Three phase elimination of oxytetracycline in veal calves; the presence of an extended terminal elimination phase

Modelling Shows the Negative Impact of Age Dependent Pharmacokinetics on the Efficacy of Oxytetracycline in Young Steers

The effect of age dependent pharmacokinetics (PK) on the clinical efficacy of oxytetracycline (OTC) against Bovine Respiratory Disease (BRD) in beef cattle was studied, using a Physiologically Based Pharmacokinetic (PBPK) model. The model includes a bodyweight dependent renal clearance. To mimic/reproduce the long terminal half-live a bone forming tissue compartment was considered. Data for the development, calibration and validation of the model were obtained from public literature. To integrate the PK with the pharmacodynamics (PD) of OTC, Monte Carlo simulations were performed using this PBPK model to predict time-concentration curves for two commonly used dosing regimens of short-acting and long-acting injectable OTC formulations in virtual populations of 5,000 steer calves of 100 kg and 400 kg. These curves were then used to calculate the value of the PKPD index for OTC, which is the ratio of the area under the concentration-time curve for 24 h (AUC_24h) over the minimum inhibitory concentration (MIC) of the target pathogen (AUC_24h/MIC). The MIC values were for Mannheimia haemolytica, the dose-limiting pathogen for BRD. This integration of PBPK and PD for OTC used for the treatment of BRD in calves indicated that the Probability of Target Attainment (PTA) was sufficient for efficacy in calves of 400 kg, but insufficient for calves of 100 kg, when using a long acting dosing regimen of 20 mg/kg BW, twice, with a 48-h interval. The use of a dosing regimen of 10 mg/kg BW/day for 4 days predicted sufficient PTAs in both age groups.

Disposition of a long-acting oxytetracycline formulation in Thai swamp buffaloes (Bubalus bubalis)

The present study aimed to characterize the pharmacokinetic profile of oxytetracycline long-acting formulation (OTC-LA) in Thai swamp buffaloes, Bubalus bubalis, following single intramuscular administration at two dosages of 20 and 30 mg/kg body weight (b.w.). Blood samples were collected at assigned times up to 504 h. The plasma concentrations of OTC were measured by high-performance liquid chromatography (HPLC). The concentrations of OTC in the plasma were determined up to 264 h and 432 h after i.m. administration at doses of 20 and 30 mg/kg b.w., respectively. The C_max values of OTC were 12.11 ± 1.87 μg/mL and 12.27 ± 1.92 μg/mL at doses of 20 and 30 mg/kg, respectively. The AUC_last values increased in a dose-dependent fashion. The half-life values were 52.00 ± 14.26 h and 66.80 ± 10.91 h at doses of 20 and 30 mg/kg b.w, respectively. Based on the pharmacokinetic data and PK-PD index (T > MIC), i.m. administration of OTC at a dose of 30 mg/kg b.w once per week might be appropriate for the treatment of susceptible bacterial infection in Thai swamp buffaloes.

PHARMACOKINETICS OF OXYTETRACYCLINE IN LOGGERHEAD SEA TURTLES (CARETTA CARETTA) AFTER SINGLE INTRAVENOUS AND INTRAMUSCULAR INJECTIONS

The pharmacokinetics of oxytetracycline in 2-yr-old loggerhead sea turtles (Caretta caretta) after single i.v. and i.m. injections were studied for biologic marking and therapeutic applications. Twenty juvenile turtles were divided into two treatment groups. Ten animals received 25 mg/kg of oxytetracycline i.v. and 10 received the same dosage i.m. Plasma oxytetracycline concentrations were analyzed by reverse-phase high-performance liquid chromatography. Data from the i.v. route best fit a three-compartment model, whereas noncompartmental analysis was used to compare data from both the i.v. and i.m routes. For the i.v. route, means for maximum plasma concentration, terminal phase half-life, systemic clearance, and apparent volume of distribution at steady state were 6.6 microg/ml, 66.1 hr, 290.7 ml/hr/kg, and 18.4 L, respectively. For the i.m. route, means for systemic availability, maximum plasma concentration, and elimination half-life were 91.8%, 1.6 microg/ml, and 61.9 hr, respectively. The remarkably high apparent volume of distribution may possibly be associated with a deep compartment of drug disposition such as bone deposition associated with the large skeletal mass of turtles and the fact that these were well-nourished, growing juveniles. Although maximum plasma concentration by i.m. administration was lower than for the i.v. route, the long elimination time indicates that an infrequent dosing interval may be effective for sensitive bacteria.

Disposition of oxytetracycline in pigs after i.m. administration of two long-acting formulations

Two commercially available long-acting oxytetracycline (OTC) formulations were administered by the intramuscular (i.m.) route to six healthy pigs at the recommended dose of 30 mg/kg. After 2 h the mean maximum concentration (C(max)) reached values of 8.1 +/- 2.2 and 15.4 +/- 11.1 microg/mL, respectively. These concentrations remained higher than 0.5 microg/mL for more than 5 days after drug administration. The area under the concentration time curve (AUC09 days) of each formulation was 255 +/- 76.5 and 399.2 +/- 123 microg. h/mL, respectively, and the mean residence time (MRT) was around 3 days for both formulations. No significant differences were observed between the pharmacokinetic parameters of the two formulations, showing the bioequivalence of the two formulations studied according to the criteria established by the Food and Drug Administration (FDA) and the Committee for Veterinary Medicinal Products (CVMP).

Pharmacokinetics and residues in milk of oxytetracyclines administered parenterally to dairy goats

OBJECTIVE

To determine for two commercial preparations of oxytetracycline (OTC) the pharmacokinetic behaviour, the presence of detectable milk residues and the penetration in milk of OTC administered by intravenous (IV) (conventional formulation [CF]) and intramuscular (IM) routes (CF and long-acting [LA] formulations) in goats producing milk. The effects of these formulations on plasma activity values of creatine kinase (CK) and lactate dehydrogenase (LDH) were also determined as indicators of tissue damage.

