Possible drug-drug interaction in dogs and cats resulted from alteration in drug metabolism: A mini review

Mass spectrometric methods for evaluation of voriconazole avian pharmacokinetics and the inhibition of its cytochrome P450-induced metabolism

Invasive fungal aspergillosis is a leading cause of morbidity and mortality in many species including avian species such as common ravens (Corvus corax). Methods were developed for mass spectral determination of voriconazole in raven plasma as a means of determining pharmacokinetics of this antifungal agent. Without further development, GC/MS/MS (gas chromatography-tandem quadrupole mass spectrometry) proved to be inferior to LC/MS/MS (liquid chromatography-tandem quadrupole mass spectrometry) for measurement of voriconazole levels in treated raven plasma owing to numerous heat-induced breakdown products despite protection of voriconazole functional groups with trimethylsilyl moieties. LC/MS/MS measurement revealed in multi-dosing experiments that the ravens were capable of rapid or ultrarapid metabolism of voriconazole. This accounted for the animals' inability to raise the drug into the therapeutic range regardless of dosing regimen unless cytochrome P450 (CYP) inhibitors were included. Strategic selection of CYP inhibitors showed that of four selected compounds including cimetidine, enrofloxacin and omeprazole, only ciprofloxacin (Cipro) was able to maintain voriconazole levels in the therapeutic range until the end of the dosing period. The optimal method of administration involved maintenance doses of voriconazole at 6 mg/kg and ciprofloxacin at 20 mg/kg. Higher doses of voriconazole such as 18 mg/kg were also tenable without apparent induction of toxicity. Although most species employ CYP2C19 to metabolize voriconazole, it was necessary to speculate that voriconazole might be subject to metabolism by CYP1A2 in the ravens to explain the utility of ciprofloxacin, a previously unknown enzymatic route. Finally, despite its widespread catalog of CYP inhibitions including CYP1A2 and CYP2C19, cimetidine may be inadequate at enhancing voriconazole levels owing to its known effects on raising gastric pH, a result that may limit voriconazole solubility.

Potential to use cannabinoids as adjunct therapy for dexamethasone: An in vitro study with canine peripheral blood mononuclear cells

Dexamethasone (dex) is a potent glucocorticoid used to treat a variety of diseases. It is widely used in veterinary medicine in many species; for instance, in dogs, it can be used for emergent cases of anaphylaxis or trauma, management of immune-mediated hemolytic anemia or thrombocytopenia, certain cancers, allergic reactions, and topically for skin or eye inflammation. Dex is not without its side effects, especially when administered systemically, which might compromise compliance and effective treatment. Thus, adjunct therapies have been suggested to allow for decreased dex dosing and reduction in side effects while maintaining immunosuppressive efficacy. The goal of this study was to evaluate the potential for cannabinoids to serve as adjunct therapies for dex. Immune function was assessed in canine peripheral blood mononuclear cells (PBMCs) after treatment with dex with and without cannabidiol (CBD) and/or Δ9-tetrahydrocannabinol (THC). Dex suppressed IFN-γ protein secretion in a concentration-dependent manner and this suppression by low concentrations of dex was enhanced in the presence of CBD, THC, or the combination of CBD and THC. Similar effects were found with INFG and TNFA mRNA expression. These findings provide a rationale for using CBD or THC in vivo to reduce dex dosing and side effects.

Multifocal cutaneous phaeohyphomycosis caused by Exophiala spinifera with clinical resolution in an immunocompromised cat

Case summary

A 3-year-old neutered domestic shorthair cat with a long history of idiopathic immune-mediated haemolytic anaemia and thrombocytopenia treated with ciclosporin and prednisolone was referred 2 months after the appearance of nodular dermatitis. A single pigmented nodule was present in the lateral carpal region of the right foreleg. The lesion was 7 mm in diameter, non-exudative and cutaneous to subcutaneous. Fine-needle aspiration of the mass revealed the presence of pigmented fungal elements. Excisional surgery was planned; in the meantime, a plaque-like lesion developed in the interorbital region. Histopathological examination confirmed the presumptive diagnosis of phaeohyphomycosis, and Exophiala spinifera was identified as the aetiological agent. Itraconazole, given orally at a dose of 10 mg/kg for 8 weeks following surgery, enabled clinical resolution despite continued use of immunosuppressants. The follow-up was carried out over 14 weeks.

Relevance and novel information

This case report provides the first evidence of multifocal cutaneous phaeohyphomycosis caused by E spinifera with clinical resolution after combined surgical and itraconazole treatment in an immunocompromised cat.

