ANTIVIRAL AGENTS

ANTIVIRAL AGENTS

Viruses cause a variety of conditions, ranging from warts, to the common cold and “flu”, to diseases such as chicken pox and measles. A single virus particle is composed of a piece of DNA or RNA inside a protein coat. To carry on any metabolic processes, including replication, a virus must enter a cell. Once a virus has injected his DNA or RNA into its host cell, that cell is altered and it is programmed to control the metabolic processes that the virus need to survive. The virus including the protein coat, replicates in the host cell. When the host cell can no longer carry out its metabolic functions because of the viral invader, the host cell dies and releases the new viruses into the body to invade other cells.

Agents for Influenza A and Respiratory Viruses
Influenza A and other respiratory viruses including Influenza B and respiratory syncytial viruses (RSV) invade the respiratory tract and cause the signs and symptoms of respiratory “flu”.

1. Amantadine (Symmetrel) – was first used to treat Parkinson’s disease. It is now used for both treatment and prevention of respiratory viral infections. It is slowly absorbed from the gastrointestinal tract reaching in peak levels of 4 hours.
2. Oseltamivir (Tamiflu) – effective in the treatment of uncomplicated influenza infections that have been symptomatic for less than 2 days. It is readily absorbed from the GI tract, extensively metabolized in the urine and excreted in the urine with a half-life of 6 to 10 hours.
3. Ribavirin (Virazole) – is effective against influenza A, RSV, and herpes virus. This agent has been used in the treatment of children with RSV and has been tested for used in several other viral conditions. Absorbed well in the respiratory tract and has a half-life of 9.5 hours.
4. Rimantadine (Flumandine) – a synthetic agent used for the prevention and treatment of Influenza A infections. It is absorbed in the GI tract with peak levels of 6 hours. Extensively metabolized and excreted in the urine. It is embryo toxic in animals. It should not be used by nursing mothers because it crosses into the breast milk and can cause toxic reactions to neonate.
5. Zanamivir (Relenza) – was approved in 1999 to treat uncomplicated influenza infections in adults and in children older than 12 years of age who have had symptoms for less than 2 days. It is absorbed through the respiratory tract and excreted unchanged in the urine with a half-life of 2.5 to 5.1 hours.

Therapeutic Actions and Indications
These viral agents prevent shedding of the viral protein coat and entry of the virus into the cell. This action prevents viral replications causing viral death. These antiviral drugs are indicated for prevention of Influenza A infection.


Contraindications and Cautions
Caution should be used when giving these antiviral agents to patients with a known allergy; to pregnant or lactating women or to patients with renal or liver disease which could alter metabolism and excretion of the drug.

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 include light headedness, dizziness and insomnia, nausea, orthostatic hypotension and urinary retention.

Clinically Important Drug-Drug Interactions
Patients who received amantadine or rimantadine may experience increased atropine-like effects if either of these drugs is given with an anticholinergic drug.

Nursing Diagnoses
The patient receiving a respiratory antiviral drug may have the following nursing diagnoses related to drug therapy.
· Acute pain related to GI, CNS, GU effects of drug
· Disturbed sensory perception related to CNS effects of drug
· Deficient knowledge regarding drug therapy

Implementation
· Start drug regimen as soon after exposure to the virus as possible to achieve best effectiveness and decrease the risk of complications of viral infection.
· Administer Influenza A vaccine before the flu season begins if at all possible, to prevent the disease and 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 patient from injury.
· Instruct the patient about the appropriate dosage scheduling regimen; safety precautions, including changing position slowly and avoiding driving and hazardous tasks, to take if CNS effects occur; and the need to report any difficulty walking or talking to enhance patient knowledge about drug therapy and to promote compliance.

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