Enhanced acyclovir delivery using w/o type microemulsion: preclinical assessment of antiviral activity using murine model of zosteriform cutaneous HSV-1 infection.

The present study was aimed to develop and evaluate a microemulsion-based dermal drug delivery of an antiviral agent, acyclovir. A water-in-oil microemulsion was prepared using isopropyl myristate, Tween 20, Span 20, water and dimethylsulphoxide. It was characterized for drug content, stability, globule size, pH, viscosity and ex vivo permeation through mice skin. In vivo antiviral efficacy of optimized formulation was assessed in female Balb/c mice against herpes simplex virus-I (HSV-I)-induced infection. It was observed that optimized formulation when applied 24-h post-infection could completely inhibit the development of cutaneous herpetic lesions vis-à-vis marketed cream.

Hybrid MC/QC simulations of water-assisted proton transfer in nucleosides. Guanosine and its analog acyclovir.

To provide an in-depth insight into the molecular basis of spontaneous tautomerism in DNA and RNA base pairs, a hybrid Monte Carlo (MC)-quantum chemical (QC) methodology is implemented to map two-dimensional potential energy surfaces along the reaction coordinates of solvent-assisted proton transfer processes in guanosine and its analog acyclovir in aqueous solution. The solvent effects were simulated by explicit inclusion of water molecules that model the relevant part of the first hydration shell around the solute. The position of these water molecules was estimated by carrying out a classical Metropolis Monte Carlo simulation of dilute water solutions of the guanosine (Gs) and acyclovir (ACV) and subsequently analyzing solute-solvent intermolecular interactions in the statistically-independent MC-generated configurations. The solvent-assisted proton transfer processes were further investigated using two different ab initio MP2 quantum chemical approaches. In the first one, potential energy surfaces of the 'bare' finite solute-solvent clusters containing Gs/ACV and four water molecules (MP2/6-31+G(d,p) level) were explored, while within the second approach, these clusters were embedded in 'bulk' solvent treated as polarizable continuum (C-PCM/MP2/6-31+G(d,p) level of theory). It was found that in the gas phase and in water solution, the most stable tautomer for guanosine and acyclovir is the 1H-2-amino-6-oxo form followed by the 2-amino-6-(sZ)-hydroxy form. The energy barriers of the water-assisted proton transfer reaction in guanosine and in acyclovir are found to be very similar - 11.74 kcal mol-1 for guanosine and 11.16 kcal mol-1 for acyclovir, and the respective rate constants (k = 1.5 × 101 s-1, guanosine and k = 4.09 × 101 s-1, acyclovir), are sufficiently large to generate the 2-amino-6-(sZ)-hydroxy tautomer. The analysis of the reaction profiles in both compounds shows that the proton transfer processes occur through the asynchronous concerted mechanism.

Phospholipid vesicle-based permeation assay and EpiSkin® in assessment of drug therapies destined for skin administration.

Cost-effective and efficient methods for permeability screening are crucial during early development of drugs, drug formulations, and cosmeceuticals. Alternatives to animal experiments are impelled for both economical and ethical reasons. The aim of this study was to determine the ability of the phospholipid vesicle-based permeation assay (PVPA) to assess the effect of different formulations on drug permeability and thus establish its utility in formulation development. Three model drugs were tested in solutions and as liposomal formulations. The permeability results for the PVPA models were compared with the results for the reconstructed human skin model, EpiSkin(®). The drugs were ranked based on their estimated penetration potentials, and the results were in accordance with what was expected considering the physicochemical properties of the drugs. PVPAs (E-80, ceramide, cholesterol, cholesteryl sulfate, and palmitic acid) was able to distinguish between drug solutions and liposomal formulations; however, EpiSkin(®) detected only small differences between the drugs in solution and formulations. In contrast with EpiSkin(®), which is limited by a 3-day testing window, PVPA barriers can be stored frozen for up to 2 weeks or even up to 16 months, depending on their compositions. The PVPA models are thus more cost effective and efficient than the EpiSkin(®) model for permeability screening during early drug development.

Assessment of the physical properties and stability of mixtures of tetracycline hydrochloride ointment and acyclovir cream.

