McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 1 0  Antiviral agents

There are no adequate studies in pregnancy and breast- feeding, so oseltamivir should be used during pregnancy and breastfeeding only if the benefits clearly outweigh the risks to the fetus or neonate. Women of childbearing age should be advised to use barrier contraceptives if they are taking ribavirin. The drug has been associated with serious fetal effects. Because of the renal excretion, zanamivir must be used cautiously in people with any renal impairment. It should be used during pregnancy and breastfeeding only if the benefits clearly outweigh the risks to the fetus or neonate. People with renal dysfunction who are taking oseltamivir require reduced doses and close monitoring to avoid altered metabolism and excretion of the drug . There are no adequate studies in pregnancy and breast- feeding, so oseltamivir should be used during pregnancy and breastfeeding only if the benefits clearly outweigh the risks to the fetus or neonate. Women of childbearing age should be advised to use barrier contraceptives if they are taking ribavirin. The drug has been associated with serious fetal effects. Because of the renal excretion, zanamivir must be used cautiously in people with any renal impairment. It should be used during pregnancy and breastfeeding only if the benefits clearly outweigh the risks to the fetus or neonate. Adverse events, including bronchospasm and/or decline in respiratory function, some of which have been serious, have been reported in association with the use of Relenza during the Northern Hemisphere influenza season. These events have been reported rarely in people with underlying respiratory disease (asthma, chronic obstructive pulmonary disease (COPD)) and have also been reported very rarely in individuals without under- lying respiratory disease. Adverse effects Use of these antiviral agents is frequently associated with various adverse effects that may be related to possible effects on dopamine levels in the brain. These adverse effects include light-headedness, dizziness and insomnia; nausea; orthostatic hypotension; and urinary retention. Clinically important drug–drug interactions People who receive amantadine may experience increased atropine-like effects if this drug is given with an anti­ cholinergic drug. Ribavirin levels may be reduced if given with antacids. The use of ribavirin should be avoided if the person is also receiving a nucleoside reverse tran- scriptase inhibitor. Rifampicin is known to decrease the effectiveness of many drugs, including antiarrhythmics, digoxin, hormonal contraceptives, corticosteroids, anti- fungals and central nervous system (CNS) depressants.

People should be monitored closely for loss of effective- ness of these drugs if this combination is used. There is an increased incidence of rifampicin-related hepatitis if it is used concurrently with isoniazid. This combination should be avoided.

Care considerations for people receiving agents for influenza A and respiratory viruses

Assessment: history and examination

■ ■ Assess for contraindications or cautions : known history of allergy to antiviral agents to avoid hypersensitivity reactions ; history of liver or renal dysfunction that might interfere with drug metabolism and excretion ; and current status related to pregnancy or breastfeeding. ■ ■ Perform a physical assessment to establish baseline data for evaluating the effectiveness of the drug and the occurrence of any adverse effects associated with drug therapy. ■ ■ Assess for orientation and reflexes to evaluate any CNS effects of the drug ; vital signs (temperature, respiratory rate, breath sounds for adventitious sounds) to assess for signs and symptoms of the viral infection; blood pressure to monitor for orthostatic hypotension; urinary output to monitor genitourinary ( GU ) effects of the drug; and renal and hepatic function tests to determine baseline function of these organs. ■ ■ Assess for adverse events such as bronchospasm or decline in respiratory function in people using zanamivir and seek medical advice immediately. Implementation with rationale ■ ■ Start the drug regimen as soon after exposure to the virus as possible to enhance effectiveness and decrease the risk of complications due to viral infection. ■ ■ Administer influenza A vaccine before the flu season begins, if at all possible, to decrease the risk of contracting the flu and also decrease the risk of complications. ■ ■ Administer the full course of the drug to obtain the full beneficial effects. ■ ■ Provide safety provisions if CNS effects occur to protect the person from injury. ■ ■ Instruct the person about the appropriate dosage scheduling regimen; safety precautions, including changing position slowly and avoiding driving and hazardous tasks, that should be taken if CNS effects occur; and the need to report any adverse effects such as difficulty walking or talking to enhance knowledge about drug therapy and to promote compliance.