OBJECTIVE To determine the pharmacokinetics of florfenicol, terbinafine, and betamethasone acetate after topical application to canine auricular skin and the influence of synthetic canine cerumen on pharmacokinetics.
SAMPLE Auricular skin from 6 euthanized shelter dogs (3 females and 3 neutered males with no visible signs of otitis externa).
PROCEDURES Skin adjacent to the external opening of the ear canal was collected and prepared for use in a 2-compartment flow-through diffusion cell system to evaluate penetration of an otic gel containing florfenicol, terbinafine, and betamethasone acetate over a 24-hour period. Radiolabeled 14C-terbinafine hydrochloride and 3H-betamethasone acetate were added to the gel to determine dermal penetration and distribution. Florfenicol absorption was determined by use of high-performance liquid chromatography–UV detection. Additionally, the effect of synthetic canine cerumen on the pharmacokinetics of all compounds was evaluated.
RESULTS During the 24-hour experiment, mean ± SD percentage absorption without the presence of synthetic canine cerumen was 0.28 ± 0.09% for 3H-betamethasone acetate, 0.06 ± 0.06% for florfenicol, and 0.06 ± 0.02% for 14C-terbinafine hydrochloride. Absorption profiles revealed no impact of synthetic canine cerumen on skin absorption for all 3 active compounds in the gel or on skin distribution of 3H-betamethasone acetate and 14C-terbinafine hydrochloride.
CONCLUSIONS AND CLINICAL RELEVANCE3H-betamethasone acetate, 14C-terbinafine hydrochloride, and florfenicol were all absorbed in vitro through healthy auricular skin specimens within the first 24 hours after topical application. Synthetic canine cerumen had no impact on dermal absorption in vitro, but it may serve as a temporary reservoir that prolongs the release of topical drugs.
Objective—To model the plasma tetracycline concentrations in swine (Sus scrofa domestica) treated with medication administered in water and determine the factors that contribute to the most accurate predictions of measured plasma drug concentrations.
Sample—Plasma tetracycline concentrations measured in blood samples from 3 populations of swine.
Procedures—Data from previous studies provided plasma tetracycline concentrations that were measured in blood samples collected from 1 swine population at 0, 4, 8, 12, 24, 32, 48, 56, 72, 80, 96, and 104 hours and from 2 swine populations at 0, 12, 24, 48, and 72 hours hours during administration of tetracycline hydrochloride dissolved in water. A 1-compartment pharmacostatistical model was used to analyze 5 potential covariate schemes and determine factors most important in predicting the plasma concentrations of tetracycline in swine.
Results—2 models most accurately predicted the tetracycline plasma concentrations in the 3 populations of swine. Factors of importance were body weight or age of pig, ambient temperature, concentration of tetracycline in water, and water use per unit of time.
Conclusions and Clinical Relevance—The factors found to be of importance, combined with knowledge of the individual pharmacokinetic and chemical properties of medications currently approved for administration in water, may be useful in more prudent administration of approved medications administered to swine. Factors found to be important in pharmacostatistical models may allow prediction of plasma concentrations of tetracycline or other commonly used medications administered in water. The ability to predict in vivo concentrations of medication in a population of food animals can be combined with bacterial minimum inhibitory concentrations to decrease the risk of developing antimicrobial resistance.
OBJECTIVE To compare the plasma pharmacokinetics of tulathromycin between 3-week-old (preweaned) and 6-month-old (weaned) calves and to characterize the distribution of tulathromcyin into pulmonary epithelial lining fluid (PELF) and interstitial fluid (ISF) of preweaned and weaned calves following SC administration of a single dose (2.5 mg/kg).
ANIMALS 8 healthy 3-week-old and 8 healthy 6-month-old Holstein steers.
PROCEDURES A jugular catheter and SC ultrafiltration probe were aseptically placed in the neck of each calf before tulathromycin administration. Blood, ISF, and bronchoalveolar lavage fluid samples were collected at predetermined times before and after tulathromycin administration for quantification of drug concentration. A urea dilution method was used to estimate tulathromycin concentration in PELF from that in bronchoalveolar lavage fluid. Tulathromycin–plasma protein binding was determined by in vitro methods. Plasma pharmacokinetics were determined by a 2-compartment model. Pharmacokinetic parameters and drug concentrations were compared between preweaned and weaned calves.
