Pharmacokinetics of foscarnet after twice-daily administrations for treatment of cytomegalovirus disease in AIDS patients

Continuous-Infusion Foscarnet Facilitates Administration in Hematopoietic Stem Cell Transplantation Patients

Infections due to herpesviruses resistant to first-line antivirals remains an ever-present and serious complication in recipients of hematopoietic cell transplantation (HCT) and other cellular therapies. Foscarnet is the most common therapy for patients who have resistant herpesvirus infections or intolerable cytopenias due to ganciclovir or valganciclovir; however, the widespread use of foscarnet is limited by its associated nephrotoxicity and challenges in administration. In the earliest published small case series investigating the optimal infusion modality, patients with acquired immunodeficiency syndrome (AIDS) due to the human immunodeficiency virus (HIV) received either continuous infusion or intermittent dosing of foscarnet. Moreover, there was no standardization of hydration strategies to minimize side effects. Eventually, intermittent foscarnet infusions became the standard of care; however, the true impact of hydration and infusion duration on nephrotoxicity has not been adequately studied, and the reports of foscarnet administration in HCT patients has been limited primarily to intermittent infusions. In this report, we characterize the administration of foscarnet as a 24-hour continuous infusion in both the inpatient and outpatient settings compared with intermittent infusion in HCT recipients. This retrospective, single-center, observational study at Stanford University Medical Center assessed HCT recipients who received foscarnet between January 2009 and May 2019. Twenty-eight of 45 patients (62.2%) who received continuous-infusion foscarnet experienced an acute kidney injury (AKI) as defined by the Kidney Disease Improving Global Outcomes classification, compared with 39 of 62 patients (62.9%) who received conventional infusion (P = .94). The average duration of outpatient antiviral days for the continuous infusion group was 9 days (range, 0 to 121 days), compared with 6.3 days (range, 0 to 70 days) in the intermittent infusion group (P = .54). Our findings suggest that foscarnet given as a continuous infusion or as an intermittent infusion have similar rates of adverse reactions, most notably similar rates of AKI. Administering foscarnet as a continuous infusion is a feasible option to facilitate outpatient treatment.

Recommended foscarnet dose is not associated with improved outcomes in cytomegalovirus salvage therapy

BACKGROUND

Cytomegalovirus (CMV) infection causes significant morbidity and mortality in transplant recipients. Ganciclovir and valganciclovir have proven efficacy but are limited by resistance and toxicity, whereas foscarnet typically retains activity when CMV has become resistant to other antivirals. Foscarnet dosing used in practice may be discordant with what is recommended in product labeling, as the result of an unconventional dosing nomogram or prescriber preference; however, it is unknown how discordant foscarnet dosing affects outcomes.

OBJECTIVE

Our purpose was to characterize the relationship between initial foscarnet dosing intensity (relative to product labeling) and key effectiveness and safety endpoints.

STUDY DESIGN

This single-center, retrospective study included immunosuppressed adults with CMV viremia who received foscarnet between January 2012-July 2017. Subjects were divided into low dose (LD) and non-low dose (NLD) groups, according to foscarnet dose intensity. The primary endpoint was time-to-CMV eradication. Secondary endpoints included time-to-CMV clearance, acute kidney injury, hematologic toxicity, and mortality.

RESULTS

Of 87 subjects, 38 met inclusion. Primary immunosuppression reasons were solid organ (63%) or hematopoietic cell transplant (29%). Seventeen and 21 subjects were in the LD and NLD groups, respectively. Median time-to-CMV eradication was 17 days (LD group) versus 13 days (NLD group), p = 0.823. Median time-to-CMV clearance was also non-significant (p = 0.505). There was no association between initial foscarnet dosing intensity and acute kidney injury, hematologic toxicity, or mortality (24% in both groups).

CONCLUSIONS

These findings suggest outcomes may be sensitive to other factors and underscore the need for further studies to improve understanding of foscarnet dosing in immunosuppressed patients.

Separation methods for antiviral phosphorus-containing drugs

Among antiviral drugs, phosphorus-containing compounds, foscarnet and cidofovir, present adverse effects including renal toxicity. Since their main therapeutic target is the treatment of CMV retinitis, which needs lifelong maintenance therapy, accurate analytical methods are required for drug monitoring. According to the high hydrophilic property of the two compounds, ion pair reversed-phase HPLC methods were proposed for their separation in drug formulations and biological samples. Their lack of UV absorption at wavelengths above 205 nm does not allow the use of this detection technique for biological fluids. Electrochemical detection methods (coulometry and amperometry) led to a quantification limit of 15 microM for foscarnet. Fluorescent derivatives obtained by modification of cidofovir cytosine nucleus with alpha-haloketones offered advantage over UV detection and allowed to reach a detection limit of 5 ng/ml, making possible investigations on the drug time-course in biological fluids.

