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Mechanism of Action

The mechanism of action of ciclopirox has been investigated using various in vitro and in vivo infection models. One in vitro study suggested that ciclopirox acts by chelation of polyvalent cations (Fe+3 or Al+3) resulting in the inhibition of the metal-dependent enzymes that are responsible for the degradation of peroxides within the fungal cell. The clinical significance of this observation is not known.

Activity in vitro and ex vivo

In vitro methodologies employing various broth or solid media with and without additional nutrients have been utilized to determine ciclopirox minimum inhibitory concentration (MIC) values for the dermatophytic molds.(1-2) As a consequence, a broad range of MIC values, 1-20 ug/mL, were obtained for Trichophyton rubrum and Trichophyton mentagrophytes species. Correlation between in vitro MIC results and clinical outcome has yet to be established for ciclopirox.

One ex vivo study was conducted evaluating 8% ciclopirox against new and established Trichophyton rubrum and Trichophyton mentagrophytes infections in ovine hoof material.(3) After 10 days of treatment the growth of T. rubrum and T. mentagrophytes in the established infection model was very minimally affected. Elimination of the molds from hoof material was not achieved in either the new or established infection models.

Susceptibility testing for Trichophyton rubrum species

In vitro susceptibility testing methods for determining ciclopirox MIC values against the dermatophytic molds, including Trichophyton rubrum species, have not been standardized or validated. Ciclopirox MIC values will vary depending on the susceptibility testing method employed, composition and pH of media and the utilization of nutritional supplements. Breakpoints to determine whether clinical isolates of Trichophyton rubrum are susceptible or resistant to ciclopirox have not been established.


Studies have not been conducted to evaluate drug resistance development in T. rubrum species exposed to 8% ciclopirox topical solution. Studies assessing cross-resistance to ciclopirox and other known antifungal agents have not been performed.

Antifungal Drug Interactions

No studies have been conducted to determine whether ciclopirox might reduce the effectiveness of systemic antifungal agents for onychomycosis. Therefore, the concomitant use of 8% ciclopirox topical solution and systemic antifungal agents for onychomycosis is not recommended.


As demonstrated in pharmacokinetic studies in animals and man, ciclopirox olamine is rapidly absorbed after oral administration and completely eliminated in all species via feces and urine. Most of the compound is excreted either unchanged or as glucuronide. After oral administration of 10 mg of radiolabeled drug (14C-ciclopirox) to healthy volunteers, approximately 96% of the radioactivity was excreted renally within 12 hours of administration. Ninety-four percent of the renally excreted radioactivity was in the form of glucuronides. Thus, glucuronidation is the main metabolic pathway of this compound.

Systemic absorption of ciclopirox was determined in 5 patients with dermatophytic onychomycoses, after application of PENLAC (ciclopirox topical solution) ® NAIL LACQUER (ciclopirox) Topical Solution, 8%, to all 20 digits and adjacent 5 mm of skin once daily for six months. Random serum concentrations and 24 hour urinary excretion of ciclopirox were determined at two weeks and at 1, 2, 4 and 6 months after initiation of treatment and 4 weeks post-treatment. In this study, ciclopirox serum levels ranged from 12-80 ng/mL. Based on urinary data, mean absorption of ciclopirox from the dosage form was < 5% of the applied dose. One month after cessation of treatment, serum and urine levels of ciclopirox were below the limit of detection.

In two vehicle-controlled trials, patients applied PENLAC® NAIL LACQUER (ciclopirox) Topical Solution, 8%, to all toenails and affected fingernails. Out of a total of 66 randomly selected patients on active treatment, 24 had detectable serum ciclopirox concentrations at some point during the dosing interval (range 10.0-24.6 ng/mL). It should be noted that eleven of these 24 patients took concomitant medication containing ciclopirox as ciclopirox olamine (Loprox® Cream, 0.77%).

The penetration of the PENLAC® NAIL LACQUER (ciclopirox) Topical Solution, 8%, was evaluated in an in vitro investigation. Radiolabeled ciclopirox applied once to onychomycotic toenails that were avulsed demonstrated penetration up to a depth of approximately 0.4 mm. As expected, nail plate concentrations decreased as a function of nail depth. The clinical significance of these findings in nail plates is unknown. Nail bed concentrations were not determined.

Clinical Trials Data

The results of use of PENLAC® NAIL LACQUER (ciclopirox) Topical Solution, 8%, in treatment of onychomycosis of the toenail without lunula involvement were obtained from two double-blind, placebo-controlled studies conducted in the US. In these studies, patients with onychomycosis of the great toenails without lunula involvement were treated with ciclopirox topical solution, 8% in conjunction with monthly removal of the unattached, infected toenail by the investigator. PENLAC® NAIL LACQUER (ciclopirox) Topical Solution, 8%, was applied for 48 weeks. At baseline, patients had 20-65% involvement of the target great toenail plate. Statistical significance was demonstrated in one of two studies for the endpoint "complete cure" (clear nail and negative mycology), and in two studies for the endpoint "almost clear" ( ≤ 10% nail involvement and negative mycology) at the end of study. These results are presented below.

At Week 48 (plus Last Observation Carried Forward) for the Intent-to-Treat (ITT) Population

  Study 312 Study 313
Active Vehicle Active Vehicle
Complete Cure* 6/110 (5.5%) 1/109 (0.9%) 10/118 (8.5%) 0/117 (0%)
Almost Clear** 7/107 (6.5%) 1/108 (0.9%) 14/116 (12%) 1/115 (0.9%)
Negative Mycology Alone*** 30/105 (29%) 12/106 (11%) 41/115 (36%) 10/114 (9%)
* Clear nail and negative mycology
** ≤ 10% nail involvement and negative mycology
*** Negative KOH and negative culture

The summary of reported patient outcomes for the ITT population at 12 weeks following the end of treatment are presented below. Note that post-treatment efficacy assessments were scheduled only for patients who achieved a complete cure.

Post-treatment Week 12 Data for Patients Who Achieved Complete Cure at Week 48

  Study 312 Study 313
Active Vehicle Active Vehicle
Number of Treated Patients 112 111 119 118
Complete Cure at Week 48 6 1 10 0
Post-treatment Week 12 Outcomes:
Patients Missing All Week 12 Assessments 2 0 2 0
Patients with Week 12 Assessments 4 1 8 0
Complete Cure 3 1 4 0
Almost Clear 2* 1 1* 0
Negative Mycology 3 1 5 0
*Four patients (from studies 312 and 313)who were completely cured did not have post-treatment Week 12 planimetry data.


1. Dittmar W., Lohaus G. 1973. HOE296, A new antimycotic compound with a broad antimicrobial spectrum. Arzneim-Forsch./Drug Res. 23:670-674.

2. Niewerth et. al., 1998. Antimicrobial susceptibility testing of dermatophytes: Comparison of the agar macrodilution and broth micro dilution tests. Chemotherapy. 44:31-35.

3. Yang et. al. 1997. A new simulation model for studying in vitro topical penetration of antifungal drugs into hard keratin. J. Mycol. Med. 7:195-98.

Last reviewed on RxList: 11/21/2016
This monograph has been modified to include the generic and brand name in many instances.

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