Human pharmacokinetics and tolerance of oral ganciclovir

Ganciclovir

Ganciclovir is synthetic nucleoside analog of guanine closely related to acyclovir but has greater activity against cytomegalovirus. This comprehensive profile on ganciclovir starts with a description of the drug: nomenclature, formulae, chemical structure, elemental composition, and appearance. The uses and application of the drug are explained. The methods that were used for the preparation of ganciclovir are described and their respective schemes are outlined. The methods which were used for the physical characterization of the dug are: ionization constant, solubility, X-ray powder diffraction pattern, crystal structure, melting point, and differential scanning calorimetry. The chapter contains the spectra of the drug: ultraviolet spectrum, vibrational spectrum, nuclear magnetic resonance spectra, and the mass spectrum. The compendial methods of analysis of ganciclovir include the United States Pharmacopeia methods. Other methods of analysis that were reported in the literature include: high-performance liquid chromatography alone or with mass spectrometry, electrophoresis, spectrophotometry, voltammetry, chemiluminescence, and radioimmunoassay. Biological investigation on the drug includes: pharmacokinetics, metabolism, bioavailability, and biological analysis. Reviews on the methods used for preparation or for analysis of the drug are provided. The stability of the drug in various media and storage conditions is reported. More than 240 references are listed at the end of the chapter.

Inhibition of Duck Hepatitis B Virus Replication in vivo by the Nucleoside Analogue Ganciclovir (9-[2-hydroxy-1-(hydroxymethyl) ethoxymethyl] Guanine)

Treatment of ducks congenitally infected with the duck hepatitis B virus (DHBV) using the guanosine analogue ganciclovir resulted in prompt and profound inhibition of viral DNA replication in serum and liver. By the end of the treatment period all the replicative intermediates, except the supercoiled DNA form, could not be detected. Within 2 weeks of cessation of treatment viral replication returned and, in some cases, rebound occurred. Sequential treatment with prednisolone followed by ganciclovir also resulted in inhibition of viral replication and, even though relapse was observed after therapy was discontinued, the rebound phenomenon was reduced. Ganciclovir significantly and selectively inhibited DHBV DNA replication but may be more efficacious if used in combination with compounds targeted to the viral supercoiled DNA form.

Possible interaction of quinolone antibiotics with peptide transporter 1 in oral absorption of peptide-mimetic drugs

The study investigated whether quinolone antibiotics inhibit the PEPT1-mediated uptake of its substrates. Among the quinolones examined, lomefloxacin, moxifloxacin (MFLX) and purlifloxacin significantly inhibited the uptake of PEPT1 substrate phenylalanine-Ψ(CN-S)-alanine (Phe-Ψ-Ala) in HeLa/PEPT1 cells to 31.6 ± 1.3%, 27.6 ± 2.9%, 36.8 ± 2.2% and 32.6 ± 1.4%, respectively. Further examination showed that MFLX was an uncompetitive inhibitor, with an IC50 value of 4.29 ± 1.29 mm. In addition, MFLX significantly decreased the cephalexin and valacyclovir uptake in HeLa/PEPT1 cells. In an in vivo study in rats, the maximum plasma concentration (C(max)) of orally administered Phe-Ψ-Ala was significantly decreased in the presence of MFLX (171 ± 1 ng/ml) compared with that in its absence (244 ± 9 ng/ml). The area under the concentration-time curve (AUC) of orally administered Phe-Ψ-Ala in the presence of MFLX (338 ± 50 ng/ml · h) tended to decrease compared with that in its absence (399 ± 75 ng/ml · h). The oral bioavailability of Phe-Ψ-Ala in the presence and absence of MFLX was 41.7 ± 6.2% and 49.2 ± 9.2%, respectively. The results indicate that administration of quinolone antibiotics concomitantly with PEPT1 substrate drugs may potentially result in drug-drug interaction.

The Effect of Excipients on the Permeability of BCS Class III Compounds and Implications for Biowaivers

Purpose

Currently, the FDA allows biowaivers for Class I (high solubility and high permeability) and Class III (high solubility and low permeability) compounds of the Biopharmaceutics Classification System (BCS). Scientific evidence should be provided to support biowaivers for BCS Class I and Class III (high solubility and low permeability) compounds.

Methods

Data on the effects of excipients on drug permeability are needed to demonstrate that commonly used excipients do not affect the permeability of BCS Class III compounds, which would support the application of biowaivers to Class III compounds. This study was designed to generate such data by assessing the permeability of four BCS Class III compounds and one Class I compound in the presence and absence of five commonly used excipients.

Results

The permeability of each of the compounds was assessed, at three to five concentrations, with each excipient in two different models: Caco-2 cell monolayers, and in situ rat intestinal perfusion. No substantial increases in the permeability of any of the compounds were observed in the presence of any of the tested excipients in either of the models, with the exception of disruption of Caco-2 cell monolayer integrity by sodium lauryl sulfate at 0.1 mg/ml and higher.

Conclusion

The results suggest that the absorption of these four BCS Class III compounds would not be greatly affected by the tested excipients. This may have implications in supporting biowaivers for BCS Class III compounds in general.

Clinical pharmacokinetics and pharmacodynamics of ganciclovir and valganciclovir in children with cytomegalovirus infection

INTRODUCTION

Among infants and immunocompromised children cytomegalovirus (CMV) is associated with significant morbidity and mortality.

