Oral herpes, also known as fever blisters or cold sores, affects up to 90 percent of Americans, according to the American Social Health Association. For many people, the disease produces mild or no symptoms. For those who do experience symptoms, most episodes of oral herpes resolve within seven to 10 days.
Acyclovir
According to Dr. Adriana R. Marques, a National Institutes of Health researcher writing in the 2008 edition of "Fitzpatrick's Dermatology in General Medicine," acyclovir was the first drug approved by the Food and Drug Administration for the treatment of herpes virus infections and it remains the only drug available for intravenous, oral and topical administration. An "acyclic guanosine anologue," acyclovir replaces the nucleic acid guanosine in chains of viral DNA. Other nucleic acids can't attach to acyclovir, so DNA replication stops, leaving the virus unable to reproduce. What sets acyclovir apart from earlier drugs that caused unacceptable side effects is that acyclovir is inactive in healthy cells. Marques explains that a viral enzyme called "thymidine kinase" is required to activate the drug. Otherwise, the drug is passed harmlessly through the kidneys into urine.
Valacyclovir
Valacyclovir represents the next generation of acyclovir. Available only in oral form, valacyclovir, says Marques, is a slightly modified form of acyclovir named for the "L-valyl ester" that it contains. Valacyclovir reaches the bloodstream in higher concentrations than acyclovir when it's ingested orally and it stays there longer, enabling patients to take the drug less often. For example, says Northeastern Ohio University internist Dr. Christina Cernik in the 2008 edition of "Archives of Internal Medicine," a standard adult dose for oral acyclovir is 400mg five times per day for seven days. A standard adult dose of valacyclovir is 1g twice a day for seven days.
Famciclovir
Famciclovir, or 6-deoxypenciclovir, is a different chemical compound from acyclovir and valacyclovir. However, University of California-San Francisco Professor Dr. Sharon Safrin explains in the 2008 edition of "Basic and Clinical Pharmacology," it works the same way. Like valacyclovir, patients must take the oral drug twice a day. Like acyclovir, it's also available as a cream for topical use. Like both acyclovir and valacyclovir, says Safrin, side effects include headache, nausea, vomiting and diarrhea. Drug resistance is uncommon, according to Safrin; however, when it occurs, it typically involves all three drugs since they share the same mechanism of action.
References
- American Social Health Association: Learn About Herpes: Oral Herpes
- "Archives of Internal Medicine"; The Treatment of Herpes Simplex Infections; C. Cernik et al.; 2008
- "Basic and Clinical Pharmacology, 11th Edition"; B.G. Katzung et al.; 2008
- "Fitzpatrick's Dermatology in General Medicine, 7th Edition"; K. Wolff et al.; 2008
