Ganciclovir Sodium

Introduction Overview

Generic Name

ganciclovir sodium

Brand Name

Cytovene

Dosage Form

injection, powder, lyophilized, for solution

Drug Class

Purine nucleosides

Pharmacokinetics

Absorption:
Ganciclovir is administered intravenously as there is no oral formulation for injection. Following a 1-hour intravenous infusion of 5 mg/kg, the total plasma area under the concentration-time curve (AUC) ranges between 22.1 ± 3.2 and 26.8 ± 6.1 mcg·hr/mL, with peak plasma concentrations (Cmax) averaging around 8.27 to 9 mcg/mL, indicating rapid systemic availability. There is no absorption phase typical of oral drugs because it is delivered directly into the bloodstream, ensuring predictable plasma concentrations. The dosing over one hour avoids high peak plasma levels that could increase toxicity.

Distribution:
Ganciclovir distributes widely in the body with a steady-state volume of distribution (Vd) approximately 0.74 ± 0.15 L/kg, reflecting distribution mainly into extracellular fluids. It crosses the placenta and can be detected in cerebrospinal fluid (CSF) at 24% to 70% of plasma levels, indicating central nervous system penetration, which is clinically relevant for CMV infections involving the brain. Protein binding is minimal, 1% to 2%, over therapeutic concentrations, which suggests most of the drug remains free and active. Its hydrophilic and polar nature influences the distribution, limiting penetration into some tissues but ensuring effective plasma and extracellular concentrations.

Metabolism:
Ganciclovir undergoes minimal metabolism, and most of the drug is eliminated unchanged. It does not undergo significant hepatic metabolism, which reduces concerns about hepatic drug interactions or effects of hepatic impairment on drug levels. This characteristic contributes to the predictable pharmacokinetic profile of ganciclovir in the bloodstream.

Elimination:
Renal clearance is the predominant route of elimination for ganciclovir, involving both glomerular filtration and active tubular secretion. Approximately 91.3 ± 5.0% of an intravenous dose is recovered unchanged in urine, indicating negligible metabolism before excretion. Systemic clearance averages 3.52 ± 0.80 mL/min/kg, with renal clearance contributing about 91% of this. The elimination half-life is approximately 3.5 ± 0.9 hours in patients with normal renal function. In patients with renal impairment, clearance decreases proportionally with the decline in creatinine clearance, prolonging half-life (up to ~10.7 hours in severe impairment). Hemodialysis reduces plasma concentrations by about 50%, which is clinically relevant for overdose or dose adjustment in dialysis patients. Dose modifications based on renal function are essential to avoid toxicity. In elderly patients, clearance is similarly reduced due to decreased renal function, warranting careful monitoring and dose adjustments.

Dosage Forms

Available Dosage Forms:
Ganciclovir is supplied as a sterile lyophilized white to off-white powder for injection to be reconstituted and administered intravenously. The commercially available vial contains 500 mg of ganciclovir equivalent to 543 mg ganciclovir sodium per single-dose vial. Upon reconstitution with 10 mL preservative-free sterile water for injection (non-bacteriostatic), the concentration is 50 mg/mL. This solution is further diluted in an infusion fluid (e.g., 0.9% sodium chloride, 5% dextrose, Ringer's injection, or lactated Ringer's injection) to a concentration not exceeding 10 mg/mL for administration.

Dosages for Adults and Adolescents:
- Treatment of CMV retinitis in immunocompromised adults (including AIDS patients):
- Induction: 5 mg/kg IV every 12 hours over 1 hour for 14 to 21 days.
- Maintenance: 5 mg/kg IV once daily for 7 days per week or 6 mg/kg once daily for 5 days per week.
- Prevention of CMV disease in adult transplant recipients at risk:
- Induction: 5 mg/kg IV every 12 hours over 1 hour for 7 to 14 days.
- Maintenance: 5 mg/kg IV once daily for 7 days per week or 6 mg/kg once daily for 5 days per week until 100 to 120 days post-transplant.

Specific Patient Populations:
- Patients with renal impairment require dose adjustment based on creatinine clearance as detailed in a dosing table, with reduced doses and increased dosing intervals to avoid toxicity.
- Patients undergoing hemodialysis should receive doses not exceeding 1.25 mg/kg three times per week post-dialysis for induction, and 0.625 mg/kg three times per week post-dialysis for maintenance.
- Elderly patients should be dosed cautiously considering renal function.

Preparation for Administration:
- Reconstitute vial with 10 mL sterile water for injection.
- Inspect solution for particulates or discoloration; discard if present.
- Infuse intravenously over 1 hour; rapid or bolus injection is contraindicated due to risk of toxicity.
- Use diluted solution within 24 hours if refrigerated; reconstituted vial stable at room temperature for 12 hours.

