Herpigel0.15%

Established / FDA-approved indications

• Treatment of cytomegalovirus (CMV) retinitis in immunocompromised patients, including patients with AIDS.
• Prevention of CMV disease in solid organ transplant recipients (e.g., kidney, heart, liver) who are at risk of CMV infection.

Guideline-supported / commonly used off-label uses

• Prevention and pre-emptive treatment of CMV disease in hematopoietic stem cell transplant recipients (per transplant infectious disease guidelines).
• Treatment of other severe CMV end-organ disease (e.g., CMV colitis, CMV pneumonitis, CMV esophagitis) in immunocompromised hosts, usually as part of specialist-directed combination management.
• Congenital CMV infection in neonates with central nervous system involvement (specialist-directed, weight-based dosing; oral valHerpigel is often preferred once feasible).

Herpigel is not indicated for the treatment of common, self-limited viral illnesses and should be reserved for confirmed or strongly suspected CMV disease in at-risk patients under specialist supervision.

Each vial contains Ganciclovir (as ganciclovir sodium), supplied as a sterile lyophilized powder for reconstitution and intravenous infusion. Strength is typically labeled as Ganciclovir 500 mg per vial (local brand strengths in Bangladesh may vary; confirm on the pack).

Herpigel is a synthetic guanine-derivative nucleoside analog with potent activity against cytomegalovirus (CMV) and other herpesviruses. It is administered only by slow intravenous infusion because oral bioavailability of Herpigel itself is poor (the oral prodrug valHerpigel is used when oral therapy is appropriate).

Herpigel is reserved for serious CMV infections in immunocompromised patients, such as those with AIDS or those who have undergone organ transplantation, because of its significant toxicity profile, which requires close laboratory monitoring during treatment.

Herpigel belongs to the class of antiviral agents (nucleoside analog, guanine derivative), specifically an anti-cytomegalovirus (anti-CMV) agent.

Ganciclovir is a synthetic analog of 2'-deoxyguanosine. Inside CMV-infected cells, it is phosphorylated (initially by a viral kinase, then by cellular kinases) to Ganciclovir triphosphate, which competitively inhibits the binding of deoxyguanosine triphosphate to viral DNA polymerase. Incorporation of Ganciclovir triphosphate into viral DNA slows and eventually terminates viral DNA chain elongation, thereby inhibiting CMV replication.

Ganciclovir triphosphate concentrations are much higher in CMV-infected cells than in uninfected cells, which provides some selectivity for virally infected cells, though it still has significant effects on host cell DNA synthesis, accounting for its hematologic and reproductive toxicity.

Pharmacokinetics: Ganciclovir is eliminated almost entirely unchanged by the kidneys via glomerular filtration and active tubular secretion; renal impairment substantially prolongs its half-life, which is why renal dose adjustment is essential (see Dosage and Administration).

Herpigel is administered as an intravenous infusion over 1 hour by a healthcare professional in a hospital or clinic setting; it is not for home self-injection. It must never be given as a rapid or bolus IV push, and must never be given intramuscularly or subcutaneously. Adequate patient hydration and renal function monitoring should accompany each course.

Clinically significant interactions

• Zidovudine (AZT) and other myelosuppressive drugs (e.g., cytotoxic chemotherapy, other antivirals with marrow toxicity): concurrent use with Herpigel substantially increases the risk of severe neutropenia and anemia; combination is often avoided or requires very close blood count monitoring and dose adjustment.
• Imipenem-cilastatin: concurrent use with Herpigel has been associated with generalized seizures; use together only if the potential benefit outweighs the risk.
• Nephrotoxic drugs (e.g., cyclosporine, tacrolimus, amphotericin B, aminoglycosides): concurrent use with Herpigel may increase the risk of additive nephrotoxicity, which can further raise Herpigel levels and toxicity due to reduced renal clearance; renal function should be monitored closely.
• Didanosine: Herpigel can increase plasma concentrations of didanosine, raising the risk of didanosine-related toxicity.
• Mycophenolate mofetil and probenecid: may increase Herpigel plasma concentrations by competing for renal tubular secretion, increasing the risk of Herpigel toxicity.

Always inform the physician of all other medicines being used before starting Herpigel.

Very common / common

• Hematologic: neutropenia (granulocytopenia), anemia, thrombocytopenia — the most important and frequent toxicities of Herpigel (see Precautions and Warnings).
• General: fever, chills, asthenia (weakness), headache.
• Gastrointestinal: nausea, vomiting, diarrhea, abdominal pain, decreased appetite.
• Others: elevated liver enzymes, elevated serum creatinine, cough, dyspnea, rash, sweating.

Serious (less common but important)

• Severe bone marrow suppression, including pancytopenia and aplastic anemia.
• Seizures, confusion, and other central nervous system effects.
• Serious skin reactions, including Stevens-Johnson syndrome (rare).
• Renal impairment/renal failure.
• Cardiac arrhythmias (reported rarely).
• Gastrointestinal bleeding or perforation (reported rarely).

Report any unusual bruising, bleeding, signs of infection (fever, sore throat), or severe rash to a physician immediately.

Pregnancy: Based on animal studies, Herpigel has shown teratogenic and embryotoxic effects at clinically relevant exposures. Herpigel should be used during pregnancy only if the potential benefit to the mother clearly justifies the potential risk to the fetus, and only under close physician supervision. Women of reproductive potential should use effective contraception during treatment and for at least 30 days after the last dose. Men should use barrier contraception during treatment and for at least 90 days after the last dose, due to potential effects on sperm.

