Pharmacokinetics and dosage regimen of enrofloxacin in buffalo bulls after intramuscular administration

Discovery and Development of Antibacterial Agents: Fortuitous and Designed

Today, antibacterial drug resistance has turned into a significant public health issue. Repeated intake, suboptimal and/or unnecessary use of antibiotics, and, additionally, the transfer of resistance genes are the critical elements that make microorganisms resistant to conventional antibiotics. A substantial number of antibacterials that were successfully utilized earlier for prophylaxis and therapeutic purposes have been rendered inadequate due to this phenomenon. Therefore, the exploration of new molecules has become a continuous endeavour. Many such molecules are at various stages of investigation. A surprisingly high number of new molecules are currently in the stage of phase 3 clinical trials. A few new agents have been commercialized in the last decade. These include solithromycin, plazomicin, lefamulin, omadacycline, eravacycline, delafloxacin, zabofloxacin, finafloxacin, nemonoxacin, gepotidacin, zoliflodacin, cefiderocol, BAL30072, avycaz, zerbaxa, vabomere, relebactam, tedizolid, cadazolid, sutezolid, triclosan and afabiacin. This article aims to review the investigational and recently approved antibacterials with a focus on their structure, mechanisms of action/resistance, and spectrum of activity. Delving deep, their success or otherwise in various phases of clinical trials is also discussed while attributing the same to various causal factors.

Pharmacokinetics and tissue distribution of enrofloxacin and its metabolite ciprofloxacin in the Chinese mitten-handed crab, Eriocheir sinensis

The pharmacokinetics of enrofloxacin and its active metabolite ciprofloxacin were investigated in the Chinese mitten-handed crab after a single intramuscular injection of enrofloxacin at 5.0mg/kg body weight. The tissue concentrations of enrofloxacin and ciprofloxacin were determined simultaneously by a high-performance liquid chromatography (HPLC) method. The data were analyzed with Practical Pharmacokinetic Program 3P97. The highest average concentrations of enrofloxacin in liver, muscle, gill, and hemolymph were 3.93, 12.42, 16.73, and 11.04 microg/g (ml), respectively. The elimination half-lives (t(1/2beta)) for enrofloxacin were 92.42, 64.86, 38.80, and 52.39 h, respectively. The AUC(0-infinity) values for enrofloxacin were 304.80, 260.74, 288.30, and 269.24 microg h/ml, respectively. Ciprofloxacin could be detected in all four tissues. The respective values of main pharmacokinetics parameters Cmax, t(1/2beta), and AUC(0-infinity) were 0.52 microg/g (ml), 38.38 h, and 35.06 microg h/ml for liver; 0.24 microg/g (ml), 65.36 h, and 25.64 microg h/ml for muscle; 0.10 microg/g (ml), 112.88 h, and 11.57 microg h/ml for gill; and 0.30 microg/g (ml), 93.33 h, and 39.99 microg h/ml for hemolymph.

Pharmacokinetic disposition of subcutaneously administered enrofloxacin in goats

The pharmacokinetic disposition of enrofloxacin was studied in goats after subcutaneous (s.c.) administration at a single dose of 7.5 mg/kg body weight. Blood samples were drawn from a jugular vein into heparinized tubes at predetermined time intervals after administration of the drug and the plasma was separated by centrifugation. The concentrations of enrofloxacin in the plasma were determined by a microbiological assay using Escherichia coli as the test organism. The plasma concentration-time data were analysed by non-compartmental methods. Enrofloxacin was rapidly absorbed, an appreciable concentration of the drug (0.30 +/- 0.13 microg/ml) being present in the plasma by 5 min after s.c. administration. The maximum plasma concentration of enrofloxacin and the time to reach that maximum were 2.91 +/- 0.39 microg/ml and 2.9 +/- 0.51 h. respectively. A detectable concentration of enrofloxacin persisted in the plasma for 12 h. The elimination half-life and mean residence time of enrofloxacin were 2.84 +/- 0.57 and 5.74 +/- 0.28 h, respectively. It is suggested that enrofloxacin given subcutaneously may be useful in the treatment of susceptible bacterial infections in goats.

Disposition kinetics of enrofloxacin (Baytril 5%) in sheep and goats following intravenous and intramuscular injection using a microbiological assay

The pharmacokinetics of enrofloxacin were determined in Desert sheep and Nubian goats after intravenous and intramuscular administration of Baytril at the dose of 5mgkg(-1) bodyweight. A two compartment open model best represented the intravenous plasma concentration versus time data in both species. Comparisons between the means of the pharmacokinetic parameters obtained after intravenous administration of enrofloxacin (Baytril) revealed a significantly smaller distribution rate constant (lambda(1)) and consequently a shorter half-life time of distribution in sheep (P<0.05). A larger volume of the central compartment (Vc) was observed in goats (P<0.05). Similar values were obtained for sheep and goats for the remaining parameters. Plasma concentrations versus time data of enrofloxacin after 5mgkg(-1) intramuscular administration of Baytril in sheep and goats were adequately described by one-compartment open model with first order absorption and elimination. There were no significant differences between sheep and goats in any of the estimated pharmacokinetic parameters. The results indicate that the pharmacokinetics of enrofloxacin did not differ significantly between sheep and goats; similar intravenous and intramuscular dose rates of enrofloxacin should therefore be applicable to both species. Owing to the high variations in MIC (minimal inhibitory concentration) of sensitive veterinary pathogens, it is recommended that enrofloxacin dosage regimens be calculated according to the sensitivity of the individual pathogen, site of infection and clinical response, than by following a preset dosage regimen.

