Dried blood spot analysis of donepezil in support of a GLP 3-month dose-range finding study in rats.

Donepezil hydrochloride is a reversible acetyl cholinesterase inhibitor approved for Alzheimer disease treatment. As an alternate therapy, a donepezil hydrochloride transdermal patch is in development. Recommended nonclinical safety studies include a 3-month Good Laboratory Practice (GLP) dose-range finding (DRF) study prior to conducting the 2-year dermal carcinogenicity study in rats. Demonstration of systemic exposure is necessary to interpret the in vivo data. Previous nonclinical reports supporting oral dosing have utilized liquid chromatography tandem mass spectrometry (LC/MS/MS) to quantify donepezil concentrations in plasma. Smaller species with limited blood volumes do not allow serial sampling to derive the full pharmacokinetic profile from a single animal. Therefore, the option of another analytical method requiring decreased sample volumes is desirable as it would decrease the required number of animals while obtaining the complete profile. The dried blood spot (DBS) technique allows drug level measurement from a few microliters; however, the method is still not widely utilized in GLP studies. Because donepezil plasma levels are known by the oral route, DBS was used to bridge the previous oral data and to support a 13-week GLP DRF study for repeated topical application in rats, comparing oral administration with 4 topical formulations. The DBS method was validated and demonstrated robustness and reproducibility for application to the DRF study. The assay results were comparable to a previously reported plasma LC/MS/MS assay-derived pharmacokinetic profile and provided justification for selection of the topical formulation and dose levels for the subsequent dermal carcinogenicity study.

Comparison of oral and transdermal administration of rasagiline mesylate on human melanoma tumor growth in vivo.

BACKGROUND/AIMS: Transdermal patch administration results in a locally high concentration of drug that induce local toxicity, including tumorogenicity. As a worst-case scenario for consequences of repeated application on neoplastic growth, the melanin-binding drug, rasagiline, was used in a transdermal formulation applied directly to a human-derived melanoma to determine the effects on tumor growth. MATERIALS AND METHODS: Rasagiline mesylate was administered either orally or transdermally to athymic mice implanted with human melanoma (SKMEL28) to determine the effects on tumor growth and survival. Over a 21-day period, animals were administered daily oral gavage (15 mg/kg) or one or two rasagiline mesylate transdermal patches every 3 days. After the last dose administration, blood samples were collected to confirm drug exposure. RESULTS: All animals from the untreated, vehicle and rasagiline groups survived to the end of the study; however, 7 out of the 10 cisplatin-treated animals died before the end of the study. Rasagiline mesylate dosed either via the oral or transdermal routes had comparable plasma exposure and, unexpectedly, significantly reduced absolute tumor volumes and tumor growth rates in the nude mouse SKMEL28 xenograft model. CONCLUSION: Transdermal delivery of melanin-binding rasagiline does not increase melanoma growth in the xenograft model. Because rasagiline decreases melanoma growth, it may be candidate for combination therapy for melanoma.

Irritant contact dermatitis: effect of age.

Knowledge on age-relationship to irritant contact dermatitis (ICD) remains of interest. We searched for articles and textbooks on age-relationship to ICD and evaluated relevant data. Irritant response may be enhanced in children and decline with increasing age. In general, older skin reacts more slowly and with less intensity to irritants when compared with young skin. Such age-related changes may depend: (i) on differences in percutaneous penetration in old and young skin, and/or on (ii) differences in the microcirculatory efficiency, which serves as the route by which inflammatory cells make their way to the site of inflammation. Additionally, stratum corneum turnover time increases with age which means that an irritant remains longer on the skin; a compromised cutaneous blood vessel network with ageing may lead to a decreased inflammatory response, decreased absorption and decreased clearance. In conclusion, age-related differences of ICD are present despite some conflicting data. Investigations elucidating this interesting subject may benefit in prevention and intervention strategies.

Allergic contact dermatitis: effect of age.

The relationship between allergic contact dermatitis (ACD) and age has not been well documented. We searched for articles and textbooks based on age-ACD relationship and evaluated relevant data. The frequency of skin reactions to allergens increased with age in some studies, whereas others showed no definite effect. This might be caused by variations in study design, genetic factors or by external influences such as from different regions and environmental exposure. In general, investigators agree that elderly patients were more likely to have multiple contact allergies than younger persons. This may be because of the frequent use of topical medicaments and having a longer time for potential allergen exposure. However, a review of marketed transdermal products for ACD shows a very low incidence, and no age-related effects were reported. One exception to this low incidence of ACD is the transdermal product, Catapres-TTS(®) (clonidine), which has a reported incidence rate of ~16%. The generally low incidence of ACD in marketed products and the conflicting findings in the prevalence of specific age-related ACD indicate the need for further investigation as to the proclivity for developing new sensitivities with age.

Immunomodulatory roles of topical dinitrochlorobenzene treatment in Herpes simplex virus infection.

Epicutaneous application of a contact sensitizer 2, 4-dinitro-1-chlorobenzene (DNCB) is known to cause an inflammatory response and a hapten-specific T cell activation. We developed a highly stable gel formulation for DNCB which is easy to apply to the skin. The present study focused on whether topical application of DNCB gel produced immunomodulation with prophylactic effects against lethal herpes simplex virus infection (HSV) type 1. Our results indicated that topical treatment with DNCB gel induced proliferation of lymph node cells, T cells as well as antigen presenting cells, the production of cytokines, especially IFN-gamma, and cutaneous inflammatory response comparable to that from freshly prepared DNCB in olive oil. Repeated topical treatment of DNCB gel resulted in prophylactic effect against lethal infection with herpes simplex virus type 1 (HSV-1). In mice repeatedly treated with DNCB gel and infected with HSV, a significant increase in serum IFN-gamma was observed. These results suggest that topical DNCB functions as a potent immunomodulator, activating anti-viral defense mechanisms.