AREAS COVERED

This review describes the clinical pharmacokinetics and pharmacodynamics of ganciclovir and valganciclovir for the treatment and prevention of CMV infection in children.

EXPERT OPINION

A 24-h ganciclovir area under the concentration versus time curve (AUC₀₋₂₄) of 40 - 60 μg h/ml decreased the risk of CMV infection for adults undergoing CMV prophylaxis. For adults undergoing treatment for active CMV disease, a target AUC₀₋₁₂ of 40 - 60 μg h/ml has been suggested. The applicability of these targets to children remains uncertain; however, with the most sophisticated dosing regimens developed to date only 21% of patients are predicted to reach these targets. Moving forward, identification of optimal pediatric ganciclovir and valganciclovir dosing regimens may involve the use of an externally validated pediatric population pharmacokinetic model for empirical dosing, an optimal sampling strategy for collecting a minimal number of blood samples for each patient and Bayesian updating of the dosing regimen based on an individual patient's pharmacokinetic profile.

Pharmacokinetics of ganciclovir and valganciclovir in the adult horse

Equine herpes myeloencephalopathy, resulting from equine herpes virus type 1 (EHV-1) infection, is associated with substantial morbidity and mortality in the horse. As compared to other antiviral drugs, such as acyclovir, ganciclovir has enhanced potency against EHV-1. This study investigated the pharmacokinetics of ganciclovir and its oral prodrug, valganciclovir, in six adult horses in a randomized cross-over design. Ganciclovir sodium was administered intravenously as a slow bolus at a dose of 2.5 mg/kg, and valganciclovir was administered orally at a dose of 1800 mg per horse. Intravenously administered ganciclovir disposition was best described by a three-compartment model with a prolonged terminal half-life of 72 ± 9 h. Following the oral administration of valganciclovir, the mean observed maximum serum ganciclovir concentration was 0.58 ± 0.37 μg/mL, and bioavailability of ganciclovir from oral valganciclovir was 41 ± 20%. Superposition predicted that oral dosing of 1800-mg valganciclovir two times daily would fail to produce and maintain effective plasma concentrations of ganciclovir. However, superposition suggested that i.v. administration of ganciclovir at 2.5 mg/kg every 8 h for 24 h followed by maintenance dosing of 2.5 mg/kg every 12 h would maintain effective ganciclovir serum concentrations in most horses throughout the dosing interval.

Antiviral therapies in children: has their time arrived?

The increase in the number and classes of antiviral agents that has occurred since the 1980s is remarkable. The rapid expansion in therapeutic options for previously untreatable illnesses challenges clinicians to gain familiarity and experience with these new drugs, especially with regard to their use in children. This article describes the clinical utilities, pharmacokinetics, and adverse effects of these new drugs to empower practitioners to use them appropriately.

Intestinal solute carriers: an overview of trends and strategies for improving oral drug absorption

A large amount of absorptive intestinal membrane transporters play an important part in absorption and distribution of several nutrients, drugs and prodrugs. The present paper gives a general overview on intestinal solute carriers as well as on trends and strategies for targeting drugs and/or prodrugs to these carriers in order to increasing oral bioavailability and distribution. A number of absorptive intestinal transporters are described in terms of gene and protein classification, driving forces, substrate specificities and cellular localization. When targeting absorptive large capacity membrane transporters in the small intestine in order to increase oral bioavailabilities of drug or prodrug, the major influence on in vivo pharmacokinetics is suggested to be dose-dependent increase in bioavailability as well as prolonged blood circulation due to large capacity facilitated absorption, and renal re-absorption, respectively. In contrast, when targeting low-capacity transporters such as vitamin transporters, dose independent saturable absorption kinetics are suggested. We thus believe that targeting drug substrates for absorptive intestinal membrane transporters could be a feasible strategy for optimizing drug bioavailability and distribution.

Antiviral therapy for cytomegalovirus infections in pediatric patients

Appreciation of the spectrum of illness caused by cytomegalovirus (CMV) infections has increased markedly during the past 2 decades. The number of immunosuppressed patients also has increased during the same time period, reflecting the central tenet that CMV disease is most severe in this patient population. Fortunately, antiviral therapies with activity against CMV also have been identified during this same time course, and they include ganciclovir, foscamet, and cidofovir. Although all 3 of these therapies can have significant toxicities associated with them, nonetheless they are employed with relative frequency to treat potentially life-threatening CMV disease. Ganciclovir is the first-line compound used, followed by foscarnet and cidofovir. This article summarizes those CMV infections that require antiviral therapy and outlines therapeutic options for each.

