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Foscarnet-induced hypocalcemia and effects of foscarnet on calcium metabolism.

Foscarnet (trisodium phosphonoformate), an investigational pyrophosphate analog increasingly used to treat refractory cytomegalovirus retinitis and mucocutaneous herpes simplex virus infections in immunocompromised patients, has been reported to cause abnormalities in serum calcium and phosphate, including cases of fatal hypocalcemia. To further elucidate the magnitude and mechanism of these abnormalities in humans treated with foscarnet for opportunistic herpes virus infections, we analyzed anaerobic serum specimens and 24-h urine samples before and after single and multiple doses of iv foscarnet and performed a series of in vitro experiments with normal human serum and plasma. Plasma ionized calcium concentrations acutely decreased by a mean 0.17 mmol/L in the 6 individuals who received a 90 mg/kg dose of foscarnet and by a mean 0.28 mmol/L in the 11 individuals who received a 120 mg/kg dose (P = 0.016, 90 vs. 120 mg/kg dose). Results of in vitro experiments showed a highly significant inverse linear relationship between foscarnet and ionized calcium concentrations, but no correlation between foscarnet and total calcium or phosphate concentration. Dialysis experiments suggested that the complexing of foscarnet with ionized calcium could be a cause of this ionized hypocalcemia. Physicians must be aware of this phenomenon and should measure serum ionized calcium during foscarnet therapy (preferably at the end of a foscarnet infusion) whenever neurological or cardiological abnormalities occur.

Antiviral Agents

Comparison of foscarnet and foscarnet esters as anti-influenza virus agents.

Foscarnet is shown to inhibit influenza A virus replication by inhibiting viral RNA synthesis in infected cells. Viral RNA synthesis by isolated nuclei from infected cells was as sensitive to foscarnet as viral RNA synthesis by enzymes from isolated virions or viral cores. It is, therefore, unlikely that the mere association of the polymerase in a replication complex, as in isolated nuclei and infected cells, is the reason for the fact that foscarnet is 10-20 times less active in inhibiting virus replication than cell-free RNA synthesis. We, therefore, tested 44 esters of foscarnet for improved antiviral effect. Of these only a few phenyl esters were more potent than foscarnet itself. These esters did not inhibit the viral RNA polymerase activity and may be hydrolyzed intracellularly to foscarnet. The increased antiviral potency of the phenyl esters was, however, accompanied by increased cellular toxicity, and these compounds, therefore, were less selective antiviral agents than foscarnet. The results suggest that it is not possible to increase the anti-influenza activity of foscarnet by converting it to an ester.

Antiviral Agents

Foscarnet nephrotoxicity: mechanism, incidence and prevention.

Foscarnet is a pyrophosphate analogue that has been successfully used in severe cytomegalovirus (CMV) infections. Little is known of the incidence and mechanisms of foscarnet-induced nephrotoxicity as most data comes from recipients of renal allografts or from patients with severe underlying disease or with other nephrotoxic drugs. We have retrospectively analyzed the evolution of renal function after 56 courses of foscarnet. In addition, we have prospectively studied the protective effects of hydration on foscarnet nephrotoxicity (2.5 liters of saline/day during the night before the foscarnet therapy and throughout the course of treatment). Foscarnet-induced acute renal failure was defined as a rise in serum creatinine of at least 25% from the basal value. An increase in serum creatinine occurred in 37 cases out of the 56 courses of foscarnet (66%). The mean serum creatinine prior to foscarnet was 80.5 +/- 3.3 mumol/l and the mean increase was 190 +/- 28.3 mumol/l (range 80-1,000). Peak serum creatinine was higher than 200 and 300 mumol/l in 16 and 13 patients, respectively. Kidney obtained at autopsy from a 30-year-old male with AIDS, CMV pneumonitis and acute renal failure secondary to foscarnet administration showed an extensive tubular necrosis. In the group which was prospectively hydrated only 1 patient had an acute renal failure. The mean serum creatinine at the peak (96 +/- 4 mumol/l) and at the end of the treatment (83 +/- 4 mumol/l) was significantly lower (p less than 0.05) than in non hydrated patients. In conclusion, foscarnet is a highly nephrotoxic drug which induces acute tubular necrosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Kidney Injury

A controlled trial comparing foscarnet with vidarabine for acyclovir-resistant mucocutaneous herpes simplex in the acquired immunodeficiency syndrome. The AIDS Clinical Trials Group.

