Here is the slightly odd twist in this comparison: valacyclovir is converted to acyclovir in the system after being swallowed.
Why make two medicines?
Valacyclovir is absorbed much more efficiently by the body, which means fewer daily doses, convenient when you have to squeeze treatment in and around a busy life.
Acyclovir is a powerful and cheap drug, its major drawback the frequency with which it needs to be taken. For shingles, for instance, oral acyclovir might need to be taken five times a day, whereas valacyclovir is three times daily.
Five doses sounds pretty straightforward when written out, by the second day one dose has been left at home, another forgotten during lunch, and the nightcap has become more of a discussion.
In reality, the easier schedule tends to win out.
Are they the same, though?
Both have excellent records as treatments for herpes viruses when the diagnosis, dose and timing are right.
Acyclovir and valacyclovir are used for cold sores, genital herpes and shingles, and can sometimes be used for chickenpox in certain patients. Intravenous acyclovir is used in hospitals for severe herpes infections, such as encephalitis or infections of the newborn.
Neither of these drugs actually clears the body of the herpes virus.
Once an outbreak has run its course, the virus lies dormant in the nerves and can be reawakened at any time in the future, perhaps by illness, stress, sun exposure or simply a bad day.
The tablets slow down the virus’s replication, which can significantly reduce the length and severity of an outbreak, as well as the pain and discomfort of the rash and speed up healing. Timing is everything in treating herpes, and it’s more important than most people think.
For a cold sore, “early” means the tingling or burning stage before the lip is covered in blisters. A recurrent episode of genital herpes is best treated as soon as possible after the first warning symptoms or the appearance of any lesions.
With shingles, it’s most effective to start treatment within 72 hours of the rash appearing, and if the rash is near an eye it should definitely not wait for a routine examination. A shingles rash near the eye can threaten vision.
Overall, valacyclovir is a convenience pill
The original drug, acyclovir, is poorly absorbed from the gut and so valacyclovir was created, a pill which is far more efficiently absorbed by the body and then turned into acyclovir by enzymes in the system.
That’s why the comparison makes so much sense.
Both medications target the same virus with a similar side effect profile, the main difference being the frequency with which they have to be taken.
For a first episode of genital herpes, current protocols may suggest three tablets of acyclovir a day or two tablets of valacyclovir each day. For suppression of recurrent episodes both can be successful although valacyclovir offers the convenience of a simpler regime.
There’s nothing to be gained by choosing the newer tablet if a person reliably takes their acyclovir and the infection is responding. Cost is likely to dictate the outcome of the choice, as generic acyclovir can be much cheaper and generic valacyclovir pills are also now available in some countries.
Genital herpes: outbreaks and suppression
Some people choose to take antiviral tablets only when an outbreak begins. This is called episodic treatment.
Other people take them every day as suppressive treatment. Taking medication each day can reduce the number of outbreaks and the chance of transmitting genital herpes to a sexual partner.
Daily treatment does not eliminate that chance entirely.
Herpes can be transmitted at any time, including when the skin looks normal, so valacyclovir tablets taken each day cannot be a complete substitute for discussing sexual activity with a partner or using a condom, especially when outbreaks or warning symptoms occur. Sex should be avoided when sores are visible.
Valacyclovir is often used for suppression because, in some patients, a once-daily dose may be possible. That’s much simpler than dividing the daily dose between several tablets taken throughout the day.
Side effects rarely tip the balance
Either drug is well tolerated by most people, and the main complaints are headache, nausea and upset stomach.
The kidneys are more important than the stomach in this context.
Acyclovir is cleared from the body via the kidneys, and if the dose is too high for a particular patient, or the person is severely dehydrated, the drug can build up in the system. Kidney damage and neurological symptoms can be the result.
Older people and those with impaired kidney function generally require lower doses. Confusion, hallucinations, sleepiness or abnormal movements should always be checked out rather than put down to age or a fever.
Drink plenty of fluids. There’s no need to drink gallons at a time, but taking acyclovir or valacyclovir with a glass of water after being sick or having a fever or heatwave is not the best idea.
Both drugs require consideration during pregnancy and breastfeeding, although acyclovir has a long-established safety record in this situation when treatment is required. The choice is based on the infection and the circumstances.
So which would I choose?
For an occasional cold sore and the saving of money, acyclovir may be entirely satisfactory.
For shingles, recurrent genital herpes or suppression treatment, I would probably go for valacyclovir if I could afford it. It’s not because it targets the virus with more aggression, but a simpler schedule is difficult to beat.
That’s the whole story told in one sentence: acyclovir is the hardworking drug and valacyclovir has a convenient delivery system.
Other antiviral treatments will target different viruses, so these tablets are not useful for the flu, COVID-19 or an unexplained rash.
Valacyclovir is often more convenient while acyclovir may be cheaper, but the winner is the drug that is prescribed early on in the course of an infection, at the right dose and actually taken.
