Cutaneous pharmacokinetics-based bioequivalence: A clinical dermal open flow microperfusion verification study using lidocaine and prilocaine combination topical products.

BACKGROUND: Using accurate, sensitive, reproducible and efficient in vivo cutaneous pharmacokinetics (PK)-based bioequivalence (BE) approaches can promote the development of topical generic drug products. A clinical dermal open flow microperfusion (dOFM) study has previously demonstrated the BE of topical drug products containing a hydrophilic drug. However, the utility of dOFM to evaluate the topical BE of drug products containing moderately lipophilic drugs, more representative of most topical drugs, has not yet been established. OBJECTIVE: To evaluate the ability of a clinical dOFM study to assess BE of topical products containing two moderately lipophilic drugs that have only minor differences in chemical and physical properties. METHODS: The study included 20 healthy subjects. Four application sites on each thigh were treated with fixed dose lidocaine/prilocaine combination products, and dermal drug concentrations were monitored with two dOFM probes per application site for 12 h. A reference cream was compared to itself and to an approved generic cream (both serving as positive controls for BE), and to a gel (negative control). BE was established based on AUC0to12h and Cmax using the scaled-average-BE approach. Systemic exposure of both drugs was assessed throughout the study. RESULTS: BE was successfully demonstrated for the positive controls, and not for the negative control, for both drugs. The systemic exposure of both drugs was negligible. CONCLUSIONS: dOFM accurately demonstrated BE between bioequivalent topical creams, sensitively discriminated between different formulations and differentiated the cutaneous PK of both study drugs, even though they differ only slightly in chemical and physical properties. These results support the utility of dOFM as a cutaneous PK-based BE approach for topical lipophilic drugs, including lidocaine and prilocaine.

Dermal open flow microperfusion for PK-based clinical bioequivalence studies of topical drug products.

Topically applied drug products have experienced an extraordinary price increase in the United States, mostly due to a lack of generic products. Generic drug development is hindered by high costs and risks associated with clinical endpoint studies required to show bioequivalence (BE) of prospective generic products relative to their reference products. There is a continued need for cost- and time-efficient alternatives to clinical endpoint studies to determine BE of topically applied dermal drug products. Cutaneous PK-based BE studies present such an alternative and dOFM (dermal open flow microperfusion) has already been successfully used in several verifications studies to show an accurate and sensitive assessment of the rate and extent at which drugs become available in the skin. dOFM technology is discussed as well as the dOFM setup of clinical pilot and main studies to achieve BE assessment with a minimum number of participants and an outlook is given on the use of dOFM technology for other drug products.

Comparative in vitro release testing (IVRT) of acyclovir products.

The aim was to evaluate whether an in vitro release test (IVRT) could differentiate the release rates from five pharmaceutically equivalent acyclovir cream products and one ointment compared to that from a reference product, Zovirax cream (USA), to identify a test product with an inequivalent drug release rate that could serve as negative control for bioequivalence (BE) in a separate in vivo study. The reference product showed equivalent drug release rates compared to itself. The six test products failed to show equivalent drug release rates compared to the reference product. Aciclovir 1A pharma cream was selected to serve as a negative control for subsequent BE studies, since it exhibited the greatest difference in release rate among all creams, compared to the reference product. The results of this study indicate that IVRT results can be highly sensitive and may discriminate clinically relevant differences between products. Results from an appropriately validated IVRT method can support a demonstration of BE by showing that the drug release rates from test and reference products are statistically equivalent, mitigating the risk that differences may exist between the products which may influence in vivo performance of the drug product.

Variability of Skin Pharmacokinetic Data: Insights from a Topical Bioequivalence Study Using Dermal Open Flow Microperfusion.

