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Abstract

Objective—To determine the pharmacokinetics of praziquantel following single and multiple oral dosing in loggerhead sea turtles.

Animals—12 healthy juvenile loggerhead sea turtles.

Procedure—Praziquantel was administered orally as a single dose (25 and 50 mg/kg) to 2 groups of turtles; a multiple-dose study was then performed in which 6 turtles received 3 doses of praziquantel (25 mg/kg, PO) at 3-hour intervals. Blood samples were collected from all turtles before and at intervals after drug administration for assessment of plasma praziquantel concentrations. Pharmacokinetic analyses included maximum observed plasma concentration (Cmax), time to maximum concentration (Tmax), area under the plasma praziquantel concentration-time curve, and mean residence time (MRTt).

Results—Large interanimal variability in plasma praziquantel concentrations was observed for all dosages. One turtle that received 50 mg of praziquantel/kg developed skin lesions within 48 hours of administration. After administration of 25 or 50 mg of praziquantel/ kg, mean plasma concentrations were below the limit of quantification after 24 hours. In the multiple- dose group of turtles, mean plasma concentration was 90 ng/mL at the last sampling time-point (48 hours after the first of 3 doses). In the single-dose study, mean Cmax and Tmax with dose were not significantly different between doses. After administration of multiple doses of praziquantel, only MRTt was significantly increased, compared with values after administration of a single 25-mg dose.

Conclusions and Clinical Relevance—Oral administration of 25 mg of praziquantel/kg 3 times at 3-hour intervals may be appropriate for treatment of loggerhead sea turtles with spirorchidiasis. (Am J Vet Res 2003;64:304–309)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine effects of pituitary pars intermedia dysfunction (Cushing's disease) and age on fecal egg count and time to egg reappearance after anthelmintic treatment in horses residing in similar environments.

Design—Cross-sectional study.

Animals—29 healthy horses (4 to 35 years old) and 13 horses with PPID (13 to 33 years old).

Procedures—Fecal egg counts were performed by use of a modified Wisconsin flotation method at 2-week intervals before and after ivermectin treatment.

Results—Horses with PPID had higher fecal egg counts before and 8, 10, and 12 weeks after ivermectin treatment, compared with counts for site-matched healthy horses. There was no difference in the period for < 90% reduction in fecal egg counts between the 2 groups. Age did not affect fecal egg counts at any time point.

Conclusions and Clinical Relevance—For similar environmental conditions, horses with PPID were more likely to have higher fecal egg counts than were healthy horses. Therefore, horses with PPID may need to have a more aggressive parasite prevention program than do healthy horses. Age did not affect fecal egg counts or time to egg reappearance after anthelmintic treatment, which suggested age alone does not likely require special consideration when designing a parasite control program for adult horses.

Restricted access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine pharmacokinetics of azathioprine (AZA) and clinical, hematologic, and serologic effects of IV and oral administration of AZA in horses.

Animals—6 horses.

Procedure—In study phase 1, a single dose of AZA was administered IV (1.5 mg/kg) or orally (3.0 mg/kg) to 6 horses, with at least 1 week between treatments. Blood samples were collected for AZA and 6-mercaptopurine (6-MP) analysis 1 hour before and at predetermined time points up to 4 hours after AZA administration. In study phase 2, AZA was administered orally (3 mg/kg) every 24 hours for 30 days and then every 48 hours for 30 days. Throughout study phase 2, blood samples were collected for CBC determination and serum biochemical analysis.

Results—Plasma concentrations of AZA and its metabolite, 6-MP, decreased rapidly from plasma following IV administration of AZA, consistent with the short mean elimination half-life of 1.8 minutes. Oral bioavailability of AZA was low, ranging from 1% to 7%. No horses had abnormalities on CBC determination or serum biochemical analysis, other than 1 horse that was lymphopenic on day 5 and 26 of daily treatment. This horse developed facial alopecia from which 1 colony of a Trichophyton sp was cultured; alopecia resolved within 1 month after the study ended.

