Pharmacokinetics and antiviral activity in simian varicella virus-infected monkeys of (R,S)-9-[4-hydroxy-2-(hydroxymethyl) butyl]guanine, an anti-varicella-zoster virus drug

Systematic Review of Antifungal-Induced Acute Liver Failure

Antifungals are effective antimicrobial agents broadly used in medical practice. Severe acute liver failure from oral or IV administration of antifungals is a rare but long-standing clinical challenge. We aimed to approximate the risk of clinical acute liver injury among users of oral antifungals in the general population. This review was completed based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Six articles were included, comprising case reports and cohort studies, after eliminating duplicate publications. No randomized control studies were found. In all studies, the duration of antifungal use was associated with significantly increased liver enzyme levels. Although it is not very common for patients on antifungals to develop acute liver failure, the prognosis is often good with swift discontinuation of the drug and proper treatment. Liver function evaluation before treatment and periodic monitoring every three to six weeks after commencement of treatment is suggested.

Inhibition of SIV and HIV-2 Replication in Cynomolgus Monkeys by (-)9-[4-Hydroxy-2-(Hydroxymethyl)-Butyl]Guanine (H2G)

The antiherpes compound (-)9-[4-hydroxy-2-(hydroxymethyl)butyl]guanine (H2G) has been found to suppress the multiplication of SIVsm and HIV-2 in cynomolgus monkeys. This was seen as a delay in the appearance of viral antigen in serum during the primary infection at drug concentrations of 3×10 mg kg−1 day−1 and higher, when H2G was given subcutaneously. These effects of H2G on SIVsm and HIV-2 replication in monkeys were similar to those observed using the same dose of 3′-azidothymidine (AZT). A complete prevention of HIV-2 infection was observed in one of four animals treated with 3×10 mg kg−1 day−1 of H2G. The enantiomeric mixture (+)H2G at 3×25 mg kg−1 day−1 also delayed the appearance of SIVsm antigen but the (+)enantiomer of H2G at 3×10 mg kg−1 day−1 had no effect on primary SIVsm infection in monkeys, indicating that only the (−)enantiomer (H2G) was inhibitory and that this effect was not influenced by the presence of the (+)enantiomer. No adverse effects on blood chemistry or haematology were observed in monkeys given 25 mg kg−1 day−1 of H2G for 9 weeks or 3×25 mg kg−1 day−1 for 10 days.

Antiviral Activity against VZV and HSV Type 1 and Type 2 of the (+) and (−) Enantiomers of (R,S)-9-[4-hydroxy-2-(hydroxymethyl)butyl]guanine, in Comparison to other Closely Related Acyclic Nucleosides

The separate (+) and (−) enantiomers of the acyclic guanosine analogue 9-[4-hydroxy-2-(hydroxymethyl)-butyl]guanine (2HM-HBG) were tested for inhibition of varicella-zoster virus (VZV), herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2). In all cases the (−) enantiomer was the most active enantiomer. The (+) enantiomer was 10 times less active than the racemate against VZV and inactive against HSV-1 and -2.

The parent compound, 9-(4-hydroxybutyl)guanine, containing an unbranched side chain, was inactive against VZV, whereas substitution with a hydroxymethyl group at the 2 or 3 position of the side chain conferred anti-VZV activity. The effect of hydroxymethyl substitution may increase the recognition of the compound by the VZV thymidine kinase by increasing its similarity to the natural substrate thymidine. Further substitution of the side chain of the parent compound with oxygen, fluorine or hydroxyl groups did not confer antiviral activity against VZV.

Two VZV strains were isolated which could be grown in the presence of high concentrations of 2HM-HBG and which were also cross-resistant to other nucleoside analogues. These strains induced very little viral thymidine kinase activity in infected cells and thus were probably deficient for a functional thymidine kinase.

2HM-HBG exhibited a persistent antiviral effect even after the nucleoside was removed from the medium of VZV-infected cells, whereas acyclovir did not show this effect.

Effect upon the anti-HIV Activity of 3′-Azido-3′-Deoxythymidine and 3′-Fluoro-3′-Deoxythymidine of Combination with anti-Herpes Nucleoside Analogues

The treatment of the severe and often life-threatening herpesvirus infections which commonly occur in AIDS patients is complicated by the need to treat simultaneously with drugs directed against the human immunodeficiency virus (HIV). Combining together different drugs in this way can lead to effects upon the activities of the individual drugs, such as synergism or antagonism. The effect upon the anti-HIV activity of 3′-azido-3′-deoxythymidine (AZT) and 3′-fluoro-3′-deoxythymidine (FLT) of combination with the anti-herpesvirus drugs 9-(1,3-dihydroxy-2-propoxymethyl-)guanine (DHPG; ganciclovir) and (-)-9-[4-hydroxy-2-(hydroxymethyl)butyl]guanine ([-]-2HM-HBG) was investigated.

