Comparative pharmacokinetics of gentamicin, neomycin and oxytetracycline in newborn calves

Pharmacokinetics and bioavailability of cefquinome and ceftriaxone in premature calves

The aim of this study was to evaluate the pharmacokinetics and bioavailability of cefquinome (CFQ) and ceftriaxone (CTX) following intravenous (IV) and intramuscular (IM) administrations in premature calves. Using a parallel design, 24 premature calves were randomly divided into the two antibiotic groups. Each of the six animals in the first group received CFQ (2 mg/kg) through IV or IM administration. The second group received CTX (20 mg/kg) via the same administration route. Plasma concentrations of the drugs were analyzed by high-performance liquid chromatography and noncompartmental methods. Mean pharmacokinetic parameters of CFQ and CTX following IV administration were as follows: elimination half-life (t_1/2λz ) 1.85 and 3.31 hr, area under the plasma concentration-time curve (AUC_0-∞ ) 15.74 and 174 hr * μg/ml, volume of distribution at steady-state 0.37 and 0.45 L/kg, and total body clearance 0.13 and 0.12 L hr^-1  kg^-1 , respectively. Mean pharmacokinetic parameters of CFQ and CTX after IM injection were as follows: peak concentration 4.56 and 25.04 μg/ml, time to reach peak concentration 1 and 1.5 hr, t_1/2λz 4.74 and 3.62 hr, and AUC_0-∞ 22.75 and 147 hr * μg/ml, respectively. The bioavailability of CFQ and CTX after IM injection was 141% and 79%, respectively. IM administration of CFQ (2 mg/kg) and CTX (20 mg/kg) can be recommended at 12-hr interval for treating infections caused by susceptible bacteria, with minimum inhibitory concentration values of ≤0.5 and ≤4 μg/ml, respectively, in premature calves. However, further research is indicated to assess the pharmacokinetic parameters following multiple doses of the drug in premature calves.

Use of pharmacokinetic modeling to assess antimicrobial pressure on enteric bacteria of beef cattle fed chlortetracycline for growth promotion, disease control, or treatment

Antimicrobial use in food animals may increase antimicrobial resistance in their enteric bacteria that can be transferred to human microbiome. Over 70% of U.S. beef feedlots use non-ionophore in-feed antimicrobials for animal disease control, treatment, or growth promotion. The fraction of feedlots feeding chlortetracycline (CTC), mostly for disease control but also for treatment, has increased since the mid-1990s to present. Quantitative information on the antimicrobial selective pressure on the enteric bacteria of cattle fed CTC is lacking. Hence, the purpose of this study was to develop a deterministic mathematical model of the pharmacokinetics of ingested CTC in a beef steer and estimate the concentration of antimicrobially active (undegraded) CTC in the animal's large intestine. To evaluate the fit of the model to existing data, we also estimated the CTC concentrations in the central circulation, and fresh and aging manure from the steer. The model accounted for CTC abiotic degradation while in the gastrointestinal tract, absorption into the central circulation and tissues, biliary and renal excretion, and removal from the intestine by defecation. The model included an increase in the large intestine volume as the steer grew. We estimated that during CTC feeding to a 300-kg steer for growth promotion, the maximal drug concentration in the large intestine was 0.3 μg/mL; during disease control it was 1.7 μg/mL; and during treatment it was 31.5 μg/mL. The estimated CTC concentrations in the central circulation and the steer's manure agreed reasonably well with published data.

Effect of tetracycline administration on serum amylase activity in calves

Tetracycline and related compounds are used extensively as broad spectrum antibiotics in the treatment of bacterial infections in ruminants. Tetracycline may cause acute pancreatitis which may result in increased serum amylase activity. However, it has been shown that administration of oxytetracycline in human results in decrease serum amylase activity. In this study changes in serum amylase activity were measured in 20 clinically healthy calves following intravenous injection of oxytetracycline hydrochloride at 10 mg/kg of body weight. Blood samples were collected at 30, 60, and 120 minutes after oxytetracycline injection. Serum amylase activity was measured using the amyloclastic assay. The activity of serum amylase was increased significantly (P < 0.05) at 30 (40.5%), 60 (35.1%), and 120 (39.3%) minutes after oxytetracycline hydrochloride administration. To the authors' knowledge this is the first study on the acute effect of tetracycline administration on serum amylase activity in calves.

