A dose-ranging study of daily maintenance intravenous foscarnet therapy for cytomegalovirus retinitis in AIDS

Treatment of alpha and beta herpesvirus infections in solid organ transplant recipients

INTRODUCTION

Human herpesviruses frequently cause infections in solid organ transplant (SOT) recipients. Areas covered: We provide an overview of the clinical impact of alpha and beta herpesviruses and highlight the mechanisms of action, pharmacokinetics, clinical indications, and adverse effects of antiviral drugs for the management of herpes simplex virus, varicella zoster virus and cytomegalovirus. We comprehensively evaluated key clinical trials that led to drug approval, and served as the foundation for management guidelines. We further provide an update on investigational antiviral agents for alpha and beta herpesvirus infections after SOT. Expert commentary: The therapeutic armamentarium for herpes infections is limited by the emergence of drug resistance. There have been major efforts for discovery of new drugs against these viruses, but the results of early-phase clinical trials have been less than encouraging. We believe, however, that more antiviral drug options are needed given the adverse side effects associated with current antiviral agents, and the emergence of drug-resistant virus populations in SOT recipients. Likewise, optimized use and strategies are needed for existing and novel antiviral drugs against alpha and beta-herpesviruses in SOT recipients.

Intracellular Metabolism of 3′-Azido-3′-Deoxythymidine in the Presence of Ganciclovir or Foscarnet

Comparisons were made between the intracellular phosphorylation of 3′-Azido-3′-deoxythymidine (AZT) alone and in combination with ganciclovir (GCV) or foscarnet (PFA) in lymphocytes, uninfected fibroblasts and CMV-infected fibroblasts. The effects of AZT and the combinations of AZT with GCV or PFA on cellular dNTP pools were also examined. The phosphorylation of AZT was not altered by the presence of GCV or PFA in lymphocytes, and neither AZT nor the combinations of AZT with GCV or PFA changed the levels of cellular dNTP pools in these cells. AZT was phosphorylated to a greater extent in lymphocytes when compared to fibroblasts, but the proportion of AZT di- and triphosphates was greater in fibroblasts. The infection of fibroblasts with CMV enhanced AZT phosphorylation and increased the levels of cellular dNTP pools. GCV caused a specific reduction in AZT phosphorylation in CMV-infected fibroblasts, with a seven-fold drop in AZT triphosphate compared to AZT alone. GCV did not affect AZT phosphorylation in uninfected fibroblasts, nor did GCV reduce the dTTP pool compared to AZT alone. The effects of GCV upon AZT phosphorylation in CMV-infected cells may shed light on the antagonistic effects of GCV upon the anti-HIV activity of AZT, and are of importance for the development of effective combination therapies for the treatment of AIDS patients infected with CMV.

Effects of intraocular rifampicin on retinal ganglion cell structure: a stereological and histopathological study

AIM

To determine the histopathological changes of rifampicin applied intravitreally on retinal ganglion cells by means of stereological and histopathological methods.

METHODS

For this study twenty-four New Zealand adult rabbits were divided into four groups (n=6 for each group). 50µg/0.1mL (group 1), 100µg/0.1mL (group 2), 150µg/0.1mL (group 3) and 200µg/0.1mL (group 4), rifampicin were injected into the vitreous of the right eyes of animals, their left eyes were used as control (group 5). After the 28(th) day of application, animals were anesthetised with xylazine (8mg/kg, IM) and then their eyes were enucleated immediately. Patterns were taken away and eyes were prepared for both stereological and electromicroscopic observation.

RESULTS

Depending on the high dose of rifampicin, some histopathological changes such as cytoplasmic dilatation and damaged membrane were observed on the electromicroscopic level. Using quantitative examination, which was done at the light microscopic level, it was shown that the number of neurons decreased linearly as rifampicin dose increased when compared with the control group.

CONCLUSION

Based on these findings, low-dose rifampicin (50µg/0.1mL) may be useful for treatment of the ocular diseases.

Antiviral drugs for viruses other than human immunodeficiency virus

Most viral diseases, with the exception of those caused by human immunodeficiency virus, are self-limited illnesses that do not require specific antiviral therapy. The currently available antiviral drugs target 3 main groups of viruses: herpes, hepatitis, and influenza viruses. With the exception of the antisense molecule fomivirsen, all antiherpes drugs inhibit viral replication by serving as competitive substrates for viral DNA polymerase. Drugs for the treatment of influenza inhibit the ion channel M(2) protein or the enzyme neuraminidase. Combination therapy with Interferon-α and ribavirin remains the backbone treatment for chronic hepatitis C; the addition of serine protease inhibitors improves the treatment outcome of patients infected with hepatitis C virus genotype 1. Chronic hepatitis B can be treated with interferon or a combination of nucleos(t)ide analogues. Notably, almost all the nucleos(t) ide analogues for the treatment of chronic hepatitis B possess anti-human immunodeficiency virus properties, and they inhibit replication of hepatitis B virus by serving as competitive substrates for its DNA polymerase. Some antiviral drugs possess multiple potential clinical applications, such as ribavirin for the treatment of chronic hepatitis C and respiratory syncytial virus and cidofovir for the treatment of cytomegalovirus and other DNA viruses. Drug resistance is an emerging threat to the clinical utility of antiviral drugs. The major mechanisms for drug resistance are mutations in the viral DNA polymerase gene or in genes that encode for the viral kinases required for the activation of certain drugs such as acyclovir and ganciclovir. Widespread antiviral resistance has limited the clinical utility of M(2) inhibitors for the prevention and treatment of influenza infections. This article provides an overview of clinically available antiviral drugs for the primary care physician, with a special focus on pharmacology, clinical uses, and adverse effects.

