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chapter 31 Antiviral Drugs 205
reads the genetic material and begins to translate
it into viral proteins. How exactly this proceeds
depends on the form in which the genetic material
exists in the virus. In some cases, the genetic material
is encoded as RNA. For some RNA viruses, host
cell ribosomes translate the RNA into proteins. In
the group of viruses known as retroviruses, the RNA
genetic material is first translated into DNA (via
an enzyme known as reverse transcriptase) before
integrating into the host genome. For these viruses
or those viruses whose genome is already encoded
as DNA, transcription into messenger RNA occurs,
followed by translation into protein. Once the pieces
of the puzzle are built, the viral enzymes assemble
them into complete virions and they are finally
released from the cell. The available antiviral drugs
are aimed at various steps in this cycle. Some are
aimed at specific receptors against specific viruses
(such as influenza), and some are aimed at more
general steps to attack multiple viruses.
The pharmacotherapy of viral infections is different
from that of bacterial infections. Patientspecific
susceptibility results are rarely available,
leaving practitioners to choose therapies based upon
general patterns of susceptibility for viral infections
(HIV is a notable exception). While viruses
can be cultured, many viral illnesses are diagnosed
through genetic testing for viral antigens or nucleic
acids. These tests can be followed quantitatively to
see if an infection improves, but symptoms are usually
followed instead. Most common viral infections
have no effective pharmacotherapeutic remedy,
which is a fancy way of saying that there is still “no
cure for the common cold.”