Concentrations Of Penciclovir Research Articles

Novel electrochemical sensor based on MoS2NSs@AgNPs/MWCNTs-COOH nanocomposites for effective detection of Penciclovir

Abnormal levels of penciclovir (PCV) in humans may lead to inflammation and renal impairment, and its frequent detection in the aquatic environment poses environmental hazards. Consequently, timely detection and regulation of PCV concentrations in the human body are crucial for drug research, disease diagnosis, and environmental protection. In this study, a PCV electrochemical sensing platform based on MoS2NSs@AgNPs/MWCNTs-COOH was constructed by in situ reduction of silver nanoparticles (AgNPs) on MoS2 nanosheets (MoS2NSs) and complexed with carboxylated multi-walled carbon nanotubes (MWCNTs-COOH). The synergistic effect of highly conductive AgNPs, high surface area MoS2NSs, and MWCNTs-COOH increased the electron transfer rate at the electrode surface and thus effectively promoted the electrooxidation process of PCV. The electrochemical performance of the sensor was investigated and optimized by cyclic voltammetry (CV) and linear scanning voltammetry (LSV). The linear response of PCV under optimal conditions was in the range of 0.5–200.0 µM, with a limit of detection (LOD) of 0.039 µM (S/N = 3), and recoveries of 98.1–101.1 %, 95.6–101.6 %, 97.0–103.6 %, and 96.0–100.9 %. The results show that the constructed MoS2NSs@AgNPs/MWCNTs-COOH /GEC sensing platform has the advantages of high sensitivity, fast response speed, and strong anti-interference ability. This work is the first to develop an electrochemical sensing platform for PCV based on MoS2NSs@AgNPs/MWCNTs-COOH, providing a new PCV quantitative detection solution.

Pilot Study of the Safety and Tolerability of a Subconjunctival Penciclovir Implant in Cats Experimentally Infected with Herpesvirus.

To assess safety and tolerability of a subconjunctival penciclovir implant in cats infected with feline herpesvirus type 1 (FHV-1). Subconjunctival blank (n = 4 cats) or penciclovir-impregnated (n = 6) silicone implants were placed bilaterally in 10 normal, FHV-1-naive cats 7-8 days before viral inoculation. Outcomes included disease score, FHV-1 serology, conjunctival viral load, Schirmer tear tests (STT), tear film break-up times (TFBUTs), conjunctival histology, goblet cell density (GCD), body weight, tear and plasma penciclovir concentration, and corneal ulcer evaluation. Both groups had similar clinical and histologic disease scores, STT values, TFBUTs, GCD, FHV-1 titers, viral loads, and body weight changes. No ocular or systemic signs of toxicity were noted. Tear penciclovir concentration varied widely among cats and across time points. Tear penciclovir concentrations exceeded the lowest published half maximal inhibitory concentration (IC50) in 5/6 treated cats. Plasma penciclovir concentrations remained below 10 ng/mL. Cats with higher tear penciclovir concentrations at inoculation and/or time of peak disease had fewer corneal ulcers than cats in which tear penciclovir concentrations were inconsistent, low, or unrecordable. Subconjunctival blank and penciclovir-impregnated implants were well tolerated at the ocular surface and not associated with systemic toxicity, adverse effect, or appreciable plasma penciclovir concentrations. Tear penciclovir concentrations >IC50 were sometimes achieved, especially during burst release soon after implant placement. Further study is necessary to determine efficacy of locally delivered penciclovir when penciclovir concentration is consistently maintained above IC50. This will be especially useful in patients unable to receive systemic therapy.

Pharmacokinetic modeling of penciclovir and BRL42359 in the plasma and tears of healthy cats to optimize dosage recommendations for oral administration of famciclovir.