Valaciclovir:development, clinical utility and potential

Valaciclovir (Valtrex, Zelitrex), the L-valine ester of aciclovir, increases aciclovir bioavailability by 3- to 5-fold over that achievable with oral aciclovir. It addresses many unmet needs of currently available anti-herpesvirus therapies. Valaciclovir extends the efficacy of aciclovir in the treatment of herpes zoster and genital HSV infections, using less frequent dose regimens but retaining the highly acceptable safety profile established for aciclovir. The potential for valaciclovir in CMV prophylaxis has now been proven, and further refining to identify the optimal dose regimen is ongoing. After oral administration, valaciclovir is rapidly absorbed and extensively converted to aciclovir and L-valine, the essential amino acid. The mode of action and spectrum of antiviral activity of valaciclovir are thus identical to aciclovir. The bioavailability of aciclovir after valaciclovir, characterised from studies in healthy adult volunteers, is similar in a wide range of patient populations, including the elderly, those with advanced HIV disease, patients with impaired liver or renal function, or undergoing bone marrow transplantation. No clinically significant drug interactions with valaciclovir have so far been identified. Dosage reductions in clinical use of valaciclovir are only necessary when renal function is severely impaired. In controlled clinical trials in herpes zoster, valaciclovir (1000 mg three times daily) is superior to aciclovir in speeding the resolution of zoster-associated pain and post-herpetic neuralgia. It is as effective as aciclovir in hastening rash healing. In patients with ophthalmic zoster, no differences were evident between valaciclovir and aciclovir treatment on zoster-associated pain or the occurrence of ocular complications. The safety profiles of valaciclovir, aciclovir and placebo were not different in this study programme. In a series of controlled, randomised trials of valaciclovir, aciclovir and placebo for the acute treatment of genital HSV infections in approximately 3000 patients, twice daily valaciclovir was proven as effective as the standard 5 times daily aciclovir regimen in resolving the clinical signs and symptoms of lesional disease. Early patient-initiated valaciclovir therapy (500 mg twice daily) of recurrent genital herpes episodes was shown significantly to increase the chance of prevention of vesicular or ulcerative lesions, a valuable clinical advantage not prospectively proven for aciclovir. When used for periods of up to one year, valaciclovir (500 mg once daily) effectively suppresses genital herpes recurrences. Long-term studies of valaciclovir for HSV suppression, evaluating doses of up to 1000 mg daily in approximately 3000 patients, about 25% of whom were HIV seropositive (CD+ > 100 cells/microl), revealed a highly acceptable clinical tolerability profile for valaciclovir that did not differ from aciclovir or placebo. There were no cases resembling thrombotic microangiopathy in these long-term studies. The aciclovir safety heritage and pharmacokinetic rationale for the development of valaciclovir have been realised through the clinical research programmes in the zoster and HSV indications. Further studies in these and related areas, including CMV prophylaxis, are in progress and aim to expand further the clinical potential of valaciclovir in the future.

Prophylaxis of herpesvirus infections in immunocompetent and immunocompromised older patients

In older patients, prophylaxis of herpesvirus infections mainly involves preventing the recurrence of herpes simplex virus (HSV) and complications of herpes zoster in immunocompetent patients, while in immunocompromised patients it is more concerned with the prevention of opportunistic virus reactivation. HSV ocular infection is the most frequent cause of corneal blindness in the US. The effectiveness of aciclovir 400mg twice daily in preventing the recurrence of HSV eye disease in immunocompetent patients has been well demonstrated. The issue of treatment duration for patients with highly recurrent ocular herpes remains unresolved. Post-herpetic neuralgia (PHN) is one of the most common neuralgic illnesses worldwide. Some progress in prevention of PHN has been made with a combination of antiviral therapy (famciclovir or valaciclovir), started within 72 hours of onset of the rash, and analgesic treatment. However, the best prevention of PHN is the prevention of herpes zoster disease, and the varicella vaccine is an option which over the next few years will be tested in clinical trials. For immunocompromised patients of any age, restoring immunity prevents herpesvirus disease, as demonstrated for cytomegalovirus (CMV) in AIDS patients receiving highly active antiretroviral therapy. Specific antiviral therapy during the initial period after transplantation could prevent reactivation of HSV or CMV in seropositive recipients. Whether pre-emptive therapy or prophylaxis with ganciclovir is the optimal approach against CMV remains controversial, and the relative merits and limitations of each approach may guide the choice. In stem cell transplantation, pre-emptive therapy with foscarnet avoids the neutropenia and related complications associated with ganciclovir. In renal transplant recipients, universal prophylaxis of CMV infection with valaciclovir has the same efficacy as ganciclovir. Although it is relatively toxic, cidofovir should be further evaluated because of its in vitro activity against most DNA viruses.

