Nanoscale determination of antiviral drug acyclovir engaging bifunctionality of single walled carbon nanotubes - nafion film.

An elementary and exemplary approach is proposed for the accurate monitoring of antiviral drug acyclovir (ACV) utilizing glassy carbon electrode (GCE) fabricated with single-walled carbon nanotubes and nafion composite film employing square wave voltammetry for the first time. The developed sensor exhibits effective and sustained electron mediating behavior displaying higher peak currents at lower potential than those obtained at bare GCE. At optimal experimental conditions, oxidation current showed a wide linear response for ACV in the concentration range from 10 nM to 30 µM. The proposed sensor exhibited pronounced analytical performance for the determination of ACV with limit of detection corresponding to 1.8 nM and high sensitivity of 15.4 µA µM-1. The modified sensor showcased high recognition selectivity, fair reproducibility and long term stability of signal response in the physiological environment. The developed prototype was successfully implemented to quantify ACV in several commercially available pharmaceuticals. The versatile method described herein was efficaciously applied further in detecting ACV in real human urine sample of patient undergoing pharmacological treatment with ACV. The results explicitly demonstrate the applicability of the developed sensor in quality control, pharmacokinetic studies and clinical analysis.

In Vitro and Clinical Evaluations of the Drug-Drug Interaction Potential of a Metabotropic Glutamate 2/3 Receptor Agonist Prodrug with Intestinal Peptide Transporter 1.

Despite peptide transporter 1 (PEPT1) being responsible for the bioavailability for a variety of drugs, there has been little study of its potential involvement in drug-drug interactions. Pomaglumetad methionil, a metabotropic glutamate 2/3 receptor agonist prodrug, utilizes PEPT1 to enhance absorption and bioavailability. In vitro studies were conducted to guide the decision to conduct a clinical drug interaction study and to inform the clinical study design. In vitro investigations determined the prodrug (LY2140023 monohydrate) is a substrate of PEPT1 with Km value of approximately 30 µM, whereas the active moiety (LY404039) is not a PEPT1 substrate. In addition, among the eight known PEPT1 substrates evaluated in vitro, valacyclovir was the most potent inhibitor (IC50 = 0.46 mM) of PEPT1-mediated uptake of the prodrug. Therefore, a clinical drug interaction study was conducted to evaluate the potential interaction between the prodrug and valacyclovir in healthy subjects. No effect of coadministration was observed on the pharmacokinetics of the prodrug, valacyclovir, or either of their active moieties. Although in vitro studies showed potential for the prodrug and valacyclovir interaction via PEPT1, an in vivo study showed no interaction between these two drugs. PEPT1 does not appear to easily saturate because of its high capacity and expression in the intestine. Thus, a clinical interaction at PEPT1 is unlikely even with a compound with high affinity for the transporter.

Hybrid molecularly imprinted polymers synthesized with 3-aminopropyltriethoxysilane-methacrylic acid monomer for miniaturized solid-phase extraction: A new and economical sample preparation strategy for determination of acyclovir in urine.

The miniaturized molecularly imprinted solid-phase extraction (mini-MISPE) coupled with high-performance liquid chromatography was proposed for the determination of acyclovir in urine. 1.5-mL tapered plastic centrifuge tube filled with hybrid molecularly imprinted polymers (HMIPs) was used as the cartridge of mini-MISPE, and the HMIPs synthesized with 3-aminopropyltriethoxy silane-methacrylic acid as monomer exhibited good recognition and selectivity for acyclovir. Under the optimized condition, good linear calibration was obtained in a range of 0.5-15µgmL(-1) with the correlation coefficient of 0.9994, and the recoveries at three spiked levels were 91.6-103.3% in urine with the relative standard deviation (RSD) of ≤3.5%. Excellent intra-day and inter-day repeatability were achieved with RSD of ≤2.6% and 4.0% in three different concentrations. This method combined the advantages of HMIPs and mini-MISPE, and it could become an alternative tool for analyzing the residues of acyclovir in complex urine matrices.

