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P A R T 3  Drugs acting on the immune system

Drug therapy across the lifespan

BOX 17.1

Immune modulators

Pharmacokinetics The interferons are generally well absorbed after sub­ cutaneous or intramuscular injection. They have a rapid onset of action and peak within 3 to 8 hours, with a half-life ranging from 3 to 8 hours, with the exception of interferon beta-1a, which has an onset of action of 12 hours and reaches peak levels in 48 hours, with a half-life of 10 hours. They are broken down in the liver and kidneys and seem to be excreted primarily through the kidneys. Contraindications and cautions The use of interferons is contraindicated in the presence of known allergy to any interferon or product compo- nents. Many of the interferons are teratogenic in animals and therefore should not be used during pregnancy. Use of barrier contraceptives is advised for women of child- bearing age. It is not known whether these drugs cross into breast milk, but because of the potential adverse effects on the baby, it is advised that the drugs not be used during breastfeeding unless the benefits to the mother clearly outweigh any risks to the baby . Caution should be used in the presence of known cardiac disease because hypertension and arrhythmias have been reported with the use of these drugs ; with myelosuppression because these drugs may further suppress the bone marrow ; and with central nervous system (CNS) dysfunction of any kind because of the potential for CNS depression and personality changes that have been reported. further complications.The person should be encouraged to seek regular follow-up and medical care. PREGNANCY AND BREASTFEEDING Immune modulators are contraindicated during pregnancy and breastfeeding because of the potential for adverse effects on the fetus or neonate and complications for the mother. Women of childbearing age should be advised to use barrier contraceptives while taking these drugs and, if breastfeeding, should be counselled to find another method of feeding the baby. Some of these drugs impair fertility, and the person should be advised of this fact before taking the drug. OLDER ADULTS Older people may be more susceptible to the effects of the immune modulators, partly because the ageing immune system is less efficient and less responsive. These people need to be monitored closely for infection, GI, renal, hepatic and CNS effects. Baseline renal and liver function tests can help to determine whether a decreased dosage will be needed before beginning therapy. Because these people are more susceptible to infection, they need to receive extensive teaching about ways to avoid infection and injury.

CHILDREN Most of the drugs that affect the immune system are not recommended for use in children or have not been tested in children.The exceptions—interferon alfa-2b, azathioprine, cyclosporin, tacrolimus and palivizumab— should be used cautiously, monitoring the child frequently for infection, GI, renal, haematological or CNS effects. The immune suppressants (azathioprine, cyclosporin, and tacrolimus) are usually needed in higher doses for children than for adults to achieve the same therapeutic effect. Protecting the child from infection and injury is a very important part of the care of a child taking an immune modulator.This can be a great challenge with an active child. ADULTS Both the adult who is receiving a parenteral immune modulator and a significant other should learn the proper technique for injection, disposal of needles and special storage precautions for the drug. It is important to stress ways to avoid exposure to infection and injury to prevent Immune modulators and pregnancy Generally, immune modulators are contraindicated for use during pregnancy and breastfeeding, largely because these drugs have been associated with fetal abnormalities, increased maternal and fetal infections, and suppressed immune responses in breastfeeding babies. Women should be informed of the risk of using these drugs during pregnancy and receive counselling in the use of barrier contraceptives. (The use of barrier contraceptives is advised because the effects of oral contraceptives may be altered by liver changes or by changes in the body’s immune response, potentially resulting in unexpected pregnancy.) If a woman taking immune modulators becomes pregnant or decides that she wants to become pregnant, she should discuss this with her healthcare provider and review the risks associated with use of the drug or drugs being taken.The monoclonal antibodies should be used with caution during pregnancy and breastfeeding. Because long-term studies of most of these drugs are not yet available, it may be prudent to advise women taking these drugs to avoid pregnancy if possible. Gender considerations BOX 17.2

and to enhance the inflammatory response. Of interest, interferon gamma-1b also acts like an interleukin, stim- ulating phagocytes to be more aggressive. See Table 17.1 for usual indications for each interferon.