Clinical pharmacology: foscarnet

Salvage Treatment of Refractory HSV Oral Lesions with Pritelivir in Allogeneic Hematopoietic Cell Transplant Recipients

We present two allogeneic hematopoietic cell transplantation recipients (HCTr) treated with pritelivir for acyclovir-resistant/refractory (r/r) HSV infection based on the expanded access program of the pritelivir manufacturer. Outpatient treatment with pritelivir was administered, with partial response by week 1 of treatment and complete response by week 4 of treatment in both patients. No adverse events were noted. Pritelivir appears to be an effective and safe option for the management of acyclovir-r/r HSV infections in highly immunocompromised patients in an outpatient setting.

Mechanisms of antimicrobial-induced nephrotoxicity in children

Drug-induced nephrotoxicity is responsible for 20% to 60% of cases of acute kidney injury in hospitalized patients and is associated with increased morbidity and mortality in both children and adults. Antimicrobials are one of the most common classes of medications prescribed globally and also among the most common causes of nephrotoxicity. A broad range of antimicrobial agents have been associated with nephrotoxicity, but the features of kidney injury vary based on the agent, its mechanism of injury and the site of toxicity within the kidney. Distinguishing nephrotoxicity caused by an antimicrobial agent from other potential inciting factors is important to facilitate both early recognition of drug toxicity and prompt cessation of an offending drug, as well as to avoid unnecessary discontinuation of an innocuous therapy. This review will detail the different types of antimicrobial-induced nephrotoxicity: acute tubular necrosis, acute interstitial nephritis and obstructive nephropathy. It will also describe the mechanism of injury caused by specific antimicrobial agents and classes (vancomycin, aminoglycosides, polymyxins, antivirals, amphotericin B), highlight the toxicodynamics of these drugs and provide guidance on administration or monitoring practices that can mitigate toxicity, when known. Particular attention will be paid to paediatric patients, when applicable, in whom nephrotoxin exposure is an often-underappreciated cause of kidney injury.

The targeting of primary effusion lymphoma cells for apoptosis by inducing lytic replication of human herpesvirus 8 while blocking virus production

Primary effusion lymphoma (PEL) is a B-cell lymphoma in which human herpesvirus-8 (HHV-8) is found within all tumor cells and represents a target for selectively destroying tumor cells. HHV-8 is latent in most PEL cells and, hence, resistant to antiviral agents that inhibit lytic replication. We demonstrate that PEL cell lines containing HHV-8 without and with coinfection with Epstein-Barr virus responded to the antiseizure medication valproate with entry into the lytic cascade and production of infectious virus. Minimal cell death occurred when noninfected BL-41 cells were incubated with valproate, whereas apoptosis occurred in response to valproate in PELs that supported lytic replication of HHV-8. The anti-viral agents ganciclovir and phosphonoformic acid (PFA) blocked valproate-induced production of infectious virus without blocking entry into the lytic cascade, and apoptosis occurred at levels that were as high as when virus production was not blocked. Ganciclovir and PFA also prevented most valproate-induced expression of the late lytic viral transcript open reading frame 26 (ORF-26), but they did not block the induction of either viral interleukin-6 (vIL-6) or viral G protein-coupled receptor (vGPCR). These studies provide evidence that incubation of PELs with valproate in the presence of ganciclovir or PFA can selectively target tumor cells for apoptosis without increasing viral load.

