Topical bioequivalence of acyclovir creams using dermal microdialysis in pigs: a new model to evaluate bioequivalence for topical formulations

Comparative Study of Dermal Pharmacokinetics Between Topical Drugs Using Open Flow Microperfusion in a Pig Model

PURPOSE

Accurate methods to determine dermal pharmacokinetics are important to increase the rate of clinical success in topical drug development. We investigated in an in vivo pig model whether the unbound drug concentration in the interstitial fluid as determined by dermal open flow microperfusion (dOFM) is a more reliable measure of dermal exposure compared to dermal biopsies for seven prescription or investigational drugs. In addition, we verified standard dOFM measurement using a recirculation approach and compared dosing frequencies (QD versus BID) and dose strengths (high versus low drug concentrations).

METHODS

Domestic pigs were topically administered seven different drugs twice daily in two studies. On day 7, drug exposures in the dermis were assessed in two ways: (1) dOFM provided the total and unbound drug concentrations in dermal interstitial fluid, and (2) clean punch biopsies after heat separation provided the total concentrations in the upper and lower dermis.

RESULTS

dOFM showed sufficient intra-study precision to distinguish interstitial fluid concentrations between different drugs, dose frequencies and dose strengths, and had good reproducibility between studies. Biopsy concentrations showed much higher and more variable values. Standard dOFM measurements were consistent with values obtained with the recirculation approach.

CONCLUSIONS

dOFM pig model is a robust and reproducible method to directly determine topical drug concentration in dermal interstitial fluid. Dermal biopsies were a less reliable measure of dermal exposure due to possible contributions from drug bound to tissue and drug associated with skin appendages.

Detailed pharmacokinetic characterization of advanced topical acyclovir formulations with IVPT and in vivo Open Flow Microperfusion

Successful treatment of herpes simplex viruses is currently limited by a lack of effective topical drugs. Commonly used topical acyclovir products only reduce the duration of lesions by a few days. Optimizing topical formulations to achieve an enhanced acyclovir solubility and penetration could increase the efficacy of topically applied acyclovir, but new formulations need to show reliable acyclovir delivery into at least the epidermis/dermis and need to provide sustained acyclovir release for extended time periods. The aim of this study was to compare pharmacokinetic data from in vitro permeation testing (IVPT) and preclinical dermal open flow microperfusion (dOFM) experiments regarding the penetration behavior of different acyclovir formulations relative to the reference product Zovirax® 5% cream. Four test formulations that delivered the best penetration data in IVPT were further tested using continuous dOFM in vivo dermal sampling. The use of dOFM identified one of the four tested formulations to perform significantly better than the other three tested formulations and the reference product. In vivo dOFM data showed differences in the dermal acyclovir concentration that had not been detected by using IVPT. Improved acyclovir delivery to the dermis was likely achieved by the new formulation that uses a much lower drug load compared to the reference product. This optimized formulation was able to achieve a dermal concentration similar to oral application and can thus provide the opportunity of more efficacious topical HSV-1 treatment with less side effects than oral systemic treatment.

Optimization and evaluation of pluronic lecithin organogels as a transdermal delivery vehicle for sinomenine

The purpose of the present study was to prepare and optimize sinomenine (SIN) pluronic lecithin organogels system (PLO), and to evaluate the permeability of the optimized PLO in vitro and in vivo. Box-Behnken design was used to optimize the PLO and the optimized formulation was pluronic F127 of 19.61%, lecithin of 3.60% and SIN of 1.27%. The formulation was evaluated its skin permeation and drug deposition both in vitro and in vivo compared with gel. Permeation and deposition studies of PLO were carried out with Franz diffusion cells in vitro and with microdialysis in vivo. In vitro studies, permeation rate (Jss) of SIN from PLO was 146.55 ± 2.93 μg/cm(2)/h, significantly higher than that of gel (120.39 μg/cm(2)/h) and the amount of SIN deposited in skin from the PLO was 10.08 ± 0.86 μg/cm(2), significantly larger than that from gel (6.01 ± 0.04 μg/cm(2)). In vivo skin microdialysis studies showed that the maximum concentration (Cmax) of SIN from PLO in "permeation study" and "drug-deposition study" were 150.27 ± 20.85 μg/ml and 67.95 μg/ml, respectively, both significantly higher than that of SIN from gel (29.66 and 6.73 μg/ml). The results recommend that PLO can be used as an advantageous transdermal delivery vehicle to enhance the permeation and skin deposition of SIN.

In vivo microdialysis for the evaluation of transfersomes as a novel transdermal delivery vehicle for cinnamic acid

In this study, cinnamic acid-loaded transfersomes were prepared and dermal microdialysis sampling was used in Sprague-Dawley rats to compare the amount of drug released into the skin using transfersomes as transdermal carriers with that released on using conventional liposomes. The formulation of cinnamic acid-loaded transfersomes was optimized by a uniform design through in vitro transdermal permeation studies. Hydration time was confirmed as a significant factor influencing the entrapment efficiency of transfersomes, further affecting their transdermal flux in vitro. The fluxes of cinnamic acid from transfersomes were all higher than those from conventional liposomes, and the flux from the optimal transfersome formulation was 3.01-fold higher than that from the conventional liposomes (p < 0.05). An in vivo microdialysis sampling method revealed that the dermal drug concentrations from transfersomes applied on various skin regions were much lower than those required with conventional liposomes. After the administration of drug-containing transfersomes and liposomes on abdominal skin regions of rats for a period of 10 h, the Cmax of cinnamic acid from the compared liposomes was 3.21 ± 0.25 μg/mL and that from the transfersomes was merely 0.59 ± 0.02 μg/mL. The results suggest that transfersomes can be used as carriers to enhance the transdermal delivery of cinnamic acid, and that these vehicles may penetrate the skin in the complete form, given their significant deformability.