Source: FDA, National Drug Code (US) Revision Year: 2016
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.
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 mcg/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.
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.
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 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.
No carcinogenicity study was conducted with PENLAC Nail Lacquer (ciclopirox) Topical Solution, 8%, formulation. A carcinogenicity study of ciclopirox (1% and 5% solutions in polyethylene glycol 400) in female mice dosed topically twice per week for 50 weeks followed by a 6-month drug-free observation period prior to necropsy revealed no evidence of tumors at the application sites.
In human systemic tolerability studies following daily application (~340 mg of PENLAC Nail Lacquer (ciclopirox) Topical Solution, 8%) in subjects with distal subungual onychomycosis, the average maximal serum level of ciclopirox was 31±28 ng/mL after two months of once daily applications. This level was 159 times lower than the lowest toxic dose and 115 times lower than the highest nontoxic dose in rats and dogs fed 7.7 and 23.1 mg ciclopirox (as ciclopirox olamine)/kg/day.
The following in vitro genotoxicity tests have been conducted with ciclopirox: evaluation of gene mutation in Ames Salmonella and E. coli assays (negative); chromosome aberration assays in V79 Chinese hamster lung fibroblasts, with and without metabolic activation (positive); gene mutation assay in the HGPRT-test with V79 Chinese hamster lung fibroblasts (negative); unscheduled DNA synthesis in human A549 cells (negative); and BALB/c3T3 cell transformation assay (negative). In an in vivo Chinese hamster bone marrow cytogenetic assay, ciclopirox was negative for chromosome aberrations at 5,000 mg/kg.
The following in vitro genotoxicity tests were conducted with PENLAC Nail Lacquer (ciclopirox) Topical Solution, 8%: Ames Salmonella test (negative); unscheduled DNA synthesis in the rat hepatocytes (negative); cell transformation assay in BALB/c3T3 cell assay (positive). The positive response of the lacquer formulation in the BALB/c3T3 test was attributed to its butyl monoester of poly[methylvinyl ether/maleic acid] resin component, which also tested positive in this test. The cell transformation assay may have been confounded because of the film-forming nature of the resin. The resin component tested nonmutagenic in both the in vitro mouse lymphoma forward mutation assay with or without activation and unscheduled DNA synthesis assay in rat hepatocytes.
Oral reproduction studies in rats at doses up to 3.85 mg ciclopirox (as ciclopirox olamine)/kg/day [equivalent to approximately 1.4 times the potential exposure at the maximum recommended human topical dose (MRHTD)] did not reveal any specific effects on fertility or other reproductive parameters. MRHTD (mg/m²) is based on the assumption of 100% systemic absorption of 27.12 mg ciclopirox (~340 mg PENLAC Nail Lacquer (ciclopirox) Topical Solution, 8%) that will cover all the fingernails and toenails including 5 mm proximal and lateral fold area plus onycholysis to a maximal extent of 50%.
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