Antibiotic concentration in the serum of dogs and cats following a single oral dose of cephalexin

Cephalexin susceptibility breakpoint for veterinary isolates: Clinical Laboratory Standards Institute revision

The Clinical and Laboratory Standards Institute (CLSI) uses cephalothin as the class representative for testing veterinary isolates for susceptibility to other first-generation cephalosporins, including cephalexin. We examined replacing cephalothin with cephalexin because cephalexin is used more often clinically. Bacterial isolates were obtained from dogs and cats from a national surveillance program. CLSI testing methods were used to determine the MIC for 4 cephalosporins used in veterinary medicine. Cephalexin clinical breakpoints for canine isolates were established by using published pharmacokinetic data and Monte Carlo simulations to calculate the probability of target attainment (PTA). For 1,112 Staphylococcus pseudintermedius isolates, the mode, MIC₅₀, and MIC₉₀ were 1, 2, and 64 µg/mL, respectively, for cephalexin, and ≤0.06, 0.12, and 2 µg/mL for cephalothin. Susceptibility of S. pseudintermedius from 2011 to 2014 did not change for the 4 cephalosporins tested. Only 4.3% of the penicillin-binding protein 2a-positive S. pseudintermedius isolates had MIC values ≤2 µg/mL for cephalexin, but 66.3% of these isolates had MIC values ≤2 µg/mL for cephalothin. There were also discrepancies between cephalexin and cephalothin for other bacteria tested, but the largest difference was for S. pseudintermedius, with a MIC difference of 4 doubling dilutions. Cephalexin interpretive categories (breakpoints) of ≤2 μg/mL (susceptible), 4 μg/mL (intermediate), and ≥8 μg/mL (resistant) were established for isolates obtained from dogs. Cephalothin should not be used for susceptibility testing of cephalexin for veterinary bacterial pathogens, and canine-specific breakpoints should be used for testing susceptibility. Breakpoints determined using the methods described herein for the interpretive categories will be added to future CLSI tables to reflect this recommendation.

Pharmacokinetics and bioavailability of a long-acting formulation of cephalexin after intramuscular administration to cats

The pharmacokinetic profile and bioavailability of a long-acting formulation of cephalexin after intramuscular administration to cats was investigated. Single intravenous (cephalexin lysine salt) and intramuscular (20% cephalexin monohydrate suspension) were administered to five cats at a dose rate of 10 mg/kg. Serum disposition curves were analyzed by noncompartmental approaches. After intravenous administration, volume of distribution (V(z)), total body clearance (Cl(t)), elimination constant (λ(z)), elimination half-life (t(½)(λ)) and mean residence time (MRT) were: 0.33±0.03 L/kg; 0.14±0.02 L/hkg, 0.42±0.05 h(-1), 1.68±0.20 h and 2.11±0.25 h, respectively. Peak serum concentration (C(max)), time to peak serum concentration (T(max)) and bioavailability after intramuscular administration were 15.67±1.95 μg/mL, 2.00±0.61 h and 83.33±8.74%, respectively.