BACKGROUND AND METHODS: Most strains of herpes simplex virus that are resistant to acyclovir are susceptible in vitro to both foscarnet and vidarabine. We conducted a randomized trial to compare foscarnet with vidarabine in 14 patients with the acquired immunodeficiency syndrome (AIDS) and mucocutaneous herpetic lesions that had been unresponsive to intravenous therapy with acyclovir for a minimum of 10 days. The patients were randomly assigned to receive either foscarnet (40 mg per kilogram of body weight intravenously every 8 hours) or vidarabine (15 mg per kilogram per day intravenously) for 10 to 42 days. In the isolates of herpes simplex virus we documented in vitro resistance to acyclovir and susceptibility to foscarnet and vidarabine. RESULTS: The lesions in all eight patients assigned to foscarnet healed completely after 10 to 24 days of therapy. In contrast, vidarabine was discontinued because of failure in all six patients assigned to receive it. The time to complete healing (P = 0.01), time to 50 percent reductions in the size of the lesions (P = 0.01) and the pain score (P = 0.004), and time to the end of viral shedding (P = 0.006) were all significantly shorter in the patients assigned to foscarnet. Three patients had new neurologic abnormalities while receiving vidarabine. No patient discontinued foscarnet because of toxicity. Although initial recurrences of herpes simplex infection after the index lesion had healed tended to be susceptible to acyclovir, acyclovir-resistant infection eventually recurred in every healed patient, a median of 42.5 days (range, 14 to 191) after foscarnet was discontinued. CONCLUSIONS: For the treatment of acyclovir-resistant herpes simplex infection in patients with AIDS, foscarnet has superior efficacy and less frequent serious toxicity than vidarabine. Once the treatment is stopped, however; there is a high frequency of relapse.

Acquired Immunodeficiency Syndrome

Mortality in patients with the acquired immunodeficiency syndrome treated with either foscarnet or ganciclovir for cytomegalovirus retinitis.

BACKGROUND AND METHODS: We performed a multicenter, randomized, unblinded clinical trial (the Foscarnet-Ganciclovir Cytomegalovirus Retinitis Trial) designed to compare ganciclovir with foscarnet in the treatment of cytomegalovirus retinitis in patients with the acquired immunodeficiency syndrome (AIDS). Of 234 patients, 127 were randomly assigned to ganciclovir and 107 to foscarnet; the study drugs were administered according to a common protocol at the 11 participating clinical centers. Antiretroviral therapy (with zidovudine, didanosine, or dideoxycytidine) was given as dictated by best medical judgment. The patients were followed for the progression of retinitis, visual loss, and death. RESULTS: Excess mortality in the ganciclovir group (as compared with the foscarnet group) led the Policy and Data Monitoring Board to recommend suspension of the treatment protocol 19 months after the trial started. As of that time, 65 of the patients assigned to ganciclovir had died, as compared with 36 of those assigned to foscarnet (51 percent vs. 34 percent, P = 0.007; relative risk, 1.79; 95 percent confidence interval, 1.17 to 2.73). The median survival was 8.5 months in the ganciclovir group and 12.6 months in the foscarnet group. Although the patients assigned to ganciclovir received less antiretroviral therapy on average than those assigned to foscarnet, the excess mortality could not be explained entirely by differences in exposure to antiretroviral drugs. In the forscarnet group, the only subgroup of patients identified as having excess mortality were those whose renal function was compromised at entry. There was no difference between the two treatment groups in the rate of progression of retinitis (relative risk, 0.95; P = 0.751). CONCLUSIONS: These results suggest that for patients with AIDS, and cytomegalovirus retinitis, treatment with foscarnet offers a survival advantage over treatment with ganciclovir, although the patients may not tolerate foscarnet as well as ganciclovir.

Acquired Immunodeficiency Syndrome

Foscarnet. A review of its antiviral activity, pharmacokinetic properties and therapeutic use in immunocompromised patients with cytomegalovirus retinitis.

