Microbiology
Mechanism of Action
The mechanism of action of ciclopirox has been investigated using various
in vitroand
in vivoinfection models. One
in vitrostudy suggested that ciclopirox acts by chelation of polyvalent cations (Fe
+3or 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 vitroand
ex vivo
In vitromethodologies 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 rubrumand
Trichophyton mentagrophytesspecies.
Correlation between
in vitroMIC results and clinical outcome has yet to be established for ciclopirox.
One
ex vivostudy was conducted evaluating 8% ciclopirox against new and established
Trichophyton rubrumand
Trichophyton mentagrophytesinfections in ovine hoof material.
(3)After 10 days of treatment the growth of
T. rubrumand
T. mentagrophytesin 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 rubrumspecies
In vitrosusceptibility testing methods for determining ciclopirox MIC values against the dermatophytic molds, including
Trichophyton rubrumspecies, 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 rubrumare susceptible or resistant to ciclopirox have not been established.
Resistance
Studies have not been conducted to evaluate drug resistance development in
T. rubrumspecies 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.
Pharmacokinetics
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 ciclopirox topical solution, 8% (Nail Lacquer), 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 ciclopirox topical solution, 8% (Nail Lacquer), 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 ciclopirox topical solution, 8% (Nail Lacquer), was evaluated in an
in vitroinvestigation. 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.