Man with cold sore

Denavir vs. Zovirax: Which Do I Need for My Herpes?


  • Zovirax and Denavir are both selective antiviral medications suitable for the treatment of herpes infections.
  • The active compounds in Zovirax and Denavir are acyclovir and penciclovir, respectively.
  • Oral Zovirax works for shingles, genital herpes, and chickenpox. You can use topical Denavir for cold sores.
  • Penciclovir (Denavir) stays in infected cells longer than Zovirax (acyclovir). Therefore, it is more effective at treating HSV-2 infections and other herpes infections like chicken pox and shingles.

Herpes eruptions strike out of nowhere. Popular wisdom links them to situations that temporarily compromise or weaken the immune system. The virus responsible for the nasty cold sores is a type of herpes simplex virus, namely HSV-1. Its close relative HSV-2 causes cold-sore-like problems below the waist, although HSV-1 has been known to venture into the nether regions on occasion, as well. 

The herpes simplex virus type 1 affects a large portion of the global population. Both HSV-1 and HSV-2 infections are lifelong. However, HSV-2 infections are less frequent and mostly affect the genital and anal areas.

So, what do you do when confronted with this relatively harmless yet painful, unsightly, and potentially embarrassing problem? You reach for a time-honored remedy such as Zovirax or Denavir.

Zovirax versus Denavir: Are They the Same?

Affects the mouth and genital areasAffects the mouth, genital, and anal areas
Highly contagious, spreads through contactTransmitted sexually, almost without exception
Infection is lifelong and not curableInfection is lifelong and not curable
Affects close to 4 billion people globallyAffects around 500 million people globally
Symptoms include painful itching, blisters at the affected areas, tingling, burning,  feverSymptoms include painful blisters, fever, painful urination
The body develops some degree of immunity to the infection over time, making outbreaks less and less intenseImmunity improves over time, although complete resolution is impossible

Although they address similar problems, Zovirax and Denavir are not the same drug. The active compounds in the two medications are different, and so are the ways in which they act on the herpes virus.

  • Zovirax is an acyclovir-based solution available in oral and topical formulations. That means you can take Zovirax in pill form, as a liquid suspension, or as an ointment or cream directly on the affected areas. In oral form, Zovirax works against shingles, chickenpox, and genital herpes. Used as an ointment or cream, it also works well against recurrent cold sores.
  • Denavir’s active compound is penciclovir. As a topical cream, Denavir is intended for the treatment of cold sores.

The Differences between Zovirax and Denavir

Viruses do their damage by replicating, or making many copies of themselves, once they gain a stronghold in the body. Zovirax and Denavir both prevent the HSV virus from replicating.

The differences between the two medications boil down to the differences in pharmacology between acyclovir and penciclovir. Pharmacology refers to the biochemical processes through which a drug acts upon a virus, bacteria, inflamed tissue, etc.

Acyclovir acts like a homing missile against HSV-1 and HSV-2. It only ‘arms’ itself once it reaches its target, the HSV-infected cell. There, acyclovir monophosphate comes into contact with enzymes of the host cell, which turn it into acyclovir diphosphate and acyclovir triphosphate.

The triphosphate form works its way into the DNA of the HSV virus and deactivates it.

Because it only targets infected cells, it has few adverse effects on healthy, uninfected cells. However, in rare cases, acyclovir can block kidney drainage because it’s eliminated from the body through the kidneys.

Acyclovir has been available in topical form since 1982.

Like acyclovir, penciclovir‘s triphosphate form results from the compound’s contact with infected cell enzymes, but it inhibits virus replication through a slightly different mechanism than acyclovir.  Also like acyclovir, penciclovir leaves the body through the kidneys. However, it generally has a longer half-life within infected cells than acyclovir (meaning it remains active in the body longer).

Zovirax versus Denavir: Which Is Better?

A search of the scientific literature comparing the two active ingredients yields conflicting results. Cold sore infections resolve on their own in patients whose immune systems work well. Thus, a 2018 literature review found both medications to be only marginally effective.

However, as we discussed above, there are significant differences between how acyclovir and penciclovir work on infected cells on the biochemical level.

Acyclovir and penciclovir seem to be equally effective against the HSV-1 virus. According to a 1992 comparative study, however, penciclovir is significantly more effective than acyclovir against the HSV-2 and Varicella-zoster (chickenpox and shingles) viruses.

Researchers have found that in HSV-2 viruses, the half-life of Zovirax is only one hour, while Denavir, with a half-life of seven hours, lasts much longer.

Bottom line: Denavir has a definite edge over Zovirax for treating HSV-2. It also has a small advantage over Zovirax for HSV-1 infections, such as cold sores, as well as shingles and chicken pox.

Zovirax and Denavir Side Effects

Depending on how you use them (orally or topically), Zovirax and Denavir can cause side effects ranging from mildly inconvenient to life-threatening.

The side effects of oral medication tend to be deeper-reaching than those of topical medications, which are mostly local. The body absorbs compounds like penciclovir, however, even when it’s used topically.

If you take it orally, Zovirax can cause:

  • Diarrhea, vomiting, and malaise
  • Headache, nausea, and stomach pains
  • Lack of appetite
  • Dizziness
  • Swelling of hands or feet

Side effects of topical Denavir can include:

  • Serious allergic reactions resulting in breathing difficulties (in rare cases only)
  • Headache
  • Throat swelling
  • Altered sense of taste
  • Local reactions, such as rashes, itching, hives, redness, numbness, and burning

If you use Zovirax or Denavir and notice breathing difficulty or other potentially serious side effects, seek medical attention immediately.

HSV-1 and HSV-2

Cold sore on a top lip.
HSV-1 mainly affects the lips/mouth.

The herpes simplex virus type 1 affects a large portion of the global population.

Both HSV-1 and HSV-2 infections are lifelong. However, HSV-2 infections are less frequent and mostly affect the genital and anal areas.

How eDrugstore Can Help

At eDrugstore, we carry both acyclovir (the generic form of Zovirax) and Denavir to help manage the symptoms of HSV-1 and HSV-2 infections and outbreaks. Take advantage of our free medical consultation with a U.S.-licensed physician. They will provide you with a prescription, and your medication will be on its way quickly and discreetly. With eDrugstore, health visits and shipping are always free.

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