Onychomycosis affects 2 to 4 percent of adults. In the past, these dermatophyte infections were thought to be incurable because topical therapy was consistently ineffective. While oral griseofulvin was sometimes used, it was irregularly absorbed, and prolonged therapy of up to 24 months was sometimes required. With the development of several new systemic antimycotics such as itraconazole, fluconazole and terbinafine, physicians now have effective treatments for patients with onychomycosis. Harrell and colleagues recently reviewed the current clinical data on terbinafine and itraconazole.

The authors performed a MEDLINE search (from 1985 through 1999) for comparative trials of itraconazole and terbinafine, and identified six trials that directly compared these two antifungal agents. Four studies compared 12 weeks of daily oral therapy with the two; one study compared intermittent terbinafine with intermittent itraconazole and continuous terbinafine; and one large study compared daily terbinafine with pulse dosing of itraconazole. Eight other studies that addressed quality-of-life issues and cost effectiveness were included in the analysis.

This review used the STEP approach: Safety, Tolerability, Effectiveness and Price. Both drugs were well tolerated and safe in all of the selected studies. Gastrointestinal side effects were by far the most common adverse events for both drugs and primarily included nausea, vomiting and diarrhea. Although results from one study revealed an adverse event rate of 47 percent, the dropout rate was consistently less than 10 percent in patients receiving either of the drugs in all but one of the selected studies. The authors concluded that no significant difference in adverse events was evident among the various treatment regimens. Drug interactions were not specifically addressed by the studies, but terbinafine appeared to have a lower potential for drug interaction. Terbinafine and itraconazole are metabolized by the hepatic cytochrome P450 system and interact with other agents. However, both drugs should be prescribed with caution, especially in patients who are taking drugs that induce or inhibit the cytochrome P450 system.

In assessing the effectiveness of daily ter-binafine compared with daily itraconazole, results from one randomized study involving 43 patients revealed that only one patient from each group still had a positive fungal culture at a final six-month follow-up. A second study reported negative fungal cultures in 81 percent of the patients receiving terbinafine and in 63 percent of the patients receiving itraconazole. Results from a similar trial revealed cure rates of 73 and 45.8 percent, respectively, for terbinafine and itraconazole treatment. Both studies also measured unaffected nail growth, and results showed that terbinafine was consistently superior. Another study reported cure rates of 94.1 percent with continuous terbinafine therapy, 80 percent with intermittent terbinafine and 75 percent for intermittent itraconazole. A trial that included 409 patients randomized to daily terbinafine or itraconazole pulse dosing reported terbinafine to be superior in regard to clinical cure and negative cultures. Final study results of daily therapy with both drugs involving 289 patients showed similar cure rates of about 55 percent after three months of treatment.

Regardless of the chosen drug, the cost of treating onychomycosis is significant. A 12-week course of itraconazole (200 mg daily) costs about $1,200 compared with $700 for terbinafine for the same regimen. In a cost-effectiveness study, it was concluded that terbinafine was more cost-effective for treating onychomycosis (see the accompanying table).

In summary, the authors conclude that a continuous-dose regimen of terbinafine is superior to pulse-dose itraconazole in the treatment of patients with onychomycosis. Continuous-dose terbinafine may be more effective than pulse-dose terbinafine. Intermittent dosing with either drug may be similar in efficacy. [ corrected]