Conclusions and Clinical Relevance—Overall, no adverse effects were observed with long-term oral administration of AZA to horses, although 1 horse did have possible evidence of immunosuppression with chronic treatment. Further investigation of the clinical efficacy of AZA in the treatment of autoimmune diseases in horses is warranted. (Am J Vet Res 2005;66:1578–1583)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine serum pharmacokinetics of pentoxifylline and its 5-hydroxyhexyl metabolite in horses after administration of a single IV dose and after single and multiple oral doses.

Animals—8 healthy adult horses.

Procedures—A crossover study design was used with a washout period of 6 days between treatments. Treatments were IV administration of a single dose of pentoxifylline (8.5 mg/kg) and oral administration of generic sustained-release pentoxifylline (10 mg/kg, q 12 h, for 8 days). Blood samples were collected 0, 1, 3, 6, 12, 20, 30, and 45 minutes and 1, 2, 4, 6, 8, and 12 hours after IV administration. For oral administration, blood samples were collected 0, 0.25, 0.5, 0.75, 1, 2, 4, 8, and 12 hours after the first dose and 0, 0.25, 0.5, 0.75, 1, 2, 4, 8, 12, and 24 hours after the last dose.

Results—Elimination of pentoxifylline was rapid after IV administration. After oral administration, pentoxifylline was rapidly absorbed and variably eliminated. Higher serum concentrations of pentoxifylline and apparent bioavailability were observed after oral administration of the first dose, compared with values after administration of the last dose on day 8 of treatment.

Conclusions and Clinical Relevance—In horses, oral administration of 10 mg of pentoxifylline/kg results in serum concentrations equivalent to those observed for therapeutic doses of pentoxifylline in humans. Twice daily administration appears to be appropriate. However, serum concentrations of pentoxifylline appear to decrease with repeated dosing; thus, practitioners may consider increasing the dosage if clinical response diminishes with repeated administration.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine induction doses, anesthetic constant rate infusions (CRI), and cardiopulmonary effects of propofol in red-tailed hawks and great horned owls and propofol pharmacokinetics in the owls during CRI.

Animals—6 red-tailed hawks and 6 great horned owls.

Procedure—The CRI dose necessary for a loss of withdrawal reflex was determined via specific stimuli. Anesthesia was induced by IV administration of propofol (1 mg/kg/min) and maintained by CRI at the predetermined dose for 30 minutes. Heart and respiratory rates, arterial blood pressures, and blood gas tensions were obtained in awake birds and at various times after induction. End-tidal CO2 (ETCO2) concentration and esophageal temperature were obtained after induction. Propofol plasma concentrations were obtained after induction and after completion of the CRI in the owls. Recovery times were recorded.

Results—Mean ± SD doses for induction and CRI were 4.48 ± 1.09 mg/kg and 0.48 ± 0.06 mg/kg/min, respectively, for hawks and 3.36 ± 0.71 mg/kg and 0.56 ± 0.15 mg/kg/min, respectively, for owls. Significant increases in PaCO2, HCO3, and ETCO2 in hawks and owls and significant decreases in arterial pH in hawks were detected. A 2-compartment model best described the owl pharmacodynamic data. Recovery times after infusion were prolonged and varied widely. Central nervous system excitatory signs were observed during recovery.

Conclusions and Clinical Relevance—Effects on blood pressure were minimal, but effective ventilation was reduced, suggesting the need for careful monitoring during anesthesia. Prolonged recovery periods with moderate-to-severe excitatory CNS signs may occur in these species at these doses. (Am J Vet Res 2003;64:677–683)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine blood cell morphologic characteristics and hematologic and plasma biochemical reference ranges for iguanas housed in a warm indoor and outdoor environment with regular exposure to direct sunlight.

Design—Original study.

Animals—51 clinically normal iguanas (18 males, 25 females, and 8 juveniles) housed in 3 Florida locations.

Procedure—Blood was collected from the coccygeal or ventral abdominal vein. Any samples that had obvious hemolysis or clot formation were not used. Leukocyte counts were determined manually; other hematologic values were obtained by use of a commercially available cell counter. Plasma biochemical values were determined by use of a spectrophotometric chemistry analyzer. Blood smears were stained with Wright-Giemsa and cytochemical stains for morphologic and cytochemical evaluation.

