In the June 9, 2008 edition of "Archives of Internal Medicine," Northeastern Ohio University dermatologist Dr. Christina Cernik says that cold sores are among the most common complaints encountered by primary care doctors. Ninety-five percent of cold sores, according to Cernik, develop on the lips or surrounding facial skin. Only about 5 percent develop inside the mouth, usually during the first outbreak. Since topical remedies aren't effective on internal surfaces, the only option to heal a cold sore inside the mouth is prescription oral antiviral drugs.
Acyclovir
In the 2008 edition of "Basic and Clinical Pharmacology," University of California San Francisco Professor of Medicine Dr. Sharon Safrin explains that acyclovir was the first drug to demonstrate effectiveness against herpes simplex virus infections such as cold sores. Acyclovir works by replacing the nucleic acid, guanosine, in chains of viral DNA. Unlike guanosine, acyclovir as no attachment site for another nucleic acid, so DNA replication stops. Since acyclovir requires a viral enzyme, thymidine kinase, to become active, it's effects are specific to infected cells. The usual dose of acyclovir is 15 mg per kg of body weight, five times daily for one week.
Valacyclovir
Valacyclovir is a chemical variant of acyclovir that offers superior absorption, allowing patients to take it less often. The usual dose, according to Cernik, is 1 g, two times per day for one week. In clinical trials, Cernik notes, valacyclovir 1 g twice daily for one week reduced the duration of cold sores inside and outside the mouth by five days with interim reductions in pain and itching. Patients also stopped shedding the virus after just one day of treatment, compared to five days in patients who took a placebo medication.
Famciclovir
Famciclovir is chemically distinct from acyclovir and valacyclovir, although it works the same way. Like valacyclovir, Safrin says, famciclovir offers superior absorption and remains in the bloodstream longer than acyclovir. Like both acyclovir and valacyclovir, common side effects include headaches, nausea, vomiting and diarrhea. Oral dosing avoids the skin irritation sometimes seen with topical preparations. Patients with kidney problems require lower doses; nonetheless, psychiatric side effects such as alterations in consciousness, mental confusion, hallucinations and delusions sometimes occur. In the April 2009 issue of the "European Journal of Neurology," Dr. Timothy Asahi of the Toyami University Department of Crisis Medicine says that delusions that the patient had already died appear to be a unique side effect of cold sore antiviral drugs including famciclovir. Doctors typically prescribe famciclovir for cold sores inside the mouth at 500 mg twice a day for one week.
References
- "Archives of Internal Medicine"; The Treatment of Herpes Simplex Infections; Dr. Christina Cernik et al.; June 9, 2008
- "Basic and Clinical Pharmacology, 11th Edition"; Dr. Bertram G. Katzung et al.; 2008
- "European Journal of Neurology"; Valacyclovir Neurotoxicity; Dr. Timothy Asahi et al.; April 2009
