In clinical studies approximately 5% of subjects receiving abacavir develop a hypersensitivity reaction; some of these cases were life-threatening and resulted in a fatal outcome despite taking precautions .
The above sentence is very complicated. Please provide me a simplified synonymous version consisting of multiple sentences:
In clinical studies , hypersensitivity reactions have been observed in approximately 5% of patients treated with abacavir . In some cases , these hypersensitivity reactions have been life-threatening and sometimes have fatal outcome , despite precautions being taken .