The invention provides microparticles for sustained release formulation for physostigmine, pyridostigmine and other therapeutically active carbamates. The microparticles comprise the active compound and a biodegradable polymer such as polyester, poly(phosphate), poly(anhydride), poly(ortho ester), or mixture thereof. In one embodiment, the polymer is poly(d,l-lactide-co-glycolide). The desired release pattern of the active compound may be readily attained by varying the type and amount of the polymer used, including by using a mixture of two polymers, one of which is more hydrophobic. The invention also provides a method of preparing the microparticles and in one embodiment, the microparticles may be prepared by spray drying.