OBJECTIVES To determine, following oral administration of famciclovir, pharmacokinetic (PK) parameters for 2 of its metabolites (penciclovir and BRL42359) in plasma and tears of healthy cats so that famciclovir dosage recommendations for the treatment of herpetic disease can be optimized. ANIMALS 7 male domestic shorthair cats. PROCEDURES In a crossover study, each of 3 doses of famciclovir (30, 40, or 90 mg/kg) was administered every 8 or 12 hours for 3 days. Six cats were randomly assigned to each dosage regimen. Plasma and tear samples were obtained at predetermined times after famciclovir administration. Pharmacokinetic parameters were determined for BRL42359 and penciclovir by compartmental and noncompartmental methods. Pharmacokinetic-pharmacodynamic (PK-PD) indices were determined for penciclovir and compared among all dosage regimens. RESULTS Compared with penciclovir concentrations, BRL42359 concentrations were 5- to 11-fold greater in plasma and 4- to 7-fold greater in tears. Pharmacokinetic parameters and PK-PD indices for the 90 mg/kg regimens were superior to those for the 30 and 40 mg/kg regimens, regardless of dosing frequency. Penciclovir concentrations in tears ranged from 18% to 25% of those in plasma. Administration of 30 or 40 mg/kg every 8 hours achieved penciclovir concentrations likely to be therapeutic in plasma but not in tears. Penciclovir concentrations likely to be therapeutic in tears were achieved only with the two 90 mg/kg regimens. CONCLUSIONS AND CLINICAL RELEVANCE In cats, famciclovir absorption is variable and its metabolism saturable. Conversion of BRL42359 to penciclovir is rate limiting. The recommended dosage of famciclovir is 90 mg/kg every 12 hours for cats infected with feline herpesvirus.

In vitrocytotoxicity and antiviral efficacy against feline herpesvirus type 1 of famciclovir and its metabolites

To assess in vitro the antiviral efficacy against feline herpesvirus (FHV-1) and cytotoxicity for cultured feline cells of famciclovir and its metabolites, BRL 42359 and penciclovir. To investigate the effect of timing of penciclovir application on in vitro antiviral activity. Plaque reduction assays were used to estimate antiviral efficacy of all compounds and the effect of penciclovir exposure before or after exposure to a FHV-1 field isolate. Cytotoxicity was evaluated by assessing cell morphology and viable cell number for 72 h following exposure to each compound. The penciclovir concentration that inhibited FHV-1-induced plaque formation by 50% (IC50 ) was 0.86 μg/mL (3.4 μm). Famciclovir and BRL 42359 had no antiviral effect against FHV-1 at any concentration assessed. Antiviral activity was significantly enhanced when cells were exposed to 4 μm penciclovir (approximate IC50 ) for 1 h but not for 24 h before viral adsorption. Delaying exposure of cells to penciclovir for 1, 2, or 4 h after viral adsorption significantly enhanced antiviral activity. Relative to untreated control wells, >88% of cells remained viable when exposed to famciclovir (100 μm), BRL 42359 (1.06 mm), or penciclovir (40 μm) for 72 h. No morphologic evidence of cytotoxicity was noted. Penciclovir demonstrates potent antiviral activity against FHV-1 and may be effective at lower tissue, tear, and plasma concentrations than previously targeted. The duration of in vitro antiviral effect of penciclovir suggests that frequent famciclovir administration may be necessary in vivo. Famciclovir and BRL 42359 showed no signs of in vitro cytotoxicity.

Intraocular penetration of penciclovir after oral administration of famciclovir: a population pharmacokinetic model

We developed a population model that describes the ocular penetration and pharmacokinetics of penciclovir in human aqueous humour and plasma after oral administration of famciclovir. Fifty-three patients undergoing cataract surgery received a single oral dose of 500 mg of famciclovir prior to surgery. Concentrations of penciclovir in both plasma and aqueous humour were measured by HPLC with fluorescence detection. Concentrations in plasma and aqueous humour were fitted using a two-compartment model (NONMEM software). Inter-individual and intra-individual variabilities were quantified and the influence of demographics and physiopathological and environmental variables on penciclovir pharmacokinetics was explored. Drug concentrations were fitted using a two-compartment, open model with first-order transfer rates between plasma and aqueous humour compartments. Among tested covariates, creatinine clearance, co-intake of angiotensin-converting enzyme inhibitors and body weight significantly influenced penciclovir pharmacokinetics. Plasma clearance was 22.8±9.1 L/h and clearance from the aqueous humour was 8.2×10(-5) L/h. AUCs were 25.4±10.2 and 6.6±1.8 μg·h/mL in plasma and aqueous humour, respectively, yielding a penetration ratio of 0.28±0.06. Simulated concentrations in the aqueous humour after administration of 500 mg of famciclovir three times daily were in the range of values required for 50% growth inhibition of non-resistant strains of the herpes zoster virus family. Plasma and aqueous penciclovir concentrations showed significant variability that could only be partially explained by renal function, body weight and comedication. Concentrations in the aqueous humour were much lower than in plasma, suggesting that factors in the blood-aqueous humour barrier might prevent its ocular penetration or that redistribution occurs in other ocular compartments.