Chronopharmacological Study of Cephalexin in Dogs

Recent studies have identified a 24 h rhythm in the expression and function of PEPT1 in rats, with significantly higher levels during the nighttime than daytime. Similarly, temporal variations have been described in glomerular filtration rate and renal blood flow, both being maximal during the activity phase and minimal during the rest phase in laboratory rodents. The aim of this study was to assess the hypothesis that the absorption of the first-generation cephalosporin antibiotic cephalexin by dogs would be less and the elimination would be slower after evening (rest span) compared to morning (activity span) administration, and whether such administration-time changes could impair the medication's predicted clinical efficacy. Six (3 male, 3 female; age 4.83+/-3.12 years) healthy beagle dogs were studied. Each dog received a single dose of 25 mg/kg of cephalexin monohydrate per os at 10:00 and 22:00 h, with a two-week interval of time between the two clock-time experiments. Plasma cephalexin concentrations were determined by microbiological assay. Cephalexin peak plasma concentration was significantly reduced to almost 77% of its value after the evening compared to morning (14.52+/-2.7 vs. 18.77+/-2.8 microg/mL) administration. The elimination half-life was prolonged 1.5-fold after the 22:00 h compared to the 10:00 h administration (2.69+/-0.9 vs. 1.79+/-0.2 h). The area under the curve and time to reach peak plasma concentration did not show significant administration-time differences. The duration of time that cephalexin concentrations remained above the minimal inhibitory concentrations (MIC) for staphylococci susceptiblity (MIC=0.5 microg/mL) was>70% of each of the 12 h dosing intervals (i.e., 10:00 and 22:00 h). It can be concluded that cephalexin pharmacokinetics vary with time of day administration. The findings of this acute single-dose study require confirmation by future steady-state, multiple-dose studies. If such studies are confirmatory, no administration-time dose adjustment is required to ensure drug efficacy in dogs receiving an oral suspension of cephalexin in a dosage of 25 mg/kg at 12 h intervals.

Metoclopramide modifies oral cephalexin pharmacokinetics in dogs

The purpose of this study was to investigate whether previous administration of metoclopramide affects cephalexin pharmacokinetics after its oral administration in dogs as well as whether these changes impair its predicted clinical efficacy. Six healthy beagle dogs were included in this study. Oral 25 mg/kg cephalexin monohydrate and intravenous 0.5 mg/kg metoclopramide HCl single doses were administered. Each dog received cephalexin or cephalexin following metoclopramide, with a 2-week washout period. Plasma concentrations of cephalexin were determined by microbiological assay. Cephalexin peak plasma concentration and area under the curve from 0 to infinity significantly increased from 18.77+/-2.8 microg/mL and 82.65+/-10.4 microg.h/mL to 21.88+/-0.8 microg/mL and 113.10+/-20.9 microg.h/mL, respectively, after pretreatment with metoclopramide. No differences between treatments were found for other pharmacokinetic parameters. Pharmacokinetic/pharmacodynamic indices calculated for highly susceptible staphylococci were similar for both experiences. Metoclopramide pretreatment may have increased cephalexin absorption by affecting its delivery to the intestine, and/or enhancing intestinal transporter PEPT1 function. Neither difference in the efficacy of cephalexin nor an increase in toxicity is expected as a result of this modification. Consequently, no dose adjustment is required in cephalexin-treated patients pretreated with metoclopramide.

Pharmacokinetics of cefovecin in cats

The pharmacokinetics of the novel cephalosporin cefovecin were investigated in a series of in vivo, ex vivo and in vitro studies following administration to adult cats at 8 mg/kg bodyweight. Bioavailability and pharmacokinetic parameters were determined in a cross-over study after intravenous (i.v.) and subcutaneous (s.c.) injections. [14C]cefovecin was used to evaluate excretion for 21 days after s.c. administration. Protein binding was determined in vitro in feline plasma and ex vivo in transudate from cats surgically implanted with tissue chambers. After s.c. administration, cefovecin was characterized by rapid absorption with mean peak plasma concentrations of 141+/-12 microg/mL being achieved within 2 h of s.c. injection with full bioavailability (99%). The mean elimination half-life was 166+/-18 h. After i.v. administration, volume of distribution was 0.09+/-0.01 L/kg and mean plasma clearance was 0.35+/-0.04 mL/h/kg. Approximately 50% of the administered radiolabelled dose was eliminated over the 21-day postdose period via urinary excretion and up to approximately 25% in faeces. In vitro and ex vivo plasma protein binding ranged from 99.8% to 99.5% over the plasma concentration range 10-100 microg/mL. Ex vivo protein binding in transudate was as low as 90.7%. From 8 h postdose, concentrations of unbound (free) cefovecin in transudate were consistently higher than in plasma, with mean unbound cefovecin concentrations being maintained above 0.06 microg/mL (MIC90 of Pasteurella multocida) in transudate for at least 14 days postdose. The slow elimination and long-lasting free concentrations in extracellular fluid are desirable pharmacokinetic attributes for an antimicrobial with a 14-day dosing interval.

