More than 200 viruses have been identified as capable of producing disease. Acute viruses, such as the common cold, have a rapid onset and quick recovery. Chronic viral infections, such as acquired immunodeficiency syndrome (AIDS), have recurrent episodes of exacerba-tions (increases in severity of symptoms of the disease) and remissions (periods of partial or complete disappearance of the signs and symptoms).Although viral infections are common, for many years only a limited number of drugs were available for their treatment. Over the past several years, the number of antiviral drugs has increased significantly. Several of the antiviral drugs will be discussed in greater detail than oth-ers. These include acyclovir (Zovirax), amantadine(Symmetrel), didanosine (Videx), ribavirin (Virazole),zanamivir (Relenza), and zidovudine (AZT, Retrovir). The Summary Drug Table: Antiviral Drugs presents a more complete listing of the antiviral drugs currently in use.
ACTIONS
Viruses can reproduce only within a living cell. A virus consists of either DNA or RNA surrounded by a protein shell. The virus is capable of reproducing only when it uses the body’s cellular materia most antiviral drugs act by inhibiting viral DNA or RNA replication in the virus, causing viral death.
USES
Although infections caused by a virus are common, antiviral drugs have limited use because they are effective against only a small number of specific viral infections.General uses of the antiviral drugs include the treatment of:
• Initial and recurrent mucosal and cutaneous herpes simplex virus (HSV) 1 and 2 infections in
immunocompromised patients, encephalitis, and herpes zoster.
• Human immunodeficiency virus (HIV) (combined with other drugs)
• Cytomegalovirus (CMV) retinitis (inflammation of the retina of the eye)
• Genital herpes
• Influenza A respiratory tract illness
• Respiratory syncytial virus (RSV), a severe lower respiratory tract infection
• Viral herpes infections
Unlabeled Uses
Because there are a limited number of antiviral drugs and more than 200 viral diseases, the primary health care provider may decide to prescribe an antiviral drug for an unlabeled use even though documentation of its effectiveness is lacking. Approval by the Food and Drug Administration (FDA) is necessary for a drug to be prescribed. On occasion, the use of a drug for a specific disorder or condition may be under investigation or may be approved for use in another country. In this instance, the drug may be prescribed by the primary health care provider for the condition under investiga-tion. The use of the drug for a specific disorder or con-
dition that is not officially approved by the FDA is called an “unlabeled use.” Examples of unlabeled uses of the antiviral drugs include treatment of CMV and HSV infections after transplant and varicella pneumonia; the treatment of CMV retinitis in immunocompro-mised patients; and the use of ribavirin for influenza A and B (aerosol form), acute and chronic hepatitis, herpes genitalis, and measles (oral form).
GENERAL ADVERSE REACTIONS
Antiviral drugs are given systemically or as topical drugs. When used systemically these drugs may be administered orally or intravenously (IV). Rapid IV administration can result in crystalluria (presence of crystals in the urine). The most common adverse reactions when these drugs are administered systemically
are gastrointestinal disturbances, such as nausea, vomit-ing, diarrhea, and anorexia. When administered topi-cally, the antiviral drugs can cause transient burning,stinging, and pruritus at the application site.
ADVERSE REACTIONS FOR
SPECIFIC DRUGS
Acyclovir
Acyclovir is available for use orally, topically, and par-enterally (for IV use). When given IV, acyclovir can cause phlebitis, lethargy, confusion, tremors, skin rashes, nau-sea, and crystalluria. Side effects when given orally include nausea, vomiting, diarrhea, headache, dizziness,and skin rashes. Topical administration causes transientburning, stinging, and pruritus.
Amantadine
Adverse reactions of amantadine include gastrointestinal upset with nausea and vomiting, anorexia, asthenia
(weakness, loss of strength), constipation, depression, visual disturbances, psychosis, urinary retention, and
orthostatic hypotension.