Intravitreal, retinal, and central nervous system foscarnet concentrations after rapid intravenous administration to rabbits

Retinal, vitreous humor, brain, and cerebrospinal fluid (CSF) foscarnet levels were measured by high-performance liquid chromatography after administration of an intravenous dose of 120 mg/kg of body weight to 32 pigmented rabbits. A pharmacokinetic analysis was done using a two-compartment model. The penetration ratios, defined as ratios of retinal, vitreous humor, brain, and CSF areas under the concentration-time curve from 0 to 2 h were 110% +/- 1%, 12.3% +/- 0.7%, 118% +/- 1%, and 20.2% +/- 2.2%, respectively. These results suggest a good penetration of foscarnet into the retinal and brain tissues, reaching higher concentrations than those estimated from vitreous humor and CSF levels.

Recent advances in the therapy and prevention of CMV infections

The introduction of highly active antiretroviral therapy (HAART) for HIV has had a major impact on the treatment of CMV disease in HIV-infected individuals. There is mounting evidence that in patients with CMV retinitis who have a sustained response to HAART, CMV maintenance treatment can be discontinued without relapse of retinitis. In HAART-naïve individuals with newly diagnosed CMV retinitis, the optimal timing for the initiation of HAART relative to the start of anti-CMV treatment is currently unknown. New local therapies for CMV retinitis (e.g. ganciclovir implant, the new antisense compound fomivirsen) provide treatment options in situations where high local drug delivery is warranted. A treatment algorithm for CMV disease in the HAART era is proposed. In the transplant setting, ganciclovir and foscarnet remain the major compounds used for treatment of CMV disease. In marrow and stem cell transplant recipients, CMV pneumonia still carries a high mortality. Ganciclovir in combination with CMV-specific immunoglobulin or regular intravenous IG remains the treatment of choice for CMV pneumonia; extended antiviral maintenance for several months is recommended in patients with continued immunosuppression. Preemptive treatment based on virologic markers (e.g. pp65 antigenemia, CMV DNA) has been very successful in reducing the incidence of early CMV disease in the transplant setting. The duration of preemptive treatment should be guided by the underlying immunosuppression and virologic markers. Late CMV disease is a challenge in marrow and stem cell transplant recipients, and occurs increasingly in highly immunosuppressed solid organ transplant recipients as well. Recent advances in prophylaxis strategies include oral ganciclovir for liver transplant recipients and valacyclovir for kidney transplant recipients.

Comparative tolerability of therapies for cytomegalovirus retinitis

Cytomegalovirus (CMV) retinitis is a potentially sight-threatening complication of advanced HIV infection. The acute infection can be controlled with one of several therapies, including intravenous ganciclovir, foscarnet or cidofovir, slow release ganciclovir intraocular implants or serial intraocular injections of ganciclovir or foscarnet. The initial induction course of therapy is typically followed by lifelong maintenance therapy. In addition to the aforementioned treatments, oral ganciclovir and intravitreal fomivirsen injections are other options for maintenance therapy. The choice of agent must take into consideration factors such as comparative short and long term toxicity of the agents, route of administration and the possible need for indwelling catheters, administration time, cost and protection afforded against systemic dissemination of CMV infection. Possible drug interactions and additive toxicities of other agents needed for the management of the underlying HIV infection must also be taken into consideration. These factors can affect the tolerability of therapy as well as the quality of life of the patient. Relapse or progression of CMV retinitis may be caused by either inadequate drug concentrations at the site of the infection or by drug resistance. This may necessitate either an increase in drug dosage, a change in route of administration or a change to an alternative agent. All of these approaches can increase the risk of toxicity of the therapy. With the initiation of highly active antiretroviral therapy and partial reconstitution of the immune system, some patients have been able to successfully discontinue anti-CMV maintenance therapy, thereby decreasing long term drug toxicity. Determination of the patient predictors of success of this approach is an active area of research.

Management of CMV retinitis in the era of highly active antiretroviral therapy

Although the epidemiological features of CMV retinitis is changing in patients receiving highly active antiretroviral therapy (HAART), continued attention must be paid to detect and treat earlier CMV infections in AIDS patients to prevent severe ophthalmic complications. Initial therapy must be based on characteristics of the CMV retinitis and patient conditions. Long term therapy of HAART must be pursued, even in patients with increased CD4 and undetectable HIV viral load, until results from large controlled studies are available. reserved.

