In recent years the use of modified-release drug formulations has increased considerably. This is partly due to advances in formulation technologies enabling one to design formulations that provide a better control of the release of the drug to the site of action. Controlled-release formulations provide several advantages over conventional immediate release formulations of the same drug such as a reduced dosing frequency, a decreased incidence and or intensity of side effects, a greater selectivity of pharmacologic activity and a reduction in drug plasma fluctuation resulting in a more constant or prolonged therapeutic effect.