Neither DHPG nor (-)-2HM-HBG showed antiviral activity against HIV-1 up to 50 [AM. When combined with AZT or FLT at ratios of antiherpes:anti-HIV drug of 10:1 or greater, both DHPG and (-)-2HM-HBG antagonized the anti-HIV activity of AZT and FLT. When combined at a lower ratio (1:1), there was no effect upon the anti-HIV activity of either AZT or FLT. The phosphorylation of FLT was found to be unchanged in the presence of DHPG or (-)-2HM-HBG, indicating that the mechanism of the antagonism was not owing to an effect of DHPG or (-)-2HM-HBG upon the metabolism of the anti-HIV drugs.

The results suggest that combination chemotherapy with the anti-herpes drugs DHPG/(-)-2HM-HBG and AZT/FLT should be used cautiously. The possibility of such antagonistic interactions should be borne in mind when considering the choice of drug and ratio for treatment of herpesvirus infections in AIDS patients on anti-HIV therapy.

Valomaciclovir versus valacyclovir for the treatment of acute herpes zoster in immunocompetent adults: a randomized, double-blind, active-controlled trial

Herpes zoster is a common infectious disease that can result in significant acute and chronic morbidity. The safety and efficacy of once-daily oral valomaciclovir (EPB-348) was evaluated for non-inferiority to 3-times daily valacyclovir, an approved therapy. In this study, 373 immunocompetent adults with onset of a herpes zoster rash within the preceding 72 hr were randomly assigned to receive one of four treatments for 7 days: (1) EPB-348 1,000 mg once-daily; (2) EPB-348 2,000 mg once-daily; (3) EPB-348 3,000 mg once-daily; or (4) valacyclovir 1,000 mg 3-times daily. A 20% margin was the reference for non-inferiority assessment. For the primary efficacy measure of time to complete crusting of the zoster rash by Day 28, non-inferiority criteria were met for once-daily EPB-348 2,000 mg and once-daily EPB-348 3,000 mg compared to 3-times daily valacyclovir. Additionally, EPB-348 3,000 mg significantly shortened the time to complete rash crusting by Day 28 compared to valacyclovir. For secondary efficacy measures, non-inferiority was achieved for the EPB-348 1,000 and 2,000 mg groups compared to the valacyclovir group for time to rash resolution by Day 28. No EPB-348 group was non-inferior to valacyclovir for time to cessation of new lesion formation or time to cessation of pain by Day 120, though no significant differences occurred between treatment groups. Nausea, headache, and vomiting were the most common adverse events. Based on these results, additional studies are warranted to define further EPB-348's potential as an effective and safe therapy for acute herpes zoster.

Macaque models of human infectious disease

Macaques have served as models for more than 70 human infectious diseases of diverse etiologies, including a multitude of agents—bacteria, viruses, fungi, parasites, prions. The remarkable diversity of human infectious diseases that have been modeled in the macaque includes global, childhood, and tropical diseases as well as newly emergent, sexually transmitted, oncogenic, degenerative neurologic, potential bioterrorism, and miscellaneous other diseases. Historically, macaques played a major role in establishing the etiology of yellow fever, polio, and prion diseases. With rare exceptions (Chagas disease, bartonellosis), all of the infectious diseases in this review are of Old World origin. Perhaps most surprising is the large number of tropical (16), newly emergent (7), and bioterrorism diseases (9) that have been modeled in macaques. Many of these human diseases (e.g., AIDS, hepatitis E, bartonellosis) are a consequence of zoonotic infection. However, infectious agents of certain diseases, including measles and tuberculosis, can sometimes go both ways, and thus several human pathogens are threats to nonhuman primates including macaques. Through experimental studies in macaques, researchers have gained insight into pathogenic mechanisms and novel treatment and vaccine approaches for many human infectious diseases, most notably acquired immunodeficiency syndrome (AIDS), which is caused by infection with human immunodeficiency virus (HIV). Other infectious agents for which macaques have been a uniquely valuable resource for biomedical research, and particularly vaccinology, include influenza virus, paramyxoviruses, flaviviruses, arenaviruses, hepatitis E virus, papillomavirus, smallpox virus, Mycobacteria, Bacillus anthracis, Helicobacter pylori, Yersinia pestis, and Plasmodium species. This review summarizes the extensive past and present research on macaque models of human infectious disease.

Simian varicella in old world monkeys

Simian varicella virus (SVV) causes a natural erythematous disease in Old World monkeys and is responsible for simian varicella epizootics that occur sporadically in facilities housing nonhuman primates. This review summarizes the biology of SVV and simian varicella as a veterinary disease of nonhuman primates. SVV is closely related to varicella-zoster virus, the causative agent of human varicella and herpes zoster. Clinical signs of simian varicella include fever, vesicular skin rash, and hepatitis. Simian varicella may range from a mild infection to a severe and life-threatening disease, and epizootics may have high morbidity and mortality rates. SVV establishes a lifelong latent infection in neural ganglia of animals in which the primary disease resolves, and the virus may reactivate later in life to cause a secondary disease corresponding to herpes zoster. Prompt diagnosis is important for control and prevention of epizootics. Antiviral treatment for simian varicella may be effective if administered early in the course of infection.