Determination of phosphonoformate (foscarnet) in calf and human serum by automated solid-phase extraction and high-performance liquid chromatography with amperometric detection

An isocratic high-performance liquid chromatographic method with automated solid-phase extraction has been developed to determine foscarnet in calf and human serums. Extraction was performed with an anion exchanger, SAX, from which the analyte was eluted with a 50 mM potassium pyrophosphate buffer, pH 8.4. The mobile phase consisted of methanol-40 mM disodium hydrogenphosphate, pH 7.6 containing 0.25 mM tetrahexylammonium hydrogensulphate (25:75, v/v). The analyte was separated on a polyether ether ketone (PEEK) column 150x4.6 mm I.D. packed with Kromasil 100 C18, 5 microm. Amperometric detection allowed a quantification limit of 15 microM. The assay was linear from 15 to 240 microM. The recovery of foscarnet from calf serum ranged from 60.65+/-1.89% for 15 microM to 67.45+/-1.24% for 200 microM. The coefficient of variation was < or = 3.73% for intra-assay precision and < or =7.24% for inter-assay precision for calf serum concentrations ranged from 15 to 800 microM. For the same samples, the deviation from the nominal value ranged from -8.97% to +5.40% for same day accuracy and from -4.50% to +2.77% for day-to-day accuracy. Selectivity was satisfactory towards potential co-medications. Replacement of human serum by calf serum for calibration standards and quality control samples was validated. Automation brought more protection against biohazards and increase in productivity for routine monitoring and pharmacokinetic studies.

Summary of the II International Symposium on Cytomegalovirus

Human cytomegalovirus (HCMV) is a highly species-specific DNA virus belonging to the Betaherpesvirinae subfamily of the herpesviridae family. Like other herpesviruses, primary infection with HCMV is followed by persistence of the virus in a latent form. The sites of latency are still largely undefined, but they probably include bone marrow progenitor cells and peripheral blood monocytes. From these sites, the virus can reactivate, resulting in renewed shedding of the virus, or, in immunocompromized persons, development of disease. Humans are the only reservoir of HCMV and transmission occurs by person-to-person contact. Infection with HCMV is common. In most developed countries, HCMV seroprevalence steadily increases after infancy and 10-20% of children are infected before puberty. In adults, the prevalence of antibodies ranges from 40 to 100%. Although HCMV has a world-wide distribution, infection with HCMV is more common in the developing countries and in areas of low socioeconomic conditions, which is predominantly related to the closeness of contacts within these populations. Except for a mononucleosis-like illness in some persons, infection with HCMV rarely causes disease in immunocompetent individuals. However, HCMV can cause severe morbidity and mortality in congenitally infected newborns and immunocompromized patients, most notably transplant-recipients and HIV-infected persons. This article provides a review of the information presented at the Second International Symposium on Cytomegalovirus organized and convened by The Macrae Group (New York City, NY) in Acapulco, Mexico on 24-28 April 1998. During this symposium, the state-of-the-art knowledge on diagnosis, treatment and prophylaxis of HCMV infections were discussed, and, based on this information, attempts to highlight the future directions in basic and clinical research areas that need to be stimulated to facilitate advancement in prevention and treatment of CMV disease.

Increasing survival in AIDS patients with cytomegalovirus retinitis treated with combination antiretroviral therapy including HIV protease inhibitors

OBJECTIVE

To assess the effect of combination antiretroviral therapy including HIV protease inhibitors on the survival of patients with cytomegalovirus retinitis (CMVR).

DESIGN AND PARTICIPANTS

A longitudinal study of patients with CMVR diagnosed between October 1992 and May 1996 and followed to May 1997.

SETTING

UK National Health Service specialist HIV medicine department.

OUTCOME MEASURE

Time to death from first diagnosis of CMVR. Data were censored on 31 May 1997.

RESULTS

Data were available on 147 patients with CMVR. Median survival of CMVR patients before December 1995 was 256 days [95% confidence interval (CI), 197-315]. Following the introduction of protease inhibitors in December 1995 this rose to 555 days (95% CI, 351-759). By 31 May 1996 median survival for the entire group of patients alive with CMVR had risen to 720 days (95% CI, 551-889). The mean survival after CMVR diagnosis was 224 days (n=89; 95% CI, 186-261; 1-year survival, 16%) in those who took no further antiretroviral therapy, 353 days in those who took nucleoside reverse transcriptase inhibitors but no protease inhibitors (n=34; 95% CI, 289-418; 1 -year survival, 50%), and 914 days in those who took a protease inhibitor (n=24; 95% CI, 768-1059; 1-year survival, 83%; P < 0.0001). Multivariate analysis showed that the strongest independent predictor of improved survival was having ever received a protease inhibitor after CMVR (relative risk of death, 0.063; 95% CI, 0.027-0.149; P < 0.0001).

CONCLUSIONS

The use of HIV protease inhibitors in combination antiretroviral therapy has been associated with a marked increase in the survival of patients with CMVR.

Adverse events and autopsy findings after intravitreous cidofovir (HPMPC) therapy in patients with acquired immune deficiency syndrome (AIDS)

OBJECTIVE

The purpose of the study is to evaluate the adverse events and autopsy findings in a series of consecutive 20-microg intravitreous cidofovir injections at a single institution.

DESIGN

The study design was a nonrandomized, consecutive case series.

