Thursday, May 1, 2008

Agents for Herpes and Cytomegalovirus

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Herpes viruses account for a broad range of conditions, including cold sores, encephalitis, shingles and genital infections. Cytomegalovirus (CMV) although slightly different from the herpes virus can affect the eye, respiratory tract and liver and reacts to many of the same drugs.

1. Acyclovir (Zovirax) – is specific for herpes virus infections. Is excreted unchanged in the urine and therefore must be used cautiously in the presence of renal impairment. It crosses into breast milk and exposes the neonate to high levels of the drug.
2. Cidofovir (Vistide) – is used to treat CMV retinitis in patients with AIDS only. It is associated with severe renal toxicity and granulocytopenia. It is excreted unchanged in the urine and must be given with probenecid to increase renal clearance of the drug. Use in children with AIDS should be very cautious because of potential.
3. Famiciclovir (Famvir) – is most effective in treating herpes infections. It is well absorbed in the GI tract, reaching peak levels in 2 to 3 hours. It is metabolized in the liver and excreted in the urine and feces.
4. Foscarnet (Foscavir) – is available in intravenous (IV) form only. It can be highly toxic to the kidneys and is reserved for treatment of CMV retinitis in immunocompromised patients and for mucocutanneous acyclovir-resistant herpes simplex infections.
5. Ganciclovir (Cytovene) – which is available in IV and oral forms and is used for long term treatment and prevention of CMV infections. Primarily excreted unchanged in the feces with some urinary excretion. It is carcinogenic and should be used only with extreme caution in children.
6. Valacyclovir (Valtrex) – is an oral agent used for the treatment of herpes zoster and recurrent genital herpes. Rapidly absorbed from the GI tract and metabolized in the liver to acyclovir. Excretion occurs through the urine so caution should be used in patients with renal impairment.
7. Valganiclovir (Valcyte) – which is the oral prodrug of ganciclovir, is used for the treatment of CMV retinitis in AIDS patients. Primarily excreted unchanged in the feces with some urinary excretion.

Therapeutic Actions and Indications
Drugs that combat herpes and CMV inhibit viral DNA replication by competing with viral substrates to form shorter, noneffective DNA chains. This action prevents replication of the virus, but it has little effect on the host cells of human because their DNA uses different substrate. These antiviral agents indicated for treatment of the DNA viruses herpes simplex, herpes zoster and CMV.

Contraindications and Cautions
Drugs indicated for the treatment of herpes and CMV should not used during pregnancy or lactation or I patients with known allergies to antiviral agents, renal disease which could interfere with excretion of the drug or severe CNS disorders.

Adverse Effects
The adverse effects most commonly associated with these antivirals include nausea and vomiting, headache and depression and rash and hair loss. Rash and inflammation and burning often occur at sites of IV injection and topical application.

Clinically Important Drug-Drug Interactions
The risk of nephrotoxicity increases when agents indicated for the treatment of herpes and CMV are used in combination with other nephrotoxic drugs. The risk of drowsiness also rises when these antiviral agents are taken with zidovudine and anti retroviral agent.

Nursing Diagnoses
The patient receiving a DNA-active antiviral agent may have the following nursing diagnoses related to drug therapy:
· Acute pain related to GI, CNS, local effects of drug
· Disturbed Sensory Perception related to CNS
· Deficient knowledge regarding drug therapy

· Ensure good hydration to decrease the toxic effects on the kidneys.
· Administer the drug as soon as possible after the diagnosis has been made to improve effectiveness of the antiviral activity.
· Ensure that the patient takes the complete course of the drug regimen to improve effectiveness and decrease the risk of the emergence of resistant viruses.
· Wear protective gloves when applying the drug topically to decrease risk of exposure to the drug and inadvertent absorption.
· Provide safety precautions if CNS effects occur (e.g., use side rails, appropriate lighting, orientation, assistance) to protect the patient from injury.
· Warn the patient that GI upset, nausea, and vomiting can occur, to prevent undue anxiety and increase awareness of the importance of nutrition.
· Monitor renal function tests periodically during treatment to detect and respond to renal toxicity as soon as possible.
· Provide the patient with instructions about the drug therapy and to promote compliance.

The patient should:
· Avoid sexual intercourse if genital herpes is being treated, because these drugs do not cure the disease.
· Wear protective gloves when applying topical agents.
· Avoid the driving and hazardous tasks dizziness and drowsiness occurs.

· Monitor patient response to the drug
· Monitor for adverse effects
· Evaluate effectiveness of the teaching plan
· Monitor for the effectiveness of comfort and safety measures and compliance with regimen

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