Electrochemical behavior of an antiviral drug acyclovir at fullerene-C(60)-modified glassy carbon electrode.

Electrochemical oxidation of acyclovir at fullerene-C(60)-modified glassy carbon electrode has been investigated using cyclic and differential pulse voltammetry. In pH 7.4 phosphate buffer, acyclovir showed an irreversible oxidation peak at about 0.96V. The cyclic voltammetric results showed that fullerene-C(60)-modified glassy carbon electrode can remarkably enhance electrocatalytic activity towards the oxidation of acyclovir. The electrocatalytic behavior was further exploited as a sensitive detection scheme for the acyclovir determination by differential pulse voltammetry. Effects of anodic peak potential (E(p)/V), anodic peak current (I(p)/µA) and heterogeneous rate constant (k(0)) have been discussed. Under optimized conditions, the concentration range and detection limit were 9.0×10(-8) to 6.0×10(-6)M and 1.48×10(-8)M, respectively. The proposed method was applied to acyclovir determination in pharmaceutical samples and human biological fluids such as urine and blood plasma as a real sample. This method can also be employed in quality control and routine determination of drugs in pharmaceutical formulations.

A qualitative study of participant adherence in a randomized controlled trial of herpes suppressive therapy for HIV prevention in Tanzania.

Poor participant adherence to treatment may contribute to lack of impact in some biomedical HIV prevention trials. This qualitative study explored adherence in a randomized controlled trial of herpes suppressive therapy to reduce HIV acquisition and infectivity among 1305 Tanzanian women. The trial found participants completed 72% of visits on treatment; 52-56% of women on treatment had > or = 90% adherence by pill count estimate; and between six and nine months 30/86 (35%) of urine samples from acyclovir recipients tested acyclovir negative, and 7/86 (8%) from placebo recipients tested acyclovir positive. Twenty in-depth interviews (IDIs) were conducted after 30 months with respondents randomly selected from "acyclovir negative" acyclovir recipients and "acyclovir positive" placebo recipients, or by preliminary pill count adherence categories ("under users," "good users," and "over users"). Almost all respondents reported appropriate adherence and positive trial attitudes, e.g., trusting staff, appreciating services, perceiving pills as beneficial. Fourteen understood placebo use, and six understood the trial purpose. Notably, 5/9 acyclovir recipients and 1/11 placebo recipients believed their pills had treated pre-existing sexually transmitted infections. Limited understanding did not negatively affect reported adherence. Reported adherence problems usually related to illness, travel, and/or family obligations (e.g., husband's disapproval). "Acyclovir positive" placebo recipients denied taking other participants' pills. The IDIs also did not resolve discrepant reports of pill loss or theft. Biomedical HIV interventions often have strong behavioral components that require close attention during intervention development, trial design, and process and impact evaluation. This study identified topics which warrant further consideration, including: information reinforcement and comprehension assessment throughout a trial for long-term participant understanding; involving partners in adherence promotion activities; strategizing with participants to maintain adherence during familial illnesses or other crises; and close monitoring, identification, and follow-up of (1) individuals with discrepant biological tests, and (2) other sources of the treatment in the trial area. Methodological research is also needed to improve adherence measures.

Measurement and predictors of adherence in a trial of HSV suppressive therapy in Tanzania.

This study estimates adherence and identifies predictors of good adherence among 1305 Tanzanian women participating in a randomised, double-blind, placebo-controlled trial of HSV suppressive therapy to reduce HIV incidence or genital HIV shedding. Women were randomised to acyclovir 400mg BD or placebo and followed every three months for 12-30 months. Adherence was assessed by tablet counts. Random urine samples, collected between 6 and 24 months, were tested for acyclovir. At 12, 24 and 30 month visits, 56%, 52% and 54% of women on treatment had adherence >or=90%, respectively. Factors independently associated with good adherence (taking >or=90% of tablets in the preceding 3-months) included older age, understanding trial concepts at enrolment, living >2 years in the screening site, receiving an unannounced tablet check visit, using oral contraception at screening, living in the same site and house as the previous visit, accessing VCT during the trial, recent malaria and not having a positive pregnancy test. Overall, 55% of urine samples from women randomised to acyclovir had detectable acyclovir. Additional, tailored adherence strategies may be needed for younger, more mobile women and those who have not used oral contraception, which may sensitise them to daily tablet-taking. Use of biomarkers may alert investigators to adherence problems.

