Antiviral agents

Adefovir is converted intracellularly in stages to the di-phosphate, which then inhibits the DNA synthesis of hepatitis B virus through competitive inhibition of reverse transcriptase and incorporation into viral DNA. At high doses it has some activity against HIV.

Acyclovir is active against herpes simplex virus type 1 and type 2 and against varicella-zoster virus. This activity requires intracellular conversion of aciclovir by viral thymidine kinase to the monophosphate with subsequent conversion by cellular enzymes to the diphosphate and the active triphosphate.

Abacavir is converted intracellularly in stages to its active form carbovir triphosphate. This halts the DNA synthesis of retroviruses, including HIV, through competitive inhibition of reverse transcriptase and incorporation into viral DNA.

Famciclovir (Famvir) is an orally active prodrug of penciclovir, a nucleoside analog related to acyclovir. These drugs act by selectively inhibiting herpesvirus DNA polymerase, thus inhibiting herpesvirus DNA synthesis. They are able to interfere with viral replication at concentrations that have little effect on host DNA synthesis.

Influenza, commonly called “the flu,“ is caused by viruses that infect the respiratory tract. Compared with most other viral respiratory infections, such as the common cold, influenza infection often causes a more severe illness.

Since the introduction of zidovudine (AZT, Retrovir) in 1987, a relatively large number of drugs have been developed for the treatment of HIV-induced AIDS. Currently available antiretroviral drugs are subclassified based on their chemical structure and site of action as nucleoside reverse transcriptase inhibitors (NRTIs: zidovudine, didanosine, zalcitabine, stavudine, lamivudine and abacavir), non­nucleoside reverse transcriptase inhibitors (NNRTIs: nevirapine, delavirdine and efavirenz) and protease inhibitors (PIs: saquinavir, ritonavir, indinavir, nelfinavir, amprenavir, and lopinavir). The use of these and all antiretrovirals as monotherapy is limited largely by the rapid development of viral resistance. Thus current Public Health Service HIV treatment guidelines recommend the use of drug combinations consisting of three or four anti-AIDS drugs.