The objective of dosage form development is to ensure the delivery of specific and reproducible amounts of pharmacologically active compounds to the body in the maximum amount possible. Today's most frequently used dosage forms are orally administered solids formulated such as tablets, capsules or powders.
Time-release products intend to improve delivery efficacy and/or effectiveness; for instance, the frequency of dosing can be reduced and, in certain cases, the actual daily dose can be reduced, offering the manufacturer a financial benefit. A variety of techniques have been used to prepare oral time-release delivery systems, and combining them is often done to maximize their advantages. One of the goals behind developing time-release products was to maintain a steady level of drug concentration in the blood. A time-release product essentially controls the rate at which a compound is available for absorption. In doing so a balance can be achieved between the amount absorbed and that being excreted. This balance can smooth the peaks and valleys (fluctuations) of the concentration of the drug in the blood, maintaining a steady level. This significantly improves the product's efficacy since the effective concentration range that a compound needs to be at any given time can be maintained. An effective range (therapeutic or pharmacological window) is determined by the body's tolerance for the compound of interest. Going over the high end of this range, one may experience toxic effects while concentrations below the lower end of the range render the product ineffective. This is achieved by most time-release delivery systems that release small amounts of active at frequent intervals.
Orally administered time-release delivery systems are preferred because they offer flexibility in dosage-form design and are relatively safe in-spite of the difficulties of releasing drug due to the variable gastrointestinal environment.