RESULTS Clearance and volume of distribution per fraction of tulathromycin absorbed were significantly greater for weaned calves than preweaned calves. Tulathromycin–plasma protein binding was significantly greater for weaned calves than preweaned calves. Maximum PELF tulathromycin concentration was significantly greater than the maximum plasma and maximum ISF tulathromycin concentrations in both groups.
CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that age affected multiple pharmacokinetic parameters of tulathromycin, likely owing to physiologic changes as calves mature from preruminants to ruminants. Knowledge of those changes may be useful in the development of studies to evaluate potential dose adjustments during treatment of calves with respiratory tract disease.
Objective—To determine the tissue depletion profile of tulathromycin and determine an appropriate slaughter withdrawal interval in meat goats after multiple SC injections of the drug.
Animals—16 healthy Boer goats.
Procedures—All goats were administered tulathromycin (2.5 mg/kg, SC) twice, with a 7-day interval between doses. Blood samples were collected throughout the study, and goats were euthanized at 2, 5, 10, and 20 days after the second tulathromycin dose. Lung, liver, kidney, fat, and muscle tissues were collected. Concentrations of tulathromycin in plasma and the hydrolytic tulathromycin fragment CP-60,300 in tissue samples were determined with ultrahigh-pressure liquid chromatography–tandem mass spectrometry.
Results—The plasma profile of tulathromycin was biphasic. Absorption was very rapid, with maximum drug concentrations (1.00 ± 0.42 μg/mL and 2.09 ± 1.77 μg/mL following the first and second doses, respectively) detected within approximately 1 hour after injection. Plasma terminal elimination half-life of tulathromycin was 61.4 ± 14.1 hours after the second dose. Half-lives in tissue ranged from 2.4 days for muscle to 9.0 days for lung tissue; kidney tissue was used to determine the withdrawal interval for tulathromycin in goats because it is considered an edible tissue.
Conclusions and Clinical Relevance—On the basis of the tissue tolerance limit in cattle of 5 ppm (μg/g), the calculated withdrawal interval for tulathromycin would be 19 days following SC administration in goats. On the basis of the more stringent guidelines recommended by the FDA, the calculated meat withdrawal interval following tulathromycin administration in goats was 34 days.
OBJECTIVE To describe plasma pharmacokinetic parameters and tissue elimination of flunixin in veal calves.
ANIMALS 20 unweaned Holstein calves between 3 and 6 weeks old.
PROCEDURES Each calf received flunixin (2.2 mg/kg, IV, q 24 h) for 3 days. Blood samples were collected from all calves before the first dose and at predetermined times after the first and last doses. Beginning 24 hours after injection of the last dose, 4 calves were euthanized each day for 5 days. Plasma and tissue samples were analyzed by ultraperformance liquid chromatography. Pharmacokinetic parameters were calculated by compartmental and noncompartmental methods.
RESULTS Mean ± SD plasma flunixin elimination half-life, residence time, and clearance were 1.32 ± 0.94 hours, 12.54 ± 10.96 hours, and 64.6 ± 40.7 mL/h/kg, respectively. Mean hepatic and muscle flunixin concentrations decreased to below FDA-established tolerance limits (0.125 and 0.025 μg/mL, respectively) for adult cattle by 3 and 2 days, respectively, after injection of the last dose of flunixin. Detectable flunixin concentrations were present in both the liver and muscle for at least 5 days after injection of the last dose.
CONCLUSIONS AND CLINICAL RELEVANCE The labeled slaughter withdrawal interval for flunixin in adult cattle is 4 days. Because administration of flunixin to veal calves represents extralabel drug use, any detectable flunixin concentrations in edible tissues are considered a violation. Results indicated that a slaughter withdrawal interval of several weeks may be necessary to ensure that violative tissue residues of flunixin are not detected in veal calves treated with that drug.