What is the difference between sustained-release preparations and controlled-release preparations?

"Sustained-release preparations" refer to formulations that can continuously release drugs for a long time after administration to achieve long-lasting effects, with drug release mainly being a first-order rate process. 

"Controlled release preparations" on the other hand, refer to formulations that can automatically release drugs at a predetermined rate within a predetermined time, keeping the blood drug concentration consistently within the effective concentration range for a long time. The drug release mainly occurs at a zero or near-zero rate within the predetermined time.