Effects of non-steroidal anti-inflammatory drugs on the pharmacokinetics and elimination of aciclovir in rats.

This study aims to investigate the effect of commonly used non-steroidal anti-inflammatory drugs (NSAIDs) on the pharmacokinetics and the renal elimination of aciclovir in rats. Pharmacokinetic parameters were determined following an intravenous administration of aciclovir (5 mg kg(-1)) to rats in the presence and absence of ketoprofen or naproxen (25 mg kg(-1)). Compared with the control (given aciclovir alone), pre-treatment with ketoprofen or naproxen 30 min before aciclovir administration significantly altered the pharmacokinetics of aciclovir. Renal clearance of aciclovir was reduced by approximately two fold in the presence of ketoprofen or naproxen. Consequently, the systemic exposure (AUC) to aciclovir in the rats pre-treated with ketoprofen or naproxen was significantly (P < 0.05) higher than that from the control group given aciclovir alone. Furthermore, the mean terminal plasma half-life of aciclovir was enhanced by 4-5 fold by pre-treatment with ketoprofen or naproxen. These results suggest that NSAIDs, such as ketoprofen and naproxen, are effective in altering the pharmacokinetics of aciclovir by inhibiting the organic anion transporter-mediated tubular secretion of aciclovir. Therefore, concomitant use of ketoprofen or naproxen with aciclovir should require close monitoring for clinical consequence of potential drug interaction.

Acyclovir concentrations in human breast milk after valaciclovir administration.

OBJECTIVE: The purpose of this study was to determine the valaciclovir and acyclovir pharmacokinetic profiles in serum and breast milk after valaciclovir administration to women after delivery. STUDY DESIGN: Valaciclovir (500 mg twice daily for 7 days) was given to 5 women after delivery who were breast-feeding healthy term infants. Matched serum and breast milk samples were obtained after the initial dose, on day 5 and 24 hours after the drug was discontinued. Infant urine was obtained on day 5. RESULTS: Valaciclovir was rapidly converted to acyclovir. The peak serum acyclovir concentration occurred 3 hours before the peak breast milk concentration (2.7 microg/mL at 1 hour vs 4.2 microg/mL at 4 hours). The serum acyclovir elimination half-life was 2.3 hours. The ratio of breast milk to serum acyclovir concentration was highest 4 hours after the initial dose at 3.4 and reached steady state ratio at 1.85. The median infant urine acyclovir concentration at steady state was 0.74 microg/mL. CONCLUSION: Valaciclovir is rapidly converted to acyclovir and concentrates in breast milk. However, the amount of acyclovir in breast milk after valaciclovir administration is considerably less (2%) than that used in therapeutic dosing of neonates.

Rapid determination of valaciclovir and acyclovir in human biological fluids by high-performance liquid chromatography using isocratic elution.

A rapid high-performance liquid chromatographic assay with isocratic elution is developed for the simultaneous quantification of valaciclovir (VACV) prodrug and its active converted compound, acyclovir (ACV), in biological fluids of treated patients. For serum, the samples are deproteinized with perchloric acid in presence of 1-methylguanosine as the internal standard (IS). For urine and dialysis liquid, the samples are diluted with a mobile phase containing the IS, then filtered. VACV, ACV and the IS are separated on a SymmetryShield RP-8 column with acetonitrile-ammonium phosphate buffer as the mobile phase and detected at 254 nm. The chromatographic time is about 12 min. The relative standard deviations (RSD) of VACV and ACV standards are between 0.5 and 3.5%. Most endogenous nucleosides and their metabolites, psychotropic drugs and drugs of abuse are shown not to interfere with this technique. The method has been applied to study the pharmacokinetics of VACV and ACV in serum, dialysis liquid and urine of renal failure patients on continuous ambulatory peritoneal dialysis (CAPD) under oral treatment of VACV.

