Different from ordinary preparations, controlled release preparations refer to a large category of preparations that use technical means to adjust the release rate, release site, or release time of the drugs. Controlled release preparations can be divided into sustained-release, controlled-release and delayed-release preparations. Compared with ordinary preparations, sustained-release and controlled-release preparations have longer-lasting drug therapeutic effects, less toxicity, fewer side effects, and fewer uses of medication, all contributing to higher degrees of patient compliance. Delayed-release preparations can delay the release of drugs so as to realize dissolution in intestines, colon-targeted release or pulsatile release.

This Guidelines focuses on oral sustained-release, controlled-release and delayed-release preparations, and can also be a reference for relevant preparations of other routes of administration.

Sustained-release preparations refer to preparations that slowly release drugs at a non-constant rate in a stipulated medium. The dosing frequency is reduced to half of or lower than that of the corresponding ordinary preparations. Thus, sustained release preparations can remarkably improve patient compliance.

Controlled-release preparations refer to preparations that slowly release drugs at a constant rate in a stipulated medium. The dosing frequency is reduced to half of or lower than that of the corresponding ordinary preparations. The plasma drug concentration is steadier than that of sustained release preparations, thus contributing to a remarkably higher degree of patient compliance.

Delayed-release preparations, including enteric-coated preparations, colon-targeted preparations, and pulsatile release preparations, do not release drugs immediately after administration. Enteric-coated preparations refer to never or hardly release the drugs in the specified acidic medium (pH 1.0–3.0), but release most or all of the drugs in pH 6.8 sodium phosphate buffer within the required time. Colon-targeted preparations refer to preparations that do not release drugs at the upper gastrointestinal tract, but can release most or all of drugs in the colon; that is to say, they never or hardly release the drugs in an acidic medium or a phosphate buffered solution at pH 6. 8 within a fixed duration, but can release most or all of the drugs in a sodium phosphate buffer solution at pH 7.5-8.0. Pulsatile release preparations refer to preparations which do not release drugs immediately after administration but release drugs in one or several bursts under certain conditions (such as staying in body fluids for a period of time, affected by certain pH value or some enzymes, etc.).

The formulation process design of sustained-release, controlled-release and delayed-release preparations may affect their quality and efficacy. Therefore, it is necessary to study the formation process design comprehensively and deeply, and screen out the formulation process suitable for industrial production tailored to the actual production. The in vitro and in vivo release behavior of sustained-release, controlled-release and delayed release preparations should meet the clinical needs. The in vitro release experimental method and control index that can evaluate the basic in vivo situation should be established to effectively control the preparation’s quality and ensure its safety and efficacy.