Armed with new phase III data, GlaxoSmithKline is planning regulatory filings for its one-dose antimalarial tafenoquine, which is designed to prevent relapses in patients infected with the parasite.
The new data shows that a single 300mg dose of tafenoquine – given alongside a three-day regimen of the older antimalarial chloroquine – can cut the chances of relapse in patients infected with the Plasmodium vivax parasite significantly.
GSK is developing the drug with the non-profit Medicines for Malaria Venture (MMV) as an alternative to primaquine, which is currently the only drug for relapsing forms of malaria but needs to be given over a 14-day period. Primaquine can cause serious side effects in some patients, with some evidence that resistance is developing to the drug.
“One of the greatest challenges for patients with P vivax malaria is preventing relapses,” said GSK’s president of R&D Patrick Vallance. “Being able to treat patients with a single dose of medicine would be an important step forward in ensuring efficacious treatment, thereby reducing the risk of relapse, particularly in areas with very limited healthcare infrastructure.”
In the DETECTIVE trial, 60% of patients on tafenoquine plus chloroquine were relapse-free over a six-month follow-up period, compared to 26% of the placebo plus chloroquine group. A third arm received the standard primaquine plus chloroquine regimen, with 64% of patients relapse-free at six months.
A second trial called GATHER showed that there was little difference between tafenoquine and primaquine on levels of haemoglobin – the oxygen-carrying molecule in the blood. The trial uses haemoglobin level as a biomarker for haemolysis, the destruction of red blood cells, which is a recognised side effect with primaquine.
P vivax is one of several species of Plasmodium parasite known to cause malaria, and is the form most likely to lie dormant in the liver, periodically reactivating to cause relapses in the disease that can leave patients incapacitated for three days or more. It causes around 8.5m clinical infections every year according to the World Health Organization.
“Without treatment to eliminate the dormant form of the parasite, patients live with the disease, never knowing when it will relapse and when its debilitating symptoms will return,” commented MMV chief executive David Reddy.
“Not only could single-dose tafenoquine help to put a stop to the relapse for individual patients but it could also help make malaria elimination a real possibility in P vivax endemic countries.”
GSK is also developing a four-dose vaccine for malaria – RTS,S/AS01 – that has shown 31-56% protective efficacy in phase III trials and is now heading for pilot deployment in Ghana, Kenya and Malawi next year. The vaccine targets P falciparum, the most deadly malaria parasite globally and the most prevalent form in Africa.