetic behaviour of antibiotics in serum. Drug disposition may be altered through several pathophysiological mechanisms including reduced hepatobiliary clearance, and modifications in the volume of distribution induced by albumin synthesis deficiency or portal hypertension-related ascites. Antibacterial agents are not affected by potential alteration in hepatic first-pass effects. Only liver cirrhosis-induced effects on serum pharmacokinetics of antibiotics have been extensively studied, unlike those possibly produced by other forms of liver disease. In liver cirrhosis, pharmacokinetic alterations of nearly all beta-lactam or quinolone agents appear not to be marked enough to require dosage adjustment, provided that renal function stays normal. Adaptation in therapeutic schedule, however, is warranted for those drugs that are substantially cleared by the hepatobiliary system, namely mezlocillin, clindamycin, erythromycin, pefloxacin, enoxacin, antituberculous agents or nitroimidazole derivatives. Special caution should also be exercised when using aminoglycosides or vancomycin because of the wide interpatient variability of their pharmacokinetic disposition and their toxic potential. When renal function is impaired and there is an increased volume of distribution due to ascites, as frequently observed in severe liver insufficiency, the elimination half-life of most antibiotics is markedly prolonged, resulting in potential side effects due to drug accumulation. Accordingly, dosage adjustment applies to all drugs. In this regard, it should be remembered that delineating the dosage guidelines for a given antibiotic on the basis of reported pharmacokinetic parameters in patients with liver cirrhosis is awkward and probably of limited value. This pattern is ascribed to large interpatient variability in the active hepatic cell mass, the degree of portal hypertension and the alteration of serum binding capacity. Furthermore, there is no way of predicting accurately the extent of liver insufficiency in an individual patient. Dosage reduction is thus done empirically in most cases. Whenever possible, direct measurements of serum antibiotic concentrations should be the reasonable approach to manage antibiotic therapy in this kind of clinical condition.

Future directions in antimicrobial chemotherapy

New developments in the treatment of bacterial infections are discussed. The most important developments include oral broad-spectrum cephalosporin derivatives and extended-spectrum injectable cephalosporins with improved activity against Gram-positive bacteria. Meropenem is a new carbapenem agent with markedly improved activity against Gram-negative bacteria. Many fluoroquinolones are in various phases of development. The most interesting new compound is sparfloxacin. Azithromycin is a new macrolide which, because of its very long half-life, attains very high levels in most tissues. Potential uses of the newer agents are discussed.

Pharmacokinetics of intravenous cefetamet and oral cefetamet pivoxil in children

The pharmacokinetics of cefetamet were determined after intravenous (i.v.) administration of cefetamet and oral administration of cefetamet pivoxil syrup to patients between the ages of 3 and 12 years. The patients were hospitalized for reconstructive urological surgery; to prevent infection, prophylactic i.v. cefetamet was administered on the day of surgery and oral cefetamet pivoxil was administered 2 days later. After i.v. administration, the mean (+/- standard deviation) half-life of cefetamet was 1.97 +/- 0.60 h (n = 18), which was different from the 2.46 +/- 0.33 h reported for nine adults (22 to 68 years old) in a previous study. The average values for the mean residence times were 2.35 +/- 0.94 and 2.83 +/- 0.34 h and the average values for the fraction of the dose eliminated unchanged in the urine were 79.9% +/- 8.99% and 80% +/- 11% in children and adults, respectively. Plots of mean systemic clearance and steady-state volume of distribution versus body weight for the children and comparative adults were linear on log-log coordinates, and the slopes of the plots were 0.661 and 0.880, respectively. These slope values suggested that mean systemic clearance values per unit of body surface area were similar in children and adults and that maintenance doses for children should be the adult maintenance dose multiplied by the child's surface area divided by 1.73 m2. The mean (+/- standard deviation) oral bioavailabilities of cefetamet pivoxil were 49.3% +/- 15.7% in 3- to 7-year-old children who received a 500-mg dose and 37.9% +/- 10.0% in 8- to 12-year-old children who received a 1,000-mg dose. These values were not different from that observed in the adult group after two 500-mg tablets. Likewise, the peak concentration of cefetamet in plasma and its time of occurrence in children were in line with the values which have been observed for adults.