128
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.
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.
Herbal and alternative therapies
BOX 10.1
BOX 10.2
Drug therapy across the lifespan
Antivirals
CHILDREN
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.
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.