Separation methods for acyclovir and related antiviral compounds

Acyclovir (ACV) is an antiviral drug, which selectively inhibits replication of members of the herpes group of DNA viruses with low cell toxicity. Valaciclovir (VACV), a prodrug of ACV is usually preferred in the oral treatment of viral infections, mainly herpes simplex virus (HSV). Also other analogues such as ganciclovir and penciclovir are discussed here. The former acts against cytomegalovirus (CMV) in general and the latter against CMV retinitis. The action mechanism of these antiviral drugs is presented briefly here, mainly via phosphorylation and inhibition of the viral DNA polymerase. The therapeutic use and the pharmacokinetics are also outlined. The measurement of the concentration of acyclovir and related compounds in biological samples poses a particularly significant challenge because these drugs tend to be structurally similar to endogenous substances. The analysis requires the use of highly selective analytical techniques and chromatography methods are a first choice to determine drug content in pharmaceuticals and to measure them in body fluids. Chromatography can be considered the procedure of choice for the bio-analysis of this class of antiviral compounds, as this methodology is characterised by good specificity and accuracy and it is particularly useful when metabolites need to be monitored. Among chromatographic techniques, the reversed-phase (RP) HPLC is widely used for the analysis. C18 Silica columns from 7.5 to 30 cm in length are used, the separation is carried out mainly at room temperature and less than 10 min is sufficient for the analysis at 1.0-1.5 ml/min of flow-rate. The separation methods require an isocratic system, and various authors have proposed a variety of mobile phases. The detection requires absorbance or fluorescence measurements carried out at 250-254 nm and at lambdaex=260-285 nm, lambdaem=375-380 nm, respectively. The detection limit is about 0.3-10 ng/ml but the most important aspect is related to the sample treatment, mainly when body fluids are under examination. The plasma samples obtained from human blood are pre-treated with an acid or acetonitrile deproteinization and the supernatant after centrifugation is successively extracted before RP-HPLC injection. Capillary Electrophoresis methods are also discussed. This new analytical approach might be the expected evolution, in fact the analyses are improved with regard to time and performance, in particular coated capillary as well as addition of stabilisers have been employed. The time of analysis is shortened arriving at less than half a minute. Furthermore by using an electrochemical detection, and having a calibration linearity in the range of 0.2-20.0 ng/ml, the detection limit is 0.15 microg/ml. The measurements of acyclovir and penciclovir have been presented but in the future other related drugs will probably be available using CE methods.

Ganciclovir pharmacokinetics and cytokine dynamics in renal transplant recipients with cytomegalovirus infection

Ganciclovir is considered to be the first-line treatment for cytomegalovirus (CMV) in renal transplant recipients. This infection is also associated with elevations of specific plasma cytokines post-transplantation. To investigate daily cytokine response to therapy and ganciclovir pharmacokinetics, 4 transplant recipients (3 males, 1 female) with stable renal allograft function diagnosed with CMV infection were enrolled less than 4 months post-transplant. A creatinine clearance (ClCr) was generated by the Cockroft-Gault (C-G) equation (range: 42.3-68.5 mL/min) to determine ganciclovir dosing. Blood samples were collected for ganciclovir and cytokine [including interleukin (IL)-1beta, IL-2, IL-3, IL-4, IL-6, IL-8, IL-10, TNF-alpha, GM-CSF, and interferon (IFN)-gamma analyses after 7 d of intravenous (i.v.) ganciclovir (dosage range: 165-400 mg daily) therapy and again after 7 d of oral (p.o.) ganciclovir (dosage range: 1000 mg, 2-3 times daily) therapy. Pharmacokinetic ganciclovir was described with a two-compartment model. Total clearance of ganciclovir was consistently greater than ClCr, suggesting tubular secretion. Peak concentrations for i.v. ganciclovir averaged 8.39+/-1.87 microg/mL with minimum concentrations of 0.48+/-0.35 microg/mL. Plasma concentrations were lower but more sustained during a p.o. dosing interval (max=2.12+/-0.58 microg/mL, min=1.15+/-0.34 microg/mL). IL-6, IL-8, IL-10, and TNF-alpha were detectable at multiple times during the study periods while the remainder of the cytokines were only intermittently detectable. Average concentrations (i.v. versus p.o. study period) for TNF-alpha were 40.1+/-17.5 versus 22.1+/-11.2 pg/mL, for IL-8 were 17.1+/-15.6 versus 4.12+/-2.59 pg/mL, and for IL-10 were 7.39+/-5.54 versus 2.64+/-1.06 pg/mL. Concentrations were similar for IL-6 during both studies (9.39+/-5.42 versus 14.7+/-14.8 pg/mL). TNF-alpha, IL-8, and IFN-gamma appeared to correlate with CMV antigenemia. Further investigation of ganciclovir disposition and changes in plasma cytokines in renal transplant recipients during CMV infection may provide insight into variable antiviral responses in renal transplant recipients.

Evaluation of human intestinal absorption data and subsequent derivation of a quantitative structure–activity relationship (QSAR) with the Abraham descriptors

The human intestinal absorption of 241 drugs was evaluated. Three main methods were used to determine the human intestinal absorption: bioavailability, percentage of urinary excretion of drug-related material following oral administration, and the ratio of cumulative urinary excretion of drug-related material following oral and intravenous administration. The general solvation equation developed by Abraham's group was used to model the human intestinal absorption data of 169 drugs we considered to have reliable data. The model contains five Abraham descriptors calculated by the ABSOLV program. The results show that Abraham descriptors can successfully predict human intestinal absorption if the human absorption data is carefully classified based on solubility and administration dose to humans.

