Experimental drug speeds up platelet recovery 

12/02/2016 00:00 
Patients with a rare blood disorder who received an experimental drug in addition to regular medication had their platelet recovery sped up by almost 40%, according to research published yesterday.
 

Patients with a rare blood disorder who received an experimental drug in addition to regular medication had their platelet recovery sped up by almost 40%, according to research published yesterday.

Researchers including UCLH haematologist Marie Scully evaluated the efficacy and safety of Caplacizumab in a clinical trial involving patients with Thrombotic Thrombocytopenic Purpura (TTP), a blood disorder where blood clots form in small blood vessels throughout the body. These clots can limit or block the flow of oxygen-rich blood to the body's organs and result in serious health problems such as strokes, epileptic events and heart damage.

The study included 75 TTP patients, 36 of whom were administered with Caplacizumab in addition to their regular treatments of immunosuppressives and daily plasma exchange; the remaining patients were administered a placebo in addition to the same regular treatments. Those who received the trial drug showed a 39% reduction in the amount of time taken to reach platelet count normalisation, an important measure of the prevention of blood clots forming in blood vessels.

The findings, published in the New England Journal of Medicine, have potential positive implications for TTP patients in the future as the amount of time they undergo plasma exchange could be significantly reduced.

Dr Scully said: “Clinical trials in rare diseases are challenging, but this therapy offers a unique approach to increasing the platelet counts in TTP patients, which is a sign of disease recovery. This is particularly important when TTP first presents and allows time for immunosuppressive therapy to take effect. Prevention of exacerbation of TTP during therapy was also reduced. The next trial will aim to prove the benefit this has on the multiple organs affected in TTP and how Caplacizumab can reduce the amount of plasma therapy.”

TTP is caused by a lack of activity in the ADAMTS13 enzyme, a type of protein in the blood. Plasma exchange is used to treat TTP by removing antibodies from the blood that damage the ADAMTS13 enzyme. TTP patients undergo plasma exchange usually until blood tests confirm their platelet count has reached a normal level, this can take days or weeks depending on the severity of the condition.

Caplacizumab is a fragment of an antibody that acts to prevent the binding of platelets to the von Willebrand factor (vWF) – a blood protein required for platelets to stop bleeding at sites of injury. vWF is processed by the ADAMTS13 enzyme and is therefore defective in TTP patients.

The trial was a multinational Phase ll study comprising 56 sites, including UCLH, where Caplacizumab demonstrated promising clinical efficacy in patients with TTP. The trial is being followed up by a Phase lll study which has already started at UCLH.

The study was funded by biopharmaceutical company Ablynx and Dr Scully's research is supported by the UCLH/UCL Biomedical Research Centre.

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