Drug Delivery Systems 4. Implants in Drug Delivery

Abstract

In comparison with many of the other drug delivery systems, implantable pumps and implants for variable rate delivery are at a crude stage of development. Although exceptions exist, the typical implantable pump consists of an electromechanically complex mechanism to regulate drug delivery from a percutaneous refillable reservoir, while power to drive the system comes from a transcutaneous energy transmission system. The potential for electrical or mechanical failure is high, and the systems are not yet sufficiently convenient or easy to use to recommend in a routine therapy. Problems with refilling of an apparently well designed implanted reservoir have been observed while, at the same time, cutaneous energy transmission systems are not well established. In most instances, the development of an elementary osmotic pump system dosage form follows a well defined path of physical-chemical formulation and clinical testing. The benefits most often provided by the dosage form are expected to be (1) increase in selectivity of drug action achieved by the system's zero-order release rate, and (2) decrease in frequency of administration. The success in achieving these values is quantifiable from the pharmacology of the drug substance and its pharmacokinetics. Osmotic and other technical approaches to producing economical, rate-controlled dosage forms will make it possible for all new pharmaecutical products to carry kinetic specification of rate as well as static specification of content. This review considers the characteristics of the ideal implantable pump, the clinical situations which require pumps, the limitations of portable pumps, and the detailed characteristics of existing implantable pumps and implants. Most of the review, however, focuses on insulin delivery because of the importance of this subject.

Implantable drug delivery systems: An overview

“…[1] The most popular biodegradable polymers currently being investigated include polyglycolic acid, polylactic acid, polyglycolic-lactic acid, polyaspartic acid, and polycaprolactone. [4] The use of ethyl vinyl acetate copolymer matrices for the delivery of macromolecular drugs such as insulin has also been studied extensively. [17,18] A new form of lactic acid/lysine copolymer, chemically attached to a biologically active peptide, is being developed and tested which could function as a matrix for the mammalian cells.…”

“…[4] The release kinetics of drug from this system suggest that if the concentration of the drug within the reservoir is in constant equilibrium with the inner surface of the enclosed membrane, the driving force for diffusional release of the agent is constant and zero-order release kinetics of the drug from the delivery system is obtained. [5] This type of system, however, has several disadvantages.…”

Surgery and new Pharmacological strategy in some atherosclerotic chronic and acute conditions

“…The success in achieving these values is quanti iable from the pharmacology of the drug substance and its pharmacokinetics. Osmotic and other technical approaches to producing economical, rate-controlled dosage forms will make it possible for all new pharmaceutical products to carry kinetic speci ication of rate as well as static speci ication of content [3].…”

Controlled Delivery Systems: From Pharmaceuticals to Cells and Genes

“…The first generation of devices developed as DDS were mainly based on polymeric implants (3,7,8). Two main approaches were used to obtain a drug-implant complex.…”