PARTICIPANTS

Seventy-six patients with acquired immune deficiency syndrome with cytomegalovirus retinitis were studied prospectively. Sixty-three patients had 1 month's follow-up or longer, and this comprised the study group. In addition, histopathologic findings from 18 eyes of 9 patients were studied at autopsy.

INTERVENTION

A total of 296 injections of 20 microg cidofovir were given in 115 eyes. Sixty-three patients who had 246 injections in 93 eyes had 1 month's follow-up or longer for the evaluation of adverse events.

MAIN OUTCOME MEASURES

Postinjection chronic hypotony associated with permanent visual loss, transient hypotony, iritis, and its long-term sequela (posterior synechia and cataract, retinal detachment, extraocular cytomegalovirus involvement) were the outcomes of interest in this study. Additionally, light and electron microscopic studies of human eyes were performed.

RESULTS

The most severe adverse event was postinjection chronic hypotony. This phenomenon was associated with permanent visual loss. This was observed in 1% of the injections and 3% of the eyes of the patients (95% confidence interval, 0%-6%). Transient hypotony associated with mild-to-moderate visual loss developed in 14%, but vision recovered to baseline levels in these eyes subsequently. Analysis showed that transient hypotony in the injected eye could predict postinjection chronic hypotony in the fellow eye (two-tailed Fisher's exact test, P = 0.02). The incidence of iritis was 32%; posterior synechia and cataract were the long-term sequela of the iritis and developed in 19% and 11% of the eyes, respectively. The incidence of retinal detachment was lower (6%). Histopathologic evaluation of the eyes showed mild-to-moderate atrophy of the nonpigmented epithelium of the ciliary body and no other evidence of intraocular toxicity.

CONCLUSIONS

The most serious adverse event was postinjection chronic hypotony, which occurred in 3% of eyes. Episodes of transient hypotony appear to indicate that the fellow eye was predisposed to chronic hypotony. Therefore, it may be prudent to give intravitreous injections at least 2 weeks apart in the fellow eye to evaluate the clinical response of the injected eye.

The impact of high-risk patients on the results of clinical trials

The results of clinical trials may not reflect equally the experiences of all their individual participants. By modeling populations where patients have very diverse baseline risks of suffering an event of interest, it can be seen that very sick patients of high risk become the major determinants of how many events occur in the whole population, even though they may represent only a small minority. Human immunodeficiency virus-related trials and trials of magnesium in acute myocardial infarction are analyzed. When the benefit or toxicity from a treatment varies with the baseline risk of each patient, the treatment effect may be markedly different in populations with a different representation of high- and low-risk patients. The results of small clinical trials studying heterogeneous populations with binary outcomes depend on the sampling and outcomes of very few high risk participants. Conversely, mega-trials studying homogeneous populations would miss subgroups or individuals with diverse treatment responses. In both cases, aggregate trial results may be misleading for the care of many individuals.

Treatment of HIV infection and its complications

Because the AIDS epidemic continues to grow, there is a sense of urgency to develop new treatment strategies, both for HIV infection and for AIDS-related illnesses. The rapid gathering of basic information related to HIV type 1 biology and opportunistic infections has led to an explosion in physicians' ability to diagnose, prevent, and treat HIV disease and its associated complications. Research in this rapidly evolving field is likely to lead to further advances in the months and years that follow.

Summary of the International Consensus Symposium on Advances in the Diagnosis, Treatment and Prophylaxis and Cytomegalovirus Infection

CMV infection and CMV disease can be difficult to differentiate and the diagnosis is usually based on a compatible clinical picture and the results of a diagnostic test for CMV. The only exception to this rule is in HIV-infected patients where fundoscopy is sufficient to diagnose CMV retinitis. Of the current diagnostic tests, qualitative and quantitative PCR, branched DNA and Hybrid Capture, are the most promising. The pp65 antigenemia assay has the disadvantage of being more labor-intensive than the DNA based tests. Preliminary data show that a positive qualitative PCR in a HIV-infected patient has a predictive value for the development of CMV retinitis. However, of the patients positive by qualitative PCR, those with high viral loads in quantitative PCR were at the greatest risk of CMV disease. This might make it possible to identify with great certainty the patients who will go on to develop CMV retinitis, thereby decreasing the number of patients eligible for preemptive or prophylactic therapy and increasing the cost-benefit of this therapeutic measure. Quantitative test might also be useful in monitoring response to therapy, but randomized trials comparing the test are needed. Prophylactic antiviral agents should not be used in seronegative transplant recipients receiving organs from seronegative donors. In high-risk transplant recipients, ganciclovir should be used. CMV vaccines are useful for the protection of babies from CMV seronegative mothers against congenital CMV disease. It also may be useful in seronegative transplant recipients receiving a seropositive donor organ, although the benefit of chemo prophylaxis may surpass that of vaccine. HIV-infected patients with CMV retinitis who relapse under either ganciclovir or foscarnet benefit from subsequent combination therapy, rather than switching to the other drug. However, the cost is high in terms of quality of life. Intravitreal therapy for CMV retinitis is very efficacious, suggesting that drug delivery is a problem in systemic therapy. However, intravitreal therapy does not protect against the development of CMV retinitis in the contralateral eye or from CMV disease elsewhere. Therefore, systemic therapy should be added. CMV disease of the CNS should be diagnosed early and treated agressively, possible with combination therapy. A diagnosis of CMV disease should be based on a compatible clinical picture and the demonstration of CMV in CSF by DNA or antigen assays which are more sensitive than culture.

