Pharmacokinetics of chloramphenicol in non-lactating cattle

Chloramphenicol pharmacokinetics after intravenous and intramuscular administration in sheep

The pharmacokinetics of chloramphenicol were studied after intravenous and intramuscular administration of 50 mg/kg body weight in Merino sheep. After intravenous administration, the drug was rapidly distributed extravascularly with a half-life of 10.5 +/- 8.83 min. Extensive distribution was confirmed by an apparent volume of distribution at steady state (1.5 +/- 0.43 1/kg). The elimination half-life was 3.24 +/- 0.60 h. After intramuscular injection, the absorption half-life was 44.33 +/- 19.21 min with a bioavailability of 65%. A maximum serum concentration of 15.57 +/- 3.95 micrograms/ml was determined 2 h after administration. Serum concentrations above 5 micrograms/ml were maintained for approximately 12 h with an elimination half-life of 5.75 +/- 1.25 h, longer than the half-life obtained after intravenous administration. In conclusion, the intramuscular administration of chloramphenical at a dose rate of 50 mg/kg permitted the maintenance of inhibitory concentrations of the antibiotic for the majority of Salmonella and Pasteurella isolates for at least 12 h.

Bioavailability, pharmacokinetics and residues of chloramphenicol in the chicken

The pharmacokinetic properties of chloramphenicol were determined in broiler chickens after two single oral doses (30 and 50 mg/kg body weight) and after a single intravenous (i.v.) dose (30 mg/kg body weight). After oral and i.v. administration, the plasma concentration-time graph was characteristic of a two-compartment open model. After oral administration (30 and 50 mg/kg), chloramphenicol was absorbed rapidly (time to maximal concentration of 0.72 or 0.60 h) and eliminated with a mean half-life (t1/2 beta) of 6.87 or 7.41 h, respectively. The bioavailability was 29% at 30 mg/kg chloramphenicol and 38% at 50 mg/kg chloramphenicol. Concentrations greater than 5 micrograms/ml were achieved at 15 min and persisted up to 2 or 4 h post-administration, respectively. Statistically significant differences between the two routes of administration were found for the pharmacokinetic variables, half-lives of both distribution and elimination phases (t1/2 alpha, t1/2 beta) and apparent volume of distribution [Vd(area)]. The mean t1/2 beta of chloramphenicol and i.v. administration was 5.23 h. Chloramphenicol was extensively metabolized into dehydrochloramphenicol (DH-CAP), nitrophenylaminopropanedione (NPAP) and nitroso-chloramphenicol (NO-CAP) derivatives. Residues of chloramphenicol (CAP) and the three metabolites DH-CAP, NPAP and NO-CAP in kidney, liver and muscle were measured in chickens that received an oral dose of 50 mg/kg once daily for 4 days. The results indicate that CAP and DH-CAP residues were cleared slowly and were at or below the detection limit of 0.005 microgram/ml within 12 days after dosing. However, at the time of slaughter (12 days), the NPAP and NO-CAP residues were detected in the tissue.

The pharmacokinetics of thiamphenicol in lactating cows

The pharmacokinetics of thiamphenicol were studied after intravenous and intramuscular administration of 25 mg/kg body weight in lactating cows. Distribution (t1/2 alpha) and elimination (t1/2 beta) half-lives of 6.10 +/- 1.39 min and 1.60 +/- 0.30 h, respectively, were obtained after intravenous administration. The body clearance was 3.9 +/- 0.077 ml/kg per min and the apparent volume of distribution was 1220.79 +/- 256.67 ml/kg. The rate at which thiamphenicol appeared in the milk, as indicated by the penetration half-life (t1/2P) (serum to quarters), was found to be 36.89 +/- 11.14 min. The equivalent elimination half-life (t1/2E) (quarters to serum) from the milk was 3.62 +/- 1.06 h and the peak thiamphenicol concentration in the milk was 23.09 +/- 3.42 micrograms/ml at 2.5 +/- 0.32 h. After intramuscular injection, the elimination half-life was 2.2 +/- 0.40 h, the absorption half-life was 4.02 +/- 1.72 min and the peak concentration in the serum was 30.90 +/- 5.24 micrograms/ml at 23 +/- 8.4 min. The bioavailability after intramuscular administration approached 100%. The penetration half-life was 50.59 +/- 6.87 min, the elimination half-life was 5.91 +/- 4.97 h and the mean peak concentration in the milk was 17.37 +/- 2.20 micrograms/ml at 3.4 +/- 0.22 h.

The pharmacokinetics of chloramphenicol in plasma and saliva of dairy cows

In the present study the pharmacokinetics of chloramphenicol were investigated in bovine plasma and saliva. The method of detection of chloramphenicol, a radio-immunoassay, requires only small sample volumes, no further clean-up, and a large number of samples can be processed simultaneously. This enabled the collection of a larger number of samples over a longer period of time than in previous studies. The intention was to obtain a complete pharmacokinetic profile of chloramphenicol, to evaluate it according to common open-compartment models, and to compare it with the results of previous studies. The radio-immunoassay results were confirmed by analysing a number of samples distributed over the concentration range of interest by a gas-chromatographic method with electron-capture detection. The suitability of saliva was evaluated as a possible means of monitoring compliance with the ban on chloramphenicol in the Federal Republic of Germany in milk-producing animals.

