McKenna's Pharmacology for Nursing, 2e

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P A R T 2  Chemotherapeutic agents

now be genetically engineered to treat particular viral infections. Other drugs that are used in treating viral infections are not natural substances and have been effec- tive against only a limited number of viruses. Viruses that respond to some antiviral therapy include influenza A and some respiratory viruses, herpes viruses, cyto- megalovirus (CMV), the human immunodeficiency virus

(HIV) that causes acquired immune deficiency syndrome (AIDS), hepatitis B, and some viruses that cause warts and certain eye infections. People need to be cautioned against using certain alternative therapies while on anti- viral medication (Box 10.1). Box 10.2 discusses the use of antivirals across the lifespan. Figures 10.2 and 10.3 show sites of action for these agents.

Herbal and alternative therapies

BOX 10.1

Alternative therapies and antiviral drugs An increasing number of people are using alternative therapies as part of their daily regimen. St John’s wort is one of the more popular alternative therapies sold today. This herb has been used as an anti-inflammatory agent, as an antidepressant, as a diuretic, and as a treatment for gastritis and insomnia. St John’s wort is promoted as being able to increase one’s sense of well-being and to decrease depression. Many people with viral infections just do not feel well.They are tired, have muscle aches and pains, and feel feverish and low on energy.This herbal remedy seems to be aimed at these people. Unfortunately, St John’s wort has been shown to interact with many prescription drugs. When taken with St John’s wort, the protease inhibitors used in treating HIV were found to have decreased serum levels, leading to possible

treatment failure. Because St John’s wort may induce the cytochrome P450 system in the liver, there is a possibility that it could increase the metabolism of many other antiviral drugs that are metabolised by that system and cause treatment failures with those drugs. People may be reluctant to discuss their use of alternative therapies with the healthcare provider because they want to maintain control over that aspect of their medical regimen or because they believe that the healthcare provider would not approve of the use of these therapies. It is important, when a person is prescribed an antiviral agent, to ask specifically about the use of herbal or alternative medicines. Explain to the person that antiviral drugs may interact with some herbal medicines and that it is important to try to avoid any adverse effects or drug failures.

Drug therapy across the lifespan

BOX 10.2

Antivirals CHILDREN

People with HIV infection who are taking antiviral medications need to be taught that these drugs do not cure the disease, that opportunistic infections can still occur and that precautions to prevent transmission of the disease need to be taken. PREGNANCY AND BREASTFEEDING Pregnant women, for the most part, should not use these drugs unless the benefit clearly outweighs the potential risk to the fetus or neonate. Women of childbearing age should be advised to use barrier contraceptives if they take any of these drugs. Zidovudine has been safely used in pregnant women. OLDER ADULTS Older people may be more susceptible to the adverse effects associated with these drugs; they should be monitored closely. People with hepatic dysfunction are at increased risk for worsening hepatic problems and toxic effects of those drugs that are metabolised in the liver. Drugs that are excreted unchanged in the urine can be especially toxic to people who have renal dysfunction. If hepatic or renal dysfunction is expected (extreme age, alcohol abuse, use of other hepatotoxic or nephrotoxic drugs), the dose may need to be lowered and the person should be monitored more frequently.

Children are very sensitive to the effects of most antiviral drugs and more severe reactions can be expected when these drugs are used in children. Many of these drugs do not have proven safety and efficacy in children, and extreme caution should be used. Most of the drugs for prevention and treatment of influenza virus infections can be used, in smaller doses, for children. Aciclovir is the drug of choice for children with herpes virus or cytomegalovirus infections. The drugs used in the treatment of AIDS are frequently used in children, even when no scientific data are available, because of the seriousness of the disease. Dose should be lowered according to body weight, and children must be monitored very closely for adverse effects on kidneys, bone marrow and liver. ADULTS Adults need to know that these drugs are specific for the treatment of viral infections.The use of antibiotics to treat such infections can lead to the development of resistant strains and superinfections that can cause more problems.