Synergistic inhibition of human immunodeficiency virus isolates (including 3'-azido-3'-deoxythymidine-resistant isolates) by foscarnet in combination with 2',3'-dideoxyinosine or 2',3'-dideoxycytidine

The combinations of foscarnet plus 2',3'-dideoxyinosine and foscarnet plus 2',3'-dideoxycytidine synergistically inhibit the replication of human immunodeficiency virus type 1 isolates, including two 3'-azido-3'-deoxythymidine-resistant isolates. The combination of 2',3'-dideoxyinosine plus 2',3'-dideoxycytidine showed additive inhibition of the majority of the human immunodeficiency virus isolates tested. All three combinations showed pronounced antagonistic cytotoxicity and thus were less toxic to the growth of peripheral blood mononuclear cells than the separate drugs.

Foscarnet 5 versus 7 days a week treatment for severe gastrointestinal CMV disease in HIV-infected patients

In a randomized open trial foscarnet 90 mg/kg b.i.d. 5 days for 3 weeks was compared to 90 mg/kg b.i.d. daily in severe gastrointestinal cytomegalovirus disease in HIV-infected patients. Thirty-eight patients were randomized, 36 were evaluable (all male, age 24-54 years, median 40 years; CD4/microliter 0-150, median 10). Treatment efficacy was evaluated based on a score consisting of symptoms, endoscopic and histologic examination. In the 5-day treatment group 10/16 (62%) patients responded to treatment, in the 7-day treatment group 13/20 (65%), with symptoms resolving in most patients after 1 week. Side effects and adverse events were seen in 13 patients in the 5-day treatment group and in 15 patients in the 7-day treatment group. Laboratory abnormalities were common in both groups, in one patient reversible renal insufficiency developed. Efficacy and safety of treatment 5 days a week was comparable to the standard regimen.

Oral ganciclovir as maintenance treatment for cytomegalovirus retinitis in patients with AIDS. Syntex Cooperative Oral Ganciclovir Study Group

BACKGROUND

Cytomegalovirus retinitis, a sight-threatening infection associated with the acquired immunodeficiency syndrome (AIDS), currently requires lifelong intravenous treatment. An effective oral treatment would be an important advance.

METHODS

We compared oral with intravenous ganciclovir in an open-label, randomized study in patients with AIDS and newly diagnosed, stable cytomegalovirus retinitis (the disease was stabilized by three weeks of treatment with intravenous ganciclovir). Sixty subjects were randomly assigned to maintenance therapy with intravenous ganciclovir at a dose of 5 mg per kilogram of body weight daily, and 63 to maintenance therapy with oral ganciclovir at a dose of 3000 mg daily. The subjects were followed for up to 20 weeks, with photography of the fundi conducted every other week. The photographs were evaluated at the completion of the study by an experienced grader who was unaware of the subjects' treatment assignments.

RESULTS

Efficacy could be evaluated in 117 subjects; photographs were ungradable for 2 of the 117. On the basis of the masked assessment of photographs from 115 subjects, the mean time to the progression of retinitis was 62 days in those given intravenous ganciclovir and 57 days in those given oral ganciclovir (P = 0.63; relative risk [oral vs. intravenous], 1.08; 95 percent confidence interval for the difference in means, -22 to +12 days). On the basis of funduscopy by ophthalmologists who were aware of the subjects' treatment assignments, the mean time to progression was 96 days in subjects given intravenous ganciclovir and 68 days in subjects given oral ganciclovir (P = 0.03; relative risk [oral vs. intravenous], 1.68; 95 percent confidence interval for the difference in means, -45 to -11 days). Survival, changes in visual acuity, the incidence of viral shedding, and the incidence of adverse gastrointestinal events were similar in the two groups. Neutropenia, anemia, intravenous-catheter-related adverse events, and sepsis were more common in the group given intravenous ganciclovir.

CONCLUSIONS

Oral ganciclovir is safe and effective as maintenance therapy for cytomegalovirus retinitis and is more convenient for patients to take than intravenous ganciclovir.

