Canine and feline P-glycoprotein deficiency: What we know and where we need to go.

In 2001 the molecular genetic basis of so-called "ivermectin sensitivity" in herding breed dogs was determined to be a P-glycoprotein deficiency caused by a genetic variant of the MDR1 (ABCB1) gene often called "the MDR1 mutation." We have learned a great deal about P-glycoprotein's role in drug disposition since that discovery, namely that P-glycoprotein transports many more drugs than just macrocyclic lactones that P-glycoprotein mediated drug transport is present in more places than just the blood brain barrier, that some cats have a genetic variant of MDR1 that results in P-glycoprotein deficiency, that P-glycoprotein dysfunction can occur as a result of drug-drug interactions in any dog or cat, and that the concept of P-glycoprotein "inhibitors" versus P-glycoprotein substrates is somewhat arbitrary and artificial. This paper will review these discoveries and discuss how they impact drug selection and dosing in dogs and cats with genetically mediated P-glycoprotein deficiency or P-glycoprotein dysfunction resulting from drug-drug interactions.

A novel transdermal ketoprofen formulation for analgesia in cattle.

Ketoprofen is registered in many countries for injectable administration in cattle. Because it is soluble in a wide range of excipients, development of a novel transdermal (TD) ketoprofen formulation was pursued to provide a convenient and pain-free route of administration in cattle. One hundred and six excipient combinations were screened using in vitro techniques (Franz diffusion cells), with a 20%(w/v) ketoprofen formulation dissolved in a combination of 45%:45%(v/v) ethanol and isopropyl myristate (IPM) and 10%(v/v) eucalyptus oil achieving maximal penetration of ketoprofen through bovine skin. A bioavailability study was then conducted using a randomized cross-over design (n = 12), including IV, IM (both 3 mg/kg) and TD (10 mg/kg) ketoprofen formulations administered with a one-week washout period between administrations. The IV and IM formulation pharmacokinetic results were as expected. The CMAX , Tmax and AUC0-Last were significantly higher (arithmetic mean ± SD) after TD administration (20.0 ± 6.5 µg/ml, 115 ± 17 min and 3940 ± 1324 µg*min/ml, respectively), compared to IM (11.0 ± 4.0 µg/ml, 74 ± 43 min and 2376 ± 738 µg*min/ml, respectively), although there were no significant differences for T½ß . However, dose corrected values CMAX and AUCinf were significantly higher for IM compared to TD. The arithmetic mean bioavailability (F) of the transdermal formulation was 50%. The plasma concentration of the TD formulation at a dose of 10 mg/kg was similar to the IM formulation at 3 mg/kg by 30 min post-dosing with an arithmetic mean ± SD of 7.97 ± 4.38 vs. 8.02 ± 3.55 µg/ml, respectively. The TD formulation was generally well tolerated by cattle, although some local irritation along the site of application was noted after 12 h of exposure during the bioavailability study. Results indicate that this novel TD formulation provides a substantial improvement in administration convenience, may improve animal welfare and end-user safety through needle-free administration, and achieves similar plasma pharmacokinetics to the IM product when administered at 10 mg/kg.

Study of feline oral squamous cell carcinoma: potential target for cyclooxygenase inhibitor treatment.

Oral squamous cell carcinoma (OSCC) is associated with high morbidity and mortality. A potential target for OSCC treatment is cyclooxygenase-2 (cox-2). Pet cats with naturally occurring OSCC may offer the opportunity to study anticancer activity of cox inhibitors. Cox-2 expression in feline OSCC was determined by immunohistochemistry. High intensity cox-2 immunoreactivity was detected in 6 of 34 (18%) feline OSCC samples. Weak immunoreactivity was noted in 22 OSCCs and in epithelial cells from oral mucosa of clinically normal cats. Pharmacokinetics of a cox inhibitor (piroxicam, 0.3 mg/kg) were studied in carcinoma-bearing cats to confirm a dose for follow-up trials. The average peak serum piroxicam concentration (948 ng/ml, which inhibited cox-2 activity) and serum half-life (15.9 h) were similar to that in normal cats. These results provide information (cox-2 expression as an inclusion criteria, 0.3 mg/kg daily piroxicam) for the design of follow-up trials of cox inhibitor treatment in pet cats with OSCC.

Quantitative determination of tilmicosin in canine serum by high performance liquid chromatography-tandem mass spectrometry.

A highly sensitive and quantitative LC/MS/MS assay for the determination of tilmicosin in serum has been developed and validated. For sample preparation, 0.2 mL of canine serum was extracted with 3 mL of methyl tert-butyl ether. The organic layer was transferred to a new vessel and dried under nitrogen. The sample was then reconstituted for analysis by high performance liquid chromatography-tandem mass spectrometry. A Phenomenex Luna C8(2) analytical column was used for the chromatographic separation. The eluent was subsequently introduced to the mass spectrometer by electrospray ionization. A single range was validated for 50-5000 ng/mL for support of toxicokinetic studies. The inter-day relative error (inaccuracy) for the LLOQ samples ranged from -5.5% to 0.3%. The inter-day relative standard deviations (imprecision) at the respective LLOQ levels were < or =10.1%.

Analysis of reports of human exposure to Micotil 300 (tilmicosin injection).

OBJECTIVE: To identify clinical signs associated with and outcome of human exposure to Micotil 300 (tilmicosin injection). DESIGN: Retrospective case series. STUDY POPULATION: Reports of 3,168 human exposures to Micotil 300. PROCEDURES: Reports of human exposure to Micotil 300 submitted to the Elanco Animal Health Pharmacovigilance Unit between March 1992 and March 2005 were reviewed. RESULTS: At least 1 clinical sign was described in 1,404 (44%) reports, whereas the remaining 1,764 (56%) exposures were presumably asymptomatic. Eighty percent of exposures involved males; mean age was 38 years. Sixty-one percent of exposures were a result of accidental injection, with injection site pain, bleeding, swelling, or inflammation being the most common signs, followed by nausea, tachycardia, dizziness, anxiety, an abnormal taste, headache, lightheadedness, limb pain, paresthesia, chest pain, and soreness. Only 156 (5%) reports involved serious adverse effects (ie, tachycardia, bradycardia, hypertension, hypotension, heart disorder, chest pain, tachypnea, or death). There were reports of 13 deaths following tilmicosin exposure, but only 2 of those deaths were related to accidental exposure. Time to onset of clinical signs was < or = 60 minutes in 63 of the 156 (40%) reports involving serious adverse effects. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the overall risk of accidental human exposure to tilmicosin resulting in serious adverse effects is low (approx 2 people for every 1 million doses administered). Nevertheless, safe handling and proper use should be emphasized.