Pritelivir Herpes Drug: FDA Approval in 101-Patient Trial

The Food and Drug Administration has approved pritelivir for herpes simplex sores that won't heal in some patients with weakened immune systems, after available antivirals have failed them.

The approval was announced Oct. 9 and covers oral tablets sold as Hovilpri. German drugmaker Aicuris developed the drug. Japan's Asahi Kasei bought Aicuris in April, so the drug's commercial future was already in Asahi Kasei's hands by the time the FDA ruled.

How it works

Acyclovir, valacyclovir and famciclovir have long been the standard herpes treatments. They target the virus's DNA-building machinery, and the virus can sometimes mutate its way around them. Pritelivir instead blocks proteins the virus needs to copy its genetic material. Researchers say hitting that different step is why it works on some resistant infections.

Most people with healthy immune systems get occasional cold sores or genital sores that clear up with standard treatment. In immunocompromised patients the sores can last weeks or months and resist every standard drug. Those are the patients this approval covers: transplant recipients, people with advanced immune disorders and others whose persistent sores haven't responded to existing antivirals. Their remaining options are few, and some, like IV foscarnet, have to be given intravenously.

The trial

The FDA based its decision on a late-stage trial of 101 immunocompromised participants. Within 28 days, the trial's main measure, 62.7 percent of patients on pritelivir had complete lesion healing. Among those given a doctor's choice of IV foscarnet, cidofovir or imiquimod, the figure was 34 percent.

Headache, diarrhea, nausea, reduced appetite, vomiting and dizziness were the most commonly reported side effects.

The trial was small because the eligible group is small. Of the millions who carry the virus, most respond to conventional therapy. Finding patients with weak immune systems and resistant, persistent sores was hard. With only 101 participants, regulators and doctors will watch real-world use for further safety signals, as they usually do with drugs approved for small groups.

For doctors and patients

Doctors treating transplant patients and others on immune-suppressing drugs have had few answers when standard antivirals stop working. Pritelivir gives them an oral drug to try before moving to intravenous therapies, which mean clinic visits and carry their own risks.

Whether Hovilpri becomes a standard choice will depend on how doctors find it in practice, on insurance coverage and on how it performs outside a controlled trial.