In Situ Complex Systems of Drug and Organic Electrolyte for Extended Release Tablets Using HPC

In situ drug and organic electrolyte complex tablets were investigated as extended release dosage forms. Incor- porating a 1:1 molar ratio of diltiazem HCl and an anionic organic electrolyte (i.e., Na deoxycholate) into HPC tablets ex- tended the total release time with a near zero - order release rate (release exponent, n = 0.85 - 0.97) due to in situ complex formation of the drug and the organic electrolyte. When the molar ratio was less than 1 (e.g., 0.5), drug release was faster and the effect of drug diffusion was only slightly observable with n = 0.82 due to the availability of uncomplexed free drug to diffuse out of the swollen HPC gel layer. Little effect was observed for the type of amine in the drug or drug solu- bility on release kinetics for diltiazem HCl, verapamil HCl, and propranolol HCl. Benzathine diacetate was used as the or- ganic electrolyte, in situ complexing agent for anionic drugs (e.g., Na salicylate). Even though the total extended release time was increased from 500 min to 1600 min, drug release kinetics for the in situ salicylate benzathine complex HPC tab- lets (n = 0.54 - 0.59) was not much improved compared to those of Na salicylate HPC tablets (0.40 - 0.41). Anionic drugs with low solubility (e.g., naproxen Na and tolmetin Na) showed slightly sigmoidal release profiles with n = 1.09 and 1.13, respectively. No difference in release kinetics among different cationic organic electrolytes (e.g., benzathine diacetate, aminodiphenylmethane HCl, and N-benzyl-2-phenethylamine HCl) for Na salicylate was found. It was found that more linear release kinetics was obtained when organic electrolytes were present in tablets more than the amount required to form 1:1 complexes with oppositely charged drugs.