induction phase, 5 mg per kilogram intravenously every 12 hours for 14-21 days, the intravenous dose given as a 1 hour infusion
maintenance phase, 5 mg per kg intravenously every day

Stable disease is treated with 1000 mg orally three times daily. Similar dosing is used to prevent disease in high-risk patients, such as those infected with human immunodeficiency virus (HIV) or those with organ transplants.

Ganciclovir is also available in slow-release formulations for insertion into the vitreous of the eye, as treatment for CMV retinitis.

Mechanism of action

Ganciclovir is a synthetic analogue of 2'-deoxy-guanosine. It is first phosphorylated to a deoxyguanosine triphosphate (dGTP) analog. This competitively inhibits the incorporation of dGTP by viral DNA polymerase, resulting in the termination of elongation of viral DNA.

Pharmacokinetics

Absorption of the oral form is very limited - about 5% fasting, about 8% with food. It achieves a concentration in the central nervous system of about 50% of the plasma level. About 90% of plasma ganciclovir is eliminated unchanged in the urine, with a half-life of 2-6 hrs, dependending on renal function (elimination takes over 24 hours in end-stage renal disease).

Side effects

Possible side effects include:

Headache
Rash
Neutropenia
Anemia
Low platelets
Kidney failure
Confusion
Seizures

Read more at Wikipedia.org

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Shortages of key drugs
From Pharmaceutical Technology, 4/1/05 by Douglas McCormick

The chemotherapy drug methotrexate (injection) in 1-g vials is the most recent entry on the ten-product FDA Current Drug Shortages List. The US Food and Drug Administration listed the product on 18 February, citing unspecified manufacturing delays at Mayne Pharma (Paramus, NJ, www.us.maynepharma.com) and American Pharmaceutical Partners (APP, Schaumburg, IL, www.appdrugs.com).

Overall, the FDA list attributes 77% of the shortages to manufacturing issues, including plant capacity restrictions, with the remaining 23% caused by supply interruptions. The figures continue to grab public attention even as the Wall Street Journal headlined the recent shortages of methotrexate and highlighted what the agency has called an increase in the number of medically significant medicines in short supply. (Amy Dockser Marcus, "Critical Cancer Drug Faces Shortage," Wall Street Journal, 15 March 2005, p. D 1.)

Another methotrexate formulation-made by Mayne, APP, and Bedford Laboratories (Bedford, OH, www.bedfordlabs. com)--had already joined the shortage list last December. The American Society of Health-System Pharmacists' (ASHSP, Bethesda, MD, www.ashp.org) index of "Drug Products with Limited Availability" cites "manufacturing delays" at all three manufacturers, which have put current requests for the product on back-order.

The other recent entry on the FDA list-Wyeth's "Trecator SC" (ethionamide 250mg tablets), listed 28 January--is the only solid oral formulation said to be in short supply. The tuberculosis treatment is scarce because of unspecified manufacturing issues; FDA indicates that normal distribution should resume this month.

According to ASHSP,"For unknown reasons, Wyeth has limited supplies of ethionamide tablets (NDC 00008.4130.01). The product is short-dated and expires July 2005. The company is allocating a single 100-count bottle per patient, for use in patients currently receiving ethionamide or for patients initiating therapy. Product is available by drop shipment to wholesalers or by direct order through Wyeth Customer Service (800.666.7248). When ordering ethionamide, the purchasing agent must specify the number of patients being treated and the date each patient started therapy. The company will not estimate a release date."

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