The challenge with antiviral chemotherapy os to find an agent which will arrest the replication of viruses without
interfering with the metabolism of mammalian cells. Great advances have been made recently in antiviral chemotherapy. A further problem is that by the time a viral infection has been diagnosed using laboratory tests, much of the damage has been done to the host tissues. Table 2.8 provides information on currently available antiviral drugs. Their doses are given are with the descriptions of individual viral diseases.
Aciclovir is an effective agent for herpes simplex and varicella zoster infections, particularly in the immunosuppressed. It does not, however, eradicate the viruses from the body. The use of this agent has been advocated in childhood chickenpox since it reduces the length of illness without reducing the immune response. Cost of this treatment is, however, likely to be prohibitive in many countries. Aciclovir is a useful agent in treating genital herpes, as both primary and prophylactic treatment. Resistance to aciclovir has now been regularly reported. Famciclovir is a newer antiherpes agent which is given as prodrug requiring metabolism first pass to produce the active form penciclovir. Famciclovir has some activity against Epstein-Barr (EB) virus and hepatitis B virus.
Ganciclovir is an antiherpes agent with activity against cytomegalovirus (CMV). Again, resistance to this agent is acquired rapidly on treatment , being detected in 8% of patients on this drug for > 3 months. Currently, ganciclovir is only indicated for life-threatening CMV infection. There is considerable toxicity to monitor when using the drug, principally involving myelosuppression. Ribovirine is active against RNA viruses and good activity has been found against influenza, parainfluenza, mumps, measles and respiratory syncytial virus (RSV). The only clinical use of this drug is in the aerosolised form for RSV infection.
| Antiviral drugs | |||
|---|---|---|---|
| Drug (doses are given in text) | Routes of administration | Indications | Side-effects |
| Aciclovir | Topical Oral Intravenous | Herpes zoster Chickenpox (esp. in immunosuppressed) Herpes simplex infection: encephalitis, genital tract, eye | Rash, headache, gastrointestinal toxicity, neurotoxicity (i.v. only) Increase in urea and creatinine |
| Famciclovir | Oral | Herpes zoster and genital H. simplex infection | Rash, headache |
| Idoxuridine | Topical | Herpes zoster H. simplex keratitis | Local irritation |
| Amantadine | Oral | Prophylaxis of influenza A | CNS symptoms Nausea |
| Ribovirine | Oral | Lassa fever Respiratory syncytial virus infection in infants (inhalation) | Reticulocytosis Respiratory depression |
| Ganciclovir | Intravenous/oral | Cytomegalovirus infection in immunosuppressed | Leucopenia, thrombocytopenia |
| Zidovudine | Oral | HIV infection (incl. AIDS) | CNS symptoms, anaemia, neutropenia, thrombocytopenia |