Determination of acyclovir and its metabolite 9-carboxymethoxymethylguanine in serum and urine using solid-phase extraction and high-performance liquid chromatography.

A reversed-phase ion-pair high-performance liquid chromatography method for the determination of acyclovir and its metabolite 9-carboxymethoxymethylguanine is described. The sample are purified by reversed-phase solid-phase extraction. The components are separated on a C18 column with a mobile phase containing 18% acetonitrile, 5 mM dodecyl sulphate and 30 mM phosphate buffer, pH 2.1, and measured by fluorescence detection using an excitation wavelength of 285 nm and an emission wavelength of 380 nm. Detection limits are 0.12 microM (plasma) and 0.60 microM (urine) for acyclovir, and 0.26 microM (plasma) and 1.3 microM (urine) for metabolite. Correlation coefficients that were better than 0.998 were obtained normally. This analytical method, which enables simultaneous measurement of parent compound and metabolite, has been used in kinetics studies and for therapeutic drug monitoring in different patient groups with variable degrees of renal dysfunction.

In vivo evaluation of acyclovir prodrug penetration and metabolism through rat skin using a diffusion/bioconversion model.

PURPOSE: In order to evaluate the in vivo penetration of prodrugs which undergo metabolism in skin, we analyzed the in vivo penetration profiles of acyclovir prodrugs based on a two-layer skin diffusion model in consideration of metabolic process. METHODS: Acyclovir prodrugs (e.g., valerate, isovalerate and pivarate) were used as model prodrugs and the amounts excreted in urine were measured after percutaneous application. In vivo penetration profiles were then estimated by employing a deconvolution method and the penetration of acyclovir prodrugs was analyzed using a diffusion model. Subsequently, diffusion, partitioning and metabolic parameters were compared under in vitro and in vivo conditions. RESULTS: Although total penetration amounts at the end of the experiment were similar for the three prodrugs, the ratio of intact prodrug to total penetration amount differed significantly. Moreover, the excretion and absorption profiles were also very different for each prodrug. Enzymatic hydrolysis rate constants calculated under in vivo conditions were considerably larger than those obtained in the skin homogenate and in vitro penetration experiments. CONCLUSIONS: The present skin diffusion/bioconversion model combined with computer analysis enables us to comprehensively account for diffusion, partitioning and metabolism during in vivo percutaneous absorption. Nevertheless, different enzymatic hydrolysis rate constants obtained under both in vivo and in vitro conditions demonstrate the difficulty of obtaining accurate values for in vivo enzymatic activity from related in vitro experiments.

Comparison of high performance capillary electrophoresis and liquid chromatography for the determination of acyclovir and guanine in pharmaceuticals and urine.

High-performance capillary electrophoresis (HPCE) and high-performance liquid chromatography (HPLC) were developed and applied to the determination of acyclovir (ACV) and guanine (G) in pharmaceuticals. The comparison study showed that two methods gave comparable results in linear range, recovery and reproducibility. HPCE was used for the determination of ACV and G in urine; the recovery was better than 81.3% and the RSD was less than 4.4%.

Hemodialysis removal of acyclovir.

