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Abstract

OBJECTIVE To establish a study cutoff for evidence of glaucoma on the basis of IOP measurements from a large population of healthy dogs and to assess the effects of IV propofol administration on IOPs in premedicated and nonpremedicated dogs with and without glaucoma defined by this method.

DESIGN Prospective, descriptive study.

ANIMALS 234 client-owned dogs.

PROCEDURES IOPs measured in 113 healthy dogs (226 eyes) were used to calculate an IOP value indicative of glaucoma. The IOPs were measured in an additional 121 dogs (237 eyes) undergoing ophthalmic surgery. Midazolam-butorphanol was administered IV as preanesthetic medication to 15 and 87 dogs with and without glaucoma, respectively. A placebo (lactated Ringer solution) was administered IV to 8 and 11 dogs with and without glaucoma, respectively. Anesthesia of surgical patients was induced with propofol IV to effect. The IOPs and physiologic variables of interest were recorded before (baseline) and after preanesthetic medication or placebo administration and after propofol administration.

RESULTS An IOP > 25 mm Hg was deemed indicative of glaucoma. Compared with baseline measurements, mean IOP was increased after propofol administration in nonpremedicated dogs without glaucoma and unchanged in nonpremedicated dogs with glaucoma. Propofol-associated increases in IOP were blunted in premedicated dogs without glaucoma; IOP in affected eyes of premedicated dogs with glaucoma was decreased after preanesthetic medication and after propofol administration.

CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that preexisting IOP influences the response to anesthetic drugs, and administration of preanesthetic medication with muscle-relaxing properties may blunt or reduce propofol-induced increases in IOP. Further research with a larger number of dogs is needed to confirm our results in dogs with glaucoma.

Full access
in Journal of the American Veterinary Medical Association
in Journal of the American Veterinary Medical Association

Summary

Mature boars were subjected to chronic treatment with a gonadotropin-releasing hormone (GnRH) agonist, goserelin (D-Ser[But]6, Azgly-NH2 10), and serum luteinizing hormone (lh) and testosterone concentrations were measured. Ten sexually mature boars were randomly assigned to treatment (n = 5) or control (n = 5) groups. On day 0, boars were implanted sc (day 0) with 2 GnRH agonist implants (1 mg of GnRH/implant) or sham implants. Blood samples were collected at 12-hour intervals on days – 2 and –1, at 6-hour intervals on days 0 through 4, and at 12-hour intervals on days 5 through 8. In addition, blood samples were collected at 15-minute intervals for 6 hours on days –1, 0, 4, and 8. Serum testosterone and (lh concentrations were determined by radioimmunoassay. Maximal (lh (7 ± 1 ng/ml) and testosterone (26 ± 3 ng/ml) concentrations were observed at 5 and 18 hours, respectively, after GnRH agonist treatment. Subsequently, (lh and testosterone concentrations decreased to pretreatment values (0.3 ± 0.1 ng/ml and 1.8 ± 0.4 ng/ml, respectively) by 24 and 48 hours, respectively, after GnRH agonist implantation. Few differences in the characteristics of pulsatile (lh release were observed between the groups. Testosterone and lh concentrations in samples collected at 6- and 12-hour intervals and pulsatile (lh release did not change after sham treatment of control boars. Whereas previous reports indicated that chronic GnRH administration suppressed serum lh and testosterone concentrations in rams, rats, and dogs, our results indicate that chronic GnRH agonist treatment induced transitory increases, without subsequent suppression, in lh and testosterone concentrations in mature boars.

Free access
in American Journal of Veterinary Research

SUMMARY

Six mature Holstein bulls were each given 10 mg of phenylbutazone (pbz)/kg of body weight, po. Of the 6 bulls, 3 were given 10 mg of pbz/kg by rapid iv administration 4 weeks later. Plasma concentration-vs-time data were analyzed, using nonlinear regression modeling (sum of exponential functions). The harmonic mean of the biologic half-life of pbz was 62.6 ± 12.9 hours after oral administration and 61.6 ± 7.2 hours after iv administration. The mean residence time was 94.61 ± 8.44 hours and 90.49 ± 8.93 hours for oral and iv administration, respectively. The mean total body clearance was 0.0015 ± 0.0003 L/h/kg, with the mean apparent volume of distribution 0.134 ± 0.021 L/kg. Mean bioavailability was 73 ± 2% after oral administration. Phenylbutazone was adequately absorbed from the gastrointestinal tract in bulls. The apparent volume of distribution was small, indicating that pbz distributed mainly into plasma and extracellular fluid. The total body clearance was also small, which accounted for the long half-life of pbz in bulls.