Pharmacodynamics of antimicrobials against Mycoplasma mycoides mycoides small colony, the causative agent of contagious bovine pleuropneumonia

BACKGROUND

Mycoplasma mycoides subspecies mycoides Small Colony (MmmSC) is the causative agent of Contagious Bovine Pleuropneumonia (CBPP), a disease of substantial economic importance in sub-Saharan Africa. Failure of vaccination to curtail spread of this disease has led to calls for evaluation of the role of antimicrobials in CBPP control. Three major classes of antimicrobial are effective against mycoplasmas, namely tetracyclines, fluoroquinolones and macrolides. Therefore, the objectives of this study were to determine the effector kinetics of oxytetracycline, danofloxacin and tulathromycin against two MmmSC field strains in artificial medium and adult bovine serum.

METHODS

Minimum inhibitory concentrations (MIC) were determined for oxytetracycline, danofloxacin and tulathromycin against MmmSC strains B237 and Tan8 using a macrodilution technique, and time-kill curves were constructed for various multiples of the MIC over a 24 hour period in artificial medium and serum. Data were fitted to sigmoid E(max) models to obtain 24 hour-area under curve/MIC ratios for mycoplasmastasis and, where appropriate, for mycoplasmacidal activity and virtual mycoplasmal elimination.

RESULTS

Minimum inhibitory concentrations against B237 were 20-fold higher, 2-fold higher and approximately 330-fold lower in serum than in artificial medium for oxytetracycline, danofloxacin and tulathromycin, respectively. Such differences were mirrored in experiments using Tan8. Oxytetracycline was mycoplasmastatic against both strains in both matrices. Danofloxacin elicited mycoplasmacidal activity against B237 and virtual elimination of Tan8; similar maximum antimycoplasmal effects were observed in artificial medium and serum. Tulathromycin effected virtual elimination of B237 but was mycoplasmastatic against Tan8 in artificial medium. However, this drug was mycoplasmastatic against both strains in the more physiologically relevant matrix of serum.

CONCLUSIONS

Oxytetracycline, danofloxacin and tulathromycin are all suitable candidates for further investigation as potential treatments for CBPP. This study also highlights the importance of testing drug activity in biological matrices as well as artificial media.

Persistence of gentamicin residues in milk after the intramammary treatment of lactating cows for mastitis

This study was designed to investigate persistence of gentamicin residues in milk after the intramammary treatment of lactating cows for mastitis. Milk samples were collected at a 1-d interval after the last administration from 34 individual cows that had received intramammary infusions of gentamicin. The doses and treatment times evaluated in this study represented those that have been applied by veterinarians in practice. The tetrazolium chloride assay was used to determine whether there were significant residues of the antibiotic in the samples. Persistence of detectable drug residues in milk from 33 cows (28 cows, Collapse

Key Words

• gentamicin
• mastitis
• intramammary infusion
• residue

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MESH Headings

• Animals
• Anti-Bacterial Agents/analysis
• Anti-Bacterial Agents/therapeutic use
• Female
• Gentamicins/analysis
• Gentamicins/therapeutic use
• Lactation/metabolism
• Mastitis/drug therapy
• Mastitis/metabolism
• Mastitis/veterinary
• Milk/chemistry
• Swine

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Grants Collapse

Affiliation(s)

Xun Tan
Ye-wen Jiang
Yi-jun Huang
Song-hua Hu †E-mail:

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Use of tissue-fluid correlations to estimate gentamicin residues in kidney tissue of Holstein steers