Clinical guidelines emphasize avoiding intramuscular or subcutaneous administration due to severe tissue irritation from the alkaline pH.

Mechanism Of Action

Ganciclovir is a synthetic antiviral agent structurally analogous to the nucleoside guanine. Its primary molecular mechanism involves selective inhibition of cytomegalovirus (CMV) DNA replication. Once administered, ganciclovir enters infected cells where it undergoes phosphorylation. The first phosphorylation step is catalyzed by the viral protein kinase pUL97, converting ganciclovir to ganciclovir monophosphate. This initial step is critical as it confers selective activation in virus-infected cells, sparing uninfected cells and reducing toxicity.

Subsequent phosphorylation steps to ganciclovir diphosphate and then triphosphate are catalyzed by cellular kinases. Ganciclovir triphosphate is the active moiety that competitively inhibits viral DNA polymerase (pUL54), the enzyme responsible for viral DNA chain elongation. By competing with the natural nucleotide substrate deoxyguanosine triphosphate, ganciclovir triphosphate is incorporated into the viral DNA, causing premature chain termination due to its altered structure.

At the cellular level, this inhibition of viral DNA polymerase halts viral replication and viral genome synthesis, leading to virustatic effects that prevent further CMV proliferation. This mode of action results in decreased viral load and limits tissue damage caused by cytopathic effects of CMV.

Clinically, the selective activation by viral kinase and inhibition of viral DNA polymerase allow effective treatment of CMV infections with relatively less impact on host cells. Compared to other antiviral agents such as acyclovir, which require activation by herpes simplex virus thymidine kinase, ganciclovir is particularly effective against CMV due to its unique viral kinase dependence. Its mechanism also overlaps with related antivirals like valganciclovir (oral prodrug) that release ganciclovir upon hepatic metabolism.

Research evidence underscores that mutations in the pUL97 or pUL54 genes confer resistance to ganciclovir by reducing phosphorylation efficiency or decreasing drug binding to DNA polymerase, highlighting the clinical importance of this activation and inhibitory pathway. Clinical studies demonstrate efficacy in preventing and treating CMV disease in immunocompromised patients, validating the molecular mechanism observed in vitro and animal models.

Pharmacological Actions

Antiviral activity against cytomegalovirus (CMV) through inhibition of viral DNA polymerase.
Selective phosphorylation and activation in CMV-infected cells mediated by viral protein kinase pUL97.
Inhibition of CMV DNA replication resulting in virustatic effects.
Minimal impact on uninfected host cells due to selective activation.
Ability to penetrate central nervous system as evidenced by cerebrospinal fluid concentrations.
Dose-dependent pharmacokinetics allowing effective plasma concentrations with intravenous administration.
Renally excreted unchanged, enabling predictable clearance and dose adjustments based on renal function.
Induction and maintenance antiviral activity in clinical settings of CMV retinitis and allograft infection prophylaxis.
Potential mutagenic and carcinogenic effects demonstrated in animal studies, necessitating caution in use.
Associated with hematological suppression, including neutropenia, anemia, thrombocytopenia, due to effects on bone marrow progenitor cells.
Demonstrated synergy and adverse interactions with drugs causing myelosuppression or nephrotoxicity.
Pharmacodynamic activity correlates with inhibition of viral proliferation and clinical improvement in CMV disease.
Resistance development through pUL97 and pUL54 gene mutations affecting drug activation and binding.
Long elimination half-life in renal impairment enhancing toxicity risk if dose not adjusted.
Intravenous formulation allows controlled infusion to minimize systemic toxicity.

Therapeutic Or Clinical Uses

Treatment of CMV retinitis in immunocompromised adult patients, including those with AIDS.
Prevention of CMV disease in adult solid organ and bone marrow transplant recipients at risk.
Management of asymptomatic CMV infection in high-risk transplant patients to prevent progression to disease.
Treatment of severe or life-threatening CMV infections where intravenous administration is required.
Use in immunocompromised patients susceptible to CMV-induced morbidity and mortality.
Prophylactic use post-transplant to reduce incidence and severity of CMV-related complications.
Adjunct therapy in combination with other antivirals in select refractory CMV infections.
Clinical use guided by monitoring of hematologic parameters to mitigate toxicity.
Not indicated for pediatric patients in injection form as safety and efficacy not established.
Usage reserved for patients who cannot receive oral valganciclovir or have severe disease warranting intravenous treatment.
Part of antiviral regimen in specialized care settings including transplant centers and HIV/AIDS clinics.
Considered first-line for intravenous CMV therapy prior to or concurrent with other agents like foscarnet or cidofovir when resistance occurs.
Restricted use due to potential teratogenicity and mutagenic risk; contraindicated in pregnancy unless benefits outweigh risks.
Employed in clinical protocols requiring precise dosing adjustments in renal impairment.
Extensively used in clinical trials for evaluation of CMV disease outcomes and prophylaxis schedules.