Foscarnet alters antidiuretic hormone-mediated transport

Therapy with foscarnet is associated with acute renal failure. Prior studies have emphasized foscarnet's proximal tubular toxicity, but there have been isolated reports of foscarnet-induced nephrogenic diabetes insipidus. As a phosphate analog, foscarnet is a competitive inhibitor of NaPO4 cotransport. However, foscarnet's effect on antidiuretic hormone (ADH)-induced transport has not been previously investigated. We studied foscarnet's modulation of transport in the toad urinary bladder. Foscarnet at 10 microM to 10 mM did not alter basal water or urea flux. Urea transport induced by a maximal dose of ADH (24 mIU/ml) was inhibited by 0.1 to 5.0 mM foscarnet. In tissues challenged with 0.5 to 1.0 mIU of ADH per ml, 1.0 to 10 mM foscarnet increased water flow but did not alter urea flux. Foscarnet also increased water flow induced by 1.0 to 10 microM forskolin. In tissues pretreated with 10 microM naproxen, foscarnet did not alter water flow induced by 0.5 to 1.0 mIU of ADH per ml or forskolin. These results indicate that foscarnet stimulates water flow induced by 0.5 to 1.0 mIU of ADH per ml at a site proximal to that of the generation of cyclic AMP and inhibits urea flux induced by a maximal dose of ADH at a separate site. In humans, foscarnet nephrotoxicity is likely not limited to the proximal nephron, but extends to the collecting duct. Patients receiving foscarnet should be closely monitored for disorders of urinary concentration.

Local therapy for cytomegalovirus retinopathy

PURPOSE

We sought to understand better the efficacy and risks of local therapies (direct placement of drug into the eye) for the treatment of cytomegalovirus retinopathy. This understanding can be used to design rational treatment regimens, to formulate indications for use of local therapy, and to establish criteria for assessment of future results in this area.

METHODS

We collected information about local therapies through a review of published literature.

RESULTS

Intraocular injection of ganciclovir and foscarnet and implantation of intraocular devices that slowly release ganciclovir are able to decrease the activity of cytomegalovirus retinopathy lesions and prevent their enlargement for variable periods of time. The time to disease progression (lesion enlargement) may be longer with intraocular devices than with current treatments using intravenously administered antiviral drugs. Local therapies have many advantages (for example, convenience, reduced cost, and lack of systemic toxicity), but there are potential disadvantages, including endophthalmitis, increased rates of retinal detachment, and development of nonocular cytomegalovirus disease and cytomegalovirus retinopathy in fellow, uninvolved eyes.

CONCLUSIONS

Local therapies are effective for the treatment of cytomegalovirus retinopathy, but their relative risks and benefits, when compared with those of intravenous drug therapy, have yet to be fully evaluated. We anticipate that local therapy will be an important treatment modality for selected patients with cytomegalovirus retinopathy. Indications include the use of local therapy as an alternative therapy for patients who are unable to receive systemic therapy (intolerance to intravenous or oral medication, or lack of intravenous access) and as supplementation in patients whose retinal disease is incompletely controlled by maximum tolerated systemic medications. The use of local therapy as sole initial treatment in lieu of systemic therapy remains controversial. Its most useful role may be in conjunction with oral forms of antiviral drugs now in development.

Viral sensitivity testing in patients with cytomegalovirus retinitis clinically resistant to foscarnet or ganciclovir

PURPOSE

Resistance to antiviral therapy is a potential cause of progression of cytomegalovirus retinitis in patients with the acquired immunodeficiency syndrome. We investigated the results of viral sensitivity testing in a series of patients with clinically resistant retinitis who had positive results of blood or urine cytomegalovirus cultures.

METHODS

All patients with newly diagnosed cytomegalovirus retinitis between January 1990 and December 1991 were prospectively studied. Blood and urine cultures for cytomegalovirus were obtained in a nonrandomized subgroup of this group. The results of in vitro sensitivity to foscarnet and ganciclovir, determined by a DNA hybridization assay, were then analyzed in seven patients with clinically resistant cytomegalovirus retinitis and whose blood or urine culture results, or both, were positive for cytomegalovirus while on a treatment regimen.

RESULTS

Foscarnet-resistant cytomegalovirus (ID50 > 300 microM) was isolated from two patients, one of whom was being treated with foscarnet. Ganciclovir-resistant cytomegalovirus (ID 50 > 6.0 microM) was isolated from four patients, three of whom were being treated with ganciclovir. Foscarnet- and ganciclovir-resistant cytomegalovirus occurred with previous ganciclovir therapy in one patient. Clinical improvement occurred in three patients whose change in therapy was based on viral sensitivity testing. In general, prolonged therapy with one drug was associated with a progressive increase in the ID 50 for that drug.

CONCLUSIONS

Viral resistance to foscarnet or ganciclovir may explain refractory cytomegalovirus retinitis in some patients.

Dose-related difference in progression rates of cytomegalovirus retinopathy during foscarnet maintenance therapy. AIDS Clinical Trials Group Protocol 915 Team

PURPOSE

A previous dose-ranging study of foscarnet maintenance therapy for cytomegalovirus retinopathy showed a positive relationship between dose and survival but could not confirm a relationship between dose and time to first progression. This retrospective analysis of data from that study was undertaken to determine whether there was a relationship between dose and progression rates, which reflects the amount of retina destroyed when progression occurs.

