The drug release principle of sustained and controlled release preparation includes

1. Sustained release: Sustained and controlled release preparations can wrap drugs with soluble or insoluble materials to form an outer protective layer, thus delaying the release rate of drugs.

2. Progressive release: This method adopts multi-layer coating technology, and the drug is gradually released in multi-layer films to realize the gradual improvement of drug efficacy.

3.pH responsive release: Some sustained and controlled release preparations can release drugs according to the change of intestinal pH value. For example, drugs can not be released in the strong acidic environment of gastric acid, but only in the alkaline environment of intestine.

4. Controlled release by magnetic field: Using magnetic materials as carriers, the release speed and efficacy of drugs can be adjusted through magnetic field control.