Zovirax (acyclovir) and Valtrex (valacyclovir) are antiviral medications. They are used against the following viruses:
- Herpes zoster, the virus that causes chickenpox and shingles
- Herpes simplex, the cause of cold sores and genital herpes
Viruses attack by taking over a cell’s nucleus, where new DNA is made, forcing it to make viral DNA instead. Acyclovir is what is known as a nucleoside analog. A nucleoside is a part of DNA. There are four types, arranged in various orders with instructions for making various proteins. Acyclovir is similar to a nucleoside called guanosine, and can replace it in DNA. Once acyclovir replaces guanosine, DNA replication of the virus stops. Valacyclovir is a pro-drug for valacyclovir, meaning that it is turned into acyclovir in the body. Both should be started as early as possible after the symptoms appear to be more effective, ideally within 72 hours.
The main difference between acyclovir and valacyclovir is that acyclovir must be taken more frequently than valacyclovir and is therefore now usually preferred for outpatient treatment.
Acyclovir may be taken orally in the form of:
Acyclovir oral dosages are as follows:
- For chicken pox–800 mg four times per day for 5 days
- For genital herpes or cold sores–200 mg 5 times a day for 10 days
- For shingles–800 mg 5 times a day for 7 to 10 days
Injectable acyclovir is given into a vein usually in the hospital settings for bad infections that are for example affecting the brain.
Acyclovir cream or ointment is applied to lip or genital lesions 5 times per day for 4 days.
Valacyclovir is available in the form of tablets.
- Chickenpox–dose is determined by patient’s weight, usually not over 1000 mg 3 times a day
- Cold sores–1000 mg twice a day for one day
- Genital herpes–1000 mg twice a day for 10 days
- Shingles–1000 mg 3 times a day for 10 days
Neither acyclovir nor valacyclovir cures viral infection, but both treat signs and discomfort of the an acute herpes infection and cut down on time that patients are contagious.
Did you know? QuickMD can treat viral infections from the convenience of your home, and provide you with a prescription for valacyclovir online (or alternatively acyclovir).