Gentamicin continues to be one of the most effective antibiotics for the treatment of gram-negative infections. Greater than 90% of the drug is rapidly eliminated from the body in <2 days, however, a small residue remains bound to the kidney cortex tissue for many months. In beef steers, the gentamicin residue is unacceptable and its presence is monitored by the FAST (Fast Antimicrobial Screen Test) applied to the kidney at the time of slaughter. The sensitivity of the FAST to gentamicin in the kidney cortex is reported to be 100 ng/g, therefore, this level of gentamicin defines the acceptable limit of gentamicin drug residue in the bovine kidney. In the present study, three doses of 4 mg/kg gentamicin was administered intramuscularly to eight steers. Gentamicin was allowed to deplete from the kidneys for a range of times from 7 to 10 months. At slaughter the level of gentamicin in the kidney cortex varied from 91 to 193 ng/g, but a total of 160 FAST tests performed on the kidneys were negative. Blood and urine samples were collected at varying times following the last dose of gentamicin. Kidney tissue samples were collected by laparoscopic surgery in the live steers as well as the final sample obtained at slaughter. Plasma levels of gentamicin declined rapidly to nondetectable within 3 days, while measurable urine persisted for 75 days before the concentration of gentamicin declined to levels too low to quantitate by the available liquid chromatography tandem mass spectrometry (LC/MS/MS) technique. An estimated correlation between an extrapolation of urine gentamicin concentration to the corresponding kidney tissue sample suggests a urine to kidney tissue relationship of 1:100. A test system sufficiently sensitive to a urine gentamicin concentration of 1 ng/mL will correlate with the estimated 100 ng/g gentamicin limit of the FAST applied to the fresh kidney of the recently slaughtered bovine.

Comparative disposition kinetics and plasma protein binding of gentamicin sulphate in three juvenile animal species

The pharmacokinetics of gentamicin was studied in lambs, calves and foals, respectively after single intravenous (i.v.) injections of 5 mg kg(-1) body weight. The plasma concentration-time curves of gentamicin sulphate were best fitted to follow a two-compartment open model in calves and foals and a three-compartment open model in lambs. Gentamicin showed high plasma level at 5 min post-injection. Then its concentration decreased gradually until its minimum detectable level at 10 and 12 h post-injection in foals and calves, respectively, was reached. In contrast, the plasma concentrations were much higher in lambs and persisted up to 48 h from the onset of injection. Values of pharmacokinetic parameters for gentamicin sulphate in different animals after i.v. injections were calculated. Pharmacokinetic data in lambs demonstrated a triphasic decline in plasma gentamicin concentration with slow terminal elimination phase (washout phase) with (t(1/2y)) of 7.7 h. Gentamicin showed a small volume of distribution Vd(ss) (80.3 ml kg(-1)) in lambs indicating that the drug is slightly distributed in extra-vascular tissues. The overall rate of total body clearance ClB in lambs was (0.46 ml kg(-1)) slower than in calves (1.5 ml kg(-1)) and foals (2.7 ml kg(-1)). In vitro protein binding per cent of gentamicin sulphate in plasma were 16.80, 11.03 and 7.98% in lambs, calves and foals. The results of this study emphasize the importance of determining the pharmacokinetics of gentamicin in each species of young animals separately.

Limited capacity of neonatal rabbits to eliminate enrofloxacin and ciprofloxacin

The pharmacokinetics of enrofloxacin (ENR) and ciprofloxacin (CIP) in newborn and young rabbits were studied. Rabbits of different ages (1-, 8-, 16-, and 30-day-old) were administered, by the intraperitoneal route (i.p.), a dose of 7.5 mg of either drug/kg. In 1-, 8-, and 16-day-old rabbits, blood samples were drawn by cardiac puncture, under light ether anaesthesia, at predetermined times after drug administration. In 30-day-old rabbits, serial blood samples were drawn through an arterial catheter. Plasma was immediately obtained and analysed using an HPLC method. ENR and CIP plasma protein binding was also determined. The plasma pharmacokinetic profiles of ENR and CIP obtained for 30-day-old rabbits agreed with those reported in the literature for healthy adult rabbits. Nevertheless, significant differences were observed for the body clearance, the slope of the terminal phase, the volume of distribution, and the area under the curve when compared with those for younger animals (1-, 8-, and 16-day-old rabbits), indicating a limited capacity of neonatal rabbits to eliminate ENR and CIP. No differences were found when we compared the calculated values for ENR or CIP plasma protein binding as a function of the postnatal age, indicating that development does not seem to alter the free fraction of these drugs in the rabbit. Taking into account that extensive placental and milk transfer has been reported for these drugs after administration to pregnant or nursing rabbits, a cautious, attitude regarding their use in these animals must be adopted.