Estimates of the pharmacokinetics of famciclovir and its active metabolite penciclovir in young Asian elephants (Elephas maximus)

To determine plasma pharmacokinetics of penciclovir following oral and rectal administration of famciclovir to young Asian elephants (Elephas maximus). 6 healthy Asian elephants (5 females and 1 male), 4.5 to 9 years old and weighing 1,646 to 2,438 kg. Famciclovir was administered orally or rectally in accordance with an incomplete crossover design. Three treatment groups, each comprising 4 elephants, received single doses of famciclovir (5 mg/kg, PO, or 5 or 15 mg/kg, rectally); there was a minimum 12-week washout period between subsequent famciclovir administrations. Serial blood samples were collected after each administration. Samples were analyzed for famciclovir and penciclovir with a validated liquid chromatography-mass spectroscopy assay. Famciclovir was tolerated well for both routes of administration and underwent complete biotransformation to the active metabolite, penciclovir. Mean maximum plasma concentration of penciclovir was 1.3 μg/mL at 1.1 hours after oral administration of 5 mg/kg. Similar results were detected after rectal administration of 5 mg/kg. Mean maximum plasma concentration was 3.6 μg/mL at 0.66 hours after rectal administration of 15 mg/kg; this concentration was similar to results reported for humans receiving 7 mg/kg orally. Juvenile Asian elephants are susceptible to elephant endotheliotropic herpesvirus. Although most infections are fatal, case reports indicate administration of famciclovir has been associated with survival of 3 elephants. In Asian elephants, a dose of 8 to 15 mg of famciclovir/kg given orally or rectally at least every 8 hours may result in penciclovir concentrations that are considered therapeutic in humans.

Pharmacokinetics of penciclovir in healthy cats following oral administration of famciclovir or intravenous infusion of penciclovir

To investigate the pharmacokinetics of penciclovir in healthy cats following oral administration of famciclovir or IV infusion of penciclovir. 6 cats. Cats received famciclovir (40 [n = 3] or 90 [3] mg/kg, PO, once) in a balanced crossover-design study; the alternate dose was administered after a ≥ 2-week washout period. After another washout period (≥ 4 weeks), cats received an IV infusion of penciclovir (10 mg/kg delivered over 1 hour). Plasma penciclovir concentrations were analyzed via liquid chromatography-mass spectrometry at fixed time points after drug administration. Mean ± SD maximum plasma concentration (C(max)) of penciclovir following oral administration of 40 and 90 mg of famciclovir/kg was 1.34 ± 0.33 μg/mL and 1.28 ± 0.42 μg/mL and occurred at 2.8 ± 1.8 hours and 3.0 ± 1.1 hours, respectively; penciclovir elimination half-life was 4.2 ± 0.6 hours and 4.8 ± 1.4 hours, respectively; and penciclovir bioavailability was 12.5 ± 3.0% and 7.0 ± 1.8%, respectively. Following IV infusion of penciclovir (10 mg/kg), mean ± SD penciclovir clearance, volume of distribution, and elimination half-life were 4.3 ± 0.8 mL/min/kg, 0.6 ± 0.1 L/kg, and 1.9 ± 0.4 hours, respectively. Penciclovir pharmacokinetics following oral administration of famciclovir were nonlinear within the dosage range studied, likely because of saturation of famciclovir metabolism. Oral administration of famciclovir at 40 or 90 mg/kg produced similar C(max) and time to C(max) values. Therefore, the lower dose may have similar antiviral efficacy to that proven for the higher dose.

Pharmacokinetics of famciclovir and penciclovir in tears following oral administration of famciclovir to cats: a pilot study

To validate a means of collecting tears from cats, develop an assay for quantifying famciclovir and penciclovir in tears, and to assess famciclovir and penciclovir concentrations and pharmacokinetics in the tears of cats being treated orally with famciclovir for suspected herpetic disease. Seven client-owned cats. Cats were treated orally with a median (range) dose of 40 (39-72) mg of famciclovir/kg three times daily for at least 24 h. At various time points following famciclovir administration, tear samples were collected using Schirmer tear test strips. Tear famciclovir and penciclovir concentrations were measured using liquid chromatography-mass spectrometry, and concentration-time profiles were analyzed noncompartmentally. The relationship between famciclovir dose and tear penciclovir concentration near its maximum was evaluated using least squares linear regression. Maximum tear famciclovir concentration of 0.305 μg/mL occurred at 2.64 h; elimination half-life was 2.28 h. Maximum tear penciclovir concentration (0.981 μg/mL) occurred 2.25 h following oral administration of famciclovir; elimination half-life was 2.77 h. A significant positive correlation was noted between famciclovir dose and tear penciclovir concentration at various time points between 0.5 and 3.75 h following drug administration (P = 0.025). Tear penciclovir concentration exceeded the concentration shown to have in vitro efficacy against feline herpesvirus (FHV-1) (0.304 μg/mL) in about half of samples collected. Oral administration of 40 mg of famciclovir/kg to cats resulted in a tear penciclovir concentration-time profile that approximated the plasma penciclovir concentration-time profile and frequently achieved a penciclovir concentration at the ocular surface likely to be effective against FHV-1.