Results—Hematologic ranges were generally higher in this study than previously reported. Thrombocytes were variable in appearance between individuals and sometimes difficult to distinguish from lymphocytes on a Wright-Giemsa preparation. Concentrations of calcium, phosphorus, total protein, globulins, and cholesterol were significantly higher, and the albumin:globulin ratio was significantly lower, in healthy gravid females than in male or nongravid female iguanas. Nongravid females had significantly higher calcium and cholesterol concentrations, compared with males. The calcium:phosphorus ratio was > 1 in all iguanas. Gravid females had a calcium phosphorus product ranging between 210 and 800. Intracytoplasmic inclusions were identified within the erythrocytes of some iguanas.

Conclusions and Clinical Relevance—Hematologic ranges for iguanas in this study are higher than those reported for iguanas. Sex and age of the iguana should be considered when evaluating biochemical values. Healthy ovulating and gravid females may have significantly increased electrolyte and protein concentrations, but maintain a calcium:phosphorus ratio > 1. (J Am Vet Med Assoc 2001;218:915–921)

Restricted access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To compare characteristics of horses recovering from 4 hours of desflurane anesthesia with and without immediate postanesthetic IV administration of propofol and xylazine.

Animals—8 healthy horses (mean ± SEM age, 6.6 ± 1.0 years; mean body weight, 551 ± 50 kg).

Procedures—Horses were anesthetized twice. Both times, anesthesia was induced with a combination of xylazine hydrochloride, diazepam, and ketamine hydrochloride and then maintained for 4 hours with desflurane in oxygen. Choice of postanesthetic treatment was randomly assigned via a crossover design such that each horse received an IV injection of propofol and xylazine or saline (0.9% NaCl) solution after the anesthetic episode. Recovery events were quantitatively and qualitatively assessed. Venous blood samples were obtained before and after anesthesia for determination of serum creatine kinase activity and plasma propofol concentration.

Results—Anesthetic induction and maintenance were unremarkable in all horses. Compared with administration of saline solution, postanesthetic administration of propofol and xylazine resulted in an increased interval to emergence from anesthesia but improved quality of recovery-related transition to standing. Compared with administration of saline solution, administration of propofol also delayed the rate of decrease of end-tidal concentrations of desflurane and carbon dioxide and added to conditions promoting hypoxemia and hypoventilation.

Conclusions and Clinical Relevance—Propofol and xylazine administered IV to horses after 4 hours of desflurane anesthesia improved the quality of transition from lateral recumbency to standing but added potential for harmful respiratory depression during the postanesthetic period.

Full access
in American Journal of Veterinary Research

Abstract

OBJECTIVE To determine whether prophylactic administration of valacyclovir hydrochloride versus initiation of treatment at the onset of fever would differentially protect horses from viral replication and clinical disease attributable to equine herpesvirus type-1 (EHV-1) infection.

ANIMALS 18 aged mares.

PROCEDURES Horses were randomly assigned to receive an oral placebo (control), treatment at detection of fever, or prophylactic treatment (initiated 1 day prior to viral challenge) and then inoculated intranasally with a neuropathogenic strain of EHV-1. Placebo or valacyclovir was administered orally for 7 or 14 days after EHV-1 inoculation or detection of fever (3 horses/group). Effects of treatment on viral replication and clinical disease were evaluated. Plasma acyclovir concentrations and viremia were assessed to determine inhibitory concentrations of valacyclovir.

RESULTS Valacyclovir administration decreased shedding of virus and viremia, compared with findings for control horses. Rectal temperatures and clinical disease scores in horses that received valacyclovir prophylactically for 2 weeks were lower than those in control horses. The severity of but not the risk for ataxia was decreased by valacyclovir administration. Viremia was decreased when steady-state trough plasma acyclovir concentrations were > 0.8 μg/mL, supporting the time-dependent activity of acyclovir.

CONCLUSIONS AND CLINICAL RELEVANCE Valacyclovir treatment significantly decreased viral replication and signs of disease in EHV-1–infected horses; effects were greatest when treatment was initiated before viral inoculation, but treatment was also effective when initiated as late as 2 days after inoculation. During an outbreak of equine herpesvirus myeloencephalopathy, antiviral treatment may be initiated in horses at various stages of infection, including horses that have not yet developed signs of viral disease.

Full access
in American Journal of Veterinary Research