Effects of age on the pharmacokinetics of single dose ceftiofur sodium administered intramuscularly or intravenously to cattle

The effects of maturation on the intravenous (IV) and intramuscular (IM) pharmacokinetics of ceftiofur sodium following a dose of 2.2 mg ceftiofur equivalents/kg body weight were evaluated in 16 one-day-old Holstein bull calves (33-53 kg body weight initially; Group 1) and 14 six-month-old Holstein steers (217-276 kg body weight initially; Group 2). Group 1 calves were fed unmedicated milk replacer until 30 days of age and were then converted to the same roughag/concentrate diet as Group 2. Groups 1-IV and 2-IV received ceftiofur sodium IV, and Groups 1-IM and 2-IM received ceftiofur sodium IM. Group 1 calves were dosed at 7 days of age and at 1 and 3 months of age; group 2 calves were dosed at 6 and 9 months of age. Blood samples were obtained serially from each calf, and plasma samples were analysed using an HPLC assay that converts ceftiofur and all desfuroylceftiofur metabolites to desfuroylceftiofur acetamide. Cmax values were similar in all calves, and were no higher in younger calves than in older calves. Plasma concentrations remained above 0.150 microgram ceftiofur free acid equivalents/mliter for 72 h in 7-day-old calves, but were less than 0.150 microgram/mliter within 48 h following IV or IM injection for 6- and 9-month-old calves. Intramuscular bioavailability, assessed by comparing the model-derived area under the curve (AUCmod) from IM and IV injection at each age, appeared to be complete. After IV administration, the AUCmod in 7-day-old and 1-month-old calves (126.92 +/- 21.1 micrograms.h/mliter and 135.0 +/- 21.6 micrograms.h/mliter, respectively) was significantly larger than in 3-, 6- and 9-month-old calves (74.0 +/- 10.7 micrograms.h/mliter, 61.0 +/- 17.7 micrograms.h/mliter and 68.5 +/- 12.8 micrograms.h/mliter, respectively; P < 0.0001). The Vd(ss) decreased linearly within the first 3 months of life in cattle (0.345 +/- 0.0616 L/kg, 0.335 +/- 0.919 L/kg and 0.284 +/- 0.0490 L/kg, respectively; P = 0.031), indicative of the decreasing extracellular fluid volume in maturing cattle. The ClB was significantly smaller in 7-day-old and 1-month-old calves (0.0178 +/- 0.00325 L/h.kg and 0.0167 +/- 0.00310 L/h.kg, respectively) than in 3-, 6- and 9-month-old calves (0.0303 +/- 0.0046 L/h.kg, 0.0398 +/- 0.0149 L/h.kg and 0.0330 +/- 0.00552 L/h.kg, respectively; P < or = 0.001). This observation may be indicative of maturation of the metabolism and/or excretion processes for ceftiofur and desfuroylceftiofur metabolites. The approved dosage regimens for ceftiofur sodium of 1.1-2.2 mg/kg administered once daily for up to 5 consecutive days will provide plasma concentrations above the MIC for bovine respiratory disease pathogens for a longer period of time in neonatal calves than in older calves. Peak plasma concentrations of ceftiofur and desfuroylceftiofur metabolites were no higher in neonatal calves than in more mature cattle, highly suggestive that peak tissue concentrations would be no higher in neonatal calves than in more mature cattle.

Pharmacokinetics of gentamicin following single-dose parenteral administration to goats

The disposition kinetics of parenterally administered gentamicin (5 mg kg-1) has been studied in Gaddi goats. The serum concentration-time profile was described by bi-exponential and mono-exponential equations following intravenous (i.v.), intramuscular (i.m.) and subcutaneous (s.c.) administration with elimination half-life values of 0.96 +/- 0.09, 2.37 +/- 0.47 and 3.56 +/- 0.39 h, respectively. The apparent volume of distribution following i.v. administration (Vdarea: 0.26 +/- 0.041 kg-1) reflected limited extracellular distribution of the drug. The bioavailability was higher following i.m. administration (96.3%) compared to s.c. (76.9%). In view of the significantly longer biological half-life and larger area under the curve values, the s.c. route may be preferred. It is concluded that a suitable and practical dosage recommendation for gentamicin in goats would be 3.35 mg kg-1 body weight given s.c. at 12 h intervals.