Evaluation of orally administered famciclovir in cats experimentally infected with feline herpesvirus type-1

To evaluate orally administered famciclovir for treatment of cats with experimentally induced disease attributable to feline herpesvirus type-1 (FHV-1). 16 nonvaccinated specific-pathogen-free cats. Cats were treated orally with famciclovir (90 mg/kg; n = 10) or a similar volume of lactose (400 mg; 6) 3 times/d for 21 days. Cats were inoculated with FHV-1 and administered the first treatment dose on day 0. Disease score; weight; results of urinalysis, serum biochemical analysis, and CBC; histologic conjunctivitis score; herpetic DNA shedding; goblet cell density; anti-FHV-1 antibody concentration; and plasma penciclovir concentration were measured. On days 4 to 18 following inoculation, disease scores were lower in famciclovir-treated cats than in lactose-treated cats. Lactose-treated cats decreased in weight during the first 7 days after inoculation, but famciclovir-treated cats increased in weight throughout the study. Percentage change in weight was greater in famciclovir-treated cats on days 7 and 14 than in lactose-treated cats. Serum globulin concentration was lower on days 3 through 9, conjunctivitis histologic score was lower on day 14, herpetic DNA was shed less frequently throughout the study, goblet cell density was greater on day 21, and circulating anti-FHV-1 antibody concentration at study end was lower in famciclovir-treated cats, compared with these measurements in lactose-treated cats. Approximate peak plasma penciclovir concentration was 2.0 μg/mL. Famciclovir administration improved outcomes for systemic, ophthalmic, clinicopathologic, virologic, and histologic variables in cats experimentally infected with FHV-1. Adjunctive topical mucinomimetic and antimicrobial treatments may also be necessary.

Pharmacokinetics of Penciclovir after Oral Administration of its Prodrug Famciclovir to Horses

We investigated the pharmacokinetics of penciclovir after oral administration of its prodrug famciclovir to horses. Following an oral dose of famciclovir at 20 mg/kg, maximum plasma concentrations of penciclovir occurred between 0.75 and 1.5 hr (mean 0.94 + or - 0.38 hr) after dosing and were in the range 2.22 to 3.56 microg/ml (mean 2.87 + or - 0.61 microg/ml). The concentrations of penciclovir declined in a biphasic manner after the peak concentration was attained. The mean half-life of the rapid elimination phase was 1.73 + or - 0.34 hr whereas that of the slow elimination phase was 34.34 + or - 13.93 hr. These pharmacokinetic profiles observed were similar to those of another antiherpesvirus drug, acyclovir, previously reported in horses following oral dosing of its prodrug valacyclovir.

Vitreous Penetration of Orally Administered Famciclovir

To determine the vitreous penetration of penciclovir (Denavir; GlaxoSmithKline, Philadelphia, Pennsylvania, USA) after oral administration of the prodrug famciclovir (Famvir; Novartis Pharmaceuticals Corp, East Hanover, New Jersey, USA). Prospective interventional case series. Ten patients undergoing elective pars plana vitrectomy at a single institution were enrolled to take 3 oral doses of famciclovir 500 mg the day preceding surgery and a fourth dose on the morning of surgery. Blood and undiluted vitreous samples were acquired from each patient during surgery. High-performance liquid chromatography was used to determine the concentration of penciclovir in each sample. Exclusion criteria included prior vitrectomy, compromised blood-retina barrier, renal or hepatic disease, human immunodeficiency virus infection, bone marrow or renal transplantation, pregnancy or breastfeeding, history of adverse reaction or allergy to famciclovir or penciclovir, and antiviral, probenecid, or cimetidine use within 1 month of surgery. Ten eyes of 10 patients ranging in age from 26 to 82 were included. All patients had normal renal and hepatic function as determined by history and laboratory values. Mean serum penciclovir concentration +/- standard deviation was 4.45 +/- 1.31 microg/ml (range, 2.51 to 6.34 microg/ml). Mean vitreous penciclovir concentration was 1.21 +/- 0.38 microg/ml (range, 0.39 to 1.88 microg/ml). Mean vitreous-to-serum concentration ratio of penciclovir was 0.28 +/- 0.09 (range, 0.16 to 0.41). Oral administration of famciclovir results in vitreous concentrations of penciclovir within the inhibitory ranges for herpes simplex 1, herpes simplex 2, and varicella zoster virus. Oral famciclovir may be a reasonable alternative to intravenous acyclovir (Zovirax; GlaxoSmithKline) in the treatment of acute retinal necrosis, especially in cases of acyclovir resistance or patient inability to tolerate prolonged intravenous treatment.

