Abstract: A hydrophilic or lipophilic drug is entrapped or microencapsulated in a polyhydroxyalkanoate homopolymer or copolymer. The homopolymer or copolymer is synthesized in an aqueous medium containing a dissolved hydrophilic drug by in vitro enzyme polymerization of a hydroxyalkanoate Coenzyme A monomer to form microporous granules entrapping the drug. The enzyme may be a polyhydroxyalkanoate synthase, and the monomer may be 3-hydroxybutyryl Coenzyme A or 3-hydroxyvalerate Coenzyme A. The monomer is produced by reaction of a carboxylic acid group of a hydroxyalkanoic acid with a thiol group of Coenzyme A. To microencapsulate a lipophilic drug, droplets of oil containing a lipophilic drug are formed dispersed in an aqueous medium such as in the form of an oil-in-water emulsion. The polyhydroxyalkanoate homopolymer or copolymer is formed in the aqueous medium by the enzyme polymerization to form microcapsules having a core of oil containing the drug. The granules or microcapsules containing the drug may be dried.