Disposition and bioavailability of neomycin in Holstein calves

The disposition and absorption kinetics of neomycin were studied in healthy ruminating dairy calves (n = 6), approximately 3-months-old. The calves were treated with single intravenous (i.v.) (12 mg/kg), intramuscular (i.m.) (24 mg/kg), oral (p.o.) (96 mg/kg) and repeated p.o. (96 mg/kg, b.i.d., 15 1/2 days) doses of neomycin. A 3-week rest period was allowed between treatments A and B, and B and C. Baseline and serial venous blood samples were collected from each calf. Plasma concentrations of neomycin were determined by a high performance liquid chromatography procedure. The resulting data were evaluated by using compartmental pharmacokinetic models and nonlinear least squares regression analysis. The mean of some selected parameters were t1/2 lambda 3 7.48 +/- 2.02 h, Clt = 0.25 +/- 0.04 L/h/kg, Vd(ss) = 1.17 +/- 0.23 L/kg, and MRT = 4.63 +/- 0.87 h for the i.v. data and t1/2 = 11.5 +/- 3.8 h, MRTabs = 0.960 +/- 1.001 h, F = 127 +/- 35.2%, and Clt/F = 0.199 +/- 0.047 L/h/kg for the i.m. data, respectively. Only one calf absorbed neomycin to any significant degree (F = 0.0042) after a single p.o. dose. Selected mean parameters determined after repeated oral dosing were: F = 0.45 +/- 0.45%, Cmax = 0.26 +/- 0.37 microgram/ml, and tmax = 2.6 +/- 2.9 h. Terminal half-lives determined for the i.v. and i.m. treatments were considerably longer than those reported previously in the literature.

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

The pharmacokinetics of oxytetracycline were studied after both intravenous (i.v.) and intramuscular (i.m.) administration to a group of five veal calves. Blood samples were taken frequently during the terminal elimination phase in order to calculate a reliable elimination rate constant. Because of the low limit of quantification of the method of analysis used, oxytetracycline plasma concentrations could be monitored over a 12-day period of time. After the intravenous administration of oxytetracycline, data were fitted according a three-compartment model. After i.m. administration, plasma-concentration-time curves could best be described by a two-compartment model. It was demonstrated that a very slow terminal elimination phase was present both after i.v. and i.m. administration with a half-life of approximately 95 h. The data show that this phase cannot be explained by slow absorption from the injection site and that release of oxytetracycline incorporated into bone is not a likely explanation.

The influence of age on the pharmacokinetics of aditoprim in pigs after intravenous and oral administration

Some pharmacokinetic parameters of aditoprim were determined in 3- and 6-month-old pigs. After intravenous administration of 5 mg/kg body weight, the mean total body clearance of the older pigs was smaller than that of the younger pigs. This difference was not reflected in the elimination half-life. After oral administration of 5 mg/kg body weight, the mean absorption rate constant was smaller and the mean absorption half-life was longer in the older pigs. The age-related changes in the pharmacokinetics of aditoprim were not sufficiently pronounced to suggest the necessity of modifying the oral dosage regimen in pigs of this age range. The favourable pharmacokinetics of aditoprim in pigs (large apparent volume of distribution, long elimination half-life and high bioavailability) may permit introduction of this drug into swine practice, after safety and residue depletion studies.

Mathematical description of the concentration of oxytetracycline and penicillin-G in tissue cages in calves as related to the serum concentration

A mathematical model based on Fick's laws of diffusion describing the concentration of drug in tissue cage models was elaborated. The model takes into account differences in protein binding, tissue cage geometry and serum pharmacokinetics. The validity of the model was tested against experimental data obtained from a tissue cage model in calves by simultaneous fitting to serum and tissue cage fluid (TCF) data in a non-linear least-squares regression computer program. Concentrations of penicillin-G (pen-G) in serum and TCF following intravenous (i.v.) administration of potassium pen-G were adequately described by the mathematical model. Concentrations in TCF after intramuscular (i.m.) administration of the same drug and of procaine pen-G could be predicted by the mathematical model. Concentrations of oxytetracycline (OTC) in serum and TCF following i.v. administration and continuous i.v. infusions were also adequately described by the model, and TCF concentrations after i.m. administration of the same drug could be roughly predicted. The results indicate that pen-G and OTC have the same permeability coefficient for transport from serum to TCF.

