Zirgan (ganciclovir)

Ganciclovir, a synthetic purine nucleoside analog of guanine, is an antiviral agent active against various Herpesviridae, including herpes simplex types 1 and 2 (HSV-1 and HSV-2).

Ganciclovir, a synthetic purine nucleoside analog of guanine, is an antiviral agent that is structurally and pharmacologically similar to acyclovir.

Ganciclovir is inactive until phosphorylated by viral and cellular thymidine kinases to form the active metabolite, ganciclovir triphosphate. The active phosphorylated form of ganciclovir accumulates in virus-infected host cells; since ganciclovir triphosphate is not recognized as a substrate by human thymidine kinase within healthy human cells, it does not accumulate in uninfected cells. Ganciclovir triphosphate interferes with viral DNA synthesis by competitively inhibiting viral DNA polymerase and by direct incorporation into viral primer strand DNA, resulting in DNA chain termination and prevention of viral replication.

Ganciclovir triphosphate is active in vitro and in vivo against herpes simplex virus types 1 and 2 (HSV-1 and HSV-2). The drug also is active in vitro against other Herpesviridae, including cytomegalovirus (CMV), Epstein-Barr virus (EBV), and varicella-zoster virus (VZV). HSV isolates resistant to ganciclovir have been reported only rarely.

However, cross-resistance between acyclovir and ganciclovir can occur. HSV clinical isolates resistant to acyclovir because of a mutation affecting viral thymidine kinase generally are cross-resistant to ganciclovir, famciclovir, and valacyclovir.

For the topical treatment of acute herpetic keratitis, ganciclovir is commercially available as a 0.15% aqueous ophthalmic gel. Each gram of the clear, colorless ophthalmic gel contains 1.5 mg of ganciclovir and also contains carbomer homopolymer, water for injection, sodium hydroxide (to adjust pH to 7.4), mannitol, and benzalkonium chloride (as a preservative). Following topical ophthalmic application, ganciclovir penetrates the corneal stroma (principally by passive diffusion) and therapeutic concentrations are attained in aqueous humor.

Only minimal systemic exposure is expected when ganciclovir 0.15% gel is administered by topical ophthalmic application. The estimated maximum daily dose of ganciclovir when the 0.15% ophthalmic gel is administered in a dosage of 1 drop 5 times daily is 0.375 mg. This topical ophthalmic daily dose is only approximately 0.04 or 0.1% of the maintenance daily dose of oral valganciclovir (900 mg) or IV ganciclovir (5 mg/kg), respectively.

USES: Ganciclovir is used to treat herpes infection of the eye. It is an anti-viral drug. Although ganciclovir stops the growth of the virus, it is not a cure for the herpes infection.

Herpes virus continues to live in the body even between outbreaks of infection. However, treating an outbreak may help the sores in the eye to heal faster and lower the risk of complications (such as decreased vision, blindness).

Generic name: ganciclovir
Pronunciation: (gan-SYE-klo-veer)
Drug class: Ophthalmic Antivirals
Therapeutic class: Ophthalmic Agents

The following indications are listed for Zirgan:

• Herpes Simplex Dendritic Keratitis

Also known as: Dendritic Keratitis Due To Hsv, Herpetic Ulceration Of The Cornea.