Cefixime absorption kinetics after oral administration to humans

Clinical pharmacokinetic of cefixime: a systematic review

Cefixime is an antibiotic from the cephalosporin class used to treat various bacterial infections. The purpose of performing this review is to thoroughly evaluate the pharmacokinetic (PK) data on cefixime.Five databases were systematically searched to identify studies on the PK of cefixime.A total of 38 articles meeting the eligibility criteria were included that provide data on concentration-time profiles or PK parameters such as peak plasma and serum concentration (C_max), area under the curve (AUC), clearance (CL), and time to reach C_max (t_max). A dose-dependent increase in AUC and Cmax of cefixime was depicted in healthy volunteers. The clearance of cefixime decreased according to the degree of renal insufficiency among haemodialysis patients. A significant difference in CL was found in comparing fasted and fed states. A biphasic decline in serum concentrations of cefixime was reported when it was taken without probenecid.This review compiles all the reports on the PK of cefixime in healthy and renally impaired patients; the summarized information can be used to optimize cefixime dosing in different disease states. Moreover, cefixime has increased time above MIC value suggesting that it may be an effective treatment for infections caused by certain pathogens.

A Phase 1 Pharmacokinetic and Safety Study of Extended-Duration, High-dose Cefixime for Cephalosporin-resistant Neisseria gonorrhoeae in the Pharynx

BACKGROUND

There are no fully oral recommended treatment regimens for gonorrhea. Inadequately treated pharyngeal gonococcal infections are a likely reservoir for transmission and development of antimicrobial resistance. We sought to determine an oral cefixime dosing regimen that would theoretically treat pharyngeal infections by gonococci with minimum inhibitory concentrations 0.5 μg/mL.

METHODS

We conducted an open-label, nonrandomized, phase I pharmacokinetic and safety study of cefixime in 25 healthy male and female volunteers divided into 4 dosing cohorts (cohort A, 400 mg; cohort B, 800 mg; cohort C, 1200 mg; and cohort D, 800 mg every 8 hours × 3 doses [total dose 2400 mg]) with a target serum concentration of at least 2.0 μg/mL for more than 20 hours. Cefixime concentrations from serum and pharyngeal fluid were determined with use of a validated liquid chromatography-tandem mass spectrometry assay. Safety measures included laboratories, physical examinations, and symptom diaries.

RESULTS

None of the single-dose regimens attained the target concentration; however, 50% of subjects in cohort D attained the target concentration. Variation in absorption and protein binding contributed to differences in concentrations. Pharyngeal fluid concentrations were negligible. The single-dose regimens were well tolerated; the multidose regimen resulted in mild to moderate gastrointestinal symptoms in 43% of subjects.

CONCLUSIONS

None of the dosing regimens achieved the target concentration. However, the proposed theoretical target was extrapolated from penicillin data; there are no empirically derived pharmacokinetic/pharmacodynamic criteria for pharyngeal gonorrhea. Under alternative cephalosporin-specific therapeutic goals, the multidose regimen may be effective, although the absence of cefixime in pharyngeal fluid is concerning. A clinical trial evaluating efficacy and defining pharmacokinetic/pharmacodynamic outcomes may be warranted.

The conduct of drug metabolism studies considered good practice (II): in vitro experiments

In vitro drug metabolism studies, which are inexpensive and readily carried out, serve as an adequate screening mechanism to characterize drug metabolites, elucidate their pathways, and make suggestions for further in vivo testing. This publication is a sequel to part I in a series and aims at providing a general framework to guide designs and protocols of the in vitro drug metabolism studies considered good practice in an efficient manner such that it would help researchers avoid common pitfalls and misleading results. The in vitro models include hepatic and non-hepatic microsomes, cDNA-expressed recombinant human CYPs expressed in insect cells or human B lymphoblastoid, chemical P450 inhibitors, S9 fraction, hepatocytes and liver slices. Important conditions for conducting the in vitro drug metabolism studies using these models are stated, including relevant concentrations of enzymes, co-factors, inhibitors and test drugs; time of incubation and sampling in order to establish kinetics of reactions; appropriate control settings, buffer selection and method validation. Separate in vitro data should be logically integrated to explain results from animal and human studies and to provide insights into the nature and consequences of in vivo drug metabolism. This article offers technical information and data and addresses scientific rationales and practical skills related to in vitro evaluation of drug metabolism to meet regulatory requirements for drug development.