Management of acyclovir-resistant herpes simplex virus

In immunocompetent patients, HSV is controlled rapidly by the human host's immune system, and recurrent lesions are small and short lived. When treated with antiviral agents, these patients rarely develop resistance to these drugs. In contrast immunocompromised patients might not be able to control HSV infection. Thus, frequent and severe reactivations are often seen and might lead to fatal herpetic encephalitis or disseminated HSV infection. Treatment in these patients is limited because immunocompromised hosts often develop severe herpes disease refractory to antiviral drug therapy. It is therefore imperative that physicians develop regimens to deal with both receptive and refractory HSV disease. The following treatment protocol (modified from Balfour and colleagues) might serve as a guide until further investigation of new drugs is performed. In all patients standard oral ACV therapy should be initiated at a dose of 200 mg orally, five times a day for the first 3 to 5 days. Prior to treatment, cultures the lesions should be obtained to verify HSV etiology. If the response is poor, the dose of oral ACV should be increased to 800 mg five times a day. If no response seen after 5 to 7 days, it is unlikely that the lesion will respond to intravenous ACV (or chemically and structurally related drugs such as VCV or famciclovir), so an alternative regimen must be assigned. First, repeat cultures for vital, fungal, and bacterial pathogens must be performed. In addition, ACV susceptibility studies should be ordered, if available. If the mucocutaneous lesion is accessible for topical treatment, TFT (as ophthalmic solution) should be applied to the area three to four times a day until the lesion is completely healed. If the lesion is inaccessible or if the response to TFT is poor, therapy with intravenous foscarnet should be given for 10 days or until complete resolution of the lesions. The dosage of foscarnet should be 40 milligrams per kilogram three times per day or 60 milligrams per kilogram twice daily. If foscarnet fails to achieve clinical clearing, consideration should be given to use of intravenous cidofovir (or application of compounded 1% to 3% topical cidofovir ointment). Vidarabine is reserved for situations in which all of these therapies fail. If lesions reoccur in the same location following clearing, the patient should started on high-dose oral ACV (800 mg, five times daily) or intravenous foscarnet (40 mg/kg tid or 60 mg/kg bid) as soon as possible. When lesions occur in a different location, the patient should be treated initially with standard doses of oral ACV (200 mg, five times daily) and the above protocol should be followed should there be clinical failure. In the future, new treatment options for patients with documented HSV resistance will be important in reducing the clinical impact of HSV.

Current pharmacological approaches to the therapy of varicella zoster virus infections: a guide to treatment

Varicella zoster virus (VZV), a member of the herpesvirus family, is responsible for both primary (varicella, chickenpox) as well as reactivation (zoster, shingles) infections. In immunocompetent patients, the course of varicella is generally benign. For varicella zoster, post-herpetic neuralgia is the most common complication. In immunocompromised patients (particularly those with AIDS), transplant recipients and cancer patients, VZV infections can be life-threatening. For these patients and also for immunocompetent patients at risk such as pregnant women or premature infants, the current treatment of choice is based on either intravenous or oral aciclovir (acyclovir). The low oral bioavailability of aciclovir, as well as the emergence of drug-resistant virus strains, have stimulated efforts towards the development of new compounds for the treatment of individuals with VZV infections. Among these new compounds, penciclovir, its oral prodrug form famciclovir and the oral pro-drug form of aciclovir (valaciclovir), rank among the most promising. As with aciclovir itself, all of these drugs are dependent on the virus-encoded thymidine kinase (TK) for their intracellular activation (phosphorylation), and, upon conversion to their triphosphate form, they act as inhibitors/alternative substrate of the viral DNA polymerase. Therefore, cross-resistance to these drugs may be expected for those virus mutants that are TK-deficient and thus resistant to aciclovir. Other classes of nucleoside analogues dependent for their phosphorylation on the viral TK that have been pursued for the treatment of VZV infections include sorivudine, brivudine, fialuridine, fiacitabine and netivudine. Among oxetanocins, which are partially dependent on viral TK, lobucavir is now under clinical evaluation. Foscarnet, which does not require any previous metabolism to interact with the viral DNA polymerase, is used in the clinic when TK-deficient VZV mutants emerge during aciclovir treatment. TK-deficient mutants are also sensitive to the acyclic nucleoside phosphonates (i.e. [s]-1-[3-hydroxy-2-phosphonylmethoxypropyl]cytosine; HPMPC); these agents do not depend on the virus-encoded TK for their phosphorylation but depend on cellular enzymes for conversion to their diphosphoryl derivatives which then inhibit viral DNA synthesis. Vaccination for VZV has now come of age. It is recommended for healthy children, patients with leukaemia, and patients receiving immunosuppressive therapy or those with chronic diseases. The protection induced by the vaccine seems, to some extent, to include zoster and associated neuralgia. Passive immuniatin based on specific immunoglobulins does not effectively prevent VZV infection and is therefore restricted to high risk individuals (i.e. immunocompromised children and pregnant women).

Review: Present and future directions in the treatment of chronic hepatitis B infection

The last decade has witnessed substantial progress in the development of chemotherapeutic agents for chronic hepatitis B. However, the only currently licensed treatment in Australia, interferon-alpha, has low initial response rates and the adverse effects are often unacceptable. Of the newer agents in the class of nucleoside analogues, famciclovir and lamivudine are in phase III clinical trials with encouraging preliminary results, while other agents, such as bis-POM PMEA (Adefovir), are at phase I/II development. Future approaches to therapy will be governed by an understanding of the effects of nucleoside analogues on the natural history of the disease as well as on the hepatitis B virus hepatocyte interaction. Combination antiviral therapy should theoretically offer improved response rates, decrease the development of viral resistance, and provide the greatest reduction in viral load, but it has not yet been widely examined in the clinical setting. In this article, we review the currently available strategies, discuss potential problem areas, and speculate on promising approaches with combination chemotherapy and the features of agents soon to be trialed.