The pyrophosphate analogue, foscarnet, selectively inhibits the DNA polymerase of human herpes viruses, including cytomegalovirus, and the reverse transcriptase of HIV. Viral replication is therefore prevented, but resumes when the drug is cleared from infected cells. In vitro, the combination of foscarnet and zidovudine (azidothymidine) has an additive effect against cytomegalovirus and acts synergistically against HIV. An improvement in cytomegalovirus retinitis is obtained in over 85% of affected AIDS patients during foscarnet induction therapy, but relapse usually occurs within a month of ceasing treatment. There is a similar duration of remission during maintenance therapy given for 5 days each week, but this can be extended 4- to 5-fold with daily administration of higher doses. In allograft recipients, progression of retinitis can be halted by foscarnet until immune function recovers and eradicates the virus. The incidence of acute renal failure, which is common during foscarnet therapy, may be reduced by dosage adjustment and adequate prehydration. Anaemia, phlebitis, nausea and vomiting, and disturbances in serum calcium and phosphate levels, perhaps resulting from uptake of foscarnet into bone or chelation with ionised calcium, have also been associated with administration of the drug. Cytomegalovirus retinitis is difficult to treat, with few therapeutic options available. Although treatment with foscarnet produces some severe adverse effects, with care these can be minimised, and the drug produces clinical improvement in a large proportion of patients; this is a highly encouraging finding at this stage in its development. Preliminary comparative data indicate that foscarnet and ganciclovir are similarly effective, but foscarnet may have some theoretical advantages in AIDS patients since it can be used in combination with zidovudine without potentiating myelosuppression.

Acquired Immunodeficiency Syndrome

Foscarnet in the treatment of cytomegalovirus infection of the esophagus and colon in patients with the acquired immune deficiency syndrome.

Foscarnet, administered via a central line, was used for the treatment of 18 episodes of cytomegalovirus (CMV) esophageal ulceration in 15 patients, and in the treatment of 27 episodes of CMV colitis in 22 patients. In 15 of the 18 episodes of the esophageal disease, there was complete loss of symptoms within 2 wk. Only three of the 15 patients responding to foscarnet therapy had a relapse of their esophageal disease. Two of these patients were successfully retreated with foscarnet. Of the 22 patients receiving foscarnet for CMV colitis, four died during foscarnet therapy. Of the 18 patients completing the course of treatment with foscarnet for first-episode CMV colitis, 11 remitted completely and six had a partial remission. All patients with partial remission had a second pathogen responsible for the continuation of their diarrhea. Only one patient completing a course of foscarnet failed to respond microscopically to treatment. Three patients experienced relapse of their CMV colitis, two of whom responded to further courses of foscarnet. Foscarnet is an effective therapy for CMV disease of the gastrointestinal tract, with rapid resolution of clinical symptoms, long-term remission of esophageal disease, and shorter disease-free periods for CMV colitis.

Acquired Immunodeficiency Syndrome

Review of the toxicities of foscarnet.

The primary dose-limiting adverse effects associated with foscarnet treatment of cytomegalovirus retinitis in patients with AIDS are renal impairment and ionized hypocalcemia. Dose-limiting renal impairment, consisting of significant alterations in serum creatinine levels or creatinine clearance or acute renal failure, has been observed in 10-20% of AIDS patients receiving foscarnet via intermittent i.v. infusion. Nephrotoxicity can be minimized by adjusting dosage according to creatinine clearance and by ensuring that adequate hydration is provided throughout foscarnet therapy. Transient decreases in serum or plasma ionized calcium levels appear to occur in all patients during foscarnet infusion, with these decreases being observed in the absence of changes in total calcium levels. Hypocalcemia produces mild symptoms in some patients and may play a role in unexplained cases of arrhythmia or seizure. Careful attention should be given to levels of total calcium and other minerals during foscarnet treatment, and the occurrence of symptomatic hypocalcemia should prompt evaluation of ionized calcium concentrations and foscarnet dose reduction. Another potentially treatment-limiting effect attributed to foscarnet is penile ulceration, which appears to result from exposure of the glans penis to unchanged foscarnet in the urine.

Antiviral Agents

Sensitivity of cytomegalovirus to intravenous foscarnet treatment.