PURPOSE: Dermal open flow microperfusion (dOFM) has previously demonstrated its utility to assess the bioequivalence (BE) of topical drug products in a clinical study. We aimed to characterize the sources of variability in the dermal pharmacokinetic data from that study. METHODS: Exploratory statistical analyses were performed with multivariate data from a clinical dOFM-study in 20 healthy adults evaluating the BE, or lack thereof, of Austrian test (T) and U.S. reference (R) acyclovir cream, 5% products. RESULTS: The overall variability of logAUC values (CV: 39% for R and 45% for T) was dominated by inter-subject variability (R: 82%, T: 91%) which correlated best with the subject's skin conductance. Intra-subject variability was 18% (R) and 9% (T) of the overall variability; skin treatment sites or methodological factors did not significantly contribute to that variability. CONCLUSIONS: Inter-subject variability was the major component of overall variability for acyclovir, and treatment site location did not significantly influence intra-subject variability. These results support a dOFM BE study design with T and R products assessed simultaneously on the same subject, where T and R treatment sites do not necessarily need to be next to each other. Localized variation in skin microstructure may be primarily responsible for intra-subject variability.

A novel human ex-vivo burn model and the local cooling effect of a bacterial nanocellulose-based wound dressing.

BACKGROUND: Burn wound progression is a significant problem as burns initially thought to be superficial can actually become full thickness over time. Cooling is an efficient method to reduce burn wound conversion. However, if the cooling agent is below room temperature, depending on the wound size the patient is at risk of hypothermia. Additionally, tissue perfusion is reduced leading to an aggravation of burn wound progression. We investigated if wound dressings based on non-pre-cooled bacterial nanocellulose (BNC) with a high water content cool a burn just by evaporation and reduce the intradermal damages in the skin. MATERIAL AND METHODS: In a human ex-vivo model, skin explants underwent contact burns using a 100 °C hot steel block. The burned areas were divided into two groups of which one was cooled with a BNC-based wound dressing. Intradermal temperature probes measured temperature in cooled and uncooled burn sites over 24 h. For histological assessments of the burned areas biopsies were taken at different time points. High mobility group box-1 (HMBG1) staining served as marker for cell vitality and necrosis in the different skin layers. RESULTS: Intradermal temperature measurement showed that application of the BNC-based wound dressing reduced temperature significantly in burned skin. This cooling effect resulted in a maximum temperature difference of 6.4 ± 1.9 °C and a significant mean reduction of the area under the curve in the first hour after burn of 62% (p < 0.0001). The histological results showed less necrosis and less dermal-epidermal separation in the cooled areas. The HMGB1 staining revealed more vital cells in the cooled group than in the uncooled group. CONCLUSION: Based on our results, BNC-based wound dressings cool a burn. Intradermal temperature as well as thermal damage of the tissue was reduced. The tested BNC-based wound dressing can be used without pre-cooling to cool a burn as well as to reduce the burn BNC-based wound progression through its evaporation cooling effect.

A comprehensive approach to qualify and validate the essential parameters of an in vitro release test (IVRT) method for acyclovir cream, 5.

The rate of release of an active pharmaceutical ingredient (API) from a topical semisolid dosage form can be influenced by its physical and structural properties. An In Vitro Release Test (IVRT) is an established method to characterize this rate of API release and compare the underlying sameness in product quality characteristics. The purpose of this work was to validate an IVRT method to compare acyclovir cream, 5% products. However, despite widespread use of the IVRT since 1997, there has been no established approach to validate an IVRT method. Our approach included: 1) qualification of the diffusion cell apparatus, 2) qualification of the laboratory, 3) validation of the HPLC analytical method, and 4) validation of numerous critical parameters of the IVRT method, itself, and resulted in a comprehensive and successful IVRT method validation. Subsequent to the IVRT validation work described here, the U.S. Food and Drug Administration (FDA) drafted a guidance on the development and validation of an IVRT method for acyclovir cream, 5%. Although there are notable differences between our approach and the approach in that guidance, this report illustrates how many of the same essential qualification parameters and validation concepts were considered and systematically addressed in our approach to IVRT validation.

Assessment of skin permeability to topically applied drugs by skin impedance and admittance.

