Drug Groups

approved

Description

A dideoxynucleoside compound in which the 3'-hydroxy group on the sugar moiety has been replaced by a hydrogen. This modification prevents the formation of phosphodiester linkages which are needed for the completion of nucleic acid chains. Didanosine is a potent inhibitor of HIV replication, acting as a chain-terminator of viral DNA by binding to reverse transcriptase; ddI is then metabolized to dideoxyadenosine triphosphate, its putative active metabolite. [PubChem]

Indication

For use, in combination with other antiretroviral agents, in the treatment of HIV-1 infection in adults.

Pharmacology

Didanosine is a nucleoside reverse transcriptase inhibitor (NRTI) with activity against Human Immunodeficiency Virus Type 1 (HIV-1). Didanosine differs from other nucleoside analogues, as it does not have any of the regular bases, instead it has hypoxanthine attached to the sugar ring. Didanosine is phosphorylated to active metabolites that compete for incorporation into viral DNA. They inhibit the HIV reverse transcriptase enzyme competitively and act as a chain terminator of DNA synthesis. Didanosine is effective against HIV, and usually used in combination with other antiviral therapy. Switching from long term AZT treatment to didanosine has been shown to be beneficial. Didanosine has weak acid stability and therefore, it is often combined with an antacid.

Toxicity

Side effects include pancreatitis, peripheral neuropathy, diarrhea, hyperuricemia and hepatic dysfunction

Affected Organisms

Biotransformation

Rapidly metabolized intracellularly to its active moiety, 2,3-dideoxyadenosine-5-triphosphate (ddA-TP). It is then further metabolized hepatically to yield hypoxanthine, xanthine, and uric acid.

Absorption

Rapidly absorbed (bioavailability 30-40%) with peak plasma concentrations appearing within 0.5 and 1.5 hrs.

Half Life

30 minutes in plasma and more than 12 hours in intracellular environment.

Protein Binding

Low (<5%)

Elimination

Based on data from in vitro and animal studies, it is presumed that the metabolism of didanosine in man occurs by the same pathways responsible for the elimination of endogenous purines. Purines are eliminated by the kidneys.

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