METHODS

Patients were randomly given one of two foscarnet maintenance therapy doses (90 mg/kg of body weight/day [FOS-90 group] or 120 mg/kg of body weight/day [FOS-120 group] after induction therapy. Using baseline and follow-up photographs and pre-established definitions and methodology in a masked analysis, posterior progression rates and foveal proximity rates for individual lesions, selected by prospectively defined criteria, were calculated in each patient. Rates were compared between groups.

RESULTS

The following median rates were greater for the FOS-90 group (N = 8) than for the FOS-120 group (N = 10): greatest maximum rate at which lesions enlarged in a posterior direction (43.5 vs 12.5 microns/day; P = .002); posterior progression rate for lesions closest to the fovea (42.8 vs 5.5 microns/day; P = .010); and maximum foveal proximity rate for either eye (32.3 vs 3.4 microns/day; P = .031).

CONCLUSION

Patients receiving higher doses of foscarnet have slower rates of progression and therefore less retinal tissue damage during maintenance therapy. A foscarnet maintenance therapy dose of 120 mg/kg of body weight/day instead of 90 mg/kg of body weight/day may help to preserve vision in patients with cytomegalovirus retinopathy.

Foscarnet. A reappraisal of its antiviral activity, pharmacokinetic properties and therapeutic use in immunocompromised patients with viral infections

The DNA polymerase of human herpes viruses, including cytomegalovirus (CMV), and the reverse transcriptase of human immunodeficiency virus (HIV) are selectively inhibited in vitro by the pyrophosphate analogue foscarnet. Inhibition is reversible on withdrawal of foscarnet and additive or synergistic effects have been demonstrated in vitro with other antiviral drugs, including ganciclovir and zidovudine. Foscarnet appears to have negligible effects on host enzymes and cells. Complete or partial clinical resolution of ocular symptoms is obtained in more than 89% of patients with acquired immunodeficiency syndrome (AIDS) and CMV retinitis during foscarnet induction therapy, but relapse occurs soon after ceasing treatment. Maintenance treatment given daily can extend the period of remission considerably. Foscarnet and ganciclovir monotherapy had similar efficacy in the treatment of CMV retinitis in patients with AIDS in several studies, and have been used concomitantly in immunocompromised patients with recalcitrant CMV infections. In 1 trial, patients receiving foscarnet survived for significantly longer than those receiving ganciclovir. Foscarnet has been used successfully in the treatment of limited numbers of immunocompromised patients with CMV-associated gastrointestinal (improvement in over 67% of patients) and other infections. Aciclovir-resistant herpes simplex infections in immunocompromised patients have also been treated successfully with foscarnet. Almost 90% of a foscarnet dose is excreted in the urine. Reversible nephrotoxicity is common during foscarnet therapy, but may be reduced by dosage adjustment and adequate hydration. Anaemia, nausea and vomiting, disturbances in electrolyte levels and genital ulceration have also been associated with administration of the drug. The different tolerability profiles of foscarnet and zidovudine facilitate the use of these agents in combination in patients with AIDS and CMV infection; whereas ganciclovir, like zidovudine, is associated with dose-limiting haematological toxicity. The apparent survival benefits seen in these patients when receiving foscarnet and zidovudine (possibly linked to synergy between zidovudine and foscarnet and/or the inherent anti-HIV activity of foscarnet), appear to offer potentially important advantages for foscarnet over ganciclovir in the treatment of selected patients with AIDS and CMV infections.

Current management of cytomegalovirus disease in patients with AIDS

Cytomegalovirus (CMV) infection is common in both homosexual and heterosexual HIV-infected patients, and causes disease in a substantial proportion of patients with AIDS and very low CD4+ cell counts. Both ganciclovir, an analog of the nucleoside guanosine, and foscarnet, an analog of pyrophosphate, are licensed for treatment of CMV retinitis. They may also have a role in the treatment of gastrointestinal disease caused by CMV. In the Studies of Ocular Complications of AIDS comparative trial the two agents were equally effective against CMV retinitis, but patients receiving foscarnet had significantly longer survival, even after adjusting for covariates including antiretroviral therapy. Ongoing studies are evaluating higher dosages of foscarnet for maintenance therapy and combined therapy with ganciclovir and foscarnet. Tolerance of ganciclovir therapy has been facilitated by adjunctive therapy with colony-stimulating factors. Because both ganciclovir and foscarnet must be administered by intravenous infusion and are associated with significant toxicities, other anti-CMV agents are under active development, including HPMPC and an oral formulation of ganciclovir. Management of CMV retinitis involves individualizing therapy, balancing side effects and administration requirements, and, in many clinical settings, the overall cost of treatment.

Pharmacodynamic relationship of pharmacokinetic parameters of maintenance doses of foscarnet and clinical outcome of cytomegalovirus retinitis

The pharmacodynamic relationship between a range of foscarnet exposure measurements obtained from studying nine patients receiving ongoing maintenance therapy for cytomegalovirus retinitis and a range of efficacy values (days to retinitis progression) obtained by independent examination of serial retinal photographs from the same nine patients was analyzed. In the resulting proportional hazards models, the foscarnet area under the concentration-time curve approached statistical significance (P = 0.11) as a predictor of decreased risk of retinitis progression.