Lactation: Because of the potential for serious adverse reactions in a breastfed infant, breastfeeding is generally not recommended during treatment with Herpigel and for a period after stopping. A physician should be consulted to weigh the mother's need for treatment against infant feeding options.

Boxed warnings

• Hematologic toxicity: Severe granulocytopenia, anemia, thrombocytopenia, and pancytopenia (including bone marrow failure) have occurred with Herpigel. Complete blood counts with differential and platelet counts should be monitored closely (e.g., before and periodically during therapy); dose reduction, treatment interruption, or discontinuation may be required for significant cytopenia.
• Impaired fertility: Based on animal data, Herpigel may cause temporary or permanent inhibition of spermatogenesis and suppression of fertility in females.
• Fetal toxicity: Based on animal data, Herpigel has the potential to cause birth defects (see Pregnancy and Lactation).
• Carcinogenic potential: Based on animal data, Herpigel is considered a potential carcinogen in humans; long-term risk cannot be excluded.

Other precautions

• Renal impairment: Dose must be adjusted based on creatinine clearance, as Herpigel is cleared renally and accumulates with reduced kidney function, increasing toxicity risk.
• Concurrent myelosuppressive or nephrotoxic drugs: Use with caution and close monitoring (see Interactions).
• Seizure risk: Use with caution in patients with a history of seizures or with concurrent use of drugs that lower seizure threshold (e.g., imipenem-cilastatin).
• Adequate hydration should be maintained during treatment.
• Herpigel must be administered exactly as prescribed, at the correct dose, rate, and duration; it should not be stopped early, doses skipped, or the medicine shared with another person, without medical advice, as inadequate treatment of CMV disease can lead to resistance and treatment failure.

Overdose with Herpigel can cause severe worsening of its known toxicities, particularly severe bone marrow suppression (neutropenia, anemia, thrombocytopenia) and renal impairment/renal failure. If an overdose of Herpigel is suspected, seek immediate medical attention or contact emergency services/poison control right away. Hemodialysis may help reduce plasma concentrations of Herpigel in overdose and is generally used under hospital supervision, along with hydration and supportive care and monitoring of blood counts and renal function. Do not attempt to manage a suspected overdose at home.

Store unopened vials at room temperature (20-25°C / 68-77°F), protected from light. After reconstitution, the solution should be used according to the pharmacy/hospital protocol (reconstituted solution is generally stable for a limited time at room temperature and must not be refrigerated or frozen once reconstituted, per product-specific instructions). Keep out of reach of children. Reconstitution and storage of prepared infusions should be handled only by trained healthcare personnel.

Renal impairment (adults)

Hepatic impairment

Herpigel has not been formally studied in hepatic impairment; since it is eliminated renally rather than hepatically, no specific dose adjustment is established, but the drug should still be used cautiously with monitoring.

Pediatric use

See "Pediatric Uses" section.

Elderly

No Herpigel dose adjustment is required based on age alone; however, elderly patients often have reduced renal function, so renal dose adjustment based on creatinine clearance is particularly important in this group.

Duration of Herpigel therapy depends on the indication and clinical response: induction therapy for CMV retinitis is typically 14-21 days and for transplant prophylaxis 7-14 days, followed by maintenance therapy that may continue for weeks to months (e.g., until approximately day 100-120 post-transplant, or as long as the immunosuppressed state and disease risk persist for CMV retinitis). The treating physician determines the exact duration based on CMV viral load, immune status, and clinical/ophthalmologic response; treatment should not be shortened, extended, or stopped without medical advice.

Each vial of Herpigel for injection (500 mg) should be reconstituted with 10 mL of sterile water for injection (preservative-free); do NOT use bacteriostatic water for injection, as it can cause precipitation. Shake gently to dissolve completely, yielding a solution containing approximately 50 mg/mL. The reconstituted solution must then be further diluted in an appropriate volume of compatible IV fluid (e.g., normal saline or 5% dextrose) before infusion, per the specific product's instructions. Reconstituted and diluted solutions should be used within the time limits specified on the product label and must be prepared and administered only by trained healthcare personnel using appropriate handling precautions (avoid contact with skin/eyes; Herpigel is a potential carcinogen/teratogen).

Ganciclovir is classified as an antiviral - nucleoside analog (guanine derivative), anti-cytomegalovirus agent.

Ganciclovir is phosphorylated intracellularly to its active triphosphate form, primarily within CMV-infected cells (via a viral protein kinase encoded by the UL97 gene, then cellular kinases). Ganciclovir triphosphate competitively inhibits CMV DNA polymerase and is incorporated into viral DNA, causing termination or marked slowing of viral DNA chain elongation. This selectively suppresses replication of CMV (and, to a lesser extent, other herpesviruses) in infected cells.

C

The safety and efficacy of intravenous Herpigel have not been definitively established in randomized controlled pediatric trials, and pediatric use should be guided by a specialist (pediatric infectious disease or transplant physician). Herpigel has nonetheless been used, based on clinical experience and case series, for treatment of severe CMV disease and prevention of CMV in immunocompromised children and neonates, including congenital CMV infection with central nervous system involvement, typically using weight-based dosing analogous to adult mg/kg regimens under close specialist and laboratory monitoring (blood counts and renal function). Because of the risk of impaired fertility and potential carcinogenicity seen in animal studies, use in children should be reserved for situations where the benefit clearly outweighs the risk, and oral valHerpigel is often preferred once the child can tolerate oral therapy and the clinical situation allows.