Treating Tinea Pedis In Patients With Diabetes
Similarly, Crawford and Hollis reviewed the effects of topical treatment interventions for both tinea pedis and onychomycosis.15 They found that while the available evidence suggests that the most effective topical antifungal agent for treating tinea pedis is terbinafine, limited studies exist for topical antifungal treatment interventions for onychomycosis. Nevertheless, there is some evidence that daily application of ciclopirox olamine (Loprox, Medicis) and butenafine (Mentax, Mylan Bertek Pharmaceuticals) over a period of a year produces effective results.15
Although studies in otherwise healthy individuals are useful, we cannot necessarily extrapolate the results of these studies to people with diabetes. People with diabetes tend to be more resistant to antifungal treatment regimens as a result of high blood glucose levels and an inability to maintain clean, dry feet (due to obesity and/or retinopathy), which fosters fungal growth.16 People with diabetes also tend to present with polypharmacy and many of these drugs have the potential to interact with antifungal medications.17 Therefore, prescribing requires careful consideration of such interactions.
We often avoid using itraconazole in people with diabetes, especially in people who are taking oral hypoglycemic medications. Itraconazole belongs to the imidazole family of antifungal agents and metabolizes by the cytochrome P450 3A4 enzyme pathway.18 Since many medications also metabolize via this pathway, itraconazole has the potential for multiple drug interactions. Some oral hypoglycemic medications such as sulfonylurea agents metabolize by this pathway. These medications include tolbutamide (Orinase, Pfizer), glibenclamide and glipizide (Glucotrol, Pfizer). Therefore, if patients take these with itraconazole, plasma levels can rise, resulting in hypoglycemia.19,20
Other medications that itraconazole may interact with include HMG-CoA reductase inhibitors, calcium channel blockers, warfarin (Coumadin, Bristol-Myers Squibb), cyclosporine, benzodiazepines and certain anti-arrhythmic medications.21 Given the nature of diabetes, it is likely that some patients would also be taking some of these medications. The advantage of itraconazole, however, is that it has broad spectrum antimicrobial activity and research has shown it to be effective against fungal organisms as well as some molds and yeasts.1,22,23
We often consider terbinafine to be the “safer” and more effective option, despite having reduced efficacy against yeast organisms. Since this drug metabolizes via the cytochrome P450 2D6 enzyme, there is a reduced risk for drug interaction, especially with insulin and/or oral hypoglycemic therapies.20,24 While it is perhaps the safer option for people taking insulin or oral hypoglycemic medications, terbinafine still has the potential to interact with a host of other medications.25 These medications include tricyclic antidepressants, beta blockers, selective serotonin reuptake inhibitors, certain anti-arrhythmic agents and monoamine oxidase inhibitors. Since people with diabetes may be taking some or many of these medications, clinicians need to carefully consider polypharmacy issues when prescribing terbinafine to a person who has diabetes.
Both itraconazole and terbinafine may cause a number of adverse side effects.1,25,26 Less common but more serious side effects of itraconazole include hepatitis and congestive heart failure. In very rare cases, terbinafine may cause liver disease.