Drug Interaction The pharmacokinetics of Foscarnet and ganciclovir were not altered in 13 patients receiving either concomitant therapy or daily alternating therapy for maintenance of CMV disease. There is no clinically significant interaction with zidovudine AZT , or probenecid. All diagnoses and determinations of retinitis progression were made from masked reading of retinal photographs. The 13 patients randomized to treatment with Foscarnet sodium had a significant delay in progression of CMV retinitis compared to untreated controls.
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Drug Interaction The pharmacokinetics of foscarnet and ganciclovir were not altered in 13 patients receiving either concomitant therapy or daily alternating therapy for maintenance of CMV disease. There is no clinically significant interaction with zidovudine AZT , or probenecid. All diagnoses and determinations of retinitis progression were made from masked reading of retinal photographs.
The 13 patients randomized to treatment with Foscavir had a significant delay in progression of CMV retinitis compared to untreated controls. Assessment of retinitis progression was performed by masked evaluation of retinal photographs. The median times to retinitis progression or death were 39 days for the Foscavir group, 61 days for the ganciclovir group and days for the combination group.
For the alternative endpoint of retinitis progression censoring on death , the median times were 39 days for the Foscavir group, 61 days for the ganciclovir group and days for the combination group.
Due to censoring on death, the latter analysis may overestimate the treatment effect. Eleven patients were nonrandomly assigned to receive treatment with Foscavir because of prior intolerance to vidarabine. Lesions in the eight patients randomized to Foscavir healed after 11 to 25 days; seven of the 11 patients nonrandomly treated with Foscavir healed their lesions in 10 to 30 days.
Fifteen of the 43 patients had healing of their lesions in 11 to 72 days with no difference in response between the two treatment groups. Combination therapy with Foscavir and ganciclovir is indicated for patients who have relapsed after monotherapy with either drug. Renal impairment is most likely to become clinically evident during the second week of induction therapy, but may occur at any time during Foscavir treatment.
Elevations in serum creatinine are usually, but not always, reversible following discontinuation or dose adjustment of Foscavir. Safety and efficacy data for patients with baseline serum creatinine levels greater than 2. Hydration may reduce the risk of nephrotoxicity.
Hydration fluid may need to be decreased if clinically warranted. After the first dose, the hydration fluid should be administered concurrently with each infusion of Foscavir. Foscavir may also be associated with a dose-related decrease in ionized serum calcium which may not be reflected in total serum calcium.
This effect is likely to be related to chelation of divalent metal ions such as calcium by foscarnet. Patients should be advised to report symptoms of low ionized calcium such as perioral tingling, numbness in the extremities and paresthesias. Particular caution and careful management of serum electrolytes is advised in patients with altered calcium or other electrolyte levels before treatment and especially in those with neurologic or cardiac abnormalities and those receiving other drugs known to influence minerals and electrolytes see PATIENT MONITORING and Drug Interactions sections.
Physicians should be prepared to treat these abnormalities and their sequelae such as tetany, seizures or cardiac disturbances. The rate of Foscavir infusion may also affect the decrease in ionized calcium. Slowing the infusion rate may decrease or prevent symptoms. Several cases of seizures were associated with death. Cases of status epilepticus have been reported. Risk factors associated with seizures included impaired baseline renal function, low total serum calcium, and underlying CNS conditions.
Hypersensitivity Serious acute hypersensitivity reactions e. If such an acute reaction occurs, therapy should be discontinued and appropriate medical therapy immediately instituted. Some of these patients had confounding risk factors such as underlying cardiac disease, electrolyte abnormalities and other concomitant medications.
Electrocardiograms ECGs and measurement of electrolytes should be obtained prior to treatment initiation and periodically during treatment with Foscavir. Local irritation and ulcerations of penile epithelium have been reported in male patients receiving Foscavir, possibly related to the presence of drug in the urine. Adequate hydration with close attention to personal hygiene may minimize the occurrence of such events. Due to the sodium content of Foscavir micromoles 5. Foscavir should also be avoided in patients on a controlled sodium diet.
