Cold sores are tiny 1- to 2-mm blisters that develop on the lip and sometimes inside the mouth or on the surrounding facial skin. In the 2008 edition of "Fitzpatrick's Dermatology in General Medicine," National Institutes of Health researcher Stephen E. Straus, M.D. explains that most cold sores are caused by the herpes simplex-1 virus. Cold sores usually resolve with no treatment at all. However, antiviral cold sore treatment can reduce the severity and duration of an outbreak when it's started soon after symptoms appear.
Types of Treatment
Straus says that The Food and Drug Administration has approved five drugs for the treatment of cold sores. The first four, acyclovir, valacyclovir, famciclovir and penciclovir are available by prescription only. The fifth, docosanol, is available over-the-counter.
Mechanism of Action
In the 2008 edition of "Basic and Clinical Pharmacology," Sharon Safrin, M.D. of the University of California-San Francisco explains that the four prescription medications share the same mechanism of action. Each, says Safrin, replaces the nucleic acid guanosine in viral DNA. None of the molecules have an attachment site for another nucleic acid, so viral DNA synthesis stops, leaving the virus unable to reproduce and spread to uninfected cells. Docosanol works differently. A 22-carbon fatty alcohol, docosanol binds to the membranes of cells and prevents the virus from crossing and infecting cells in the first place.
Formulation
Penciclovir and docosanol are dispensed as creams for topical use. Valacyclovir and famciclovir are dispensed as tablets for oral ingestion. Acyclovir is available as a tablet or liquid suspension. The suspension is intended for children and, in rare cases, adult patients who are unable to swallow pills. Acyclovir is also available as an intravenous infusion that is usually reserved for patients with complications of cold sores, such as encephalitis.
Dosing
Topical antiviral medications come in standard doses of 1 percent for penciclovir and 10 percent for docosanol. Doctors base the dose of oral medication on the patient's age, weight and other considerations, such as kidney function. Patients typically use the medication two to five times per day for up to seven days during the first episode of cold sores and for about five days during a recurrent episode.
Risks
Safrin says that all of the medications used to treat cold sores are generally considered safe and well-tolerated. Oral medications produce side effects such as headache, nausea, vomiting or diarrhea in about 10 percent of patients. Penciclovir produces the same side effects, as well as a low incidence of skin irritation. Docosanol is associated with headaches and, less frequently, skin irritation.
Benefits
According to Cernik, in clinical trials, oral antiviral drugs reduce the duration of cold sores during the first outbreak of cold sores from an average of nine days to about four days. Symptoms such as pain or itching usually resolve two days before the lesions. Topical medications, says Cernik, produce less impressive results, usually reducing healing time by about one day, or just 18 hours, as in the case of docosanol. MayoClinic.com characterizes these benefits as "modest" and cautions that they only apply to people who start the drugs within 48 hours of symptom onset.
References
- "Fitzpatrick's Dermatology in General Medicine, 7th Edition"; K. Wolff et al.; 2008
- "Archives of Internal Medicine"; "The Treatment of Herpes Simplex Infections; C. Cernik et al.; 2008
- MayoClinic.com: Cold Sores: Treatments and Drugs
- "Fitzpatrick's Dermatology in General Medicine, 7th Edition"; K. Wolff et al.; 2008