In vitro and in vivo activity of 1-O-hexadecylpropanediol-3-phospho-ganciclovir and 1-O-hexadecylpropanediol-3-phospho-penciclovir in cytomegalovirus and herpes simplex virus infections

Human cytomegalovirus (HCMV) and herpes simplex virus (HSV) can cause a wide variety of clinical manifestations in man. Ganciclovir (GCV) is effective against HCMV infection when administered by the intravenous route and may be used orally in large doses for prophylaxis of HCMV infections in organ transplantation patients and in AIDS patients. In previous studies with acyclovir (ACV), we found that covalent attachment of an alkyl glycerol phosphate moiety greatly increased oral bioavailability and increased antiviral activity against hepatitis B virus. Adducts of ACV with alkyl propanediol phosphate were more active than the alkyl glycerol phosphate analogue in vitro in 2.2.15 cells, which constitutively produce hepatitis B virus. To see if this strategy would work for two other poorly absorbed nucleoside analogues, we synthesized 1-O-hexadecylpropanediol-3-phospho-GCV (HDP-P-GCV) and 1-O-hexadecyl-propanediol-3-phospho-penciclovir (HDP-P-PCV), and evaluated the in vitro antiviral activity, selectivity and oral antiviral activity of both compounds versus GCV or PCV in mice infected with HSV-1 or HDP-P-GCV versus murine cytomegalovirus (MCMV). HDP-P-GCV is orally active in both MCMV and HSV-1 infection in mice with antiviral activity equivalent to (HSV-1) or greater than oral GCV (MCMV). Oral HDP-P-PCV was more active than PCV orally versus intranasal HSV-1 infection in mice.

Management and Prevention of Opportunistic Infections in the HIV-Infected Patient

With the introduction of potent antiretroviral therapy, the incidence of opportunistic infections (OIs) as well as death has dramatically decreased since 1996. Opportunistic infections are seen mainly in three groups: (1) newly diagnosed patients not receiving antiretroviral therapy and presenting with an OI, (2) patients nonadherent to antiretroviral and OI treatment regimens or (3) patients whose antiretroviral therapy has failed. This article will review the most common opportunistic infections (OIs) seen in the HIV-infected individual and their treatment. The current guidelines for the prophylaxis against these OIs will also be discussed.

Development of a sensitive method for the determination of ganciclovir by reversed-phase high-performance liquid chromatography

Ganciclovir is a nucleoside analogue widely used in the treatment of cytomegalovirus infections, which affects mainly immunocompromised patients. Recently, new pharmaceutical dosage forms based on the use of albumin nanoparticles have been developed for improving the efficacy of this drug. The aim of this study was to develop an analytical HPLC method for the determination of ganciclovir in both pharmaceuticals (i.e. albumin nanoparticles) and biological medium samples. The chromatography was performed on a reversed-phase encapped column (LiChrospher Select B C8) with a mobile phase consisting of acetonitrile in 0.05 M ammonium acetate (pH 6.5; 2: 98, v/v). Acyclovir was used as internal standard and the detection wavelength was 254 nm. The limit of quantitation of ganciclovir was 50 ng/ml and the average recoveries over a concentration range of 0.05-10 microg/ml ranged from 98 to 102%. Precision did not exceed 5%. In summary, this assay is a selective, sensitive and reproducible method for the determination of the ganciclovir in albumin nanoparticles. It can be successfully applied to the estimation of the ganciclovir uptake by cultured human corneal fibroblasts.

A rapid, sensitive HPLC method for the determination of ganciclovir in human plasma and serum

A method for ganciclovir determination in human serum and plasma has been developed and validated. The method has a lower limit of quantification (LLOQ) adequate for sensitive pharmacokinetic studies ( < or = 0.05 microg/ml), has run times of < or = 15 min, and uses aliquot volumes adequate for pediatric studies (0.25 ml). In the method, proteinaceous material in serum or plasma is precipitated by trichloroacetic acid. An aliquot of the supernatant is analyzed by HPLC; automated column switching removes late-eluting materials that might interfere with the analyte peak in subsequent runs. Detection and quantification of ganciclovir is by fluorescence (lambda(ex) = 278 nm; lambda(em) = 380 nm). The method has a validated range of 0.0400-4.00 microg/ml and an LLOQ of 0.0400 microg/ml. All intra- and inter-assay % C.V. values were < 8%; all recoveries (accuracy) were within 7% of nominal values. No interference was observed by mycophenolic acid or its glucuronide metabolite, by AZT, salicylic acid, acetaminophen, ibuprofen, naproxen prednisone, acyclovir, or cyclosporine. Ganciclovir is very stable in the samples and the extract during storage and sample processing. Both serum and plasma methods have been validated for use and have been successfully used to analyze samples from clinical studies.

Recovery of long-term natural protection against reactivation of CMV retinitis in AIDS patients responding to highly active antiretroviral therapy

OBJECTIVES

To see whether in severely immunosuppressed AIDS patients (with prior Cytomegalovirus retinal disease) who have significant increases in CD4+ lymphocytes following the initiation of highly active antiretroviral therapy (HAART) anti-Cytomegalovirus (CMV) maintenance therapy can be withdrawn with no subsequent progression of CMV retinitis.

METHODS

Eight patients with AIDS and one or more previous episodes of CMV retinitis interrupted anti-CMV maintenance therapy following the successful beginning of HAART. CD4 cell counts and HIV-RNA were monitored monthly while measurement of CMV antigenemia and ophthalmoscopy were carried every 2 weeks thereafter.

RESULTS

The HAART recipients in whom anti-CMV maintenance therapy had been interrupted had measureable increases of CD4+ T lymphocytes, substantial control of both HIV-RNA and CMV viraemia and did not show recurrence of retinitis during a mean follow-up of 98.4 weeks (range 78-120, SD 15.2).

CONCLUSIONS

Anti-CMV maintenance therapy can be interrupted with no subsequent progression of retinal damage over a long time in patients with AIDS who successfully respond to HAART with a significant increase in CD4 cell count.

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)purin es (1-8) and 2-amino-9-(3-alkoxycarbonyl-oxymethyl-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 degrees 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.