Intravenous foscarnet was given on an emergency basis to 30 immunosuppressed patients with cytomegalovirus (CMV) disease, of whom 28 were organ transplant recipients. Thirteen patients responded to foscarnet by cessation of CMV secretion. The in vitro sensitivity to foscarnet of the CMV isolates from non-responders before, during and after foscarnet treatment was similar to that of viral isolates from responders before or during foscarnet treatment and also to CMV isolates from non-treated patients, with mean in vitro IC50 values of 239-294 microM of foscarnet. Thus, there was no evidence of increased resistance of the CMV isolates obtained after foscarnet treatment. A higher total foscarnet dose appeared to favor response.

Antiviral Agents

Design of a randomized controlled trial of foscarnet in patients with cytomegalovirus retinitis associated with acquired immunodeficiency syndrome.

In a controlled trial of foscarnet in the treatment of cytomegalovirus (CMV) retinitis in patients with the acquired immunodeficiency syndrome (AIDS), patients with non-immediately sight-threatening lesions were randomized to receive immediate treatment with foscarnet or foscarnet treatment delayed until the first signs of retinitis progression. Foscarnet induction therapy was administered at a dosage of 60 mg/kg 3 times/day via 1-hour intravenous infusion for 21 days. Foscarnet maintenance therapy was administered at a dosage of 90 mg/kg/day via 2-hour infusion. Foscarnet was well tolerated and effective in delaying progression of CMV retinitis in these patients. Final analysis of data from this study and data from other studies will help to determine what role foscarnet will have in the treatment of CMV retinitis in patients with AIDS.

Acquired Immunodeficiency Syndrome

Effect of foscarnet therapy on human immunodeficiency virus p24 antigen levels in AIDS patients with cytomegalovirus retinitis.

Circulating human immunodeficiency virus (HIV) p24 antigen levels were measured in 22 AIDS patients who had detectable serum antigen at baseline after induction and maintenance therapy of foscarnet for cytomegalovirus retinitis in phase I/II multicenter trials. The HIV p24 antigen levels decreased from a baseline value of 199 +/- 236 (mean +/- SD) and 140 pg/mL (median) to 106 +/- 218 and 28 pg/mL after 14 days of foscarnet induction therapy (60 mg/kg every 8 h). During chronic foscarnet maintenance, there was a sustained decrease in mean HIV p24 antigen levels below pre-foscarnet therapy baseline concentrations for a median of 16 weeks after foscarnet induction. These results provide evidence for a sustained clinical antiretroviral effect of chronic foscarnet maintenance therapy, consistent with a recent report that foscarnet-treated AIDS patients live longer than ganciclovir-treated patients.

Acquired Immunodeficiency Syndrome

Foscarnet therapy in five patients with AIDS and acyclovir-resistant varicella-zoster virus infection.

OBJECTIVE: To determine whether foscarnet has potential efficacy in the treatment of acyclovir-resistant mucocutaneous varicella-zoster infection in patients with the acquired immunodeficiency syndrome (AIDS). DESIGN: Open-label study. SETTING: Three university medical centers. PATIENTS: Five patients with AIDS who were infected with thymidine-kinase-deficient or -altered strains of varicella-zoster virus. INTERVENTION: Foscarnet, 40 mg/kg body weight every 8 hours in 1-hour infusions for 10 or more days. MAIN RESULTS: Four patients had healing in response to foscarnet therapy, and each of four tested patients became culture negative for virus during foscarnet therapy. Results of fluorescent antigen testing remained positive during therapy in two patients; one of these patients had concomitant clinical failure but the other patient healed fully. One patient had complete healing despite the emergence of resistance to foscarnet in serial specimens obtained during foscarnet therapy. CONCLUSION: Foscarnet is a potentially effective and tolerable antiviral agent for patients with acyclovir-resistant, varicella-zoster virus infection; however, the optimal dosage and duration of therapy require further study, as does the relation between clinical findings and in-vitro susceptibility results.

Acquired Immunodeficiency Syndrome

Clinical pharmacology: foscarnet.