Sensitivity of Kaposi's sarcoma-associated herpesvirus replication to antiviral drugs. Implications for potential therapy

Using a cell line (termed BCBL-1) derived from a peripheral effusion (body cavity-based) lymphoma latently infected with Kaposi's sarcoma-associated herpesvirus (KSHV), we recently reported the successful induction of KSHV replication in culture (Renne, R., W. Zhong, B. Herndier, M. McGrath, N. Abbey, D. Kedes, and D. Ganem. 1996. Nat. Med. 2:342-346). Here we report the first use of this system for establishing the susceptibility of KSHV to available antiviral drugs. Latently infected BCBL-1 cells were induced to lytic replication with phorbol esters; such cells secrete large numbers of KSHV virions into the culture medium. We assayed the ability of the antivirals to block KSHV production, as measured by the release of encapsidated viral DNA. The results show that KSHV replication is insensitive to acyclovir (9-[(2-hydroxyethoxy)-methyl]guanine) (50% inhibitory concentration [IC50] = 60-80 microM), but sensitive to ganciclovir (9-[1,3-dihydroxy-2-propoxymethyl]guanine) (IC50 = 2.7-4 microM), foscarnet (trisodium phosphonoformate hexahydrate) (IC50 = 80-100 microM), and cidofovir (1-[(S)-3-hydroxy-2-(phosphonomethoxy)propyl]cytosine) (IC50 = 0.5-1 microM).

Use of phosphonocarboxylic acids as inhibitors of sodium-phosphate cotransport

Phosphonocarboxylic acids, initially developed as antiviral agents, are found to be specific inhibitors of phosphate (P(i)) transport across cell membranes. Foscarnet (PFA), the most potent and the most widely used compound, can induce phosphaturia both after parenteral and oral administration. Furthermore, it can inhibit intestinal phosphate absorption when administered orally. PFA absorption and bioavailability are increased in animals on phosphate-restricted diets. PFA also blunts the adaptive increase in intestinal and renal Na(+)-P(i) cotransport which accompanies dietary phosphorus restriction. Finally, PFA is shown to inhibit hydroxyapatite crystal formation and calcium-phosphate precipitation when tested in in vitro systems. These properties, and the low toxicity of PFA, point to potential new applications for PFA and some of its analogs in clinical conditions such as chronic renal insufficiency, where phosphate retention may lead to progression of renal failure and to other serious complications.

Infectious causes of hydrops fetalis

A variety of infectious agents have been associated with nonimmune hydrops fetalis, most notably parvovirus B19, cytomegalovirus, herpes simplex virus, Toxoplasma gondii, and Treponema pallidum. These agents produce hydrops through effects on fetal bone marrow, myocardium, or vascular endothelium. Knowledge of the epidemiology and clinical characteristics of maternal and fetal infection can be used to select a diagnostic approach. Etiologic diagnosis will guide prognosis and the selection of specific chemotherapy.

Penetration of foscarnet into cerebrospinal fluid of AIDS patients

The diffusion of foscarnet into cerebrospinal fluid (CSF) was studied in 27 patients with AIDS. Foscarnet was administered intravenously at various dosages at 12-h intervals. Concentrations in plasma and CSF at the end of foscarnet infusion or 1, 3, 5, 6, and 12 h after infusion were determined by high-performance liquid chromatography. Thirty-seven samples were obtained. The median concentration of foscarnet in CSF was 80 mumol/liter (range, 0 to 500 mumol/liter). The CSF foscarnet concentration was greater than the 50% inhibitory concentration for human immunodeficiency virus type 1 and was equal to or greater than the 50% inhibitory concentration for cytomegalovirus in most cases. The penetration of foscarnet into CSF, as expressed by the ratio of the concentration in CSF to the simultaneous concentration in plasma, ranged from 0 to 3.4 (median, 0.27) and was highly correlated with the presence of cells within CSF and the length of foscarnet therapy. Good diffusion of foscarnet in CSF allows evaluation of this drug in central nervous system cytomegalovirus and human immunodeficiency virus infections in patients with AIDS.