Single-dose pharmacokinetics of valganciclovir in HIV- and CMV-seropositive subjects

As a result of the low oral bioavailability of ganciclovir, a prodrug was developed to improve the bioavailability of ganciclovir. This study was designed to investigate the fasting, single-dose pharmacokinetics as well as the absolute and relative bioavailability of a valine ester prodrug of ganciclovir, valganciclovir, as compared to oral and intravenous ganciclovir in asymptomatic HIV+ and CMV+ subjects. In this open-label, randomized, three-period crossover study, 18 subjects received, in random order, single oral doses of valganciclovir 360 mg and ganciclovir 1000 mg and an intravenous infusion of ganciclovir 5 mg/kg over 1 hour. Valganciclovir was rapidly and extensively hydrolyzed to ganciclovir, resulting in significantly greater bioavailability compared to 1000 mg oral ganciclovir (60.9% vs. 5.6%, respectively). Higher peak serum concentrations were reached earlier following valganciclovir (ganciclovir [2.98 +/- 0.77 micrograms/mL at 1.0 +/- 0.3 h]) than following oral ganciclovir (0.47 +/- 0.17 microgram/mL and 2.2 +/- 1.0 h). Mean total ganciclovir AUCs following oral ganciclovir (1000 mg) and 360 mg valganciclovir (3.8 +/- 1.2 and 10.8 +/- 1.9 micrograms-h/mL) were less than that following a standard 5 mg/kg intravenous infusion of ganciclovir (25.1 +/- 3.8 micrograms-h/mL). In summary, valganciclovir is a prodrug with a favorable safety profile with enhanced bioavailability and significantly higher serum concentrations of ganciclovir than following oral administration of ganciclovir itself.

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 monoisobutyrate 11 was the most efficiently absorbed and metabolized to 7, showing the mean maximum total concentration of penciclovir (5.5 microg/mL) and 7 (10.8 microg/mL) in the blood was much higher than the mean maximum concentration of penciclovir (11.5 microg/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.

Synthesis and evaluation of amino acid esters of 6-deoxypenciclovir as potential prodrugs of penciclovir

The amino acid ester derivatives of 6-deoxypenciclovir, 11-20, were synthesized as potential prodrugs of penciclovir, and were evaluated for their oral penciclovir bioavailability in mice and rats. Esterification of 6-deoxypenciclovir with N-carbobenzyl-oxyglycine, -L-alanine, -L-valine, -L-leucine, or -L-isoleucine (3.75equiv.) using conventional coupling method (DCC/DMAP) afforded the mono-O-ester derivatives 1-5 in 47-55% yields as a mixture of two diastereomers along with the di-O-ester derivatives 6-10 in 20-29% yields. Reductive cleavage of carbobenzyloxy (Cbz) group (10% Pd/C, 1 atmosphere of H2, room temperature in methanol) followed by subsequent treatment of the resulting free amine with methanolic HCI solution provided the mono-O-ester derivatives 11-15 as di-HCl salt in 51-98% yields and the di-O-ester derivatives 16-20 as tri-HCl salt in 65 98% yields. Of the prodrugs tested in mice and rats, 6-deoxypenciclovir O-L-valinate (13), O-L-isoleucinate (15), and O,O-di-glycinate (16) showed significantly higher urinary recovery of penciclovir compared with that of penciclovir, but those are somewhat lower than that of famciclovir.

Effect of food on high-dose oral ganciclovir disposition in HIV-positive subjects

The effect of food on the steady-state pharmacokinetics of ganciclovir following high-dose oral ganciclovir in HIV- and CMV-seropositive subjects was investigated in an open-label, randomized, two-treatment crossover study. Over 2 consecutive weeks, subjects received in random order multiple oral doses of ganciclovir 2,000 mg tid for 3 consecutive days either on an "empty stomach " (i.e., at least 1 hour before or 2 hours after a meal or snack) or within 30 minutes of finishing a meal. For the 3 days of dosing each week, the breakfast consisted of a standardized 602 calorie, high-fat (46.5%) meal, while the contents of lunch, dinner, and snacks met American Dietetic Association recommendations (25%-35% fat). Serial blood samples over 24 hours were obtained on day 3 of each regimen over the first dosing interval. When ganciclovir was administered within 30 minutes following the breakfast, there was a mean increase of 110.6% +/- 79.0% and 114.1% +/- 81.7% in Cmax0-5 and AUC0-5, respectively, with a prolongation of mean Tmax from 1.8 to 2.7 hours. Over the total day of dosing, there was a mean increase of 47.6% +/- 12.3% and 97.2% +/- 30.9% in Cmax0-24 and AUC0-24, respectively, and a 36.0% +/- 18.0% decrease in half-life when doses were taken following a meal as compared to when taken on an empty stomach. Since food increases the systemic availability of ganciclovir, it is recommended that patients be instructed to take each dose of ganciclovir with food.

