Recent Trends and Progress in Sustained or Controlled Oral Delivery of Some Water Soluble Drugs: Morphine Salts, Diltiazem and Captopril

Abstract

The development of oral controlled release systems has been a challenge to formulation scientists due to their inability to restrain and localise the system at targeted areas of the gastrointestinal (GI) tract. Controlled/sustained release preparations using alternative routes have been formulated but the oral route still remains the most desirable. For obvious reason, water soluble drugs are more difficult to deliver orally in sustained or controlled release manner than lipophilic drugs. Attempts have been made to regulate the release process by incorporating hydrophobic fillers within the system or by coating the drug with poorly soluble, swollen or non-swollen polymers or other substances. Others used the so called ‘hydrodynamically balanced systems’ which float in the gastric fluid at the stomach thereby increase the residence time for the device in the GI tract. A new approach has been the use of mucoadhesive systems to increase the residence time of the device within the GI tract. This review focuses on the progress made in the design of controlled/sustained release delivery systems for some water soluble drugs. Highly/freely water soluble diltiazem, captopril and morphine salts have been selected as model drugs due to the leading role they play in their respective field of therapy and their widespread use in treating chronic patients. Particular emphasis is given to delivery systems designed to achieve their once a day dose treatment.