Lack of predictability of chloramphenicol toxicity in paediatric patients

We studied 45 patients (new-born to 12 year olds) who received 50-100 mg/kg/day chloramphenicol sodium succinate i.v. over 2-49 days for the treatment of central nervous system infections. Multiple blood samples were obtained to measure serum concentrations of chloramphenicol and its succinate ester by high pressure liquid chromatography (HPLC). Haematological parameters (haemoglobin, white cell, neutrophil, eosinophil and platelet counts) were also determined. Chloramphenicol therapy was effective in all patients. Anaemia was present in 10, leukopenia in four, neutropenia in four, and eosinophilia in 16 patients. These adverse effects occurred between 3 and 34 days after the initiation of therapy. Chloramphenicol therapy had to be discontinued only in three patients, who had absolute neutrophil counts less than 800/mm3. All adverse effects were reversible. Demographic factors, daily dose, duration of therapy, steady-state peak and trough serum concentrations, area under the serum concentration-time curve normalized for dose, and the elimination half-life were not correlated with the occurrence of adverse effects of chloramphenicol. The mean cumulative dose of chloramphenicol succinate was the only factor always higher but not statistically different in patients with adverse effects compared to those without. The mean cumulative dose of chloramphenicol succinate ranged from 1.2 to 1.8 g/kg in patients with adverse effects and 0.9-1.1 g/kg in those without. These data suggest that the adverse effects of chloramphenicol may not be predictable in paediatric patients. However, a high cumulative dose may possibly be an important factor in predisposing some patients to certain chloramphenicol toxicity.

Pharmacokinetics of a long-acting chloramphenicol formulation administered by intramuscular and subcutaneous routes in cattle

The pharmacokinetic properties of a long-acting formulation of chloramphenicol were determined in six yearling cattle after a single intravenous (i.v.) administration (40 mg/kg body weight) and after two sequential subcutaneous (s.c.) or intramuscular (i.m.) administrations (90 mg/kg/48 h). The two extravascular routes were studied during a crossover trial for a bioequivalence test. After i.v. administration, the plasma concentration-time graph was characteristic of a two-compartment open model. Mean values were a half-life of 4.1 h, a volume of distribution of 0.86 l/kg and a body clearance of 0.128 l/kg/h. Plasma concentrations of chloramphenicol following i.m. and s.c. administrations increased slowly to a broad peak at 10-15 micrograms/ml between 9 and 12 h. Bioavailability was 19.1% after i.m. injection and 12.4% after s.c. administration. The extent of absorption from the two routes did not differ significantly. The rate of absorption was significantly lower after s.c. application than it was after i.m. injection. The time necessary for the plasma concentration to exceed 5 micrograms/ml was the same for the two routes. Thus, i.m. and s.c. routes are bioequivalent.

Florfenicol in non-lactating dairy cows: pharmacokinetics, binding to plasma proteins, and effects on phagocytosis by blood neutrophils

Serial blood samples were collected and plasma concentrations of florfenicol (FLO) were measured following the administration of an intravenous bolus of 50 mg/kg FLO to five healthy non-lactating dairy cows. A triexponential equation provided the best fit of the data for four of the five cows. The mean value for beta corresponded to a half-life of 3.2 h. The mean apparent volume of distribution was 0.67 l/kg, and the mean body clearance was 0.15 l/kg/h. The extent of binding of FLO to bovine plasma proteins was determined in vitro at concentrations of 5 micrograms/ml and 50 micrograms/ml by equilibrium dialysis and ultrafiltration. The drug was 18% and 19% bound by equilibrium dialysis, and 23% and 19% bound by ultrafiltration, at 5 micrograms/ml and 50 micrograms/ml, respectively. Phagocytosis of 32phosphorus-labelled Staphylococcus aureus by bovine blood neutrophils was compared in vitro between neutrophils incubated in phosphate-buffered saline alone or in combination with 5, 125, or 1000 micrograms/ml chloramphenicol or FLO. There was no significant effect of chloramphenicol at any concentration. Florfenicol significantly inhibited phagocytosis at all concentrations, but the percentage inhibition was small. The clinical significance, if any, of this effect of FLO remains to be demonstrated.

Pharmacokinetics of chloramphenicol in cows after intramuscular application

The concentrations of chloramphenicol and its water-soluble metabolites in the plasma of six clinically healthy heifers were measured at intervals during five days after intramuscular administration of free chloramphenicol (20 mg/kg) in a vehicle containing 40% of an organic solvent. Estimations were carried out by a colorimetric method and by high pressure liquid chromatography (for the very low values beyond the second day). For free chloramphenicol a peak concentration of 1.7 micrograms/ml at 7.3 h after injection was found (MIC: 5 micrograms/ml). Bioavailability was calculated to be 63%. It is shown that absorption was apparently not a uniform process but occurred rather slowly (t 1/2 (ab) = 10.2 h) for the main part of the available dose, whereas one sixth was quickly absorbed (t'1/2 (ab) = 0.7 h). The apparent half-time of elimination was 10.2 h for the unchanged drug. At the fifth day after administration the plasma concentration was below the limit of detectability (10 ng/ml) in all animals.

Pharmacokinetic aspects of penicillins, aminoglycosides and chloramphenicol in birds compared to mammals. A review

Based on a review of the literature, a comparison is made of the pharmacokinetics of penicillins, aminoglycosides, and chloramphenicol in birds and mammals. Penicillins in birds are likely to be more dependent for their elimination on biotransformation than in mammals. Amoxycillin had a relatively low availability (0.34) after p.o. administration. Higher doses (2 to 8 times) were needed to achieve the same peak levels in birds and mammals. Aminoglycosides, which for their elimination largely depend on renal excretion by glomerular filtration, show only minor differences in pharmacokinetics between birds and mammals. Chloramphenicol is mainly excreted after biotransformation and large differences in pharmacokinetic parameters are to be found, not only between birds and mammals, but also between avian species.