In dermatology, ointments are often mixed as part of drug therapy, but mixing often leads to incompatibility. Three combinations of tetracycline ointment (TC-o) and acyclovir cream (ACV-cr) were prepared at a TC-o:ACV-cr ratio of 1:1 using a brand-name ACV-cr and two generic ACV-cr (samples TC-o+ACV-A, TC-o+ACV-B, and TC-o+ACV-C). Microscopic examination revealed separation in TC-o+ACV-C. Viscosity and elasticity measurement indicated that the storage modulus (G') and loss modulus (G″) of each of the TC-o+ACV-cr mixtures behaved similarly to those of an ACV-cr and the loss tangent (tanδ) behaved similarly to that of a TC ointment. In addition, differences in the storage modulus (G') and loss modulus (G″) of the TC-o+ACV-cr mixtures were noted. To assess stability, each TC-o+ACV-cr mixture was stored away from direct sunlight at 25 °C and an RH of 84% and at 4 °C (in a refrigerator). HPLC revealed that the ACV content in each TC-o+ACV-cr mixture remained at 95-105% for up to 14 days under both sets of storage conditions. A decline in TC content in each TC-o+ACV-cr mixture was not noted with storage at 4 °C but was noted over time with storage at 25 °C and an RH of 84%. In addition, significant differences in the percent decline in TC content in each TC-o+ACV-cr mixture occurred with storage at 25 °C and an RH of 84%. Thus, differences in physical properties and stability may occur when combining brand-name and generic drugs, and temperature and humidity may be the cause of the TC-o's incompatibility.

Resistance of herpes simplex viruses to nucleoside analogues: mechanisms, prevalence, and management.

Herpes simplex viruses (HSV) type 1 and type 2 are responsible for recurrent orolabial and genital infections. The standard therapy for the management of HSV infections includes acyclovir (ACV) and penciclovir (PCV) with their respective prodrugs valacyclovir and famciclovir. These compounds are phosphorylated by the viral thymidine kinase (TK) and then by cellular kinases. The triphosphate forms selectively inhibit the viral DNA polymerase (DNA pol) activity. Drug-resistant HSV isolates are frequently recovered from immunocompromised patients but rarely found in immunocompetent subjects. The gold standard phenotypic method for evaluating the susceptibility of HSV isolates to antiviral drugs is the plaque reduction assay. Plaque autoradiography allows the associated phenotype to be distinguished (TK-wild-type, TK-negative, TK-low-producer, or TK-altered viruses or mixtures of wild-type and mutant viruses). Genotypic characterization of drug-resistant isolates can reveal mutations located in the viral TK and/or in the DNA pol genes. Recombinant HSV mutants can be generated to analyze the contribution of each specific mutation with regard to the drug resistance phenotype. Most ACV-resistant mutants exhibit some reduction in their capacity to establish latency and to reactivate, as well as in their degree of neurovirulence in animal models of HSV infection. For instance, TK-negative HSV mutants establish latency with a lower efficiency than wild-type strains and reactivate poorly. DNA pol HSV mutants exhibit different degrees of attenuation of neurovirulence. The management of ACV- or PCV-resistant HSV infections includes the use of the pyrophosphate analogue foscarnet and the nucleotide analogue cidofovir. There is a need to develop new antiherpetic compounds with different mechanisms of action.

A modified Franz diffusion cell for simultaneous assessment of drug release and washability of mucoadhesive gels.

A modified Franz cell is proposed to simultaneously measure the amount of drug diffused from semisolid preparations into the receptor chamber and the amount washed away by a tangential buffer stream. Four gels containing acyclovir as model drug and based on hydrophilic polymers (sodium carboxymethylcellulose, methylvinyl ether/maleic anhydride copolymer, methacrylic acid/methacrylic acid methylester copolymer, and polyacrylic acid) were tested. The drug release profiles to the receptor chamber of a standard Franz cell apparatus were obtained and compared to the profiles obtained with the modified apparatus at two buffer stream rates (1.0 and 0.3 ml/min). Some significant differences were observed between the wash-away profiles obtained with the two buffer stream rates. At both flux rates the amount of drug washed away was quite high, and in turn, the drug release profiles to the receptor chamber were lower with respect to those obtained with the standard Franz cell test. The importance of this phenomenon was not the same for all of the polymers: the polyacrylic acid sample, because of the presence of slight crosslinking, was less sensitive to wash away. For all of the other samples, when 1.0 ml/min tangential stream was used, the amount of drug released to the receptor chamber was significantly lower with respect to the standard method. With 0.3 ml/min buffer stream, some significant reduction in release amounts could be observed for the methacrylic acid/methacrylic acid methylester copolymer sample only, which was also the most erodible sample. The method proposed appears suitable to differentiate the examined samples for sensitivity to the washing effect.