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.

Neoglycolipid conjugates of foscarnet with enhanced antiviral activity in cells infected with human cytomegalovirus and herpes simplex virus type 1

The synthesis of a series of neoglycolipid conjugates of foscarnet as potential drug targeting forms or lipophilic prodrugs of foscarnet is described. The compounds were obtained from suitably protected neoglycolipids, in which the lipid chain consisted of 12 to 20 carbon atoms, by ethoxycarbonylphosphonylation at the 6-hydroxyl or 4-hydroxyl group followed by deprotection. The in vitro antiviral activity of the compounds was determined in human foetal lung cells infected with human cytomegalovirus (HCMV) or herpes simplex virus type 1 (HSV-1). Compounds in which the lipid chain consisted of 14 to 20 carbon atoms showed pronounced antiviral activity against HCMV and HSV-1, the highest activity being shown by trans-9-octadecen-1-yl 6-O-carboxyphosphonyl-alpha-D-glucopyranoside against HCMV (approximately 50 times that of foscarnet) and by eicosyl 6-O-carboxyphosphonyl-beta-D-galactopyranoside against HSV-1 (approximately 15 times that of foscarnet). Cytotoxicity was determined by assessing the capability of mitochondrial enzymes to metabolise MTT and gave TC50 values for the compounds that were 30 to 350 times higher than their IC50 values against HCMV and 5 to 15 times higher than their IC50 values against HSV-1. Foscarnet was not liberated on incubation of n-tetradecyl 6-O-carboxyphosphonyl-alpha-D-glucopyranoside with rat liver or intestine homogenate, neither could the neoglycolipid conjugate nor foscarnet be detected in rat plasma following oral administration. Further metabolic and pharmacokinetic studies are required in order to determine whether neoglycolipid conjugates of foscarnet can find a use as drug targeting forms of foscarnet.

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.

Is there a pharmacokinetic interaction between foscarnet and zalcitabine during concomitant administration?

Foscarnet, an antiviral agent used in the treatment of cytomegalovirus infection, and zalcitabine, an antiretroviral nucleoside analogue used in the treatment of human immunodeficiency virus infection, are commonly used concomitantly. Foscarnet and zalcitabine may interact pharmacokinetically, as both compounds are partially eliminated by renal tubular secretion. Owing to dose-related toxicities associated with these two drugs, it is essential that we have data regarding their pharmacokinetic disposition during concomitant therapy. Twelve patients randomly received either foscarnet (four doses) or zalcitabine (five doses) (Phase 1), followed by concomitant foscarnet (four doses) and zalcitabine (six doses) (Phase 2), followed by dosing with the drug not received in Phase 1 (Phase 3). Following the last dose in each phase of the study, serial plasma samples were collected over 8 hours for zalcitabine and over 12 hours for foscarnet to determine the pharmacokinetics of each drug using noncompartmental analysis. Foscarnet plasma and urine levels were determined using high-performance liquid chromatography, and zalcitabine levels were determined using radioimmunoassay. No clinically significant alterations in the pharmacokinetics of foscarnet or zalcitabine occurred in this study. Thus despite the potential for foscarnet and zalcitabine to compete for renal tubular secretion, no apparent pharmacokinetic interaction exists between these two drugs at the clinically relevant doses studied.

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.

Effects of drugs on 2',3'-dideoxy-2',3'-didehydrothymidine phosphorylation in vitro

