In vitro delivery of novel, highly potent anti-varicella zoster virus nucleoside analogues to their target site in the skin

FV-100 for the Treatment of Varicella-Virus (VZV) Infections: Quo Vadis?

The bicyclic nucleoside analogue (BCNA) Cf1743 and its orally bioavailable prodrug FV-100 have unique potential as varicella-zoster virus (VZV) inhibitors to treat herpes zoster (shingles) and the therewith associated pain, including post-herpetic neuralgia (PHN). The anti-VZV activity of Cf1743 depends on a specific phosphorylation by the VZV-encoded thymidine kinase (TK). The target of antiviral action is assumed to be the viral DNA polymerase (or DNA synthesis in the virus-infected cells).

Pluronic F127-tailored lecithin organogel of acyclovir: preclinical evidence of antiviral activity using BALB/c murine model of cutaneous HSV-1 infection

Herpes is a well-known contagious infection equally affecting both sexes. Among many antiviral drugs employed for its treatment, acyclovir (ACY) is the drug of choice. The currently available therapies of ACY suffer from limitations like poor oral bioavailability (10-15%) and high-dose requirement. The present scientific study aims to explore pluronic lecithin organogel (PLO) as a novel drug delivery platform for ACY to bring an improvement in its delivery through topical route. The properties of organogel like biocompatibility and amphiphilic nature which facilitates dissolution of various drugs of different solubility characteristics along with enhancing the permeation potential of active molecules make it a favorable drug delivery platform for the management of topical diseases. The developed PLO formulations were characterized for micromeritic characteristics, viz., zeta potential, percentage drug content, organogel morphology, skin permeation, retention, and stability studies. The selected topical formulation was further compared with the marketed one for its therapeutic efficacy by inducing cutaneous Herpes simplex virus type 1 infection followed by confirmation of viral load by immunofluorescence and PCR analyses. The developed formulation showed significant improvement over the marketed product as reflected in lesion scoring index and PCR analysis. Further, it proved better to the marketed formulation in t.i.d. treatment regimen in comparison to control. The improvement in overall performance leading to enhanced bioavailability and safety is attributed to the synergism between excipient properties and formulation characteristics. The drug ACY in this micro environment not only finds an improved delivery vehicle but it also offers enhanced drug-target interactions.

Evaluation of the in vitro skin permeation of antiviral drugs from penciclovir 1% cream and acyclovir 5% cream used to treat herpes simplex virus infection

BACKGROUND

Herpes simplex virus infection (HSV) is a common and ubiquitous infection of the skin which causes mucocutaneous lesions called cold sores (herpes labialis) or fever blisters. It is estimated that approximately 80% of the population worldwide are carriers of the Herpes simplex virus, approximately 40% suffer from recurrent recurrent infections. This study evaluates the in vitro skin permeation and penetration of penciclovir and acyclovir from commercialized creams for the treatment of herpes labialis (cold sores), using non viable excised human abdominal skin samples, which were exposed to 5 mg/cm2 of acyclovir 5% cream or penciclovir 1% cream.

METHODS

After 24 h of cream application, excess cream was washed off and layers of stratum corneum were removed by successive tape stripping. Amounts of active ingredients having penetrated through the skin were measured, as well as the amounts in the washed-off cream, in skin strips and creams remaining in the skin. Molecular modelling was used to evaluate physico-chemical differences between the drugs. Western blot analysis enabled to determine whether the marker of basal cells keratin 5 could be detected in the various tape strips.

RESULTS

Application of penciclovir 1% cream yielded higher concentration of drug in the deeper layers of the epidermis as well as a higher drug flux through the skin. Molecular modelling showed two higher hydrophobic moieties for acyclovir. Presence of the basal cell marker keratin 5 was underscored in the deeper tape strips from the skin, giving evidence that both drugs can reach their target cells.

CONCLUSION

Penciclovir 1% cream has the tendency to facilitate the diffusion of the drug through the stratum corneum into the deeper epidermis layers, in which it could reach the target basal cells at effective therapeutical concentration. The small difference in the surface properties between both molecules might also contribute to favour the passage of penciclovir through the epidermis into the deeper basal cells.

Assessment of drug permeability distributions in two different model skins

Past in vitro studies with human skin have indicated that drug permeability coefficient (Kp) distributions do not always follow a Gaussian-normal pattern. This has major statistical implications, exemplified by the fact that use of t-tests to evaluate significance is limited to normally distributed populations. Percutaneous absorption research often involves using animal or synthetic skins to simulate less readily available human skin. However, negligible work has been performed on assessing the permeability variabilities of these model membranes. This paper aims to fill this gap. To this end, four studies were undertaken representing two different drugs (caffeine and testosterone) with each drug penetrating through two different model skins (silicone membrane and pig skin). It was determined that in the silicone membrane studies, both compounds' Kp distributions could be fitted to a normal pattern. In contrast, in the pig skin studies, there were notable differences between each drug. While the testosterone Kp values could be fitted to a normal distribution, this was not possible with the caffeine Kp data, which could be fitted to a log-normal distribution. There is some evidence from the literature as well as physicochemical considerations that these outcomes may reflect general trends that are dependent upon both membrane and penetrant properties.