Didanosine
Adverse reactions reported with didanosine include headache, peripheral neuropathy, rhinitis, cough, diar-rhea, nausea, vomiting, anorexia, hepatotoxicity, and pancreatitis.
Ribavirin
Ribavirin is given by inhalation and can cause worsening of respiratory status, hypotension, and ocular irritation,including erythema (redness of skin), conjunctivitis, and blurred vision.
Zanamivir
Common adverse effects include headache, nausea, diarrhea, anorexia, rhinitis, and flu-like symptoms. The
most serious adverse reactions are related to respiratory effects and include severe bronchospasm that may lead to death.
Zidovudine
Adverse reactions associated with zidovudine include headache, weakness, malaise, nausea, abdominal pain,and diarrhea. Hematologic changes include anemia and granulocytopenia (low levels of granulocytes, a type of white blood cell, in the blood).
GENERAL CONTRAINDICATIONS,
PRECAUTIONS, AND INTERACTIONS
All antiviral drugs are contraindicated in patients with previous hypersensitivity to the individual antiviral drug. The antiviral drugs are also contraindicated in patients with congestive heart failure, seizures, renal dis-ease, and during lactation. The antiviral drugs are given with caution in patients with renal impairment and require dosage adjustments. Antivirals are used with caution in children, during pregnancy (except ribavirin,a Pregnancy Category X drug), and during lactation.Other contraindications and precautions are listed below, according to the specific drug. Numerous interactions are possible with the antiviral drugs. Only the most significant interactions are listed for selected drugs. The nurse should consult an appropriate source for a more extensive listing of interactions.
Acyclovir
This drug is used cautiously in patients with pre-exist- ing neurologic, renal, hepatic, respiratory, or fluid and electrolyte abnormalities. The nurse gives the drug with caution to patients with a history of seizures. Acyclovir
is a Pregnancy Category C drug and is used cautiously during pregnancy and lactation. Incidences of extreme drowsiness have occurred when acyclovir is given with zidovudine. There is an increased risk of nephrotoxicity when acyclovir is administered with other nephrotoxic drugs. When administered with amphotericin B, the risk of nephrotoxicity is increased. Administration with probenecid causes a decrease in the renal excretion of acyclovir, prolonging the effects of acyclovir and increasing the risk of drug toxicity.
Amantadine
Amantadine is used cautiously in patients with seizure disorders, psychiatric problems, renal impairment, and cardiac disease. Amantadine is a Pregnancy Category B drug and is used cautiously during pregnancy and lacta-tion. Concurrent use of antihistamines, phenothiazines,tricyclic antidepressants, disopyramide, and quinidine may increase the anticholinergic effects (dry mouth,blurred vision, constipation) of amantadine.
Didanosine
This drug is used cautiously in patients with peripheral vascular disease, neuropathy, chronic pancreatitis, or impaired liver function. Didanosine is a Pregnancy Cate- gory B drug and is used cautiously during pregnancy and lactation. There may be a decrease in the effectiveness of dapsone in preventing Pneumocystis carinii pneumonia when didanosine is administered with dapsone. Use of didanosine with zalcitabine may cause additive neuropa-thy. Absorption of didanosine is decreased when it isadministered with food.
Ribavirin
Ribavirin may be teratogenic and embryotoxic (Pregnancy Category X) and is contraindicated during pregnancy, in patients with chronic obstructive pulmonary disease (COPD), and during lactation. Ribavirin is used cautiously at all times during administration of the drug. Ribavirin may antagonize the antiviral
action of zidovudine and potentiate the hematologic toxic effects of zidovudine. When ribavirin is used con-
currently with digitalis, the risk of digitalis toxicity increases.
Zanamivir
Zanamivir is used cautiously with pregnancy (Category C), lactation, asthma, COPD, or other underlying respi-ratory diseases. No significant drug interactions have been reported with the use of zanamivir.