Development of a quantitative real-time TaqMan PCR assay for testing the susceptibility of feline herpesvirus-1 to antiviral compounds

Feline herpesvirus-1 (FHV-1) is considered as the most common viral infection of domestic cats worldwide. It causes a disease characterized by upper respiratory and ocular clinical signs. Several attempts are currently underway to develop antiviral chemotherapy for treating FHV-1 infections. The availability of a rapid quantitative method for detecting FHV-1 would greatly facilitate prompt therapy, and hence enhance the success of any antiviral regime. In this study, a TaqMan real-time PCR assay was established for measuring FHV-1 DNA levels in culture supernatants. This assay was shown to be highly specific, reproducible and allows quantitation over a range of 2 to 2 × 10 8 copies per reaction. The assay was then applied to measure the reduction of FHV-1 DNA levels in the presence of increasing concentrations of acyclovir (ACV), penciclovir (PCV) and cidofovir (CDV). The 50% inhibitory concentrations (IC 50s) obtained with the B927 laboratory strain of FHV-1 were 15.8 μM for ACV, 7.93 μM for CDV and 1.2 μM for PCV. The assay described here is sensitive, time-saving and does not involve prior titration of virus stocks or monitoring virus-induced cytopathic effects. Therefore, it is suitable for routine anti-FHV-1 drug susceptibility testing in veterinary clinics.

팜비어 정 750밀리그람(팜시클로버 750밀리그람)에 대한 팜시버 정 750밀리그람의 생물학적동등성

Famciclovir, 9-(4-hydroxy-3-hydroxymethylbut-1-yl) guanine, is an oral prodrug of the antiherpesvirus nucleoside analogue, penciclovir. In human, famciclovir is orally well absorbed and then undergoes extensive first pass metabolism to penciclovir and essentially no parent compound is recovered from plasma or urine. The purpose of the present study was to evaluate the bioequivalence of two famciclovir tablets, Famvir tablet 750 mg (Novartis Korea Ltd.) and Famcivir tablet 750 mg (Hanmi Pharmaceutical. Co., Ltd.), according to the guidelines of the Korea Food and Drug Administration (KFDA). The release of famciclovir from the two famciclovir formulations in vitro was tested using KP VIII Apparatus II method with water. Twenty six healthy male subjects, years in age and in body weight, were divided into two groups and a randomized cross-over study was employed. After a single tablet containing 750 mg as famciclovir was orally administered, blood samples were taken at predetermined time intervals and the concentrations of penciclovir in serum were determined using HPLC with UV detector. The dissolution profiles of two formulations ere similar at water. The pharmacokinetic parameters such as , and were calculated and ANOVA test was utilized for the statistical analysis of the parameters using logarithmically transformed , and untransformed . The results showed that the differences between two formulations based on the reference drug, tablet 750 mg, were -0.53%, 1.12% and -24.82% for , and , respectively. There were no sequence effects between two formulations in these parameters. The 90% confidence intervals using logarithmically transformed data were within the acceptance range of log 0.8 to log 1.25 (e.g., and for and , respectively). Thus, the criteria of the KFDA bioequivalence guideline were satisfied, indicating Famcivir tablet 750 mg was bioequivalent to Famvir tablet 750 mg.