Effect of high-dose oral ganciclovir on didanosine disposition in human immunodeficiency virus (HIV)-positive patients

This study was designed to investigate the interaction between high-dose oral ganciclovir (6,000 mg/day) and didanosine at steady state in patients who were seropositive for human immunodeficiency virus (HIV) and cytomegalovirus (CMV) infection. The study was conducted as an open-label, randomized, three-period crossover study. Patients received (in random order) multiple oral doses of didanosine 200 mg every 12 hours alone, ganciclovir 2,000 mg every 8 hours alone, and ganciclovir 2,000 mg every 8 hours in combination with didanosine 200 mg every 12 hours. Blood and urine samples for determinations of drug concentrations were obtained on day 3 of each dose regimen. When ganciclovir was administered either before or 2 hours after didanosine, the mean increases in maximum concentration (Cmax), area under the concentration-time curve (AUC0-12), and percent excreted in urine of didanosine were 58.6% and 87.3%, 87.3% and 124%, and 100% and 153%, respectively. There were no statistically significant effects of didanosine on the steady-state pharmacokinetics of ganciclovir in the presence of didanosine, irrespective of sequence of administration. There were no significant changes in renal clearance of didanosine, suggesting that the mechanism for the interaction does not involve competition for active renal tubular secretion. The mechanism responsible for increased didanosine concentrations and percent excreted in urine during concurrent ganciclovir therapy may be a result of increased bioavailability of didanosine. However, the mechanism appears to be saturated at oral ganciclovir doses of 3 g/day.

Synthesis and evaluation of 2-amino-9-(3-hydroxymethyl-4-alkoxycarbonyloxybut-1-yl)purines as potential prodrugs of penciclovir

A series of 2-amino-9-(3-hydroxymethyl-4-alkoxycarbonyloxybut-1-yl)purines (4-10) and 2-amino-9-(2-(2-oxo-1,3-dioxan-5-yl)ethyl)purine (1) were synthesized as potential prodrugs of penciclovir and evaluated for their oral penciclovir bioavailability in mice and rats. Treatment of 2-(2-benzyloxyethyl)propane-1,3-diol (11) with 1,1'-carbonyldiimidazole in THF followed by hydrogenolytic removal of the benzyl group of the resulting cyclic carbonate 12 gave 5-(2-hydroxyethyl)-1,3-dioxan-2-one (13). Mesylation of the alcohol 13 and then a coupling reaction of the resulting mesylate 14 with 2-amino-6-chloropurine using anhydrous Cs2CO3 in DMF afforded 2-amino-6-chloro-9-(2-(2-oxo-1,3-dioxan-5-yl)ethyl)purine (16) after purification by flash column chromatography on silica gel using EtOAc/MeCN/Et3N as eluent. Hydrogenation of the 6-chloro cyclic carbonate 16 followed by a ring-opening reaction of the 6-deoxy cyclic carbonate 1 in a mixture of an appropriate alcohol and CHCl3 using activated SiO2 as a Lewis acid afforded the corresponding alkyl monocarbonate derivatives 3-10 in fair to good yields. Of the prodrugs tested in mice, the isopropyl monocarbonate 6 achieved the highest mean urinary recovery of penciclovir (53%), followed in order by the propyl monocarbonate 5 (51%), the isopentyl monocarbonate 10 (51%), the ethyl monocarbonate 4 (50%), and famciclovir (48%). In rats, the methyl monocarbonate 3, 4, 6, the n-butyl monocarbonate 7, and 10 (39-41%) showed levels of mean urinary recovery of penciclovir similar to that from famciclovir (40%). The alkyl monocarbonates 4-10 were found to be quite stable in the aqueous buffer solutions, and among them, 6 was the most stable with the half-lives (t1/2) of 88, >200, 61, and 26 days at pH 1.2, 6.0, 7.4, and 8.0, respectively. In addition, 6 was highly soluble in H2O (138.8 mg/mL, 20 degrees C).

Prediction of human intestinal absorption of drug compounds from molecular structure

The absorption of a drug compound through the human intestinal cell lining is an important property for potential drug candidates. Measuring this property, however, can be costly and time-consuming. The use of quantitative structure-property relationships (QSPRs) to estimate percent human intestinal absorption (%HIA) is an attractive alternative to experimental measurements. A data set of 86 drug and drug-like compounds with measured values of %HIA taken from the literature was used to develop and test a QSPR mode. The compounds were encoded with calculated molecular structure descriptors. A nonlinear computational neural network model was developed by using the genetic algorithm with a neural network fitness evaluator. The calculated %HIA (cHIA) model performs wells, with root-mean-square (rms) errors of 9.4%HIA units for the training set, 19.7%HIA units for the cross-validation (CV) set, and 16.0%HIA units for the external prediction set.

Pharmacokinetics of oral ganciclovir alone and in combination with zidovudine, didanosine, and probenecid in HIV-infected subjects