Zidovudine
This drug is used cautiously in patients with bone mar-row depression or severe hepatic or renal impairment.Zidovudine is a Pregnancy Category C drug and is used cautiously during pregnancy and lactation. There is an increased risk of bone marrow depression when zidovudine is administered with antineoplastic drugs,other drugs causing bone marrow depression, and in patients having or recently taking radiation therapy.An additive neurotoxicity may occur when zidovu-dine is administered with acyclovir. Clarithromycin de-creases blood levels of zidovudine. The blood levels of zidovudine are increased when it is given with lamivudine.
ACTIONS
Viruses can reproduce only within a living cell. A virus consists of either DNA or RNA surrounded by a protein shell. The virus is capable of reproducing only when it uses the body’s cellular materia most antiviral drugs act by inhibiting viral DNA or RNA replication in the virus, causing viral death.
USES
Although infections caused by a virus are common, antiviral drugs have limited use because they are effective against only a small number of specific viral infections.General uses of the antiviral drugs include the treatment of:
• Initial and recurrent mucosal and cutaneous herpes simplex virus (HSV) 1 and 2 infections in
immunocompromised patients, encephalitis, and herpes zoster.
• Human immunodeficiency virus (HIV) (combined with other drugs)
• Cytomegalovirus (CMV) retinitis (inflammation of the retina of the eye)
• Genital herpes
• Influenza A respiratory tract illness
• Respiratory syncytial virus (RSV), a severe lower respiratory tract infection
• Viral herpes infections
Unlabeled Uses
Because there are a limited number of antiviral drugs and more than 200 viral diseases, the primary health care provider may decide to prescribe an antiviral drug for an unlabeled use even though documentation of its effectiveness is lacking. Approval by the Food and Drug Administration (FDA) is necessary for a drug to be prescribed. On occasion, the use of a drug for a specific disorder or condition may be under investigation or may be approved for use in another country. In this instance, the drug may be prescribed by the primary health care provider for the condition under investiga-tion. The use of the drug for a specific disorder or con-
dition that is not officially approved by the FDA is called an “unlabeled use.” Examples of unlabeled uses of the antiviral drugs include treatment of CMV and HSV infections after transplant and varicella pneumonia; the treatment of CMV retinitis in immunocompro-mised patients; and the use of ribavirin for influenza A and B (aerosol form), acute and chronic hepatitis, herpes genitalis, and measles (oral form).
GENERAL ADVERSE REACTIONS
Antiviral drugs are given systemically or as topical drugs. When used systemically these drugs may be administered orally or intravenously (IV). Rapid IV administration can result in crystalluria (presence of crystals in the urine). The most common adverse reactions when these drugs are administered systemically
are gastrointestinal disturbances, such as nausea, vomit-ing, diarrhea, and anorexia. When administered topi-cally, the antiviral drugs can cause transient burning,stinging, and pruritus at the application site.
ADVERSE REACTIONS FOR
SPECIFIC DRUGS
Acyclovir
Acyclovir is available for use orally, topically, and par-enterally (for IV use). When given IV, acyclovir can cause phlebitis, lethargy, confusion, tremors, skin rashes, nau-sea, and crystalluria. Side effects when given orally include nausea, vomiting, diarrhea, headache, dizziness,and skin rashes. Topical administration causes transientburning, stinging, and pruritus.
Amantadine
Adverse reactions of amantadine include gastrointestinal upset with nausea and vomiting, anorexia, asthenia
(weakness, loss of strength), constipation, depression, visual disturbances, psychosis, urinary retention, and
orthostatic hypotension.
Didanosine
Adverse reactions reported with didanosine include headache, peripheral neuropathy, rhinitis, cough, diar-rhea, nausea, vomiting, anorexia, hepatotoxicity, and pancreatitis.
Ribavirin
Ribavirin is given by inhalation and can cause worsening of respiratory status, hypotension, and ocular irritation,including erythema (redness of skin), conjunctivitis, and blurred vision.
Zanamivir
Common adverse effects include headache, nausea, diarrhea, anorexia, rhinitis, and flu-like symptoms. The
most serious adverse reactions are related to respiratory effects and include severe bronchospasm that may lead to death.