Pharmacokinetics and safety of penciclovir following oral administration of famciclovir to cats

To investigate penciclovir pharmacokinetics following single and multiple oral administrations of famciclovir to cats. 8 adult cats. A balanced crossover design was used. Phase I consisted of a single administration (62.5 mg, PO) of famciclovir. Phase II consisted of multiple doses of famciclovir (62.5 mg, PO) given every 8 or 12 hours for 3 days. Plasma penciclovir concentrations were assayed via liquid chromatography-mass spectrometry at fixed time points after famciclovir administration. Following a single dose of famciclovir, the dose-normalized (15 mg/kg) maximum concentration (C(max)) of penciclovir (350 +/- 180 ng/mL) occurred at 4.6 +/- 1.8 hours and mean +/- SD apparent elimination half-life was 3.1 +/- 0.9 hours. However, the dose-normalized area under the plasma penciclovir concentration-time curve extrapolated to infinity (AUC(0-->)) during phase I decreased with increasing dose, suggesting either nonlinear pharmacokinetics or interindividual variability among cats. Accumulation occurred following multiple doses of famciclovir administered every 8 hours as indicated by a significantly increased dose-normalized AUC, compared with AUC(0-->) from phase 1. Dose-normalized penciclovir C(max)following administration of famciclovir every 12 or 8 hours (290 +/- 150 ng/mL or 780 +/- 250 ng/mL, respectively) was notably less than the in vitro concentration (3,500 ng/mL) required for activity against feline herpesvirus-1. Penciclovir pharmacokinetics following oral famciclovir administration in cats appeared complex within the dosage range studied. Famciclovir dosages of 15 mg/kg administered every 8 hours to cats are unlikely to result in plasma penciclovir concentrations with activity against feline herpesvirus-1.

팜비어 정 250밀리그람(팜시클로버 250 mg)에 대한 팜시버 정의 생물학적동등성

Famciclovir is an oral prodrug of the antiherpesvirus nucleoside analogue, penciclovir. In human, famciclovir is orally well absorbed and then undergoes extensive first pass metabolism to penciclovir and essentially no parent compound is recovered from plasma or urine. The purpose of the present study was to evaluate the bioequivalence of two famciclovir tablets, tablet 250 mg (Novartis Korea Ltd.) and Famcivir (Hanmi Pharmaceutical Co., Ltd.), according to the guidelines of the Korea Food and Drug Administration (KFDA). The release of famciclovir from the two famciclovir formulations in vitro was tested using KP VIII Apparatus II method with water. Twenty six healthy male subjects, years in age and kg in body weight, were divided into two groups and a randomized cross-over study was employed. After a single tablet containing 250 mg as famciclovir was orally administered, blood samples were taken at predetermined time intervals and the concentrations of penciclovir in serum were determined using HPLC with UV detector. The dissolution profiles of two formulations were similar at water. In addition, the pharmacokinetic parameters such as , and were calculated and ANOVA test was utilized for the statistical analysis of the parameters using logarithmically transformed , and untransformed . The results showed that the differences between two formulations based on the reference drug, tablet 250 mg, were -2.93, -8.02 and 10.47% for , and , respectively. There were no sequence effects between two formulations in these parameters. The 90% confidence intervals using logarithmically transformed data were within the acceptance range of log0.8 to log1.25 (e.g., and for and , respectively). Thus, the criteria of the KFDA bioequivalence guideline were satisfied, indicating Famcivir was bioequivalent to tablet 250 mg.

The role of stratum corneum and dermal microvascular perfusion in penetration and tissue levels of water-soluble drugs investigated by microdialysis.

Hydrophilic drugs are poorly absorbed when applied topically, due to low partitioning through the lipid matrix of the stratum corneum. Cutaneous blood flow rapidly clears the absorbed drug, which may result in low tissue levels. This is of importance for topically applied drugs whose site of action is within the epidermis or dermis. Dermal drug levels can be measured using cutaneous microdialysis, which is a means of continuously sampling substances from the dermal extracellular fluid. To measure the contribution of stratum corneum barrier and microvascular perfusion in determining dermal tissue levels of hydrophilic drugs (aciclovir and penciclovir) in vivo. Studies were performed using microdialysis of the volar surface of the forearm of healthy volunteers (n = 55) over a 5-h collection period. Stratum corneum was removed by tape stripping, and barrier disruption quantified by measurement of transepidermal water loss (TEWL); dermal microvascular perfusion was modulated by inclusion of noradrenaline in the microdialysis perfusate. With intact skin and normal cutaneous blood flow the concentration of penciclovir recovered was below assay threshold (0.05 ng x mL(-1). With noradrenaline-induced local vasoconstriction, the area under the curve of drug absorbed through normal skin (+/- SEM) was 13.3 +/- 2.9 ng mL(-1) h(0-5) for penciclovir and 27.6 +/- 10.6 ng mL(-1) h(0-5) for aciclovir. Removal of the stratum corneum (to glistening) by tape stripping increased penciclovir absorption by 1300-fold and aciclovir absorption by 440-fold, confirming the stratum corneum as the major barrier to hydrophilic drug absorption. Sequential barrier disruption by tape stripping gave a close correlation between penciclovir concentration absorbed per hour and barrier disruption measured by TEWL (r2 = 0.9283). There was a 15.6-fold difference in the recovery of penciclovir through barrier-deficient skin with and without cutaneous blood flow. There was no relationship between fibre depth and amount of drug dialysed, which suggests free movement of antiviral drug on reaching the aqueous environment of the dermis. This study defines for the first time the relationship between the degree of mechanical barrier impairment and drug absorption at the same anatomical site in humans, and the role of blood flow in drug clearance in vivo.