Side Or Adverse Effects

Hematologic toxicities including granulocytopenia (neutropenia), anemia, thrombocytopenia, and pancytopenia are common and clinically significant.
Renal impairment with increased serum creatinine is reported, particularly in elderly and transplant patients receiving concomitant nephrotoxins.
Gastrointestinal effects such as nausea, diarrhea, abdominal pain, vomiting, and pancreatitis.
Central nervous system effects including headache, dizziness, seizures, confusional states, insomnia, somnolence, and tremor.
General systemic symptoms like pyrexia (fever), asthenia, fatigue, malaise, and hyperhidrosis.
Infections and infestations, including candidiasis and upper respiratory infections, potentially related to immunosuppression.
Injection site reactions such as phlebitis and inflammation due to intravenous administration.
Cardiac disturbances including arrhythmias, torsade de pointes, and ventricular tachycardia reported postmarketing.
Visual disturbances including retinal detachment, macular edema, visual impairment, vitreous disorders, and eye pain.
Skin reactions ranging from rash, urticaria, dry skin, alopecia, dermatitis to severe cutaneous adverse reactions like Stevens-Johnson syndrome and exfoliative dermatitis.
Immune hypersensitivity reactions including anaphylaxis and vasculitis.
Hepatic abnormalities including increased liver enzymes, hepatitis, hepatic failure, and cholestasis.
Musculoskeletal complaints such as myalgia, arthralgia, muscle spasms, and leg cramps.
Psychiatric symptoms including depression, anxiety, agitation, hallucinations, psychotic disorders, and confusion.
Postmarketing reports of hemolytic anemia, agranulocytosis, infertility, testicular hypotrophy, and renal tubular disorders.

Precautions

Use with caution in patients with pre-existing hematologic abnormalities or prior myelosuppression.
Careful monitoring of complete blood counts is essential especially when initiating therapy or in patients with renal impairment.
Dose adjustment required in renal impairment to prevent accumulation and toxicity.
Avoid rapid or bolus intravenous administration to reduce risk of toxic plasma concentrations and infusion site reactions.
Ensure adequate hydration during administration to prevent renal toxicity.
Pregnancy testing recommended before treatment initiation in females of reproductive potential.
Use effective contraception during treatment and for defined periods post-therapy (30 days for females, 90 days for males) due to teratogenicity risks.
Advise against breastfeeding during treatment due to potential for serious adverse effects in nursing infants.
Avoid use with other myelosuppressive or nephrotoxic drugs unless benefits outweigh risks and under close monitoring.
Handle and dispose according to antineoplastic drug guidelines due to carcinogenic and mutagenic potential.
Periodic ophthalmological examinations required for patients treated for CMV retinitis to monitor disease progression.
Monitor for signs of CNS toxicity such as seizures or confusion.
Discontinue treatment if severe hematologic toxicity develops unless clinical benefits justify continuation.
Exercise caution in elderly patients due to increased risk of renal impairment and toxicity.
Patients should be informed about the potential for impaired fertility and advised accordingly.

Warnings

Hematologic Toxicity: Risk of granulocytopenia, anemia, thrombocytopenia, and pancytopenia; may cause severe bone marrow suppression.
Impairment of Fertility: May induce temporary or permanent suppression of spermatogenesis and female fertility.
Fetal Toxicity: Teratogenic and embryotoxic effects demonstrated in animal studies; potential to cause birth defects.
Mutagenesis and Carcinogenesis: Evidence from animal studies indicates potential carcinogenicity and mutagenicity; considered a potential human carcinogen.
Nephrotoxicity: Increased risk of renal impairment especially when combined with nephrotoxic drugs like cyclosporine or amphotericin B.
Not for Intramuscular or Subcutaneous Use: Administration by these routes causes severe tissue irritation due to alkaline pH.
Risk of Seizures: Concomitant use with imipenem-cilastatin not recommended due to reports of generalized seizures.
Severe Injection Site Reactions including pain and phlebitis may occur with improper infusion technique.
Monitor Hematologic and Renal Function Frequently: Periodic testing critical to detect toxicity early.
Risk of Viral Resistance: Prolonged treatment may select for resistant CMV strains with mutations in viral kinase or polymerase.
Potential for Serious Adverse Reactions in Nursing Infants: Breastfeeding contraindicated during treatment.
Dose adjustments necessary in renal impairment to prevent accumulation and toxicity.
Use with Caution in Elderly: Due to decline in renal function and polypharmacy risks.
Advise Patients About Contraception: To avoid fetal harm and genetic risks.
Risk of Progressive CMV Disease: Ganciclovir is not curative; patients require ophthalmologic follow-up.