Foscarnet exerts its antiviral effects via reversible inhibition of viral polymerases. Pharmacodynamic data indicate that herpesvirus and human immunodeficiency virus replication is inhibited by therapeutically achievable concentrations of foscarnet; however, the concentrations of foscarnet required for such inhibition have been found to vary widely. Pharmacokinetic data indicate that foscarnet is eliminated via the renal route, undergoes negligible metabolism, and appears to be distributed widely from the circulation. However, the available data indicate that the pharmacokinetics of the drug varies among patients and within the individual patient, particularly with regard to plasma drug levels; furthermore, such factors as the intracellular kinetics of the drug have yet to be well characterized. It is thus difficult to formulate optimal dosing regimens on the basis of what is known of foscarnet pharmacodynamics and pharmacokinetics. Nevertheless, dosages that produce clear-cut therapeutic benefits without unacceptable toxicity have been identified in clinical trials of foscarnet in acquired immunodeficiency syndrome (AIDS) patients with cytomegalovirus (CMV) retinitis.

Antiviral Agents

Foscarnet treatment of acyclovir-resistant herpes simplex virus infection in patients with acquired immunodeficiency syndrome: preliminary results of a controlled, randomized, regimen-comparative trial.

Herpes simplex virus (HSV) resistant to acyclovir can produce persistent mucocutaneous ulcerative disease in patients with the acquired immunodeficiency syndrome (AIDS). The incidence of clinically significant acyclovir-resistant HSV disease has dramatically increased since the advent of the AIDS epidemic. The primary mechanism of acyclovir resistance is induction of viral mutants defective or deficient in thymidine kinase, the viral-encoded enzyme, which catalyzes the rate-limiting step in the triphosphorylation of acyclovir to its active form (acyclovir triphosphate). Foscarnet, a potent inhibitor of HSV DNA polymerase, does not require phosphorylation for its antiviral activity. This compound has been found to be effective in the treatment of acyclovir-resistant HSV infection by several investigators. A recently completed dose-comparative trial of foscarnet in AIDS patients with acyclovir-resistant HSV has confirmed the safety and efficacy of two doses of foscarnet (40 mg/kg every 8 or 12 hours) in the treatment of this disease, as well as providing preliminary evidence supporting the utility of foscarnet maintenance therapy in delaying recurrence of HSV lesions. Analysis of data from this trial has been complicated by the tremendous variability in lesion size at initiation of therapy, making any statistically valid comparison of treatment regimens almost impossible. A further trial in AIDS patients with acyclovir-resistant HSV infection has been designed to define better the role of foscarnet maintenance and, in light of evidence that a significant proportion of initial recurrences are due to acyclovir-sensitive HSV, to examine the potential utility of acyclovir maintenance following foscarnet induction therapy.

Acquired Immunodeficiency Syndrome

Foscarnet treatment of cytomegalovirus retinitis in patients with the acquired immunodeficiency syndrome.

Ten patients with acquired immunodeficiency syndrome with newly diagnosed cytomegalovirus (CMV) retinitis were treated with an induction regimen of intravenous foscarnet, 60 mg/kg of body weight, administered as a 2-h infusion and repeated every 8 h for 14 days. At the end of induction, 9 of 10 patients had stabilized (no new retinal lesions and stable old lesions [7 patients]) or improved (decreased retinal opacification [2 patients]). All eight patients with CMV in urine or blood upon entry into the study had negative urine and blood cultures at the end of induction. After induction therapy, seven patients continued maintenance foscarnet therapy, 60 mg/kg as a single daily infusion, 5 days/week. In six patients, retinal lesions increased in size after 2 to 32 weeks of maintenance therapy. One was invaluable because a retinal detachment developed. Only 9 of 42 blood and urine cultures obtained during maintenance foscarnet therapy yielded CMV, compared with 7 of 14 obtained prior to the initiation of foscarnet induction therapy (P = 0.04). Foscarnet toxicity was mild and infrequent: elevation in serum creatinine by 0.5 to 1.3 mg/dl over the base line (two patients), muscle twitching (three patients), hemoglobin decrease by 1 mg/dl (two patients), nausea (two patients), absolute neutrophil count decrease by 50% (one patient), rise in serum phosphorus to greater than 5.5 mg/dl (four patients), and proteinuria (two patients). Intermittently administered intravenous foscarnet appears to be an effective, relatively nontoxic therapy for CMV retinitis. Additional studies to determine the optimal dosage for maintenance therapy are needed, as are comparative trials with ganciclovir.