Synthesis and evaluation of 2-Amino-9-(3-acyloxymethyl-4-alkoxycarbonyloxybut-1-yl)purines and 2-Amino-9-(3-alkoxycarbonyloxymethyl-4-alkoxycarbonyloxybut-1-yl)purines as potential prodrugs of penciclovir

A series of 2-amino-9-(3-acyloxymethyl-4-alkoxycarbonyloxybut-1-yl)purines (1–8) and 2-amino-9-(3-alkoxycarbonyloxymethyl-4-alkoxycarbonyloxybut-1-yl)purines (9–12) were synthesized as potential prodrugs of penciclovir. Treatment of 6-deoxypenciclovir with trimethyl orthoacetate or triethyl orthopropionate (1.2 equiv) in DMF in the presence of p-TsOH·H2O (0.1 equiv) followed by quenching with excess H2O gave the corresponding mono-O-acetyl or mono-O-propionyl compound, 17 or 18, in excellent yields of 95 and 92%, respectively. Reactions of 17 or 18 with an appropriate alkyl (Me, Et, n-Pr, and i-Pr) 4-nitrophenyl carbonate (1.2 equiv) in pyridine in the presence of a catalytic amount of DMAP (0.1 equiv) at 80°C afforded the monoacyl, monocarbonate derivatives of 6-deoxypenciclovir, 1–8, in 86–94% yields. Similar reactions of 6-deoxypenciclovir with 2.1 equiv of alkyl 4-nitrophenyl carbonate produced the dicarbonate derivatives 9–12 in 81–83% yields. Of the prodrugs tested in rats, 2-amino-9-(3-acetoxymethyl-4-isopropoxycarbonyloxybut-1-yl)purine (4) achieved the highest mean urinary recovery of penciclovir (36%), followed in order by compounds 2 (35%), 6 (35%), 7 (34%), 10 (34%), 8 (32%), 3 (32%), and famciclovir (31%). The mean urinary recovery of penciclovir and concentrations of penciclovir in the blood from 4 in mice were also slightly higher than those from famciclovir. The in vivo antiviral efficacy of 4 in HSV-1-infected normal BALB/c mice was higher than those of famciclovir and valaciclovir in terms of mortality (100, 80, and 40%) and mean survival time (>21, 13±5.0 (SEM), and 13±1.6 days). Compound 4 demonstrated an effective anti-hepadnaviral response with intrahepatic viral load being reduced by 90%, the viral supercoiled DNA levels reduced by 70% and Pre-S expression inhibited by 30% against duck hepatitis B virus (DHBV) in vivo, and did not cause any significant hepatotoxicity after 4 weeks of treatment.

Synthesis and evaluation of 2-amino-6-fluoro-9-(4-hydroxy-3-hydroxymethylbut-1-yl)purine mono- and diesters as potential prodrugs of penciclovir

2-Amino-6-fluoro-9-(4-hydroxy-3-hydroxymethylbut-1-yl)purine (7), and its mono- and diesters 8–15 were prepared and evaluated for their potential as prodrugs of penciclovir. Treatment of 2-amino-6-chloro-9-(4-hydroxy-3-hydroxymethylbut-1-yl)purine (5) with trimethylamine in THF followed by a reaction of the resulting trimethylammonium chloride salt 6 with KF in DMF afforded 2-amino-6-fluoro-9-(4-hydroxy-3-hydroxymethylbut-1-yl)purine (7) in 80% yield. Esterification of 7 with an appropriate acid anhydride [Ac2O, (EtCO)2O, (n-PrCO)2O, or (i-PrCO)2O] in DMF in the presence of a catalytic amount of DMAP produced the mono-esters 8–11 in 42–45% yields and diesters 12–15 in 87–99% yields. Of the prodrugs tested in rats, the mono-isobutyrate 11 was the most efficiently absorbed and metabolized to 7, showing the mean maximum total concentration of penciclovir (5.5μg/mL) and 7 (10.8μg/mL) in the blood was much higher than the mean maximum concentration of penciclovir (11.5μg/mL) from famciclovir. However, the mean concentrations of penciclovir from 11 were lower than those from famciclovir because of the limited conversion of a major metabolite 7 to penciclovir by adenosine deaminase.

