Pharmaceutical 
prodrug compositions are provided comprising 
azide derivatives of drugs which are capable of being converted to the 
drug in vivo. 
Azide derivatives of drugs having amine, 
ketone and hydroxy substituents are converted 
in vivo to the corresponding drugs, increasing the half-life of the drugs. In addition 
azide prodrugs are often better able to penetrate the blood-brain barrier than the corresponding drugs. Especially useful are 
azide derivatives of 
cordycepin, 2′-F-ara-ddI, AraA, acyclovir, 
penciclovir and related drugs. Useful azide prodrugs are azide derivatives of therapeutic alicyclic amines, ketones, and hydroxy-substituted compounds, including aralkyl, heterocyclic aralkyl, and cyclic aliphatic compounds, where the amine or 
oxygen moiety is on the ring, or where the amine or 
oxygen moiety is on an aliphatic 
side chain, as well as therapeutic purines and pyrimidines, 
nucleoside analogs and phosphorylated 
nucleoside analogs.