Pharmaceutical gastroretentive drug delivery systems for the controlled release of an active agent in the gastrointestinal tract are disclosed, which comprise: (a) a single- or multi-layered matrix comprising a polymer that does not retain in the stomach more than a conventional dosage form selected from (1) degradable polymers that may be hydrophilic polymers not instantly soluble in gastric fluids, enteric polymers substantially insoluble at pH less than 5.5 and/or hydrophobic polymers and mixtures thereof; (2) non-degradable polymers; and any mixtures of (1) and (2); (b) a continuous or non-continuous membrane comprising at least one polymer having a substantial mechanical strength; and (c) a drug; wherein the matrix when affixed or attached to the membrane prevents evacuation from the stomach of the delivery system for a period of time of from about 3 to about 24 hours.

Bioerodible poly(orthoesters) useful as orthopedic implants or vehicles for the sustained delivery of pharmaceutical, cosmetic and agricultural agents contain hydrogen bonding groups and .alpha.-hydroxy acid-containing groups.

Degradable polyacetal polymers and functionalized degradable polyacetal polymers have properties favorable for use in pharmaceutical and biomedical applications. The degradable polyacetal polymers are relatively stable at physiological pH with favorable biodistribution profiles, and degrade readily in low pH conditions. Conjugates of the polymers with drugs, especially anticancer drugs, and methods of treatment of cancer.

Block copolymers based on poly(ortho esters) containing amine groups. These block copolymers have both hydrophilic and hydrophobic blocks. They form micelles in aqueous solution, making them suitable for encapsulation or solubilization of hydrophobic or water-insoluble materials; and they also form bioerodible matrices for the sustained release of active agents.