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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.

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in American Journal of Veterinary Research

Calfhood diseases have major negative economic consequences on beef and dairy operations owing to costs associated with treatment, long-term effects on growth and performance, and death of affected calves. 1–3 The number of drugs approved for the treatment of diseased calves by the FDA is limited; however, veterinarians have the authority to administer drugs in an extralabel manner to that class of animals under provisions established by AMDUCA. 4 Nevertheless, drug labels that state, “a withdrawal period has not been established for this product in preruminating calves” can cause confusion about whether those drugs can or cannot be

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in Journal of the American Veterinary Medical Association

Flunixin meglumine is an NSAID that is approved by the FDA for the treatment of inflammatory conditions in cattle, horses, and swine and alleviation of pain associated with musculoskeletal disorders and colic in horses; it is not labeled for alleviation of pain in food-producing animals. Currently, there are no FDA-approved drugs for the treatment of pyrexia, inflammatory conditions, or pain in minor food-producing species such as sheep and goats. Owing to the lack of alternatives, veterinarians often administer food-producing animals products containing flunixin in an extralabel manner for the treatment of signs of pain. In the United States, NSAIDs are

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in Journal of the American Veterinary Medical Association