indication

For the treatment of Human immunovirus (HIV) infections in conjunction with other antivirals.

pharmacology

Zalcitabine is an analog of 2'-deoxycytidine that is pharmacologically related to but structurally different from other nucleotide reverse transcriptase inhibitors (NRTIs). Zalcitabine inhibits the activity of HIV-1 reverse transcriptase (RT) both by competing with the natural substrate dGTP and by its incorporation into viral DNA.

mechanism of action

Zalcitabine is a nucleoside reverse transcriptase inhibitor (NRTI) with activity against Human Immunodeficiency Virus Type 1 (HIV-1). Within cells, zalcitabine is converted to its active metabolite, dideoxycytidine 5'-triphosphate (ddCTP), by the sequential action of cellular enzymes. ddCTP interferes with viral RNA-directed DNA polymerase (reverse transcriptase) by competing for utilization of the natural substrate deoxycytidine 5'-triphosphate (dCTP), as well as incorpating into viral DNA. Due to it's lack of a 3'-OH group, the formation of a 5' to 3' phosphodiester linkage that is necessary for DNA chain elongation is inhibited, thus leading to the termination of viral DNA growth.

toxicity

Acute overdose: Inadvertent pediatric overdoses have occurred with doses up to 1.5 mg/kg zalcitabine. Chronic overdose: in an initial dose-finding study in which zalcitabine was administered at doses 25 times (0.25 mg/kg every 8 hours) the currently recommended dose, one patient discontinued zalcitabine after 1½ weeks of treatment subsequent to the development of a rash and fever.

biotransformation

Hepatic

absorption

Bioavailability is over 80% following oral administration.

half life

2 hours

route of elimination

Renal excretion of unchanged drug appears to be the primary route of elimination, accounting for approximately 80% of an intravenous dose and 60% of an orally administered dose within 24 hours after dosing (n=19). Renal clearance exceeds glomerular filtration rate suggesting renal tubular secretion contributes to the elimination of zalcitabine by the kidneys.

drug interactions

Didanosine: Additive toxicities (peripheral neuropathy)

Lamivudine: Lamivudine may reduce the efficacy of zalcitabine. Combination therapy is not recommended.

Pentamidine: Additive risk of pancreatitis. Concomitant therapy should be avoided.

Ribavirin: Ribavirin may increase the hepatotoxicity of zalcitabine. May cause lactic acidosis. MOnitor for lactic acidosis during concomitant therapy.