Zidovudine
Adverse reactions associated with zidovudine include headache, weakness, malaise, nausea, abdominal pain,and diarrhea. Hematologic changes include anemia and granulocytopenia (low levels of granulocytes, a type of white blood cell, in the blood).
GENERAL CONTRAINDICATIONS,
PRECAUTIONS, AND INTERACTIONS
All antiviral drugs are contraindicated in patients with previous hypersensitivity to the individual antiviral drug. The antiviral drugs are also contraindicated in patients with congestive heart failure, seizures, renal dis-ease, and during lactation. The antiviral drugs are given with caution in patients with renal impairment and require dosage adjustments. Antivirals are used with caution in children, during pregnancy (except ribavirin,a Pregnancy Category X drug), and during lactation.Other contraindications and precautions are listed below, according to the specific drug. Numerous interactions are possible with the antiviral drugs. Only the most significant interactions are listed for selected drugs. The nurse should consult an appropriate source for a more extensive listing of interactions.
Acyclovir
This drug is used cautiously in patients with pre-exist- ing neurologic, renal, hepatic, respiratory, or fluid and electrolyte abnormalities. The nurse gives the drug with caution to patients with a history of seizures. Acyclovir
is a Pregnancy Category C drug and is used cautiously during pregnancy and lactation. Incidences of extreme drowsiness have occurred when acyclovir is given with zidovudine. There is an increased risk of nephrotoxicity when acyclovir is administered with other nephrotoxic drugs. When administered with amphotericin B, the risk of nephrotoxicity is increased. Administration with probenecid causes a decrease in the renal excretion of acyclovir, prolonging the effects of acyclovir and increasing the risk of drug toxicity.
Amantadine
Amantadine is used cautiously in patients with seizure disorders, psychiatric problems, renal impairment, and cardiac disease. Amantadine is a Pregnancy Category B drug and is used cautiously during pregnancy and lacta-tion. Concurrent use of antihistamines, phenothiazines,tricyclic antidepressants, disopyramide, and quinidine may increase the anticholinergic effects (dry mouth,blurred vision, constipation) of amantadine.
Didanosine
This drug is used cautiously in patients with peripheral vascular disease, neuropathy, chronic pancreatitis, or impaired liver function. Didanosine is a Pregnancy Cate- gory B drug and is used cautiously during pregnancy and lactation. There may be a decrease in the effectiveness of dapsone in preventing Pneumocystis carinii pneumonia when didanosine is administered with dapsone. Use of didanosine with zalcitabine may cause additive neuropa-thy. Absorption of didanosine is decreased when it isadministered with food.
Ribavirin
Ribavirin may be teratogenic and embryotoxic (Pregnancy Category X) and is contraindicated during pregnancy, in patients with chronic obstructive pulmonary disease (COPD), and during lactation. Ribavirin is used cautiously at all times during administration of the drug. Ribavirin may antagonize the antiviral
action of zidovudine and potentiate the hematologic toxic effects of zidovudine. When ribavirin is used con-
currently with digitalis, the risk of digitalis toxicity increases.
Zanamivir
Zanamivir is used cautiously with pregnancy (Category C), lactation, asthma, COPD, or other underlying respi-ratory diseases. No significant drug interactions have been reported with the use of zanamivir.
Zidovudine
This drug is used cautiously in patients with bone mar-row depression or severe hepatic or renal impairment.Zidovudine is a Pregnancy Category C drug and is used cautiously during pregnancy and lactation. There is an increased risk of bone marrow depression when zidovudine is administered with antineoplastic drugs,other drugs causing bone marrow depression, and in patients having or recently taking radiation therapy.An additive neurotoxicity may occur when zidovu-dine is administered with acyclovir. Clarithromycin de-creases blood levels of zidovudine. The blood levels of zidovudine are increased when it is given with lamivudine.
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Unknown - Wednesday 21 April 2010