Sensitive liquid chromatography–tandem mass spectrometry method for the determination of cefixime in human plasma: Application to a pharmacokinetic study

A sensitive and selective liquid chromatographic-tandem mass spectrometric (LC-MS-MS) method was developed to determine cefixime ((6R,7R)-7-[(Z)-2-(2-amino-4-thiazolyl)-2-(carboxymethoxyimino)acetamido]-8-oxo-3-vinyl-5-thia-1-azabicyclo-[4,2,0]-oct-2-ene-2-carboxylic acid) in human plasma. After a simple protein precipitation using acetonitrile, the post-treatment samples were analyzed on a C(8) column interfaced with a triple quadrupole tandem mass spectrometer. Positive electrospray ionization was employed as the ionization source. The mobile phase consisted of acetonitrile-water-formic acid (40:60:0.5, v/v/v). The analyte and internal standard cefetamet were both detected by use of selected reaction monitoring mode. The method was linear in the concentration range of 0.05-8.0 microg/ml. The lower limit of quantification was 0.05 microg/ml. The intra- and inter-day relative standard deviation across three validation runs over the entire concentration range was less than 12.7%. The accuracy determined at three concentrations (0.05, 0.80 and 7.2 microg/ml for cefixime) was within +/-2.0% in terms of relative error. Each plasma sample was chromatographed within 3.5 min. The method herein described was successfully applied for the evaluation of pharmacokinetic profiles of cefixime capsule in 24 healthy volunteers.

Pharmacokinetic strategies in deciphering atypical drug absorption profiles

Drug absorption is a very complex process that manifests itself through potential interaction with a host of physicochemical and physiological variables. Some factors that may affect the absorption processes include presystemic metabolism/efflux, the "absorption window" along the gastrointestinal tract, disease states, demographics (gender, age, ethnicity), and biopharmaceutical classification of solid dosage forms. Despite the complexity of the absorption processes, the analysis of the absorption kinetic data is mostly empirical, and the assumption of first-order absorption is axiomatic. Nevertheless, we often encounter irregular drug absorption profiles (such as double-peak, absorption window-type absorption profiles, etc.) that cannot be satisfactorily described by a simple first-order absorption process. The selection of an inappropriate absorption model would result in the misspecification of the pharmacokinetic model and subsequent erroneous prediction of the dosing regimen. This article presents several pharmacokinetic strategies in analyzing typical and atypical absorption profiles. The atypical absorption profiles discussed in this article include parallel first-order absorption, mixed zero-order and first-order absorption, Weibull-type absorption, absorption window with or without Michaelis-Menton absorption, time-dependent absorption, and inverse Gaussian density absorption. In any event, intravenous drug concentration-time data are generally needed to avoid the ambiguousness in the absorption analyses.

Absorption kinetics and bioavailability of cephalexin in the dog after oral and intramuscular administration

The pharmacokinetics of cephalexin, a first generation cephalosporin, were investigated in dogs using two formulations marketed for humans, but also often employed by practitioners for pet therapy. Cephalexin was administered to five dogs intravenously and intramuscularly as a sodium salt and by the oral route as a monohydrate. The dosage was always 20 mg/kg of active ingredient. A microbiological assay with Sarcina lutea as the test organism was adopted to measure cephalexin concentrations in serum. The mean residence time (MRT) median values after intravenous (i.v.), intramuscular (i.m.) and oral administration (p.o.) were 86 min, 200 min, and 279 min, respectively. After i.m. and oral dosing the peak serum concentrations (24.2 +/- 1.8 micrograms/mL and 20.3 +/- 1.7 micrograms/mL, respectively) were attained at 90 min in all dogs and bioavailabilities were 63 +/- 10% and 57 +/- 5%, respectively. The time course of the cephalexin serum concentrations after oral administration was best described by a model incorporating saturable absorption kinetics of the Michaelis-Menten type: thus in the gastrointestinal tract of dogs a carrier mediated transport for cephalexin similar to that reported in humans, may exist. The predicted average serum concentrations of cephalexin after repeated i.m. and oral administration indicated that, in order to maintain the therapeutic concentrations, the 20 mg/kg b.w. dosage should be administered every 6-8 h.