Contraindication

Known hypersensitivity to ganciclovir or valganciclovir.
History of anaphylaxis or severe allergic reactions to ganciclovir or components of the formulation.
Do not administer via intramuscular or subcutaneous routes due to risk of severe local tissue injury.
Patients with severe neutropenia (absolute neutrophil count < 500 cells/µL).
Patients with severe anemia (hemoglobin < 8 g/dL) or thrombocytopenia (platelet count < 25,000 cells/µL) unless benefits outweigh risks.
Use contraindicated in breastfeeding women due to risk to the infant.
Concomitant use with imipenem-cilastatin generally not recommended due to risk of seizures unless benefits outweigh risks.

Drug Interactions

Imipenem-cilastatin: Concomitant use not recommended due to reports of generalized seizures.
Cyclosporine: May increase risk of nephrotoxicity; monitor renal function closely.
Amphotericin B: Increased nephrotoxicity risk when coadministered, requiring renal monitoring.
Mycophenolate mofetil (MMF): No significant PK interaction, but increased hematologic and renal toxicity reported; monitor blood counts and renal function.
Other myelosuppressive or nephrotoxic drugs (e.g., dapsone, doxorubicin, flucytosine, hydroxyurea, pentamidine, tacrolimus, trimethoprim/sulfamethoxazole, vinblastine, vincristine, zidovudine): Increased toxicity risk; use only if benefits outweigh risks.
Didanosine: Ganciclovir increases didanosine plasma levels; monitor for didanosine toxicity such as pancreatitis.
Probenecid: Increases ganciclovir plasma levels by decreasing renal clearance; dose adjustment and toxicity monitoring advised.
Trimethoprim: No significant effect on ganciclovir pharmacokinetics.
Oral cyclosporine: No major effect on cyclosporine blood levels observed in liver transplant recipients.
Concomitant use with drugs eliminated by renal secretion can alter plasma concentrations due to competition for elimination pathways.
Potential additive bone marrow suppression with other cytotoxic agents; monitor complete blood counts frequently.
Agents that reduce renal function may affect ganciclovir clearance and increase toxicity.
Careful dose adjustment and monitoring required when coadministered with drugs affecting renal function or bone marrow.
Ganciclovir does not significantly induce or inhibit cytochrome P450 enzymes, limiting certain drug interactions.
Clinical monitoring and patient counseling on potential interactions essential.

Preparations Of The Drug

Ganciclovir for Injection, USP supplied as a sterile lyophilized powder in single-dose vials containing 500 mg of ganciclovir (equivalent to 543 mg ganciclovir sodium).
Lyophilized powder intended for reconstitution with 10 mL of preservative-free sterile water for injection, producing a solution concentration of 50 mg/mL.
The reconstituted solution is stable at room temperature (25°C) for 12 hours; do not refrigerate or freeze.
For intravenous infusion, the reconstituted solution is diluted to a final concentration not exceeding 10 mg/mL using compatible infusion fluids such as 0.9% sodium chloride, 5% dextrose, Ringer's injection, or lactated Ringer's injection.
Diluted infusion solutions should be refrigerated at 2° to 8°C and used within 24 hours; frozen storage is not recommended.
Reconstitution must be performed under aseptic conditions, with visual inspection of the solution for particulates or discoloration before administration; discard if abnormal.
Ganciclovir solutions are alkaline (pH ~11), requiring use of plastic cannulas and slow infusion to minimize tissue irritation.
Wear disposable gloves during preparation and handling due to potential carcinogenic and mutagenic properties; follow antineoplastic drug handling guidelines.
Discard any unused portion of reconstituted or diluted solutions to prevent contamination and degradation.
Packaging: Cartons typically contain ten 10 mL single-dose vials.
Storage of unopened vials at controlled room temperature (20° to 25°C) is recommended to maintain stability.
Product labeling and patient information conform to regulatory requirements to ensure safe handling and administration.
Distributed by Hikma Pharmaceuticals USA Inc.; manufactured by THYMOORGAN PHARMAZIE GmbH.
Not for intramuscular or subcutaneous use due to severe tissue irritation risk.
Detailed instructions provided in the prescribing information for reconstitution, dilution, and administration.