Antifungal agents: An overview. Part I

Oral terbinafine: a new antifungal agent

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, adverse effects, drug interactions, and dosage guidelines of terbinafine. Available comparative data of terbinafine and other antimycotic agents are described for understanding the potential role of terbinafine in patient care.

DATA SOURCES

A MEDLINE search restricted to English language during 1966-1996 and extensive review of journals was conducted to prepare this article. MeSH headings included allylamines, terbinafine, SF 86-327, dermatophytosis, dermatomycosis.

DATA EXTRACTION

The data on pharmacokinetics, adverse effects, and drug interactions were obtained from open-label and controlled studies and case reports. Controlled single- or double-blind studies were evaluated to describe the efficacy of terbinafine in the treatment of various fungal infections.

DATA SYNTHESIS

Terbinafine is the first oral antimycotic in the allylamines class: a fungicidal agent that inhibits ergosterol synthesis at the stage of squalene epoxidation. Terbinafine demonstrates excellent in vitro activity against the majority of dermatophyte species including Trichophyton rubrum, Trichophyton mentagrophytes, and Epidermophyton floccosum; less activity is seen against Dematiaceae and the filamentous fungi. It is least active against the pathogenic yeast and this correlates with the relatively poor efficacy against these organisms in vivo. High concentrations of terbinafine are achieved in keratinous tissues, the site of superficial infections, and these concentrations are maintained for up to 3 months. The clinical efficacy of terbinafine against a number of dermatophyte infections exceeds that of the current standard of therapy, griseofulvin. The efficacy of terbinafine may be as good or better than that of the azole antifungals. Additional studies are required to confirm these observations. Terbinafine demonstrates a good safety profile, and relatively few drug interactions have been identified.

CONCLUSIONS

Terbinafine is more effective than the gold standard, griseofulvin, in the treatment of tinea pedis and tinea unguinum, with considerably shorter treatment duration in the latter. It has been proven as effective as griseofulvin in the treatment of tinea capitis, tinea corporis, and tinea cruris. Terbinafine does not appear to offer any advantage in the treatment of nondermatophyte infections; its utility in the treatment of systemic infections has yet to be established. Depending on individual institutional costs, terbinafine may be a front-line drug for some superficial infections responding poorly to the current standard of therapy.

Current management of onychomycosis. An overview

Until recently pedal onychomycosis, particularly when it affected several nails or involved a large nail plate area, was often regarded as untreatable. The advent of new therapies such as itraconazole, terbinafine, and fluconazole has been a significant and welcome addition to the armamentarium of therapies at the disposal of the physician. These drugs appear in the nail plate within days of starting oral therapy, being taken up by both the nail matrix and the nail bed. The duration required for effective therapy has been reduced, while the efficacy rates and cost-effectiveness have increased compared with the older treatments, such as griseofulvin. Some of the newer agents appear to have a wider spectrum of activity. Thus far, the newer agent have exhibited a low risk to benefit ratio. I may be possible to combine oral therapies with topical and surgical treatments, thereby further increasing efficacy rates and the cost-effectiveness while decreasing adverse effects and duration of oral therapy.

Traditional management of onychomycosis

The traditional management of onychomycosis includes mechanical, chemical, and surgical approaches, as well as topical and oral antifungal medications. Topical preparations have been consistently disappointing, and the tendency in later years has been to rely on two systemic agents-griseofulvin and ketoconazole-for management of more severe or recalcitrant infections. However, both drugs require a long duration of therapy (4 to 6 months for fingernails, 10 to 18 months for toenails). Even with such prolonged treatment, the overall success rate is only about 15% to 30% for toenail infections and 50% to 70% for fingernail infections. Furthermore, both griseofulvin and ketoconazole have numerous potential side effects and drug/drug interactions. Therefore, laboratory monitoring should be performed during the course of treatment with these agents and they should be used only after evaluation of the patient's current medical status and a review of concomitant medications.

Tinea capitis

Tinea capitis is dermatophytosis of the scalp hair follicles, generally producing inflammatory or noninflammatory alopecia. Infection occurs predominantly in prepubertal children older than 6 months, although infection can occur in all age groups. Tinea capitis is one of the most common infectious conditions in children, and it occurs worldwide.

In vitro susceptibility of Trichophyton rubrum isolates to griseofulvin and tioconazole. Induction and isolation of a resistant mutant to both antimycotic drugs. Mutant of Trichophyton rubrum resistant to griseofulvin and tioconazole

The in vitro susceptibility of three clinical Trichophyton rubrum isolates to griseofulvin and tioconazole, determined by the minimal inhibitory concentration (MIC), was 2 and 0.5 to 1.0 micrograms/ml, respectively. One mutant (gril) obtained after mutagenic treatment of one of these isolates was selected and showed simultaneous resistance to griseofulvin (MIC > 2000 micrograms/ml) and tioconazole (MIC = 1.0 microgram/ml). The clinical importance and the possibility of a multidrug resistance (MDR)-type mechanism being involved in this event is discussed.

Recent developments in antifungal therapy

There have been many advances during the past few years relating to the treatment of superficial fungal infections. This article focuses on recent developments, particularly in oral therapy, but in topical therapy as well. First, the newer agents (especially fluconazole, itraconazole, and terbinafine) are reviewed, and then the use of these agents in many disorders is discussed, with emphasis on tinea corporis or cruris, tinea pedis, tinea capitis, and onychomycosis.

Terbinafine in onychomycosis of the toenail: a novel treatment protocol

BACKGROUND

Current treatment of onychomycosis of the toenail is poor and relapse is common.

OBJECTIVE

Our purpose was to assess the efficacy and safety of oral terbinafine and placebo in onychomycosis of the toenail with the use of a novel treatment protocol.

METHODS

This was a randomized, double-blind, 48-week study. Twelve weeks of terbinafine (250 mg daily) or placebo was followed by 12 weeks of observation. Responders received no further treatment and nonresponders were offered 12 weeks of terbinafine (250 mg daily) from week 28.

RESULTS

Of 111 evaluable patients, 88% (49 of 56) of the patients given terbinafine and 29% (16 of 55) of the patients given placebo had a negative mycologic culture at week 24 (p < 0.001), 57% (32 of 56) of the terbinafine group and 6% (3 of 55) of the placebo group were responders (p < 0.001). By week 48, after the terbinafine nonresponders were given a second 12-week course of terbinafine, the overall mycologic cure rate for the patients given terbinafine was 94%.

CONCLUSION

High mycologic cure rates in onychomycosis of the toenail can be achieved by terbinafine by this novel treatment regimen.