The securing of antiviral medicines has always been much more difficult than that of the (antibacterial) antibiotics, since the viruses depend obligatorily to live and to multiply ("to answer") of the metabolism of the proper cell that they infect. Therefore, the medicines that block the viral replicación alter also the functioning of the normal cells, and the limits between the therapeutic doses and the poisonous doses are very narrow.

In general, the antiviral existing ones inhibit of some form the synthesis of the acids nucleinos (DNA ó RNA) and/or of the proteins of the virus. The infection for the virus of the human immunodeficiency (to See infection HIV, AIDS) has impelled in the last years the investigation in antiviral medicines.

Amantadina and rimantadina it has been used in the prophylaxis and the treatment of the flu in risk patients. Tromantadina is used locally for viriasis of the skin (herpes).

RIBAVIRINA. There is very active opposite to the respiratory virus sincitial, which is a very aggressive virus that it affects to nursing and children, producing serious respiratory processes. It is used in aerosol in nursing of high risk.

IDOXURIDINA. It acts on the DNA, so much that of the virus like that of the normal cell, therefore it is very poisonous. For it, only it is used locally for viriasis of the skin and the cornea (herpes).

VIDARABINA (ARABINóSIDO DE ADENINA ó Ara A). It is used locally for herpes of the skin and the cornea, and for intravenous route in the encephalitis for simple herpes (infection of the brain, mortal without treatment) and in the serious chicken pox of the inmunodeprimidos (patients with shaken defenses).

TRIFLURIDINA (TRIFLUOROTIMIDINA). It is used locally for herpes of the cornea.

The infection for the virus of the human immunodeficiency (to See infection VIH, AIDS) has impelled in the last years the investigation in antiviral medicines.

The ANTIRRETROVIRALES are an increasing group of medicines that inhibit the "replicación" of the VIH for different mechanisms. Used in different combinations, they have increased the survival of the patients of spectacular form.

Foscarnet (acid fosfonofórmico). It acts both against the VIH and against the virus of the simple herpes and the citomegalovirus (CMV), which usually produce serious infections in the infected one by VIH.

Similar of nucleótidos. Zidovudina (ZDU, earlier AZT), inhibits to an enzyme of the called VIH "transcriptasa inverse", and it was the first medicine that, inhibiting the "replicación" of the VIH and increasing the nº of lymphocytes T-4 (the cells of defense to which it attacks the VIH), it managed to prolong the life of the infected ones and slow down the beginning of infections "opportunists" in these patients. He treats neither the infection VIH nor his associate infections. Similar others of nucleótidos alone personnel or in combination with ZDU they are zalcitabina (ddC), didanosina (ddI), stavudina (d4T) and lamivudina (3TC).

Inhibiting of the proteasa. There are a new group of medicines antirretrovirales, that includes molecules like saquinavir, ritonavir, indinavir, nelfinavir, and VX-478.