Distribution of oxytetracycline to tissue cages and granuloma pouches in calves and effect of acute inflammation on distribution to tissue cages

The effect of acute inflammation on oxytetracycline (OTC) distribution was studied in a tissue cage model in calves. An acute inflammatory reaction was induced in tissue cages by injecting lipopolysaccharide (LPS) from Salmonella typhimurium. The distribution of OTC to tissue cage fluid (TCF) was also compared with distribution to fluid from granuloma pouches (GPF). Tissue from LPS-injected cages showed histological changes indicating an acute inflammatory reaction. Concentrations of OTC were higher in LPS cages than in controls; at 1, 2, 4 and 10 h the difference was statistically significant (P less than 0.05). Numerically the overall elimination rate constant (kel) was larger, elimination half-life (t1/2) shorter, peak concentration (Cmax) higher, and time of peak concentration (Tmax) shorter in LPS cages than in controls. The area under the curve (AUC) of OTC was greater and the ratio AUCTCF/AUCserum was higher in LPS cages than in controls. Although statistically significant differences were not found for all the pharmacokinetic parameters, it was concluded that distribution to and elimination from LPS cages were both faster than in controls. Concentration-time profiles of OTC were similar in TCF and GPF in that concentrations were lower and elimination was more prolonged than in serum. Levels were higher in GPF than in TCF up to 3 h after injection; thereafter the relationship was reversed. Distribution to and elimination processes from GPF appeared to be faster than from TCF as numerically kel was higher, t1/2 shorter and Tmax shorter in GPF than in TCF. It was concluded that the granuloma pouch model and the tissue cage model have similarities in distribution and elimination patterns and that differences are most probably due to differences in the ratio of the surface area to the volume.

Clinical pharmacology of antimicrobial drugs for the treatment of septic neonatal calves

For a given infection, each antibiotic will have a probability of producing a beneficial outcome. Decisions that increase the antibacterial activity of the therapeutic regimen against the bacterial infection will increase the probability of a beneficial outcome. Unfortunately, such decisions may increase the cost of therapy or the risks of toxicity. Finally, neonatal calves presented for therapy are not of uniform value. It is logical to employ different antimicrobial drugs and ancillary therapies when the value of the individual calf is considered. A constructive balance between efficacy, cost, and toxicity establishes the value of a therapeutic approach for the client.

Ruminant pharmacology

Aspects of drug disposition, metabolism, and toxicity in the ruminant animal are discussed, and illustrative examples are provided. The effects of the reticulo-rumen on drug disposition in the ruminant are highlighted.

Pharmacokinetics and urinary excretion of gentamicin in Bubalus bubalis calves following intramuscular administration

The pharmacokinetics and urinary excretion of gentamicin was studied in buffalo calves after a single intramuscular administration (10 mg kg-1). Kinetic determinants were calculated by using a two compartment open model. The absorption (t1/2Ka) and biological half lives (t1/2 beta) were calculated to be 0.43 +/- 0.08 and 3.79 +/- 0.23 h, respectively. The value of the apparent volume of distribution (VdB) was found to be 0.38 +/- 0.07 litre kg-1. The satisfactory intramuscular dosage regimen of gentamicin for buffalo calves would be 3.23 mg kg-1 as priming dose and 2.88 mg kg-1 as maintenance dose to be repeated at 12 hour intervals to achieve and maintain the therapeutic plasma levels within safe limits. Urinary excretion of gentamicin was very rapid during the first 12 hours as 48.07 +/- 1.39 per cent of the total administered dose was excreted unchanged during this period.

Perioperative antimicrobial considerations for gastrointestinal surgery of cattle

Perioperative use of antimicrobial drugs constitutes extra-label use of those drugs. Principles of therapeutic and prophylactic use of antimicrobial drugs can guide decisions about their perioperative use. Regimens currently suggested are based on those principles, theoretical information, pharmacokinetic and pharmacodynamic data, extrapolation from studies with other species, empirical data, personal bias, and experience. Controlled clinical investigations are necessary to provide objective data from which specific recommendations can be derived.

Disposition kinetics and urinary excretion of gentamicin in buffalo bulls (Bubalus bubalis)

The disposition kinetics and urinary excretion of gentamicin sulphate were studied in young buffalo bulls following a single intramuscular administration of the drug at 5 mg kg-1 body weight. The time course of the serum gentamicin concentration was adequately described by the one-compartment open model. The values of the absorption and elimination halflives were 12.2 +/- 2.2 and 167.0 +/- 29.7 min respectively. The apparent volume of distribution was 0.29 +/- 0.01 L kg-1. During the first 12 h, 63% of the total administered dose was excreted in urine. On the basis of the kinetic data, a satisfactory intramuscular dosage regimen for gentamicin sulphate would be at least 6 mg kg-1 body weight repeated at 8 h intervals.