Antiviral drugs limitations

Although the term nucleoside was once limited to the compounds in Table 28.2 and a few others, cunent use is more permissive. Pyrimidine derivatives of D-arabinose, for exfflnple, occur in the free state in certain sponges and are called spongonticleosides. The powerful antiviral drug ribavirin, used to treat hepatitis C and Lassa fever, is a synthetic nucleoside analog in which the base, rather than being a pyrimidine or purine, is a triazole. 

Because there are a limited number of antiviral drug s 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 dis-... 

Treatment — Vaccinia immune globulin must be used in conjunction with a vaccinia vaccine if exposure to a smallpox case occurred more than 4 days earlier. However, only the vaccinia vaccine is required less than 4 days after such contact. The vaccine starts to be protective in approximately 7 days. This vaccine does not provide life-long immunity. Revaccination is recommended at 5- to 10-year intervals. Certain antiviral drugs such as Cidofovir have demonstrated that they confer some protection against infection. Unfortunately, because smallpox has been eradicated, limited research on such drugs has been conducted.3... 

T-20 is intended for patients with advanced HIV infection, and will be tested in patients who have experienced all three classes of marketed antiviral drugs. These patients have limited treatment options... 

The only time that surrogate markers are of no value is in the discovery of antibiotics and antivirals, where with PCR to amplify the bacterial or viral nucleic acids within a few hours, one knows directly whether the antibiotic or antiviral drug works it kills microbes or stops their division, or it does not work. Hence, antibiotics almost never fail on efficacy, but their nasty side effects may yet stop for them or limit the dose patients tolerate therefore, they might not show efficacy because the dose cannot be achieved that would kill the microbes. 

ANTIVIRAL AGENTS The antiviral drugs used in ophthalmology are summarized in Table 63-3 see Chapter 49 for more details about these agents). The primary indications for antiviral drugs in ophthalmology are viral keratitis, herpes zoster ophthalmicus, and retinitis. There currently are no antiviral agents for the treatment of viral conjunctivitis caused by adenoviruses, which usually has a self-limited course and is treated by symptomatic relief of irritation. 

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