Toxicity induced by ciprofloxacin and enrofloxacin: oxidative stress and metabolism

Ciprofloxacin (CIP) (human use) and enrofloxacin (ENR) (veterinary use) are synthetic anti-infectious medications that belong to the second generation of fluoroquinolones. They have a wide antimicrobial spectrum and strong bactericidal effects at very low concentrations via enzymatic inhibition of DNA gyrase and topoisomerase IV, which are required for DNA replication. They also have high bioavailability, rapid absorption with favorable pharmacokinetics and excellent tissue penetration, including cerebral spinal fluid. These features have made them the most applied antibiotics in both human and veterinary medicine. ENR is marketed exclusively for animal medicine and has been widely used as a therapeutic veterinary antibiotic, resulting in its residue in edible tissues and aquatic environments, as well as the development of resistance and toxicity. Estimation of the risks to humans due to antimicrobial resistance produced by CIP and ENR is important and of great interest. Moreover, in rare cases due to their overdose and/or prolonged administration, the development of CIP and ENR toxicity may occur. The toxicity of these fluoroquinolones antimicrobials is mainly related to reactive oxygen species (ROS) and oxidative stress (OS) generation, besides metabolism-related toxicity. Therefore, CIP is restricted in pregnant and lactating women, pediatrics and elderly similarly ENR do in the veterinary field. This review manuscript aims to identify the toxicity induced by ROS and OS as a common sequel of CIP and ENR. Furthermore, their metabolism and the role of metabolizing enzymes were reported.

Comparing Potential Drug-Drug Interactions in Companion Animal Medications Using Two Electronic Databases

Multiple-drug prescriptions can cause drug–drug interactions (DDIs), which increase risks associated with healthcare in veterinary medicine. Moreover, many human medicines are used in canine patients under the responsibility of veterinarians and may cause severe problems due to off-label use. Currently, many electronic databases are being used as tools for potential DDI prediction, for example, Micromedex and Drugs.com, which may benefit the prediction of potential DDIs for drugs used in canine. The purpose of this study was to examine different abilities for the identification of potential DDIs in companion animal medicine, especially in canine patients, by Micromedex and Drugs.com. Micromedex showed 429 pairs of potential DDIs, while Drugs.com showed 842 pairs of potential DDIs. The analysis comparing results between the two databases showed 139 pairs (12.28%) with the same severity and 993 pairs (87.72%) with different severities. The major mechanisms of contraindicated and major potential DDIs were cytochrome P450 induction–inhibition and QT interval prolongation. Veterinarians should interpret potential DDIs from several databases with caution and keep in mind that the results might not be reliable due to differences in sensitivity to drugs, drug-metabolizing enzymes, and elimination pathway between animals and humans.

A study of the pharmacokinetics and thromboxane inhibitory activity of a single intramuscular dose of carprofen as a means to establish its potential use as an analgesic drug in white rhinoceros

The alleviation of pain and prevention of suffering are key aspects of animal welfare. Unfortunately, analgesic drugs are not available for all species. White rhinoceros (Ceratotherium simum), representing one of such species, which survive poaching attempts inflicted with severe facial injuries and gunshot wounds, nonetheless require analgesic support. To improve treatment conditions, this study explored the use of carprofen for the treatment of pain and inflammation in white rhinoceros. The pharmacokinetics of 1 mg/kg intramuscular carprofen was evaluated in six healthy white rhinoceros. The half-life of λ_z and mean residence time was 105.71 ± 15.67 and 155.01 ± 22.46 hr, respectively. The area under the curve and the maximum carprofen concentration were 904.61 ± 110.78 μg ml^-1  hr^-1 and 5.77 ± 0.63 μg/ml, respectively. Plasma TXB₂ inhibition demonstrated anti-inflammatory properties and indicated that carprofen may be effective for a minimum of 48 hr in most animals. With its long half-life further indicating that a single dose could be effective for several days, we suggest that carprofen may be a useful drug for the treatment of white rhinoceros.

A novel non-azole topical treatment reduces Malassezia numbers and associated dermatitis: a short term prospective, randomized, blinded and placebo-controlled trial in naturally infected dogs

BACKGROUND

Malassezia yeast overgrowth on the skin is a common and often recurrent cause of dermatitis in dogs; it can be an exacerbating factor of atopic dermatitis. Anti-fungal drugs have been a standard treatment, but there is some concern that resistance may be evolving in a spectrum of Malassezia species. Safe, efficient and easy-to-use alternatives are needed.

OBJECTIVES

To assess if a commercially available topical non-azole solution applied to paws affected by Malassezia-associated dermatitis (MAD), could ameliorate Malassezia numbers and associated signs over a short term (14 day) trial.

ANIMALS

Eighteen dogs with MAD affecting at least two paws.

METHODS

The study design was prospective, randomized, blinded and placebo-controlled, using a split-body protocol. Dogs were treated once daily with the test solution on one paw and placebo on the other. Dogs were examined at days 0 and 14 ± 3. The primary end-point was Malassezia numbers assessed cytologically. Secondary end-points were clinical scores for lesion severity and pruritus as assessed by a pruritus Visual Analog Scale (PVAS). Owner compliance and adverse effects were assessed.

RESULTS

There was a statistically significant reduction in Malassezia numbers and clinical scores for paws treated with the test solution versus placebo. No statistical difference in PVAS was found.

CONCLUSION

Daily topical application of the test solution was effective in reducing the Malassezia burden, as well as improving clinical scores in dogs with MAD of the paws. No adverse effects were reported and owners described the product as either "easy" or "very easy" to use.