title: Topical formulations containing finasteride. Part II: determination of finasteride penetration into hair follicles using the differential stripping technique.
abstract: The differential stripping technique consists of a tape-stripping phase followed by a cyanoacrylate biopsy. This technique not only allows the quantification of drug retained in the stratum corneum (SC) and in the hair follicles but also differentiates transepidermal from transfollicular penetration. Our study aimed at both validating the differential stripping procedure on hairless rat skin and assessing the role of the hair follicle in the cutaneous penetration of finasteride (FNS) after application of two experimental formulations for 6 or 24 h: P-08-016, a hydroxypropyl chitosan (HPCH)-based formulation and P-10-008, an anhydrous formulation devoid of HPCH. Microscopic and histological evaluation showed that after 15 tape strips both the SC and the viable epidermis were completely removed. A subsequent cyanoacrylate skin surface biopsy led to the removal of the infundibula content. The largest amounts of FNS were found in the epidermis and in the appendages after application of P-08-016, regardless of the time from application. In contrast, smaller and statistically significant amounts of FNS were recovered with P-10-008 6 h after application, compared with that at 24 h. In conclusion, the differential stripping technique allowed determination of the amount of FNS localized in different skin districts, focusing particularly on the follicular contribution.
authors.affiliation: Department of Pharmacy, University of Pisa, Pisa, I-56126, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Tampucci
authors.forename: Susi
authors.initials: S
authors.lastname: Burgalassi
authors.forename: Patrizia
authors.initials: P
authors.lastname: Chetoni
authors.forename: Carla
authors.initials: C
authors.lastname: Lenzi
authors.forename: Andrea
authors.initials: A
authors.lastname: Pirone
authors.forename: Federico
authors.initials: F
authors.lastname: Mailland
authors.forename: Maurizio
authors.initials: M
authors.lastname: Caserini
authors.forename: Daniela
authors.initials: D
authors.lastname: Monti
mesh_terms: D058891:5-alpha Reductase Inhibitors / Q000008:administration & dosage / Q000493:pharmacokinetics*; D000279:Administration, Cutaneous; D000818:Animals; D018120:Finasteride / Q000008:administration & dosage / Q000493:pharmacokinetics*; D018859:Hair Follicle / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D051381:Rats; D054772:Rats, Hairless; D012867:Skin / Q000378:metabolism / Q000648:ultrastructure; D012869:Skin Absorption
chemical_list: D058891:5-alpha Reductase Inhibitors; D018120:Finasteride
keywords: differential stripping technique; distribution; finasteride; formulation; hair follicles; hydroxypropyl chitosan; in vitro models; passive diffusion/transport; skin