Onychomycosis — fungal infection of the nail — is one of the most prevalent dermatological conditions encountered in podiatric practice, accounting for approximately 50% of all nail disorders. It is caused primarily by dermatophytes, most commonly Trichophyton rubrum and Trichophyton mentagrophytes, though non-dermatophyte moulds and Candida species are increasingly recognised as causative organisms, particularly in immunocompromised individuals. The condition disproportionately affects the toenails over the fingernails, and its prevalence rises markedly with age, peripheral vascular disease, diabetes mellitus, and immunosuppression. Despite being perceived by some as a cosmetic nuisance, onychomycosis carries significant clinical implications including pain, difficulty ambulating, secondary bacterial infection, and considerable psychological distress. Effective management therefore demands a thorough, evidence-based approach.
Diagnosis Before Treatment
Accurate diagnosis is the essential prerequisite to any treatment programme. Clinical presentation alone — thickened, discoloured, dystrophic nails — is insufficient to confirm onychomycosis, as similar appearances can result from psoriasis, trauma, lichen planus, and other non-fungal conditions. Mycological confirmation via nail clippings sent for microscopy and culture remains the gold standard, with a sensitivity improved further by polymerase chain reaction (PCR) testing where available. Commencing antifungal therapy without laboratory confirmation risks not only treatment failure but unnecessary systemic drug exposure and cost.
Topical Antifungal Therapy
For mild to moderate onychomycosis — particularly distal and lateral subungual onychomycosis with less than 50% nail plate involvement and no matrix involvement — topical antifungal agents represent a reasonable first-line option. Amorolfine 5% nail lacquer, applied weekly, and ciclopirox 8% nail lacquer, applied daily, are the most widely used preparations. These agents penetrate the nail plate and exert their fungicidal activity directly at the site of infection, avoiding systemic side effects.
However, topical monotherapy has significant limitations. Penetration through the nail plate is inherently difficult, and cure rates with topical agents alone are modest — typically ranging from 5–15% mycological cure at 48 weeks for amorolfine monotherapy in distal subungual onychomycosis. Newer topical agents, including efinaconazole 10% solution and tavaborole 5% solution, demonstrate superior penetration profiles and have shown improved mycological cure rates in clinical trials, reaching 53% and 31% respectively in pivotal studies. These agents represent an advance in topical therapy, particularly for patients in whom systemic treatment is contraindicated.
Topical treatment is most effective when combined with nail debridement — the mechanical reduction of nail thickness — which reduces the fungal burden and improves drug penetration. Podiatrists routinely perform debridement as an adjunct to both topical and systemic treatment.
Systemic Antifungal Therapy
For moderate to severe onychomycosis, matrix involvement, or failure of topical therapy, systemic antifungal agents are the treatment of choice and offer substantially higher cure rates. Two oral agents dominate current practice: terbinafine and the triazole antifungals, principally itraconazole.
Terbinafine, an allylamine that inhibits squalene epoxidase and thus ergosterol synthesis, is considered the gold standard for dermatophyte onychomycosis. A continuous 12-week course for toenail infection achieves mycological cure rates of approximately 70–80%, with complete cure rates (mycological plus clinical) of around 35–50%. Its fungicidal rather than fungistatic mode of action and its high nail keratin affinity contribute to its efficacy. Terbinafine is generally well tolerated, though clinicians must remain alert to rare but serious adverse effects including hepatotoxicity and severe cutaneous reactions such as Stevens-Johnson syndrome. Baseline liver function testing is recommended in those with pre-existing liver disease.
Itraconazole, a triazole that inhibits cytochrome P450-dependent lanosterol 14?-demethylase, may be administered continuously (200 mg daily for 12 weeks) or via pulse dosing (400 mg daily for one week per month, for three pulses). Pulse therapy reduces drug accumulation and cost while retaining acceptable efficacy, with mycological cure rates of approximately 54–63% for toenail infection. Itraconazole has a broader spectrum of activity than terbinafine, making it preferable for non-dermatophyte and Candida-associated infections. Its significant cytochrome P450 3A4 inhibition creates numerous drug interactions, and its negative inotropic properties necessitate caution in patients with cardiac failure.
Fluconazole, administered weekly at 150–300 mg, represents an alternative for patients intolerant of or contraindicated to first-line agents, though evidence for its use in toenail onychomycosis is less robust.
Laser and Device-Based Therapies
Over the past decade, laser therapy has attracted considerable attention as a non-pharmacological treatment option. Nd:YAG lasers operating at 1064 nm, as well as diode and fractional CO2 lasers, have been investigated. The proposed mechanism involves selective photothermal destruction of fungal organisms within the nail. While short-term mycological improvement has been reported, systematic reviews have found the evidence for laser therapy to be of generally low quality, with heterogeneous methodologies and high recurrence rates. Laser treatment is not currently recommended as a primary therapy by major dermatological or podiatric guidelines, though it may have a role as an adjunct or in patients unable to tolerate pharmacological treatment.
Photodynamic therapy (PDT), using photosensitising agents activated by visible light, has also been explored with some promise, particularly for milder cases, but similarly awaits more robust evidence before entering mainstream practice.
Surgical and Mechanical Interventions
Surgical nail avulsion — partial or complete removal of the nail plate — is occasionally employed, particularly when there is marked thickening preventing adequate drug penetration, or in the context of painful subungual hyperkeratosis. Chemical avulsion using 40% urea preparations offers a less invasive alternative, softening and dissolving the nail plate over several weeks to facilitate drug delivery and reduce fungal burden.
Permanent nail ablation via matricectomy — chemical (phenol), surgical, or laser — may be considered in refractory cases or where quality of life is severely impacted by recurrent infection, accepting the consequence of permanent nail loss.
Recurrence and Prevention
Recurrence following successful treatment is a major challenge, affecting up to 50% of patients within five years. Contributing factors include re-infection from environmental reservoirs (shoes, socks, communal areas), concurrent tinea pedis, and host susceptibility factors. Long-term management must therefore incorporate prophylactic measures: antifungal foot powders, replacement of contaminated footwear, treatment of concurrent tinea pedis, and patient education on hygiene practices in communal bathing environments. In high-risk individuals — particularly those with diabetes or peripheral vascular disease — regular podiatric monitoring and preventive nail care are essential components of ongoing management.
The treatment of onychomycosis in the foot requires a patient-centred, stepwise approach guided by accurate diagnosis, severity assessment, and individual risk factors. While topical agents suffice for mild disease, systemic antifungals — principally terbinafine — remain the cornerstone of treatment for most cases. Mechanical debridement, adjunctive topical therapy, and preventive education are integral to achieving durable cure. Emerging technologies such as novel topical agents and laser therapy broaden the therapeutic landscape, though further evidence is needed to establish their definitive role. Given its high prevalence, tendency to recur, and impact on quality of life, onychomycosis warrants the careful, sustained clinical attention that effective podiatric practice affords.