Drugs commonly administered to patients infected with the human immunodeficiency virus (HIV) have been studied for their propensity to alter the intracellular phosphorylation of the anti-HIV nucleoside analog stavudine (2',3'-dideoxy-2',3'-didehydrothymidine; d4T) in peripheral blood mononuclear cells (PBMCs) and U937 cells in vitro. PBMCs isolated from the blood of healthy volunteers were stimulated by the mitogen phytohemagglutinin (10 microg/ml) for 72 h. Stimulated PBMCs (3 x 10(6) cells/plate) were then incubated with [3H]d4T (0.65 microCi; 3 microM) and either acyclovir, dapsone, ddC, ddI, fluconazole, foscarnet, ganciclovir, itraconazole, lobucavir, ranitidine, ribavirin, rifampin, sorivudine, sulfamethoxazole, trimethoprim, lamivudine (3TC), zidovudine, or thymidine (30 and 300 microM) for 24 h. Doxorubicin and drugs showing some evidence of inhibition were also studied at 0.3 and 3 microM. Cells were extracted overnight with 60% methanol prior to analysis by radiometric high-performance liquid chromatography. Additional data for nine of the drugs were obtained by incubation with [3H]d4T in U937 cells for 24 h. The effect of d4T (0.2 to 20 microM) on zidovudine (0.65 microCi; 0.018 microCi) phosphorylation was also studied. Zidovudine significantly reduced d4T total phosphates in PBMCs and U937 cells (in PBMCs to 33% [P < 0.001] and 17% [P < 0.001] of that in control cells at 3 and 30 microM, respectively). A small reduction in zidovudine phosphorylation was seen with d4T but only at d4T:zidovudine ratios of 100 and 1,000. Of the other compounds screened, only thymidine, ribavirin, and doxorubicin produced inhibition of d4T phosphorylation in both PBMCs and U937 cells. However, doxorubicin was cytotoxic at 3 microM. The decrease in d4T phosphorylation in the presence of ribavirin is consistent with previous findings with zidovudine. Although ddC significantly inhibited the phosphorylation of d4T in PBMCs, this was not seen in U937 cells, and it is probable that the findings in PBMCs are related to mitochondrial toxicity [based on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide cytotoxicity assay]. The only drugs screened which may interfere with d4T phosphorylation at clinically relevant concentrations were zidovudine, ribavirin, and doxorubicin.

Renal excretion and pharmacokinetics of foscarnet in HIV sero-positive patients: effect of probenecid pretreatment

AIMS

The present study was undertaken to test whether the anti-viral agent foscarnet undergoes significant tubular secretion, by using probenecid, an inhibitor of the organic acid secretory pathway in the proximal segment of the nephron.

METHODS

The pharmacokinetics and renal excretion of foscarnet (90 mg kg-1 infused over 2 h) have been investigated, in the absence and presence of probenecid pretreatment (1 g twice daily for 3 days) in a group of 10 HIV seropositive patients.

RESULTS

Mean (+/-s.d.) peak plasma concentrations were 904 +/- 65 microM (foscarnet) and 862 +/- 97 microM (foscarnet+probenecid) whilst the plasma AUC values were 3326 +/- 451 microM h and 3133 +/- 476 microM h respectively. Terminal elimination half-life remained unchanged at 5.6 +/- 0.7 h and the respective volumes of distribution at steady state were 23 +/- 31 (foscarnet) and 25 +/- 31 (foscarnet+probenecid). Mean total body clearance was 110 +/- 17 ml min-1 (foscarnet) and 113 +/- 13 ml min-1 (foscarnet+probenecid) and the corresponding renal clearances of foscarnet were 102 +/- 5 ml min-1 and 105 +/- 5 ml min-1 respectively. There were no significant differences in the total amount of foscarnet excreted by the kidney with 95 +/- 5% (foscarnet) and 91 +/- 6% (foscarnet+probenecid) of the intravenous dose excreted within 24 h. Glomerular filtration rates at 109 +/- 12 ml min-1 (foscarnet) and 100 +/- 13 ml min-1 (foscarnet+probenecid) and respective creatinine clearances at 120 +/- 15 and 119 +/- 10 ml min-1 remained unchanged throughout the study.

CONCLUSIONS

The study shows that foscarnet is not transported via the probenecid-sensitive organic acid secretory pathway in the proximal tubule; the renal elimination of foscarnet is via glomerular filtration.

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.

Drug interactions with zidovudine phosphorylation in vitro

We have investigated the effect of a range of drugs (some commonly coadministered with zidovudine [ZDV] to human immunodeficiency virus-positive patients) on intracellular phosphorylation of ZDV by stimulated peripheral blood mononuclear cells, Molt 4 cells, and U937 cells in vitro. Of the drugs tested (azoles, antiviral agents, antibiotics, and anticancer agents), only doxorubicin and ribavirin caused inhibition of anabolite formation as measured by high-performance liquid chromatography. This in vitro approach may provide important leads to potential interactions at the phosphorylation level in patients with human immunodeficiency virus disease. It is reassuring that so many commonly administered drugs do not alter ZDV phosphorylation.

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.

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.