Antiviral prodrugs - the development of successful prodrug strategies for antiviral chemotherapy

Following the discovery of the first effective antiviral compound (idoxuridine) in 1959, nucleoside analogues, especially acyclovir (ACV) for the treatment of herpesvirus infections, have dominated antiviral therapy for several decades. However, ACV and similar acyclic nucleosides suffer from low aqueous solubility and low bioavailability following oral administration. Derivatives of acyclic nucleosides, typically esters, were developed to overcome this problem and valaciclovir, the valine ester of ACV, was among the first of a new series of compounds that were readily metabolized upon oral administration to produce the antiviral nucleoside in vivo, thus increasing the bioavailility by several fold. Concurrently, famciclovir was developed as an oral formulation of penciclovir. These antiviral 'prodrugs' thus established a principle that has led to many successful drugs including both nucleoside and nucleotide analogues for the control of several virus infections, notably those caused by herpes-, retro- and hepatitisviruses. This review will chart the origins and development of the most important of the antiviral prodrugs to date.

Mode of action of (R)-9-[4-hydroxy-2-(hydroxymethyl)butyl]guanine against herpesviruses

The activity, metabolism, and mode of action of (R)-9-[4-hydroxy-2-(hydroxymethyl)butyl]guanine (H2G) against herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) and varicella-zoster virus (VZV) were studied. Compared to acyclovir (ACV), H2G has superior activity against VZV (50% inhibitory concentration of 2.3 microM) and Epstein-Barr virus (50% inhibitory concentration of 0.9 microM), comparable activity against HSV-1, and weaker activity against HSV-2. The antiviral effect on HSV-1 showed persistence after removal of compound. H2G was metabolized to its mono-, di- and triphosphate derivatives in virus-infected cells, with H2G-triphosphate being the predominant product. Only small amounts of H2G-triphosphate were detected in uninfected cells (1 to 10 pmol/10(6) cells), whereas the level in HSV-1-infected cells reached 1,900 pmol/10(6) cells. H2G was a substrate for all three viral thymidine kinases and could also be phosphorylated by mitochondrial deoxyguanosine kinase. The intracellular half-life of H2G-triphosphate varied in uninfected (2.5 h) and infected (HSV-1, 14 h; VZV, 3.7 h) cells but was always longer than the half-life of ACV-triphosphate (1 to 2 h). H2G-triphosphate inhibited HSV-1, HSV-2, and VZV DNA polymerases competitively with dGTP (Ki of 2.8, 2.2, and 0.3 microM, respectively) but could not replace dGTP as a substrate in a polymerase assay. H2G was not an obligate chain terminator but would only support limited DNA chain extension. Only very small amounts of radioactivity, which were too low to be identified by high-performance liquid chromatography analysis of the digested DNA, could be detected in purified DNA from uninfected cells incubated with [3H]H2G. Thus, H2G acts as an anti-herpesvirus agent, particularly potent against VZV, by formation of high concentrations of relatively stable H2G-triphosphate, which is a potent inhibitor of the viral DNA polymerases.

Efficacy of (-)-9-[4-hydroxy-2-(hydroxymethyl)butyl]guanine in African green monkeys infected with simian varicella virus

(-)-9-[4-Hydroxy-2-(hydroxymethyl)butyl]guanine was evaluated for its efficacy in African green monkeys infected with simian varicella virus. Treatment by intramuscular injection was initiated 48 h after virus inoculation and was continued for 10 days; the treatment showed therapeutic effects on rash and viremia at dosages down to 1 mg/kg of body weight per day.

Screening for new agents

Screening for new antiviral drugs is concentrated on a search for inhibitors of the human immunodeficiency virus, herpesviruses, influenza virus, hepatitis B virus and rhinovirus. The first step in the process is usually the screening of virus-infected cell cultures followed by secondary screening in infected animals. The relevance of the different screening methods for predicting clinical efficacy is at present uncertain due to the low number of compounds evaluated in double-blind placebo-controlled clinical trials. As a consequence of the con-siderable activity in ongoing research on antiviral drugs the predictive value of the screening systems is expected to improve.

Improvement of the absorption of oral (R,S)-9-[4-hydroxy-2-(hydroxymethyl)butyl]guanine, an anti-varicella-zoster virus drug, in rats and monkeys

In an effort to improve the gastrointestinal absorption of (R,S)-9-[4-hydroxy-2-(hydroxymethyl)butyl]guanine [(+/-)2HM-HBG], various salts and esters of the compound were synthesized and pharmacokinetic experiments were performed in rats and monkeys. The sodium or hydrochloride salts and short-chain esters of (+/-)2HM-HBG showed bioavailability characteristics that were equally as poor as those of (+/-)2HM-HBG. However, the esters given as salts tended to be better absorbed than the parent compound. The 6-deoxy and 6-deoxydiacetate analogs were extensively oxidized in vivo and represent prodrugs with considerable potential in improving the absorption of oral (+/-)2HM-HBG.