A 59-y-old with a history of chronic renal failure on hemodialysis was diagnosed with herpes zoster and begun on 800 mg acyclovir 5 times daily. Two days later the patient developed visual hallucinations, ataxia, confusion and memory loss along with focal myoclonus, nausea and vomiting. No fever, elevated WBC count or significant electrolyte imbalance was found. CT scan of the brain was unremarkable. The patient was then dialyzed for presumed acyclovir toxicity. Her acyclovir level was later found to have been 3.4 micrograms/ml (normal peak range 0.4-2 micrograms/ml) prior to dialysis. After 3 h of hemodialysis, her post-dialysis acyclovir level was 1.9 micrograms/ml. After a second course of hemodialysis the next day the patient's mental status improved, and she was discharged 5 d later. Due to its low volume of distribution (0.6 L/kg), low protein binding (about 15%) and water solubility, acyclovir is an example of the ideal drug that can be removed by hemodialysis. About 45% of the total body amount can be extracted through a 3-h course of hemodialysis with resultant improvement in symptoms.

Pharmacokinetics of famciclovir in subjects with chronic hepatic disease.

The pharmacokinetic profile of penciclovir was determined after a single 500-mg dose of its oral precursor, famciclovir, in 9 healthy volunteers and in 14 patients with chronic hepatic disease. Plasma and urine samples were analyzed for concentrations of penciclovir and 6-deoxy-penciclovir using a reverse-phase high-performance liquid chromatography (HPLC) method. Famciclovir was not quantifiable in patients with hepatic disease, and 6-deoxy-penciclovir was quantifiable in only a limited number of specimens. The extent of systemic availability of penciclovir, as measured by AUC0-infinity, was similar in patients with hepatic disease and in healthy subjects. In contrast, Cmax was significantly lower (average decrease of 43%) in subjects with hepatic disease relative to healthy normal subjects. Median Tmax for subjects with hepatic disease was significantly increased (by 0.75 hours) compared with subjects with normal liver function. These data suggest a decrease in the rate, but not the extent, of systemic availability of penciclovir in patients with hepatic disease. It should be unnecessary to modify the dose of famciclovir for subjects with compensated hepatic disease and normal renal function.

In vivo and in vitro analysis of skin penetration enhancement based on a two-layer diffusion model with polar and nonpolar routes in the stratum corneum.

In vitro and in vivo skin penetration of three drugs with different lipophilicities and the enhancing effects of 1-geranylazacycloheptan-2-one (GACH) were studied in rats. In vivo drug absorption profiles obtained by deconvolution of urinary excretion profiles were compared to the corresponding in vitro data obtained with a diffusion experiment. In vivo skin penetration of lipophilic butylparaben was considerably greater than that observed in vitro, while hydrophilic mannitol and acyclovir showed low penetration in both systems without GACH pretreatment. On the other hand, GACH enhanced mannitol and acyclovir penetration, especially in the in vivo system. Analysis of absorption profiles, using a two-layer skin model with polar and nonpolar routes in the stratum corneum, suggested that the diffusion length of a viable layer (viable epidermis and dermis) was shorter in vivo than in vitro and the effective area of the polar route in the stratum corneum was larger in vitro without GACH pretreatment. GACH increased the partitioning of acyclovir into the nonpolar route to the same extent in both systems. In addition, GACH increased the effective area of the polar route in vivo, probably because of enhanced water permeability; however, this effect was smaller in vitro since the stratum corneum was already hydrated even without GACH pretreatment.

Metabolic disposition of the acyclovir prodrug valaciclovir in the rat.