PROCEDURE

Five healthy lactating goats producing 1.5+/-0.5 L/d milk and weighing 56.0+/-4.8 kg were used. Single doses of OTC chlorhydrate (CF) were administered (20 mg OTC/kg) by IV (Trial 1 IV) and IM (Trial 1 IM) routes and OTC dehydrate (LA) by the IM route. The same goats were first given IV CF, then IM CF followed by IM LA with 3 weeks between each treatment. Blood and milk samples were taken. The quantification of OTC was performed by HPLC and the plasma activities of CK and LDH enzymes were determined by spectrophotometry. The presence of OTC residues in milk was determined by a commercial reagent. The plasma pharmacokinetic parameters were calculated using a two-compartment model.

RESULTS

Estimates of kinetic variables following IV administration were: Vss= 400.0+/-120.0 mL/kg and CL= 110.0+/-14.0 (mL/h)/kg. The t(fi) for IV= 3.0+/-0.3 h; IM, CF = 10.5+/-2.1 h and IM, LA = 15.1+/-3.1 h. The concentration of OTC in milk at 48 h was: IV= 0.6+/-0.4; IM CF= 1.1+/-0.2 and at 72 h (IM LA)= 0.6+/-0.1 microg/mL and the penetration in milk of OTC was: IV= 70.0+/-18.0; IM CF= 79.0+/-14.0 and IM LA= 66.0+/-6.0%. The areas under the curve of CK and LDH activities in plasma were calculated by the trapezoidal method. Values of CK and LDH IM, LA were greater (P < 0.05) than those observed for IM, CF at 2 and 3 days after administration of the antibiotic. Finally, the bioavailability of OTC CF = 92.0+/-22.0 and LA= 78.0+/-23.0% was suitable for its usage by the IM route in lactating goats.

CONCLUSION

Plasma concentration-time values of OTC administered parenterally in production dairy goats showed similar bioavailability for the two pharmaceutical preaprations. The presence of detectable residues in milk indicates that milk should not be used for human consumption for 2 and 3 days after administration of conventional and long-acting formulations, respectively. The increments in CK and LDH activities after the IM administration of LA are consistent with the presence of tissue damage provoked by the pharmaceutical preparations at the injection site.

Some pharmacokinetic parameters and dosage regimens for a long-acting formulation of oxytetracycline in 6- to 8-month-old male calves

A two-way crossover study was conducted in crossbred male calves (6-8 months old) to determine the bioavailability, pharmacokinetics and dosage regimens for a long-acting formulation of oxytetracycline (OTC-LA). The half-lives of oxytetracycline after intravenous and intramuscular administration were 7.8 h and 24 h, respectively. The volume of distribution and total body clearance values of the drug were 0.86+/-0.07 L and 76.1+/-3.3 (ml/h)/kg, respectively. The maximum concentration of the drug in the serum (4.7-7.4 microg/ml) was achieved 8-10 h after intramuscular administration. The minimum therapeutic serum concentration of drug of > or = 0.5 microg/ml was maintained between 15 min and 84 h after intramuscular administration. The intramuscular bioavailability of the drug was 89.1+/-4.2%. The dosage regimens to maintain the minimum therapeutic serum concentrations of OTC following intramuscular administration of OTC-LA were computed.

Pharmacokinetics of oxytetracycline after intramuscular administration with lidocaine in sheep, comparison with a conventional formulation

The pharmacokinetic behaviour of oxytetracycline (OTC) was studied in 11 sheep after intravenous and intramuscular administration at a single dosage of 20 mg kg(-1) bodyweight. A conventional formulation was injected by the intravenous route and two different preparations were administered by the intramuscular route: a conventional formulation (T-100) and an aqueous solution of OTC with lidocaine (1 per cent) (OTC-L). The objective was to determine whether there are differences between both formulations in the disposition kinetics of OTC after intramuscular administration to sheep. After intravenous administration of the conventional formulation, plasma oxytetracycline concentrations were best fitted to an open two-compartment model. Mean apparent volume of distribution was 0.77+/-0.02 litre kg(-1) and the harmonic mean half-life was three hours. The OTC transfer process between central and peripheral compartments was fast and that did not influence the elimination process. After intramuscular administrations of both formulations, half-lives were longer than after intravenous administration (mean values of 14.1 and 58.2 hours for T-100 and OTC-L respectively). In both cases, a biphasic absorption, a 'flip-flop' model and a complete bioavailability were found. OTC-L provided therapeutic plasma concentrations over 0.5 microg ml(-1) (the minimum inhibitory concentration for most susceptible pathogens) for a longer period of time than T-100 (72 hours compared with 36 or 48 hours).

Correlation between tissue and plasma concentrations of oxytetracycline in veal calves

Mercer et al. (1977) proposed a three-phase experimental design to establish withdrawal times, based on plasma pharmacokinetics. This approach was the premise of a study in which plasma pharmacokinetics and tissue depletion data of oxytetracycline after intramuscular administration were correlated. Correlations between estimated and measured concentrations were shown to be significant for kidney tissue (r = .9236, p < .001), liver tissue (r = .9302, p < .01) as well as for muscle tissue (r = .9045, p < .001). The data presented support the pharmacokinetic approach as proposed by Mercer et al. (1977) and demonstrate that tissue elimination rates correlate highly with elimination rates in plasma. Although generalizations must be applied with caution, this article shows that when certain criteria are fulfilled, plasma pharmacokinetics can reliably predict tissue withdrawal times.