Antiviral agent — resiquimod
Genital herpes is a distressing sexually transmitted disease, caused by the virus Herpes simplex. The virus exists in two forms: type I is generally responsible for cold sores and type II for genital herpes, although both types can cause either condition. It manifests itself as a collection of tiny blisters, which can be extremely painful and unsightly. The virus is transmitted by skin-to-skin contact. It may lie dormant for life, but the sores are frequently recurrent, particularly when the patient is under stress.
The blisters can be treated topically or orally with nucleoside analogue antiviral agents such as aciclovir, penciclovir and ganciclovir. These drugs can reduce the severity of the symptoms, but do not eliminate the virus. A new drug under development, originally known as R-848 and now referred to as resiquimod, works in a different way, as it is an immune response modulator. Its precise mechanism of action is still unclear, but it is believed to reduce CD23 expression and induce interferon γ in stimulated cells, giving herpes-specific cellular immunity.1 It is thought that an immune response modulator could extend the time between and even prevent recurrences of the disease without the need for daily drug treatment.
The drug has been given in topical gel form to 52 patients suffering from genital herpes in a randomised, double blind, vehicle controlled study. The patients were treated for three weeks, and those given the active gel had dramatically reduced recurrence rates for the sores, with a third seeing no recurrence, compared with 6% in patients treated with the vehicle alone. Time to recurrence was extended to 169 days in patients given the drug, from an average 57 days in vehicle treated patients. Few side effects affected the continuance of treatment, with only two patients given the active gel and one using the vehicle experiencing dose-limiting adverse events.2
The drug has been being investigated by 3M Pharmaceuticals, and the company has just entered into a collaboration agreement with Eli Lilly for its further development. It has entered Phase III trials in both the US and Europe, and could be on the market by 2005.