Dermatologic problems can be frustrating to treat. Pentoxifylline, tacrolimus, pimecrolimus, interferon, and imiquimod offer
potential new therapeutic options. Although few veterinary studies showing positive results with these drugs are available,
veterinary dermatologists have been using them with varying degrees of success. This article highlights what has worked for
us and other veterinary dermatologists and discusses the results of drug studies.
Pentoxifylline is a member of a class of drugs that inhibit phosphodiesterase (PDE) enzymes, referred to as PDE inhibitors. Pentoxifylline makes red blood cells more pliable and decreases blood viscosity. It also decreases fibronectin, reduces
the production of cytokines (tumor necrosis factor-alpha, interleukin-1, interleukin-6, interleukin-8), decreases leukocyte
response to interleukin-1, impairs t lymphocyte binding to keratinocytes, decreases fibroblast activity, and, with long-term
use, may decrease fibrosis.1,2
Figure 1. A dog with dermatomyositis. Note the alopecia, hyperpigmentation, and scarring on the front limbs, muzzle, and periocular
Pentoxifylline is beneficial in treating a variety of canine skin diseases.3-5 Its effectiveness may be due to any one or a combination of its different actions on the immune response. Pentoxifylline
has been evaluated most thoroughly in well-designed studies for treating atopic dermatitis3 and has been reported effective in treating dermatomyositis4 (Figures 1 & 2) and contact dermatitis.5
Figure 2. The same dog as in Figure 2 four months after beginning pentoxifylline therapy. Note the resolution of the lesions.
Veterinary dermatologists have also recommended pentoxifylline to treat vasculitis, ischemic dermatopathy, pinnal thrombovascular
necrosis, idiopathic mucinosis, and erythema multiforme and as an adjunctive therapy for idiopathic onychomadesis, immune-mediated
dermatoses, fibrosing deep pyoderma, and pododermatitis. However, studies supporting pentoxifylline's efficacy in treating
these conditions are lacking. For example, only one of seven dogs with cutaneous vasculitis exhibited a definitively favorable
response to pentoxifylline treatment,6 and only two of five dogs with lupoid onychodystrophy showed excellent treatment responses.7 Poor responses were seen in four of four dogs with vesicular cutaneous lupus erythematosus treated with pentoxifylline alone
or in combination with other drugs.8
Initially, many veterinary dermatologists administered 10 mg/kg pentoxifylline orally two or three times a day. It has been
suggested that a frequency of three times a day might be preferable for some diseases, such as atopic dermatitis.9 In addition, some veterinary dermatologists have reported doses of 15 to 25 mg/kg to be more effective than 10-mg/kg doses.
One study showed a good response in 10 of 10 dogs with dermatomyositis at an average dosage of 25 mg/kg (range 18 to 31 mg/kg)
given orally twice a day. The median response time was six weeks with a range of four to 10 weeks.4
A pharmacokinetic study in dogs showed that after a single oral dose of 30 mg/kg pentoxifylline, plasma pentoxifylline concentrations
reached 1,000 ng/ml (the therapeutic concentration in people) and persisted for 510 minutes (± 85 min), suggesting that twice-a-day
administration may be effective at that dose.10 However, one caution is that bioavailability varied from about 25% to 75%.10 In contrast, another study in dogs showed that 15 mg/kg given orally three times a day produced plasma concentrations equivalent
to therapeutic concentrations in people.11
The efficacy of generic pentoxifylline is uncertain. No comparative studies exist, but some veterinary dermatologists report
better responses to the brand name formulation Trental (Sanofi-Aventis).
No serious adverse effects of pentoxifylline have been reported with any frequency in dogs. Vomiting and diarrhea are the
major concerns in dogs and are dose-related in people. Two dogs receiving pentoxifylline reportedly developed erythema multiforme12 ; however, one author (Griffin) has used it to treat erythema multiforme with some cases showing a beneficial effect.