Pharmacokinetics and pharmacodynamics of a novel analgesic with a deterrent to human opioid abuse (methadone-fluconazole-naltrexone) after oral administration in dogs

Fungal diversity and drug susceptibility of the oral mycobiome of domestic dogs

The purpose of this study was to characterize the variety and diversity of the oral mycobiome of domestic dogs and to identify the commensal and potentially pathogenic fungi present. Two hundred fifty-one buccal swabs from domestic dogs were obtained and struck onto a chromogenic fungal growth medium that distinguishes between fungal species based on colony color and morphology. After isolating and harvesting single colonies, genomic DNA was extracted from pure cultures. PCR was used to amplify a fungal-specific variable rDNA region of the genome, which was then sent for sequencing. Sequencing results were input into the NCBI BLAST database to identify individual components of the oral mycobiome of tested dogs. Of the 251 dogs swabbed, 73 had cultivable fungi present and 10 dogs had multiple fungal species isolated. Although the dogs did not show signs of oral infections at the time, we did find fungal species that cause pathogenicity in animals and humans. Among fungal isolates, Malassezia pachydermatis and species from the genus Candida were predominant. Following fungal isolate identification, antifungal drug susceptibility tests were performed on each isolate toward the medically important antifungal drugs including fluconazole, ketoconazole, and terbinafine. Drug susceptibility test results indicated that a large number of isolates had high MIC values for all three drugs. Exploring the oral mycobiome of dogs, as well as the corresponding drug susceptibility profiles, can have important implications for canine dental hygiene, health, and medical treatment. Identifying the microorganisms within the canine mouth can illustrate a common pathway for fungal pathogens of One Health concern to spread from our canine companions to humans.

Dosing protocols to increase the efficacy of butorphanol in dogs

The purpose of this study was to improve butorphanol dosing in dogs. Twelve Beagles (6 males, 6 females) were enrolled. Six were randomly allocated to each butorphanol treatment: IV (0.4 mg/kg), IV loading dose (0.2 mg/kg) with IV CRI (0.2 mg/kg/h for 8 h), SC (0.4 mg/kg), SC (0.8 mg/kg) with an equal volume sodium bicarbonate (SC-bicarbonate), and IV after CYP inhibitors. We hypothesized that the CRI would produce longer durations than IV bolus, and SC-bicarbonate suspension would produce longer durations than SC. Hypothermia, an opioid effect paralleling antinociception in dogs, and sedation were evaluated. Pharmacokinetics and CYP inhibitor effects on butorphanol pharmacokinetics were determined. Rectal temperatures were significantly lower than baseline from 1.5-4 h (IV), 1-5 h (CRI), and 2-7 h (SC-bicarbonate), but not after SC. Dogs in all treatments had sedation. Butorphanol's half-life was ~1.5 h. SC-bicarbonate had lower bioavailability (61%) relative to SC, with no sustained release, and the CRI mean steady-state plasma concentration was 43.1 ng/ml. CYP inhibitors had minor pharmacokinetic effects on butorphanol. Butorphanol 0.4 mg/kg IV and 0.2 mg/kg loading dose with 0.2 mg/kg/h CRI decreased rectal temperature, but 0.4 mg/kg SC did not. Further studies are required to determine clinical analgesia of butorphanol.

Multiple-dose pharmacokinetics and opioid effects of a novel analgesic with a deterrent to human opioid abuse (methadone-fluconazole-naltrexone) after oral administration in dogs

OBJECTIVE

To assess the pharmacokinetics and opioid effects of methadone after administration of multiple doses by means of 2 dosing regimens of methadone-fluconazole-naltrexone.

ANIMALS

12 healthy Beagles.

PROCEDURES

Dogs were randomly allocated (6 dogs/group) to receive 1 of 2 oral dosing regimens of methadone-fluconazole-naltrexone. Treatment 1 doses were administered at 0 (methadone-to-fluconazole-to-naltrexone ratio of 1:5:0.25 mg/kg), 14 (1:5:0.25), 24 (0.5:2.5:0.125), and 38 (0.5:2.5:0.125) hours. Treatment 2 doses were administered at 0 (1:5:0.25), 4 (0.5:2.5:0.125), 10 (0.5:2.5:0.125), and 24 (0.5:2.5:0.125) hours. Blood samples, rectal temperatures, and von Frey antinociceptive measurements were obtained at designated times.

RESULTS

Compared with baseline, temperatures significantly decreased for treatment 1 group dogs at 2 to ≥ 4 hours and from 16 to ≥ 50 hours (12 hours after last dose) and for treatment 2 group dogs at 2 to ≥ 36 hours (12 hours after last dose), when trough methadone concentrations were ≥ 21.3 ng/mL. Antinociception occurred after the first dose but was not maintained throughout the study. Lesions were noted in some dogs at the application site of the von Frey device. Naltrexone and β-naltrexol were sporadically detected in plasma, and naltrexone glucuronide was consistently detected.

CONCLUSIONS AND CLINICAL RELEVANCE

Opioid effects were noted after oral administration of the first dose, and data suggested that administering a second dose 6 hours later and every 12 hours thereafter was necessary to maintain opioid effects. Antinociception may have been lost because dogs became averse or hyperalgesic to the von Frey device, such that the antinociception model used here may not be robust for repeated measurements in dogs.