Information for Patients CMV Retinitis: Patients should be advised that Foscavir is not a cure for CMV retinitis, and that they may continue to experience progression of retinitis during or following treatment. They should be advised to have regular ophthalmologic examinations. While complete healing is possible, relapse occurs in most patients. Because relapse may be due to acyclovir-sensitive HSV, sensitivity testing of the viral isolate is advised. In addition, repeated treatment with Foscavir has led to the development of resistance associated with poorer response.
In the case of poor therapeutic response, sensitivity testing of the viral isolate also is advised. Effects on Ability to Drive and Use Machines: Adverse effects such as dizziness and convulsions may occur during Foscavir therapy.
Patients who experience seizures, dizziness, somnolence or other adverse reactions that could result in impairment, should be advised to avoid driving or operating machinery. General: Patients should be informed that the major toxicities of foscarnet are renal impairment, electrolyte disturbances, and seizures, and that dose modifications and possibly discontinuation may be required.
The importance of close monitoring while on therapy must be emphasized. Patients should be advised of the importance of reporting to their physicians symptoms of perioral tingling, numbness in the extremities or paresthesias during or after infusion as possible symptoms of electrolyte abnormalities. Patients should also be advised to promptly report any cardiac symptoms. Should such symptoms occur, the infusion of Foscavir should be stopped, appropriate laboratory samples for assessment of electrolyte concentrations obtained, and a physician consulted before resuming treatment.
The potential for renal impairment may be minimized by accompanying Foscavir administration with hydration adequate to establish and maintain a diuresis during dosing. Drug Interactions A possible drug interaction of Foscavir and intravenous pentamidine has been described.
Concomitant treatment of four patients in the United Kingdom with Foscavir and intravenous pentamidine may have caused hypocalcemia; one patient died with severe hypocalcemia. Toxicity associated with concomitant use of aerosolized pentamidine has not been reported.
Because Foscavir can reduce serum levels of ionized calcium, extreme caution is advised when used concurrently with other drugs known to influence serum calcium levels e. Renal impairment and symptomatic hypocalcemia have been observed during concurrent treatment with Foscavir and intravenous pentamidine. When diuretics are indicated, thiazides are recommended over loop diuretics because the latter inhibit renal tubular secretion, and may impair elimination of Foscavir, potentially leading to toxicity.
Abnormal renal function has been observed in clinical practice during the use of Foscavir and ritonavir, or Foscavir, ritonavir, and saquinavir. Because of the risk of QT prolongation and the potential for torsades de pointes, the use of Foscavir should be avoided in combination with agents known to prolong the QT interval including Class IA e.
Pregnancy There are no adequate and well-controlled studies of Foscavir in pregnant women. Because animal reproduction studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.
Animal Data: Foscavir did not adversely affect fertility and general reproductive performance in rats. The results of peri- and post-natal studies in rats were also negative. However, these studies used exposures that are inadequate to define the potential for impairment of fertility at human drug exposure levels. These studies are inadequate to define the potential teratogenicity at levels to which women will be exposed.
Because of the potential for serious adverse events in nursing infants, a decision should be made whether to discontinue nursing or discontinue drug, taking into consideration the importance of the drug to the mother. Pediatric Use The safety and effectiveness of Foscavir in pediatric patients have not been established.
Foscavir is deposited in teeth and bone and deposition is greater in young and growing animals. Foscavir has been demonstrated to adversely affect development of tooth enamel in mice and rats. The effects of this deposition on skeletal development have not been studied. Since deposition in human bone has also been shown to occur, it is likely that it does so to a greater degree in developing bone in pediatric patients. Administration to pediatric patients should be undertaken only after careful evaluation and only if the potential benefits for treatment outweigh the risks.
Geriatric Use No studies of the efficacy or safety of Foscavir in persons 65 years of age or older have been conducted. However, Foscavir has been used in patients age 65 years of age and older. The pattern of adverse events seen in these patients is consistent across all age groups.
This drug is known to be substantially excreted by the kidney, and the risk of toxic reactions to this drug may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, care should be taken in dose selection, and renal function should be monitored. The higher percentages were derived from those patients receiving hydration.
Risk factors associated with seizures included impaired baseline renal function, low total serum calcium, and underlying CNS conditions predisposing the patient to seizures. The rate of seizures did not increase with duration of treatment. In five controlled U. These figures were calculated without reference to drug relationship or severity.