Cytovene-IV (Ganciclovir Sodium) - Drug Interactions, Contraindications, Overdosage

DRUG INTERACTIONS

Didanosine

When the standard intravenous ganciclovir induction dose (5 mg/kg infused over 1 hour every 12 hours) was coadministered with didanosine at a dose of 200 mg orally every 12 hours, the steady-state didanosine AUC_0-12 increased 70 ± 40% (range: 3% to 121%, n=11) and C_max increased 49 ± 48% (range: -28% to 125%). In a separate study, when the standard intravenous ganciclovir maintenance dose (5 mg/kg infused over 1 hour every 24 hours) was coadministered with didanosine at a dose of 200 mg orally every 12 hours, didanosine AUC_0-12 increased 50 ± 26% (range: 22% to 110%, n=11) and C_max increased 36 ± 36% (range: -27% to 94%) over the first didanosine dosing interval. Didanosine plasma concentrations (AUC_12-24) were unchanged during the dosing intervals when ganciclovir was not coadministered. Ganciclovir pharmacokinetics were not affected by didanosine. In neither study were there significant changes in the renal clearance of either drug.

Zidovudine

At an oral dose of 1000 mg of ganciclovir every 8 hours, mean steady-state ganciclovir AUC_0-8 decreased 17 ± 25% (range: -52% to 23%) in the presence of zidovudine, 100 mg every 4 hours (n=12). Steady-state zidovudine AUC_0-4 increased 19 ± 27% (range: -11% to 74%) in the presence of ganciclovir. No drug-drug interaction studies have been conducted with IV ganciclovir and zidovudine.

Since both zidovudine and ganciclovir have the potential to cause neutropenia and anemia, some patients may not tolerate concomitant therapy with these drugs at full dosage.

Probenecid

At an oral dose of 1000 mg of ganciclovir every 8 hours (n=10), ganciclovir AUC_0-8 increased 53 ± 91% (range: -14% to 299%) in the presence of probenecid, 500 mg every 6 hours. Renal clearance of ganciclovir decreased 22 ± 20% (range: -54% to -4%), which is consistent with an interaction involving competition for renal tubular secretion. No drug-drug interaction studies have been conducted with IV ganciclovir and probenecid.

Imipenem-cilastatin

Generalized seizures have been reported in patients who received ganciclovir and imipenem-cilastatin. These drugs should not be used concomitantly unless the potential benefits outweigh the risks.

Other Medications

It is possible that drugs that inhibit replication of rapidly dividing cell populations such as bone marrow, spermatogonia and germinal layers of skin and gastrointestinal mucosa may have additive toxicity when administered concomitantly with ganciclovir. Therefore, drugs such as dapsone, pentamidine, flucytosine, vincristine, vinblastine, adriamycin, amphotericin B, trimethoprim/sulfamethoxazole combinations or other nucleoside analogues, should be considered for concomitant use with ganciclovir only if the potential benefits are judged to outweigh the risks.

No formal drug interaction studies of CYTOVENE-IV and drugs commonly used in transplant recipients have been conducted. Increases in serum creatinine were observed in patients treated with CYTOVENE-IV plus either cyclosporine or amphotericin B, drugs with known potential for nephrotoxicity (see ADVERSE EVENTS). In a retrospective analysis of 93 liver allograft recipients receiving ganciclovir (5 mg/kg infused over 1 hour every 12 hours) and oral cyclosporine (at therapeutic doses), there was no evidence of an effect on cyclosporine whole blood concentrations.

OVERDOSAGE

Overdosage with CYTOVENE-IV has been reported in 17 patients (13 adults and 4 children under 2 years of age). Five patients experienced no adverse events following overdosage at the following doses: 7 doses of 11 mg/kg over a 3-day period (adult), single dose of 3500 mg (adult), single dose of 500 mg (72.5 mg/kg) followed by 48 hours of peritoneal dialysis (4-month-old), single dose of approximately 60 mg/kg followed by exchange transfusion (18-month-old), 2 doses of 500 mg instead of 31 mg (21-month-old).

Irreversible pancytopenia developed in 1 adult with AIDS and CMV colitis after receiving 3000 mg of CYTOVENE-IV solution on each of 2 consecutive days. He experienced worsening GI symptoms and acute renal failure that required short-term dialysis. Pancytopenia developed and persisted until his death from a malignancy several months later. Other adverse events reported following overdosage included: persistent bone marrow suppression (1 adult with neutropenia and thrombocytopenia after a single dose of 6000 mg), reversible neutropenia or granulocytopenia (4 adults, overdoses ranging from 8 mg/kg daily for 4 days to a single dose of 25 mg/kg), hepatitis (1 adult receiving 10 mg/kg daily, and one 2 kg infant after a single 40 mg dose), renal toxicity (1 adult with transient worsening of hematuria after a single 500 mg dose, and 1 adult with elevated creatinine (5.2 mg/dL) after a single 5000 to 7000 mg dose), and seizure (1 adult with known seizure disorder after 3 days of 9 mg/kg). In addition, 1 adult received 0.4 mL (instead of 0.1 mL) CYTOVENE-IV solution by intravitreal injection, and experienced temporary loss of vision and central retinal artery occlusion secondary to increased intraocular pressure related to the injected fluid volume.

Since ganciclovir is dialyzable, dialysis may be useful in reducing serum concentrations. Adequate hydration should be maintained. The use of hematopoietic growth factors should be considered (see DOSAGE AND ADMINISTRATION: Renal Impairment).

CONTRAINDICATIONS

CYTOVENE-IV is contraindicated in patients with hypersensitivity to ganciclovir or acyclovir.