Pharmacokinetics of pefloxacin in goats after intravenous or oral administration

The plasma concentrations and pharmacokinetics of the fluoroquinolone antimicrobial agent pefloxacin, following the administration of a single intravenous (10 mg/kg) or oral (20 mg/kg) dose, were investigated in healthy female goats. The antimicrobial activity in plasma was measured at predetermined times after drug administration by an agar well diffusion microbiological assay, using Escherichia coli (ATCC 25922) as the test organism. Concentrations of the drug > or = 0.25 microg/ml were maintained in plasma for up to 6 and 10 h after intravenous (i.v.) or oral administration of pefloxacin, respectively. The concentration time data for pefloxacin in plasma after i.v. or oral administration conformed to two- and one-compartment open models, respectively. Plasma pefloxacin concentrations decreased rapidly during the initial phase after i.v. injection, with a distribution half-life (t(1/2alpha)) of 0.10 +/- 0.01 h. The terminal phase had a half-life (t(1/2beta)) of 1.12 +/- 0.21 h. The volume of distribution at steady state (Vdss), mean residence time (MRT) and total systemic clearance (ClB) of pefloxacin were 1.08 +/- 0.09 L/kg, 1.39 +/- 0.23 h and 821 +/- 88 (ml/h)/kg, respectively. Following oral administration of pefloxacin, the maximum concentration in the plasma (Cmax) was 2.22 +/- 0.48 microg/ml and the interval from administration until maximum concentration (tmax) was 2.3 +/- 0.7 h. The absorption half-life (t(1/2ka)) mean absorption time (MAT) and elimination half-life of pefloxacin were 0.82 +/- 0.40, 4.2 +/- 1.0 and 2.91 +/- 0.50 h, respectively. The oral bioavailability of pefloxacin was 42% +/- 5.8%. On the basis of the pharmacokinetic data, a dosage regimen of 20 mg/kg, i.v. at 8 h intervals or orally twice daily, is suggested for treating infections caused by drug-sensitive pathogens in goats.

Pharmacokinetics of enrofloxacin and its metabolite ciprofloxacin in goats given enrofloxacin alone and in combination with probenecid

The pharmacokinetics of enrofloxacin and its active metabolite ciprofloxacin were investigated in goats given enrofloxacin alone or in combination with probenecid. Enrofloxacin was administered i.m. at a dosage of 5 mg x kg(-1) alone or in conjunction with probenecid (40 mg x kg(-1), i.v.). Blood samples were drawn from the jugular vein at predetermined time intervals after drug injection. Plasma was separated and analysed simultaneously for enrofloxacin and ciprofloxacin by reverse-phase high performance liquid chromatography. The plasma concentration-time data for both enrofloxacin and ciprofloxacin were best described by a one-compartment open pharmacokinetic model. The elimination half-life (t(1/2beta)), area under the plasma concentration-time curve (AUC), volume of distribution (V(d(area))), mean residence time (MRT) and total systemic clearance (Cl(B)) were 1.39 h, 7.82 microg x h x mL, 1.52 L x kg(-1), 2.37 h and 802.9 mL x h(-1) x kg(-1), respectively. Enrofloxacin was metabolized to ciprofloxacin in goats and the ratio between the AUCs of ciprofloxacin and enrofloxacin was 0.34. The t(1/2beta), AUC and MRT of ciprofloxacin were 1.82 h, 2.55 microg x h x mL and 3.59 h, respectively. Following combined administration of probenecid and enrofloxacin in goats, the sum of concentrations of enrofloxacin and ciprofloxacin levels > or = 0.1 microg x mL(-1) persisted in plasma up to 12 h.Co-administration of probenecid did not affect the t(1/2beta), AUC, V(d (area)) and Cl(B) of enrofloxacin, whereas the values of t(1/2beta) (3.85 h), AUC (6.29 microg x h x mL), MRT (7.34 h) and metabolite ratio (0.86) of ciprofloxacin were significantly increased. The sum of both enrofloxacin and ciprofloxacin levels was > or = 0.1 microg x mL(-1) and was maintained in plasma up to 8 h in goats after i.m. administration of enrofloxacin alone. These data indicate that a 12 h dosing regime may be appropriate for use in goats.