The aim of this study was to determine whether oral ganciclovir interacted pharmacokinetically with zidovudine (AZT), didanosine (ddI), or probenecid. A multicenter, open-label, randomized, crossover pharmacokinetic study with four phases was undertaken at an outpatient private research center and at university research clinics. Twenty-six HIV-infected adults (23 men, 3 women) with cytomegalovirus (CMV) seropositivity and CD4+ T-lymphocyte count > or =100 cells/microl were studied. Patients had to be stable on antiretroviral therapy for at least 4 weeks. Patients with a history of opportunistic infection or gastrointestinal symptoms were excluded. Measurements included serial blood and urine samples during the dosing intervals at steady state. The steady-state pharmacokinetics of ganciclovir were determined after the participants had stabilized and were tolerating AZT or ddI therapy. When a 1000-mg dose of oral ganciclovir was taken every 8 hours, there was a significant mean increase in Cmax and dosing interval area under the serum concentration time curve over a dosing interval (AUC) for the two antiretroviral drugs: for AZT, 61.6% and 19.5%, respectively; for ddI when administered sequentially (2 hours before ganciclovir), 116.0% and 114.6%; and for ddI administered simultaneously with ganciclovir, 107.9% and 107.1%, respectively. There was no significant change in renal clearance for either antiretroviral drug, suggesting that the interaction did not occur through a renal mechanism. There was no significant change in mean ganciclovir Cmax and AUC(0-8) when coadministered with AZT. Mean increases in Cmax and AUC(0-8) of oral ganciclovir averaged 40.1% and 52.5%, respectively, when coadministered with probenecid, but decreased by 22.1% and 22.7%, respectively, when oral ganciclovir was administered 2 hours after ddI. There was no change in the mean ganciclovir Cmax or AUC(0-8) when administered simultaneously with ddI. The mean renal clearance of oral ganciclovir was not affected by AZT or ddI coadministration intake, but there was a mean decrease of 19% when coadministered with probenecid. We conclude the increased serum concentration and reduced renal clearance of ganciclovir suggests competition with probenecid for secretion at the renal tubule. The mechanism of the interaction of oral ganciclovir with either AZT or ddI remains to be determined. The magnitude of the effect of oral ganciclovir on ddI pharmacokinetics may result in an increase in ddI concentration-related toxicities. Similarly, the small but significant decrease in ganciclovir concentration with sequential combination ddl therapy may impair the efficacy of oral ganciclovir. For HIV-infected patients receiving ganciclovir and ddI, clinicians should recommend administering the two drugs simultaneously, and patients should be monitored closely for ddI-associated toxicities.

Pharmacokinetics and absolute bioavailability of oral foscarnet in human immunodeficiency virus-seropositive patients

The pharmacokinetics, absolute bioavailability, accumulation, and tolerability over 8 days of an oral formulation of foscarnet (90 mg/kg of body weight once daily [QD] [n = 6], 90 mg/kg twice daily [BID] [n = 6], and 180 mg/kg QD [n = 31) were investigated in 15 asymptomatic, human immunodeficiency virus-seropositive male patients free of active cytomegalovirus infection and with normal upper gastrointestinal function. Peak plasma drug concentrations were (mean +/- standard deviation) 46.4 +/- 10.8 microM (90 mg/kg QD), 45.7 +/- 6.9 microM (90 mg/ kg BID), and 64.9 +/- 31.7 microM (180 mg/kg QD) on day 1 and rose to 86.2 +/- 35.8, 78.7 +/- 35.2, and 86.4 +/- 25.0 microM, respectively, on day 8. The mean peak concentration in plasma following the intravenous administration of foscarnet (90 mg/kg) was 887.3 +/- 102.7 microM (n = 13). The terminal half-life in plasma remained unchanged, averaging 5.5 +/- 2.2 h on day 1 (n = 15) and 6.6 +/- 1.9 h on day 8 (n = 13), whereas it was 5.7 +/- 0.7 h following intravenous dosing. Oral bioavailabilities were 9.1% +/- 2.2% (90 mg/kg QD), 9.5% +/- 1.7% (90 mg/kg BID), and 7.6% +/- 3.7% (180 mg/kg QD); the accumulation ratios on the 8th day of dosing were 2.1 +/- 1.1, 1.8 +/- 0.4, and 1.7 +/- 0.7, respectively. The overall 24-h urinary excretion of oral foscarnet averaged 7.8% +/- 2.6% (day 1) and 13.4% +/- 6.0% (day 8), whereas it was 95.0% +/- 4.9% after intravenous dosing. The glomerular filtration rate and creatinine clearance remained constant, and the mean 24-h renal clearances of foscarnet for the entire study group were 96 +/- 18 ml/min (day 1), 88 +/- 13 ml/min (day 8), and 103 +/- 16 ml/min after intravenous dosing. Adverse effects were largely confined to gastrointestinal disturbances, with all subjects experiencing diarrhea that was dose dependent in its severity. The results suggest that the formulation studied would require significant improvement with respect to tolerability and bioavailability to gain clinical acceptance.

Adverse effects and drug interactions of medications commonly used in the treatment of adult HIV positive patients

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New antiherpesvirus agents. Their targets and therapeutic potential

Of the large number of agents under development for the treatment of herpes virus infections [herpes simplex virus types 1 and 2 (HSV-1 and HSV-2), varicella zoster virus (VZV), cytomegalovirus (CMV), Epstein-Barr virus (EBV)], only ten have apparently reached clinical development. Aciclovir was approved for the treatment of HSV infections over 10 years ago, and it remains an important and reliable antiviral agent. Recent approvals in some countries of valaciclovir for VZV infection and famciclovir for both HSV and VZV infections demonstrate the rapidity of change in this field. Intravenous ganciclovir and foscarnet are approved for the treatment of CMV infection in the immunocompromised patient. Five of the antiherpetic drugs under current clinical development are nucleoside analogues or their prodrugs; another is a phosphorylated nucleoside (nucleotide). Four of the nucleoside agents-penciclovir, famciclovir, valaciclovir and lobucavir-are being developed for the management of HSV and VZV infections. Valaciclovir is also being developed for the prevention of CMV infections and famciclovir and lobucavir for the treatment of hepatitis B virus infection. Oral ganciclovir, lobucavir, ISIS 2922 and cidofovir are being developed for the suppression of CMV infections in immunocompromised patients. Sorivudine has been studied in VZV infections. n-Docosanol is under development for HSV infections, and cidofovir is being developed for both HSV and CMV infections, as well as for treatment of other viral diseases. Traditionally, the adverse effects associated with anti-CMV compounds have been more difficult to manage and are acceptable clinically only because of the severity of the underlying infection and lack of safer therapeutic alternatives. In general, toxicity issues continue to be problematic in the anti-CMV arena, although newer agents have improved the situation to some extent. In contrast, the safety of anti-HSV compounds has traditionally been excellent, establishing a safety standard that must be met by newer agents entering the field.