Free access
in American Journal of Veterinary Research

Abstract

Objective

To examine, in horses, the disposition and excretion of the active metabolite 6-methoxy-2-naphthylacetic acid (6MNA) of the nonsteroidal anti-inflammatory prodrug nabumetone.

Design

Pharmacokinetic analysis of 6MNA after oral administration of nabumetone and IV administration of 6MNA.

Procedure

Using a crossover design, 5 horses were orally administered 3.7 mg of nabumetone/kg of body weight. After a 3-week washout period, 4 horses were administered 2.5 mg of 6MNA/kg, IV.

Results

Absorption of nabumetone from the gastrointestinal tract and its metabolism to 6MNA had a median appearance half-life of 0.88 hour. The elimination half-life was 11 hours. Area under the plasma concentration time curve for 6MNA after oral administration of nabumetone was 120.6 mg/h/L. A dose of 2.5 mg/kg of 6MNA administered IV resulted in plasma concentration nearly equivalent to that induced by the orally administered dose. Disposition of 6MNA was modeled as a one-compartment, first-order elimination. The area under the plasma concentration time curve for IV administration of 6MNA was 117.0 mg/h/L, and the specific volume of distribution was 0.247 L/kg. The distribution half-life and the elimination half-life were 0.56 and 7.90 hours, respectively. Percentage of total dose recovered in urine for the 36-hour collection period after the oral and IV administrations was 7.4 and 5.3%, respectively.

Conclusions

Metabolism of nabumetone to 6MNA, as reported in other species, also occurs in horses. There were a number of additional metabolites of nabumetone in urine that could not be fully identified and characterized. (Am J Vet Res 1996;57:517–521)

Free access
in American Journal of Veterinary Research

Summary:

The effects of propofol on anesthetic induction were evaluated in 40 dogs anesthetized with isoflurane. Propofol is a rapidly acting, nonbarbiturate drug that induces anesthesia of ultrashort duration with iv administration. Four preanesthetic regimens were used: anesthesia without preanesthetic drugs; or with preanesthetic administration of acepromazine (0.1 mg/kg of body weight, im), diazepam (0.2 mg/kg, iv), or acepromazine (0.02 mg/kg) and butorphanol (0.4 mg/kg) im. Heart rate, systolic arterial blood pressure (sap), respiration, quality of induction and recovery, and adverse effects were recorded. Intravenous propofol administration induced a variable period of apnea in 34 of 40 dogs. Cyanosis (in 2 dogs) and signs of pain on injection (in 3 dogs) were infrequently observed during induction. One dog developed ventricular premature depolarizations after propofol administration. Venous CO2 tension increased and pH decreased immediately after propofol administration, regardless of preanesthetic regimen. The sap significantly (P < 0.05) decreased after propofol administration in dogs treated with acepromazine (sap, 178 mm of Hg before vs 128 mm of Hg after propofol) and with acepromazine/butorphanol (sap, 184 mm of Hg before vs 98 mm of Hg after propofol). When used for induction, propofol induces anesthetic-related adverse effects, some of which can be minimized by preanesthetic medication. Recovery characteristics varied with preanesthetic medication, independent of propofol administration.

Free access
in Journal of the American Veterinary Medical Association

SUMMARY

Six mature Holstein bulls were given an 8-day course of phenylbutazone (pbz) orally (loading dose, 12 mg of pbz/kg of body weight and 7 maintenance doses of 6 mg of pbz/kg, q 24 h). Plasma concentration-vs-time data were analyzed, using nonlinear regression modeling. The harmonic mean ± pseudo-sd of the biologic half-life of pbz was 61.8 ± 12.8 hours. The arithmetic mean ± sem of the total body clearance and apparent volume of distribution were 0.0021 ± 0.0001 L/h/kg and 0.201 ± 0.009 L/kg, respectively. The predicted mean minimal plasma concentration of pbz with this dosage regimen was 75.06 ± 4.05 μg/ml.

The predicted minimal plasma drug concentration was compared with the observed minimal plasma drug concentration in another group of bulls treated with pbz for at least 60 days. Sixteen mature Holstein bulls were given approximately 6 mg of pbz/kg, po, daily for various musculoskeletal disorders. The mean observed minimal plasma concentration of pbz in the 16 bulls was 76.10 ± 2.04 μg/ ml, whereas the mean predicted minimal plasma concentration was 74.69 ± 3.10 μg/ml.

Dosages of 4 to 6 mg of pbz/kg, q 24 h, or 10 to 14 mg of pbz/kg, q 48 h, provided therapeutic plasma concentrations of pbz with minimal steady-state concentrations between 50 and 70 μg/ml.

Free access
in American Journal of Veterinary Research
in Journal of the American Veterinary Medical Association