Experimental Hemophilia A Drug Shows Promising Phase 1/2 Trial Results

According to a release from Sangamo Therapeutics and published by PR Newswire, experimental severe hemophilia A drug SB-525 proved to be well-tolerated and generally safe in a phase 1/2 clinical trial that involved eight hemophilia patients.

Results seemed to be dose-dependent, suggesting that the drug may very well indeed be responsible for the positive uptick in factor VIII (an essential blood-clotting protein) levels across the group.

About Hemophilia A

Hemophilia A (or “classic“ hemophilia) is an X-linked recessive genetic disorder. Because women have two X chromosomes, they are much likely to develop hemophilia.  Men, however, only have to inherit one hemophilia-carrying chromosome to develop the condition, because they inherit only one copy of the X chromosome. Women with one copy of a hemophilia-carrying X chromosome are “carriers,” and can potentially pass the condition to their children. Because men do not pass an X chromosome to offspring, it is impossible for them to pass on the condition.

“Severe“ hemophilia makes up about 60% of hemophilia cases. Hemophilia is determined to be severe when blood plasma factor VIII levels make up less than 1% of the blood. Normal factor VIII levels range between 50% and 150% – blood containing levels below 50% will not clot. When factor VIII levels are this low, severe, prolonged bleeding may ensue following an injury. Some may even experience spontaneous bleeding episodes into their joints or muscles.

About the Trial

The study divided eight participants into four groups of two receiving varying doses of SB-525. Groups receiving larger doses reported better results, with the cohort administered the largest does reporting 140% and 94% blood factor VIII levels during a one-time clotting assessment after a week six infusion.

Though one patient reported hypotension and fever, the drug was determined to be generally safe and well tolerated in the study. Researchers were encouraged by the early findings, and follow-up trials are likely.

Though the results are promising, it is important to note that even the smoothest of clinical trials can go on for years. Even if SB-525 eventually gains FDA approval, which might very well never be the case, it could be many months away.


A <1% factor VIII level jumping to 94% or 140% is impressive. Why do you think more individuals might need to be studied before such a result can be called typical? Do you think eight respondents is enough? Share your thoughts with Patient Worthy!

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