Acquired Immunodeficiency Syndrome

Pharmacokinetics of foscarnet and distribution to cerebrospinal fluid after intravenous infusion in patients with human immunodeficiency virus infection.

To investigate the pharmacokinetics and effects of intravenous foscarnet, 13 relatively healthy male patients with human immunodeficiency virus infection and a mean CD4+ lymphocyte value of 0.45 x 10(-9) cells per liter were given a continuous intravenous infusion of foscarnet (0.14 to 0.19 mg/kg per min) for 8 to 21 days. Blood and urine samples were taken during and after drug administration to monitor foscarnet concentrations. Lumbar puncture was performed during the infusion in five patients. The concentrations in plasma showed large variations both within and between patients. The disposition of foscarnet could be explained by a triexponential equation (t1/2 lambda 1, 0.40 to 2.52 h; t1/2 lambda 2, 3.20 to 16.7 h; t1/2 lambda 3, 36 to 196 h). Renal clearance accounted for most of the plasma clearance, the difference probably reflecting the passage of foscarnet into bone. Up to 20% of the cumulative dose may have been deposited in bone 7 days postinfusion. Foscarnet was distributed to the cerebrospinal fluid in a concentration varying from 13 to 68% of the simultaneous concentration in plasma. Polyuria and polydipsia were recorded in all patients. There appears to be an association between the degree of malaise, including symptoms such as nausea, vomiting, fatigue, and headache, and concentrations in plasma above 350 mumol/liter.

Acquired Immunodeficiency Syndrome

Foscarnet and ganciclovir in the treatment of cytomegalovirus retinitis.

Induction regimens of foscarnet and ganciclovir are highly effective in arresting cytomegalovirus (CMV) retinitis in patients with AIDS. Chronic maintenance therapy is nonetheless required to forestall progression of disease following induction. In open studies of these two agents in AIDS patients with CMV retinitis at dosages similar to those currently recommended, median times to retinitis progression during maintenance therapy of as long as greater than 100 days have been observed. In a randomized comparative trial of immediate and delayed foscarnet treatment utilizing rigorously defined end points, the mean times to retinitis progression were 13.3 weeks among patients receiving immediate foscarnet therapy and 3.2 weeks among those receiving no treatment. In a similar trial of ganciclovir, the mean times to progression were 68.5 days among patients receiving immediate treatment and 22.9 days among those receiving no treatment. Experience in a number of studies not designed to assess mortality has suggested that specific antiviral treatment for CMV retinitis is associated with prolongation of survival. One retrospective analysis of survival patterns in patients treated with ganciclovir has suggested a significant effect of this agent on survival; another analysis has shown no association between anti-CMV therapy and survival, with the relative hazard of death among patients receiving foscarnet therapy being equivalent to that among patients receiving ganciclovir therapy. In the one randomized study comparing the mortality of patients receiving initial treatment with either foscarnet or ganciclovir, foscarnet-treated patients had a median survival of 12.6 months compared with 8.5 months for ganciclovir-treated patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytomegalovirus Infections

Maintenance therapy for cytomegalovirus retinitis in patients with acquired immunodeficiency syndrome: foscarnet.

The use of ganciclovir in the treatment of cytomegalovirus (CMV) retinitis in patients with acquired immunodeficiency syndrome (AIDS) is limited by marrow toxicity and by the development of resistance to this agent in CMV strains capable of causing progressive disease. Foscarnet retains activity against ganciclovir-resistant CMV and has an adverse effect profile different from that of ganciclovir. Preliminary data from studies conducted under the AIDS Clinical Trials Group (ACTG) program indicate that intravenous foscarnet maintenance therapy at 60, 90, and 120 mg/kg/day in AIDS patients with CMV retinitis successfully completing foscarnet induction therapy is associated with median times to retinitis progression of 90, 95, and greater than 123 days, respectively. An ACTG trial of foscarnet in patients failing ganciclovir therapy has been initiated, as has a trial jointly sponsored by the National Eye Institute and the National Institute of Allergy and Infectious Diseases comparing the safety and efficacy of foscarnet and ganciclovir. Also underway is a trial evaluating the effects of combination and alternating regimens of these two agents.

Antiviral Agents