The prodrug valaciclovir demonstrated good oral absorption, rapid distribution and elimination, and extensive biotransformation to acyclovir in male CD rats. The mean urinary excretion of radioactivity following oral and intravenous administration of [8-14C]valaciclovir (25 mg/kg) was 65% and 95% of the dose, respectively. Acyclovir was the predominant radiolabeled urinary metabolite accounting for 57% and 65% of the dose, respectively, with valaciclovir accounting for 2% and 23% of the dose, respectively. Radioactivity from an oral dose of [8-14C]valaciclovir (10 mg/kg) was distributed to all 14 tissues examined 20 min postdose. The stomach, small intestine, kidney, liver, lymph nodes, and skin received the highest exposure to radioactivity, and the brain received the lowest exposure. Radioactivity in most tissues cleared by 24 hr postdose, and that in urine and feces accounted for essentially all of the administered dose by 48 hr postdose. Acyclovir derived from valaciclovir (10 and 25 mg/kg) exhibited dose-independent pharmacokinetics. The Cmax and AUC for acyclovir achieved with orally administered valaciclovir were 8- and 4-fold higher, respectively, than those estimated for an equivalent dose of acyclovir. The half-life of acyclovir derived from valaciclovir was approximately 1 hr, whereas that of valaciclovir was approximately 7 min. Valaciclovir was more efficiently metabolized when administered orally, indicating first-pass intestinal and/or hepatic metabolism. Rapid hydrolysis of valaciclovir in rat liver and intestinal homogenates further suggested the significance of presystemic metabolism. These studies indicate that valaciclovir is an efficient acyclovir prodrug particularly suited for oral administration.

Metabolic fate and pharmacokinetics of the acyclovir prodrug valaciclovir in cynomolgus monkeys.

Valaciclovir, the L-valyl ester of acyclovir (ZOVIRAX), demonstrated good oral absorption and nearly complete conversion to acyclovir in cynomolgus monkeys, indicating its suitability as an orally administered prodrug. The major urinary metabolites of [8-14C]valaciclovir, administered orally (10 and 25 mg/kg) or intravenously (10 mg/kg) to male monkeys, were acyclovir (46%-59% of urinary radioactivity), 8-hydroxyacyclovir (25%-30%), and 9-(carboxymethoxymethyl)guanine (CMMG) (11%-12%). Following oral and intravenous dosing, intact prodrug accounted for only 0.5% and 6% of urinary radioactivity, respectively. Dose-independent kinetics were observed for acyclovir derived from orally administered [8-14C]valaciclovir at the 10 and 25 mg/kg dose levels, with both AUC (24 and 60 microM.hr, respectively) and Cmax (8 and 23 microM, respectively) increasing nearly in proportion to the dose. Acyclovir was present in plasma at all sampling times (5 min to 7 hr postdose) after both oral doses, whereas the prodrug was not detected following either oral dose. The elimination of acyclovir after oral administration was monophasic, with an apparent half-life of 1.3-1.5 hr. Similar to acyclovir, both 8-hydroxyacyclovir and CMMG demonstrated dose-independent kinetics with apparent elimination half-lives of 1-1.6 hr. Intravenously administered [8-14C]valaciclovir (10 mg/kg) was rapidly converted to acyclovir, with the elimination half-life of acyclovir (0.9 hr) being 1.5-fold that of the prodrug (0.6 hr). The oral bioavailability of acyclovir derived from valaciclovir in cynomolgus monkey was 67 +/- 13%, representing a significant improvement over the limited bioavailability after acyclovir administration to primates.

Linear pharmacokinetics of penciclovir following administration of single oral doses of famciclovir 125, 250, 500 and 750 mg to healthy volunteers.

Twenty healthy male volunteers received single oral doses of famciclovir (125-750 mg), in a randomized, single-blind, crossover study. Plasma and urine concentrations of penciclovir and its 6-deoxy precursor, BRL 42359, were determined and penciclovir plasma concentration-time data submitted to model-independent pharmacokinetic analysis. Peak plasma concentrations of penciclovir were obtained at median times of 0.5-0.75 h after dosing. The areas under the concentration versus time curves (AUC) and the peak penciclovir concentration (Cmax) increased linearly with dose of famciclovir. Time to Cmax, elimination half-life, urinary recovery and renal clearance of penciclovir did not change with increasing dose. Famciclovir was excreted via the kidneys as penciclovir (60%) and BRL 42359 (5%), respectively. Famciclovir was well tolerated by all subjects with a low incidence of adverse effects. In conclusion, penciclovir thus displays linear pharmacokinetics in the anticipated therapeutic dose range of famciclovir.