Antiviral susceptibility testing of cytomegalovirus from primary culture using shell vial assay to detect the late viral antigen

Susceptibility testing of 68 cytomegalovirus (CMV) peripheral blood isolates to Ganciclovir (DHPG) and 11 blood isolates to Foscarnet (PFA), was performed on primary culture isolates using the shell vial assay methodology (SVA-IFA, that is, quantitation of fluorescent focus units, FFUs), with an anti-CMV monoclonal antibody to the late viral antigen. A positive reaction in monolayer cultures of MRC-5 cells was characterized by cytoplasmic fluorescence with inclusions at both or more commonly off one end of the elongated fibroblast nucleus. Isolates from conventional MRC-5 tube cultures displaying a 1+ (10% cytopathic effect) were inoculated into shell vials containing DHPG concentrations of 0, 1.5, 3, 6, 12, or 24 microliters/ml shell vials containing 400, 500, 800, or 1200 microM PFA. The optimal readability of monolayers (expressed as FFUs per monolayer) occurred at 96 h after treatment with DHPG and at 36-48 h with PFA. Resistance to DHPG was determined at the concentration of antiviral agent necessary to reduce the number of FFUs to 90% or 50% of the control [that is, the 90% minimum inhibitory concentration (MIC90) or MIC50]. Six of 68 isolates showed an MIC90 > 12 or an MIC50 > 1.5 microgram/ml, and were considered DHPG resistant. Three of the six isolates were from AIDS patients with late-stage disease who had never received DHPG therapy. All but one (specimen 2400) DHPG-resistant isolates revealed MIC90 values to a PFA concentration of 500 microM, which is considered an achievable peak plasma level in patients undergoing PFA therapy. The single DHPG- and FPA-resistant isolate was obtained from a patient displaying marked clinical resistance to both drugs.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Antiviral therapy in human immunodeficiency virus infections. Current status (Part II)

Part I of this article reviewed the targets against which anti-HIV drugs can be directed, problems in assessing active compounds (e.g. resistance development and use of surrogate end-points). and nucleoside analogues effective against HIV reverse transcriptase. Intensive research is currently being undertaken in laboratories and hospitals to design and evaluate new inhibitors of HIV. In this work, combining different drugs is one important approach, both to decrease toxicity and to offset the rate of resistance development, which seems to be a major problem associated with therapy directed against the ever-changing HIV. Therapeutic vaccines and immunomodulators are other modalities being actively evaluated against HIV and AIDS, although this effort has not yet yielded any licensed treatment. It appears likely that new antiviral drugs and immunotherapies will be forthcoming during the next 5 years, that they will be used in a variety of combinations, and that the treatment options available for opportunistic infections will increase. These developments should improve the survival and the quality of life of patients with HIV infection.

Foscarnet penetrates the blood-brain barrier: rationale for therapy of cytomegalovirus encephalitis

Foscarnet (phosphonoformate) is a potent virustatic drug against herpes-like viruses and is widely used in the therapy of cytomegalovirus infections in immunosuppressed patients. To obtain data on its penetration across the blood-brain barrier, we determined concentrations of foscarnet in cerebrospinal fluid and in plasma specimens from 26 patients with human immunodeficiency virus (stages 2 to 6 by Walter Reed Army Institute of Research classification) after a single infusion of 90 mg of foscarnet per kg of body weight and at steady state by electrochemical detection by high-pressure liquid chromatography. Penetration coefficients were correlated with the integrity of the blood-brain barrier. After a single infusion of foscarnet, levels in plasma ranged from 297 to 1,775 micrograms/ml (990 to 5,920 mumol/liter), with a mean of 766 +/- 400 micrograms/ml. Corresponding levels in cerebrospinal fluid were 57 to 225 micrograms/ml (190 to 750 mumol/liter), with a mean of 131 +/- 52 micrograms/ml. The penetration coefficient was 0.05 to 0.72 (mean, 0.23 +/- 0.16). At steady state, mean foscarnet levels in plasma were 464 +/- 219 micrograms/ml (1,553 mumol/liter) and mean levels in cerebrospinal fluid were 308 +/- 155 micrograms/ml (1,023 mumol/liter). The penetration coefficient was 0.66 +/- 0.11. Although penetration coefficients were highly variable after a single administration and at steady state, the concentrations of foscarnet attained in cerebrospinal fluid are sufficient for complete inhibition of cytomegalovirus replication in vitro. In conclusion, we show that foscarnet seems to be the drug of choice for the treatment of cytomegalovirus encephalitis, because it penetrates the blood-brain barrier and is found in the cerebrospinal fluid in virustatic concentrations. Foscarnet might be considered for additive therapy for human immunodeficiency virus encephalitis in combination with zidovudine or dideoxyinosine.