Pritelivir: The New Herpes Drug Facing an FDA Decision

Almost every herpes pill sold in the US works the same way. Acyclovir was approved in 1982, and valacyclovir (Valtrex) and famciclovir are improved versions of the same idea. They work well for most people, which is why so little has changed in forty years. Pritelivir is interesting because it attacks the virus from a completely different angle. Here is what it is, who it is for, and what it could mean for the rest of us.

What pritelivir is

Pritelivir is an antiviral pill made by the German company AiCuris. It belongs to a class called helicase primase inhibitors. That is a mouthful, so here is the plain version. To copy itself, the herpes virus has to unzip its DNA and prepare it for copying. The helicase primase complex is the tool that does that job. Pritelivir jams that tool, so the virus cannot copy itself.

In April 2026 the FDA accepted its New Drug Application with Priority Review and set a decision target in the fourth quarter of 2026. It had already received Breakthrough Therapy designation (source). Priority Review means the FDA aims to decide in about six months instead of the usual ten. It does not mean approval is guaranteed.

How it differs from Valtrex and acyclovir

The key difference is how the drug gets switched on. Acyclovir, valacyclovir and famciclovir are all inactive until an enzyme made by the virus itself, called thymidine kinase, turns them on (source). That works brilliantly until the virus changes that enzyme. When it does, the drug never switches on and stops working. That is the most common way herpes becomes resistant.

Pritelivir does not need the virus to switch it on. It blocks a different target altogether, so a virus that has learned to dodge acyclovir has no defence against it.

	Pritelivir	Valacyclovir (Valtrex)	Acyclovir
Drug class	Helicase primase inhibitor	Nucleoside analogue	Nucleoside analogue
Needs the virus to switch it on?	No	Yes	Yes
Works on acyclovir resistant herpes?	Yes, in trials	No	No
Who it is for	Immunocompromised, treatment resistant	Most people with HSV-2	Most people with HSV-2
Status in the US	FDA decision Q4 2026	Approved, cheap generic	Approved since 1982

What the Phase 3 trial showed

The main trial is called PRIOH-1 (source). It enrolled 101 people with weakened immune systems, including transplant recipients, people with cancer and people with HIV, whose herpes had not cleared on standard treatment. They were randomly given either pritelivir or whatever treatment their doctor would normally choose, which for resistant herpes usually means foscarnet or cidofovir, two older drugs that are given by drip and can be hard on the kidneys.

The trial met its main goal: more people fully healed on pritelivir. With treatment extended to 42 days, 82.4% of people on pritelivir had complete healing of their lesions, compared with 42.0% on the comparison treatment. The adjusted difference was 40.2 percentage points (source). AiCuris also reported that it was well tolerated.

For this group, that is a big deal. These are people who have run out of good options, and the backup drugs are unpleasant. A pill that heals twice as many of them would matter a lot.

Who pritelivir is for, and who it is not for

The application the FDA is reviewing covers one specific use: refractory herpes, with or without proven resistance, in people who are immunocompromised (source). In plain terms:

• Likely to be relevant: transplant recipients, people having chemotherapy, people with advanced HIV, and anyone else with a weakened immune system whose herpes will not heal on acyclovir or valacyclovir.
• Not what it is being approved for: the average person with HSV-2 who has occasional outbreaks, or who takes daily Valtrex and does well on it.

Resistance to acyclovir is rare in people with healthy immune systems and far more common in people whose immune systems are weakened (source). So for most readers of this site, the drug they already have still works. If you think your outbreaks are not responding to treatment, that is worth raising with a doctor, because there are tests that can check for resistance.

What happens next

When	What happens
April 2026	FDA accepts the application with Priority Review
Q4 2026	FDA decision due (the PDUFA target date)
If approved	Launch for immunocompromised patients with refractory herpes, most likely through specialists and hospitals first
Later, if at all	Any use in everyday HSV-2 would need new trials in that group

No price has been announced. Drugs for small, serious patient groups usually cost far more than generic valacyclovir, so do not expect it to be cheap. We will update this page the day the FDA decides.

What it means for everyone else with HSV-2

Directly, not much yet. Indirectly, quite a lot. If pritelivir is approved, it will be the first helicase primase inhibitor approved in the US, and it will prove to regulators and drug companies that this class works in people. A related drug, amenamevir, has been sold in Japan since 2017, mainly for shingles.

That matters because the most exciting drugs in the herpes pipeline are in the same class. Assembly Biosciences is developing once a week helicase primase pills, and one of them cut HSV-2 shedding by 94% in a small trial (source). Those are aimed at ordinary people with recurrent genital herpes. A successful pritelivir makes that path easier. You can follow all of these on our vaccine and cure tracker.

What to do in the meantime

For almost everyone, the best treatment is still the one that exists today. Daily valacyclovir reduces outbreaks and, in a large trial, cut the risk of passing HSV-2 to a partner by about 48% (source). It is on the CDC’s list of recommended treatments (source) and costs little as a generic. Our valacyclovir guide covers doses and cost, and the antiviral comparison covers the other options.

Related: Vaccine and cure tracker | Antiviral comparison | Valacyclovir guide | Treatment options