Elidel Pharmacology, Pharmacokinetics, Studies, Metabolism - Pimecrolimus

Elidel Pharmacology, Pharmacokinetics, Studies, Metabolism - Pimecrolimus

CLINICAL PHARMACOLOGY

The mechanism of action of pimecrolimus in atopic dermatitis is not known. While the following have been observed, the clinical significance of these observations in atopic dermatitis is not known. It has been demonstrated that pimecrolimus binds with high affinity to macrophilin-12 (FKBP-12) and inhibits the calcium-dependent phosphatase, calcineurin. As a consequence, it inhibits T cell activation by blocking the transcription of early cytokines. In particular, pimecrolimus inhibits at nanomolar concentrations Interleukin-2 and interferon gamma (Th1-type) and Interleukin-4 and Interleukin-10 (Th2-type) cytokine synthesis in human T cells. In addition, pimecrolimus prevents the release of inflammatory cytokines and mediators from mast cells in vitro after stimulation by antigen/IgE.

In adult patients being treated for atopic dermatitis [13%-62% Body Surface Area (BSA) involvement] for periods up to a year, blood concentrations of pimecrolimus are routinely either at or below the limit of quantification of the assay (< 0.5 ng/mL). In those subjects with detectable blood levels they are routinely < 2 ng/mL and show no sign of drug accumulation with time. Because of the low systemic absorption of pimecrolimus following topical application the calculation of standard pharmacokinetic measures such as AUC, C_max, T_1/2, et cetera cannot be reliably done.

In vitro studies of the protein binding of pimecrolimus indicate that it is 74%-87% bound to plasma proteins.

Following the administration of a single oral radiolabeled dose of pimecrolimus numerous circulating O-demethylation metabolites were seen. Studies with human liver microsomes indicate that pimecrolimus is metabolized in vitro by the CYP3A sub-family of metabolizing enzymes. No evidence of skin mediated drug metabolism was identified in vivo using the minipig or in vitro using stripped human skin.

Based on the results of the aforementioned radiolabeled study, following a single oral dose of pimecrolimus ~81% of the administered radioactivity was recovered, primarily in the feces (78.4%) as metabolites. Less than 1% of the radioactivity found in the feces was due to unchanged pimecrolimus.

The systemic exposure to pimecrolimus from Elidel^® (pimecrolimus) Cream 1% was investigated in 26 pediatric patients with atopic dermatitis (20%-69% BSA involvement) between the ages of 2-14 yrs. Following twice daily application for three weeks, blood concentrations of pimecrolimus were consistently low (< 3 ng/mL), with the majority of the blood samples being below the limit of quantification (0.5 ng/mL). However, the children (20 children out of the total 23 children investigated) had at least one detectable blood level as compared to the adults (13 adults out of the total 25 adults investigated) over a 3-week treatment period. Due to the low and erratic nature of the blood levels observed, no correlation could be made between amount of cream, degree of BSA involvement, and blood concentrations. In general, the blood concentrations measured in adult atopic dermatitis patients were comparable to those seen in the pediatric population.

In a second group of 22 pediatric patients aged 3- 23 months with 10%-92% BSA involvement, a higher proportion of detectable blood levels was seen ranging from 0.1 ng/mL to 2.6 ng/mL (limit of quantification 0.1 ng/mL). This increase in the absolute number of positive blood levels may be due to the larger surface area to body mass ratio seen in these younger subjects. In addition, a higher incidence of upper respiratory symptoms/infections was also seen relative to the older age group in the PK studies. At this time a causal relationship between these findings and Elidel use cannot be ruled out. Use of Elidel in this population is not recommended (see Pediatric Use).

The effect of renal insufficiency on the pharmacokinetics of topically administered pimecrolimus has not been evaluated. Given the very low systemic exposure of pimecrolimus via the topical route, no change in dosing is required.

The effect of hepatic insufficiency on the pharmacokinetics of topically administered pimecrolimus has not been evaluated. Given the very low systemic exposure of pimecrolimus via the topical route, no change in dosing is required.

Three randomized, double-blind, vehicle-controlled, multi-center, Phase 3 studies were conducted in 1335 pediatric patients ages 3 months -17 years old to evaluate Elidel^® (pimecrolimus) Cream 1% for the treatment of mild to moderate atopic dermatitis. Two of the three trials support the use of Elidel Cream in patients 2 years and older with mild to moderate atopic dermatitis (see Pediatric Use). Three other trials provided additional data regarding the safety of Elidel Cream in the treatment of atopic dermatitis. Two of these other trials were vehicle-controlled with optional sequential use of a medium potency topical corticosteroid in pediatric patients and one trial was an active comparator trial in adult patients with atopic dermatitis (see Pediatric Use and ADVERSE REACTIONS).

Two identical 6-week, randomized, vehicle-controlled, multi-center, Phase 3 trials were conducted to evaluate Elidel Cream for the treatment of mild to moderate atopic dermatitis. A total of 403 pediatric patients 2-17 years old were included in the studies. The male/female ratio was approximately 50% and 29% of the patients were African American. At study entry, 59% of patients had moderate disease and the mean body surface area (BSA) affected was 26%. About 75% of patients had atopic dermatitis affecting the face and/or neck region. In these studies, patients applied either Elidel Cream or vehicle cream twice daily to 5% to 96% of their BSA for up to 6 weeks. At endpoint, based on the physician’s global evaluation of clinical response, 35% of patients treated with Elidel Cream were clear or almost clear of signs of atopic dermatitis compared to only 18% of vehicle-treated patients. More Elidel patients (57%) had mild or no pruritus at 6 weeks compared to vehicle patients (34%). The improvement in pruritus occurred in conjunction with the improvement of the patients’ atopic dermatitis. In these two 6-week studies of Elidel, the combined efficacy results at endpoint are as follows:

In the two pediatric studies that independently support the use of Elidel Cream in mild to moderate atopic dermatitis, a significant treatment effect was seen by day 15. Of the key signs of atopic dermatitis, erythema, infiltration/papulation, lichenification, and excoriations, erythema and infiltration/papulation were reduced at day 8 when compared to vehicle. The following graph depicts the time course of improvement in the percent body surface area affected as a result of treatment with Elidel Cream in 2-17 year olds.