Curative potential of herpes simplex virus thymidine kinase gene transfer in rats with 9L gliosarcoma

The transfer of the gene coding for the thymidine kinase of the herpes simplex virus (HSV-tk), followed by ganciclovir (GCV) administration, has been described for the treatment of several types of cancer, especially brain tumors. We further studied the efficacy of this approach by using the 9L rat gliosarcoma model, and cells producing 5 x 10(3), 9 x 10(4), 3 x 10(5) HSV-tk retroviral particles per milliliter. Their stereotactic injection in 9L brain tumors and GCV treatment did not result in any increase of survival. To study a model of optimal in vivo transduction, we examined the survival of rats with tumors growing from 9L cells that had been previously transduced in vitro with the HSV-tk vectors (9LTk cells). We observed that GCV administration cured 26% (n = 42) of the animals with 9LTk brain tumors, with most of the relapsing tumors remaining HSV-tk positive. The increase of either the dose or the duration of GCV treatment did not improve the survival rate. But the cerebral localization of the tumor played an important role, because this survival rate reached 67% (n = 12) when similar tumors were growing subcutaneously. No or only marginal antitumoral responses were induced by the presence of a selectable marker gene in the HSV-tk vectors. These results demonstrate that in vitro HSV-tk gene transfer in 9L tumor cells, but not in vivo gene transfer, followed by GCV treatment, is able to cure rats at a rate that is higher for subcutaneous than for intracerebral tumors.

Efficacy of BMS-180194 against experimental cytomegalovirus infections in immunocompromised mice

A new antiviral nucleoside, BMS-180194 [1R-(1 alpha, 2 beta, 3 alpha)]- 2-amino-9[2,3-bis(hydroxymethyl)cyclobutyl]-1,9dihydro-6H-purin-6- one, is a broad spectrum antiviral agent. The antiviral effectiveness of BMS-180194 against murine cytomegalovirus (MCMV) infection in immunocompromised C57BL/6 mice was investigated and was compared to that of ganciclovir (GCV). LP-BM5 murine retrovirus complex-induced immunocompromised C57BL/6 mice were challenged with MCMV then treated intraperitoneally or per os with various doses of BMS-180194 ranging from 30 to 3 mg/kg/day. When administered intraperitoneally, BMS-180194 was effective against MCMV-mediated mortality in a dose-dependent manner demonstrating a 50% protective dose (PD50) of 3.12 mg/kg/day which was comparable to that of GCV. There was a marked reduction in organ MCMV titers in BMS-180194-treated animals (10-10,000- fold lower than the placebo controls). Similar findings were observed when the compound was administered orally. Interestingly, oral BMS-180194 demonstrated a similar antiviral efficacy as that obtained by the parental route of administration suggesting a high oral bioavailability of the compound. Oral ganciclovir treatment, however, required more than a 4-fold higher amount of GCV to confer the same degree of protection obtained by a parenteral route of administration. Oral BMS-180194 was also effective in reducing the organ MCMV titer in genetically severe combined immunodeficient (SCID) mice. The parenteral or oral antiviral efficacy of BMS-180194 was comparable to that of parenteral ganciclovir against MCMV infection in the present study. Doses of BMS-180194 employed in the present study showed no toxicity to mice. These results suggest that BMS-180194 may be of value as an oral antiviral agent for treatment of opportunistic CMV infections in immunocompromised individuals.

In vitro potency of inhibition by antiviral drugs of hematopoietic progenitor colony formation correlates with exposure at hemotoxic levels in human immunodeficiency virus-positive humans

Inhibition of in vitro colony formation of human hematopoietic progenitors (CFU-granulocyte-macrophage, burst-forming unit-erythroid) by the antiviral nucleoside drugs alovudine, zalcitabine, zidovudine, ganciclovir, stavudine, didanosine, lamivudine, and acyclovir was measured. Significant correlations between in vitro 50% inhibitory concentrations and the daily human exposures (area under the concentration-time curve from 0 to 24 h; in micromolar.hour) of these chronically administered drugs in human immunodeficiency virus-positive patients that induced neutropenia or anemia were demonstrated by both linear regression and Spearman rank-order analyses. These quantitative correlations allow estimation of the exposure at which bone marrow toxicity may occur with candidate compounds.

Simple reversed-phase high-performance liquid chromatography quantitation of ganciclovir in human serum and urine

A fast, simple, and cost-effective HPLC method for the quantitation of the antiviral drug ganciclovir is described. The serum samples are extracted with perchloric acid and neutralized with potassium phosphate buffer, and urine samples are diluted with distilled water. A reversed-phase column with isocratic elution by 15 mM potassium phosphate buffer (pH 2.5) containing 0.25% acetonitrile is used to separate ganciclovir; quantitation is by UV absorbance at 254 nm. Total turnaround time is 22 min; more than 3000 samples can be run on a single column without loss of peak quality. The limit of quantitation is 0.05 micrograms/ml. Recoveries varied from 91 to 107% with coefficients of variation ranging from 0.387 to 7.95%.