Herpes simplex virus (HSV) sores usually respond to common antiviral medicines. But if you have a weakened immune system, sores can be harder to clear, and they may not get better with the usual treatments. Until now, options to treat these sores have included medicines given through a vein (by IV infusion) or applied to the skin.
In October 2026, the FDA approved Hovilpri (pritelivir), a once-daily tablet for adults with weakened immune systems who have HSV sores that haven't healed with the use of antiviral medicines such as acyclovir, famciclovir, or valacyclovir. Hovilpri is the first medicine in a group called helicase-primase inhibitors to be approved for this use.
This article covers how Hovilpri works, who it's approved for, how to take it, and what clinical studies found. You may also be interested in reading about Hovilpri side effects and interactions.
Understanding HSV Sores When Your Immune System Is Weakened
HSV is a common virus that causes painful sores, often blisters that break open and crust over. These sores can show up on the skin or on moist surfaces called mucous membranes, such as the lips, nostrils, eyes, and genitals. Health care providers call sores in these places mucocutaneous lesions.
Once you have an HSV infection, the virus stays in your body for life. It can stay quiet for a long time and then reactivate, which is why sores can come back. Medicines can help sores heal, but they don't cure the infection.
People with weakened immune systems can have HSV outbreaks that are more frequent and more serious. Sometimes, the sores don't respond well to standard treatments because the virus has become resistant to the medicine. In other cases, the sores simply don't improve even without a test showing resistance. Health care providers call this refractory HSV, which means the infection doesn't get better with usual treatment.
How Does Hovilpri Work for HSV Sores?
Hovilpri is an antiviral medicine that works against both types of HSV, HSV-1 and HSV-2. To make more copies of itself, the virus has to copy its genetic material, called DNA. Viruses use a group of proteins called the helicase-primase complex to start that process. Hovilpri blocks this complex, so the virus can't make new DNA.
Older antiviral medicines target different steps. Acyclovir, famciclovir, and valacyclovir must first be converted into their active form by a viral enzyme. Once activated, they work by interfering with the copying of the virus's DNA. Foscarnet blocks the virus's DNA-copying enzyme directly. Because Hovilpri targets a different step, lab testing shows it keeps its activity against HSV that has become resistant to acyclovir or foscarnet. Changes in the virus that cause resistance to those medicines don't make it less sensitive to Hovilpri.
Is Hovilpri Right for Me?
Hovilpri is approved for adults with weakened immune systems who have skin or mucous membrane sores caused by HSV that haven't healed with the use of acyclovir, famciclovir, or valacyclovir. This applies whether or not testing has shown that your virus is resistant to those medicines.
Your health care provider can help decide if Hovilpri fits your situation. Here are a few things to know:
- Hovilpri hasn't been studied in children and teens. It isn't established as safe and effective for people who are 18 years and younger.
- In the main study, people 65 years and older didn't have different results or safety findings from younger adults.
- You don't need a lower or higher dose if you have kidney problems. Hovilpri hasn't been studied in people who need dialysis.
- You don't need a different dose if you have mild or moderate liver problems. It hasn't been studied in people with severe liver problems.
- No information is available on Hovilpri use in pregnant people or people who are breastfeeding. Talk with your health care provider about the possible risks and benefits if you are pregnant, plan to become pregnant, or are breastfeeding.
How Do I Take Hovilpri?
Hovilpri comes as a 100-mg tablet. Your treatment starts with a larger first-day dose:
- Day 1: Take four tablets (400 mg) at one time.
- After day 1: Take one tablet (100 mg) once a day.
You can take Hovilpri with or without food. You'll keep taking it once a day until your HSV sores have healed. Your health care provider will tell you how long to take it, so don't stop it on your own.
If you miss a dose, take it as soon as you remember. If you don't remember until the time your next dose is due the following day, take two tablets at that time.
How Was Hovilpri Studied for HSV Sores?
The FDA approved Hovilpri based on a clinical study of 101 adults with weakened immune systems who had HSV sores on their skin and/or mucous membranes that hadn't healed with the use of acyclovir, famciclovir, or valacyclovir. People with HSV in the eyes, the brain and spinal cord, or that had spread through the body weren't included.
At the start of the study, participants were, on average, 53 years old (ages ranged from 19 to 84 years), and 53% were men. About half (49%) were White, 23% were Black or African American, 16% were American Indian or Alaska Native, 3% were Asian, and 10% were of another race. About 26% were Hispanic or Latino. Participants had a wide range of one or more conditions that weaken the immune system, including:
- Blood cancer or blood disorder (47%)
- Stem cell transplant (40%)
- Human immunodeficiency virus (HIV) infection (38%)
- Autoimmune or inflammatory conditions (29%)
- Cancer other than blood cancer (26%)
- Organ transplant (4%)
At the start of the study, most people (71%) had HSV that was refractory, and 29% had lab-confirmed resistance to acyclovir.
People were randomly assigned to one of two groups. About half got Hovilpri (a 400 mg first-day dose, then 100 mg once a day). The other half got a treatment chosen by the study team. Most of these people (70%) got foscarnet by IV. Others got imiquimod cream (14%), cidofovir by IV (12%), or cidofovir applied to the skin (4%). This was an open-label study, which means both the participants and the study team knew which treatment each person was getting.
People were treated for up to 28 days, until all their sores healed. If sores were getting better but hadn't healed completely by day 28, treatment could continue for up to 42 days in total.
What Are the Main Benefits of Hovilpri Based on the Study?
The main goal of the study was to see how many people had all their sores heal within 28 days. "Healed" meant new skin had fully covered all sores, and no new sores showed up after treatment ended.
Within 28 days, all sores healed in about 63% of people who took Hovilpri (32 out of 51 people). In the comparison group, all sores healed in 34% of people (17 out of 50 people).
This means people who took Hovilpri were nearly twice as likely to have their sores fully heal within 28 days as people who got the other treatments.
Your results may differ from what was seen in clinical studies.
Additional potential benefits based on the study
The study also looked at how many people had their sores heal within 42 days. This was a secondary goal, so these results are less certain than the main result above. By day 42, sores healed in about 82% of people who took Hovilpri and 42% of people in the comparison group. About 1 in 3 people who took Hovilpri (33%) needed treatment past day 28 because their sores were getting better but hadn't healed fully.
Is There Longer-Term or Additional Data?
Hovilpri was also studied in a second group of 35 adults with weakened immune systems whose HSV was refractory to both acyclovir and foscarnet or who couldn't tolerate foscarnet. Everyone in this group took Hovilpri, and there was no comparison group. Sores healed in about 40% of people within 28 days and in about 66% within 42 days.
In the main study, people who took Hovilpri did so for about 27 days on average (the range was 6-43 days). In some people whose sores didn't heal, lab tests found changes in the virus that can make it less sensitive to Hovilpri. This was found in a small number of people who had testable samples. If your sores don't improve, tell your health care provider.
Your results may differ from what was seen in clinical studies.
What Else Should I Know About Hovilpri?
Hovilpri treats sores caused by HSV. It isn't a cure for the infection, and the virus stays in your body after your sores heal. Ask your health care provider what to expect and what to do if new sores appear after you finish treatment.
Is There Any Cost Assistance Available?
Ask your pharmacist or other health care provider about options to help pay for Hovilpri. The drugmaker can also answer questions at 844-835-6947 or at hovilpri.com.
