Therapeutic response to pentoxifylline and its active metabolites in dogs with familial canine dermatomyositis.

Ten dogs diagnosed with familial canine dermatomyositis based on clinical findings and skin biopsy results were treated PO with pentoxifylline (25 mg/kg twice daily) for 3 months. Blood and urine samples were collected biweekly for complete blood counts, serum chemistries, and urinalysis. Additionally, serum was analyzed for pentoxifylline and its two primary metabolites (metabolites 1 [M1] and 5 [M5]); physical examinations were performed; and skin lesions were photographed and subjectively scored biweekly. The median time to response (regrowth of hair) was 6 weeks (range = 4 to 10 weeks). Clinical chemistries, hematology, and urinalysis variables did not differ between the first sampling time and the final evaluation (Week 12). In general, pentoxifylline and its two metabolites were detectable only at the peak (3-hour) sampling time. M5 concentrations were the highest of the three compounds at each sampling time and were characterized by the least variability. Statistical differences in concentrations between Week 2 and Week 12 did not exist. Four of the 10 dogs were characterized as having a complete clinical response to treatment, and six dogs had a partial response. Based on these responses, 25 mg/kg every 12 hours appeared to be an effective beginning dosage of pentoxifylline for dogs with familial canine dermatomyositis. Because of the variability in disposition, including metabolite formation, monitoring of pentoxifylline concentrations may not offer a therapeutic advantage.