Emergence of resistance to acyclovir and penciclovir in varicella-zoster virus and genetic analysis of acyclovir-resistant variants

We have characterized the differential actions of acyclovir and penciclovir against varicella-zoster virus (VZV) in cell culture by comparing the frequency of appearance of resistant viruses followed by their characterization. Cells were infected with cell-free virus and the cultures were successively treated with increasing concentrations of acyclovir or penciclovir. Drug-resistant viruses were selected in the presence of 6 μg/ml of acyclovir or penciclovir. The emergence frequency of resistant viruses was significantly higher following acyclovir exposure than following penciclovir exposure (Fisher’s exact test, P<0.0001), possibly reflecting virus growth differences under these experimental conditions. Based on antiviral drug susceptibility and thymidine kinase (TK) activity assays, 11 acyclovir-resistant variants from seven experiments using three virus strains (Kawaguchi strain, Oka varicella vaccine strain and a clinical isolate from a zoster patient) were found to be TK-deficient. Sequence analysis of TK-deficient variants of the Kawaguchi strain revealed deletions that caused frameshifts, resulting in premature termination in the TK gene.

The effects of combining T-cell immunosuppression with antiviral chemotherapy studied in a murine model for cutaneous HSV: Field, H.J. & Thackray, A.M. Centre for Veterinary Science, Cambridge University, Madingley Road Cambridge, CB3 0ES, UK

A series of 2-amino-9-(3-acyloxymethyl-4-alkoxycarbonyloxybut-1-yl)purines Chart 1, Scheme 2 and 2-amino-9-(3-alkoxycarbonyloxymethyl-4-alkoxycarbonyloxybut-1-yl)purines Chart 1, Scheme 2 were synthesized as potential prodrugs of penciclovir. Treatment of 6-deoxypenciclovir with trimethyl orthoacetate or triethyl orthopropionate (1.2 equiv) in DMF in the presence of p-TsOH·H2O (0.1 equiv) followed by quenching with excess H2O gave the corresponding mono-O-acetyl or mono-O-propionyl compound, Scheme 2, Scheme 4 or 18, in excellent yields of 95 and 92%, respectively. Reactions of Scheme 2, Scheme 4 or 18 with an appropriate alkyl (Me, Et, n-Pr, and i-Pr) 4-nitrophenyl carbonate (1.2 equiv) in pyridine in the presence of a catalytic amount of DMAP (0.1 equiv) at 80°C afforded the monoacyl, monocarbonate derivatives of 6-deoxypenciclovir, Chart 1, Scheme 2, in 86–94% yields. Similar reactions of 6-deoxypenciclovir with 2.1 equiv of alkyl 4-nitrophenyl carbonate produced the dicarbonate derivatives Chart 1, Scheme 2 in 81–83% yields. Of the prodrugs tested in rats, 2-amino-9-(3-acetoxymethyl-4-isopropoxycarbonyloxybut-1-yl)purine Chart 1, Scheme 2 achieved the highest mean urinary recovery of penciclovir (36%), followed in order by compounds Chart 1, Scheme 2 (35%), Chart 1, Scheme 2 (35%), Chart 1, Scheme 2 (34%), Chart 1, Scheme 2 (34%), Chart 1, Scheme 2 (32%), Chart 1, Scheme 2 (32%), and famciclovir (31%). The mean urinary recovery of penciclovir and concentrations of penciclovir in the blood from Chart 1, Scheme 2 in mice were also slightly higher than those from famciclovir. The in vivo antiviral efficacy of Chart 1, Scheme 2 in HSV-1-infected normal BALB/c mice was higher than those of famciclovir and valaciclovir in terms of mortality (100, 80, and 40%) and mean survival time (>21, 13±5.0 (SEM), and 13±1.6 days). Compound Chart 1, Scheme 2 demonstrated an effective anti-hepadnaviral response with intrahepatic viral load being reduced by 90%, the viral supercoiled DNA levels reduced by 70% and Pre-S expression inhibited by 30% against duck hepatitis B virus (DHBV) in vivo, and did not cause any significant hepatotoxicity after 4 weeks of treatment.