OBJECTIVE: Pharmacokinetic and pharmacodynamic studies of topically applied drugs are commonly performed by sampling of interstitial fluid with dermal open flow microperfusion and subsequent analysis of the samples. However, the reliability of results from the measured concentration-time profile of the penetrating drug suffers from highly variable skin permeability to topically applied drugs that is mainly caused by inter- and intra-subject variations of the stratum corneum. Thus, statistically significant results can only be achieved by performing high numbers of experiments. To reduce the expenditures needed for such high experiment numbers we aimed to assess the correlation between skin permeability and skin impedance/skin admittance. APPROACH: We performed an ex vivo drug penetration study with human skin, based on the hypothesis that inter-subject variations of the respective concentration-time profiles can be correlated with variations of the passive electrical properties of the skin. Therefore, skin impedance and skin admittance were related to the skin permeability to the model drug Clobetasol-17-proprionate. MAIN RESULTS: The measured low frequency skin impedance and the skin admittance correlated linearly with the drug concentration-time profiles from dermal sampling. SIGNIFICANCE: Skin permeability can be assessed by measuring the passive electrical properties of the skin, which enables correction of skin permeability variations. This allows reduction of experiment numbers in future pharmacokinetic and pharmacodynamic studies with human skin ex vivo and in vivo and leads to diminished study costs.

Quantification of Basal Insulin Peglispro and Human Insulin in Adipose Tissue Interstitial Fluid by Open-Flow Microperfusion.

BACKGROUND: Restoration of the physiologic hepatic-to-peripheral insulin gradient may be achieved by either portal vein administration or altering insulin structure to increase hepatic specificity or restrict peripheral access. Basal insulin peglispro (BIL) is a novel, PEGylated basal insulin with a flat pharmacokinetic and glucodynamic profile and altered hepatic-to-peripheral action gradient. We hypothesized reduced BIL exposure in peripheral tissues explains the latter, and in this study assessed the adipose tissue interstitial fluid (ISF) concentrations of BIL compared with human insulin (HI). METHODS: A euglycemic glucose clamp was performed in patients with type 1 diabetes during continuous intravenous (IV) infusion of BIL or HI, while the adipose ISF insulin concentrations were determined using open-flow microperfusion (OFM). The ratio of adipose ISF-to-serum concentrations and the absolute steady-state adipose ISF concentrations were assessed using a dynamic no-net-flux technique with subsequent regression analysis. RESULTS: Steady-state BIL concentrations in adipose tissue ISF were achieved by ∼16 h after IV infusion. Median time to reach steady-state glucose infusion rate across doses ranged between 8 and 22 h. The average serum concentrations (coefficient of variation %) of BIL and HI were 11,200 pmol/L (23%) and 425 pmol/L (15%), respectively. The ISF-to-serum concentration ratios were 10.2% for BIL and 22.9% for HI. CONCLUSIONS: This study indicates feasibility of OFM to measure BIL in ISF. The observed low ISF-to-serum concentration ratio of BIL is consistent with its previously demonstrated reduced peripheral action.

Open Flow Microperfusion as a Dermal Pharmacokinetic Approach to Evaluate Topical Bioequivalence.

BACKGROUND: The availability of generic topical dermatological drug products is constrained by the limited methods established to assess topical bioequivalence (BE). A novel cutaneous pharmacokinetic approach, dermal open-flow microperfusion (dOFM), can continuously assess the rate and extent to which a topical drug becomes available in the dermis, to compare in vivo dermal bioavailability (BA) and support BE evaluations for topical products. OBJECTIVE: To evaluate whether dOFM is an accurate, sensitive, and reproducible in vivo method to characterize the intradermal BA of acyclovir from 5 % acyclovir creams, comparing a reference (R) product either to itself or to a different test (T) product. METHODS: In a single-center clinical study, R or T products were applied to six randomized treatment sites on the skin of 20 healthy human subjects. Two dOFM probes were inserted in each treatment site to monitor the intradermal acyclovir concentration for 36 h. Comparative BA (of R vs. R and T vs. R) was evaluated based on conventional BE criteria for pharmacokinetic endpoints (area under the curve and maximum dermal concentration) where the 90 % confidence interval of the geometric mean ratio between the T and R falls within 0.80-1.25. RESULTS: The positive control products (R vs. R) were accurately and reproducibly confirmed to be bioequivalent, while the negative control products (T vs. R) were sensitively discriminated not to be bioequivalent. CONCLUSIONS: dOFM accurately, sensitively, and reproducibly characterized the dermal BA in a manner that can support BE evaluations for topical acyclovir 5 % creams in a study with n = 40 (20 subjects in this study).