Pharmacokinetics of two once-daily parenteral cephalexin formulations in dogs

The aims of this study were to describe and compare the pharmacokinetic profiles and T(>MIC90) of two commercially available once-daily recommended cephalexin formulations in healthy adult dogs administered by the intramuscular (i.m.) route. Six beagle dogs received a 10 mg/kg dose of an 18% parenteral suspension of cephalexin of laboratory A (formulation A) and laboratory B (formulation B) 3 weeks apart. Blood samples were collected in predetermined times after drug administration. The main pharmacokinetic parameters were (mean +/- SD): AUC((0-infinity)), 72.44 +/- 15.9 and 60.83 +/- 13.2 microg.h/mL; C(max), 10.11 +/- 1.5 and 8.50 +/- 1.9 microg/mL; terminal half-life, 3.56 +/- 1.5 and 2.57 +/- 0.72 h and MRT((0-infinity)), 5.86 +/- 1.5 and 5.36 +/- 1.2 h for formulations A and B, respectively. T(>MIC90) was 63.1 +/- 14.7 and 62.1 +/- 14.7% of the dosing interval for formulations A and B, respectively. Median (range) for t(max) was 2.0 (2.0-3.0) h and 3.0 (2.0-4.0) for formulations A and B, respectively. Geometric mean ratios of natural log-transformed AUC((0-infinity)) and C(max) and their 90% confidence intervals (CI) were 0.84 (0.72-0.98) and 0.83 (0.64-1.07), respectively. The plasma profiles of cephalexin following the administration of both formulations were similar. No statistical differences between pharmacokinetic parameters or T(>MIC90) were observed, however, bioequivalence between both formulations could not be demonstrated, as lower 90% CI failed to fell within the selected range of 80-125% for bioequivalence.

Pharmacokinetics of cephalexin in cats after oral administration of the antibiotic in tablet and paste preparations

OBJECTIVE

To determine the bioequivalence of a paste formulation of cephalexin with that of the tablet form.

DESIGN

A two-way cross-over study.

ANIMALS

Ten adult cats of mixed breed.

PROCEDURE

The cats, randomly allocated to two groups, received either the paste preparation or the tablet orally at 12-hour intervals for 48 h before a 12-hour blood collection period. Two weeks later the treatments were reversed and the blood sampling repeated. The serum concentrations of the antibiotic were determined. The pharmacokinetic factors were analysed using a computer.

RESULTS

There were no significant differences between the peak concentration of cephalexin, or the other pharmacokinetic factors obtained from the tablet and paste formulations. The serum profiles of cephalexin following four 12-hourly doses of each formulation were similar with the peak serum values occurring at approximately 2 h after administration.

CONCLUSION

The paste formulation and the tablet form are bioequivalent.

Clarithromycin pharmacokinetics after oral administration with or without fasting in crossbred beagles

Clarithromycin was administered to eight dogs intravenously and orally. A suspension or a tablet was given to animals both immediately after feeding and on an empty stomach. Neither the formulation nor the time of administration in relation to feeding significantly influenced the pharmacokinetic parameters. The lowest mean (+/-SD) maximum plasma concentration (Cmax) of 3.0 +/- 0.6 micrograms/ml, the lowest bioavailability (F) of approximately 69 per cent and the shortest time above the proposed breakpoint of susceptibility (L) of 2.9 +/- 1.3 hours were observed with the suspension after feeding. The highest Cmax of 3.6 +/- 0.8 micrograms/ml, the highest F of 83 per cent and the longest L of 4.5 +/- 2.0 hours were observed with the suspension in the fasted group. The mean time at which Cmax occurred (tmax) was between one and two hours after administration. In conclusion, clarithromycin is potentially suitable for therapeutic use in dogs, pending species-specific studies of safety and therapeutic efficacy.

Therapy of gram-positive bacterial infections

This article considers the important features of gram-positive bacteria that relate to chemotherapy and the clinical pharmacology of the drugs of choice for treating these infections.