Formulation of sustained - release lithium carbonate matrix tablets: influence of hydrophilic materials on the release rate and in vitro-in vivo evaluation.: Conventional lithium carbonate (LC) tablets not only produce rapid and relatively high peak blood levels resulting in adverse effects but also should be administered 3 to 4 times daily. These drawbacks can be overcome by designing a suitable sustained-release LC preparation. ). The therapeutic index of the drug is narrow (4.2 to 8.3 mg/L) and adverse effects are common even at therapeutic serum lithium concentrations. Long-term therapy has to be adjusted to get serum concentrations between 0.6 and 1.25 mEq/L (4.2 to 8.3 mg/L) (1-5). Conventional LC tablets make the drug immediately available for absorption producing rapid and relatively high peak blood levels resulting in adverse effects associated with high lithium serum concentrations and require frequent daily dosing in maintenance therapy that influence patient compliance (1-5). These drawbacks can be overcome by designing a suitable sustained-release LC preparation. The development of sustained-release or controlled-release formulations of this drug is therefore of therapeutic relevance and has drawn the attention of the pharmaceutical industries. The manufacturing procedures of presently available sustained release LC are generally patented. Probably the simplest and least expensive way to control the release of an active agent is to disperse it in an inert polymeric matrix. In polymeric systems, the active agent is physically blended with the polymer powder and then fused together by compression molding, which is a common process in the pharmaceutical industry (6). Different types of polymers including carbopol (CP), sodium carboxymethylcellulose (Na CMC) and hydroxypropylmethylcellulose (HPMC) have been used to control the release of drug from the dosage forms (7-14).