Ampholytic starch excipients for high loaded drug formulations: Mechanistic insights

Ampholytic starch derivatives are proposed as a new class of excipients carrying simultaneously anionic carboxymethyl (CM) and cationic aminoethyl (AE) groups on starch (St) polymeric chains. Three different types of derivatives were obtained by using the same reagents and varying only the order of their addition in the reaction medium: in one step method (OS) the two reactants were added simultaneously, whereas in two steps method (TS) either CMSt or AESt were prepared separately in the first step, followed by subsequent addition of the second reactant. It was found that all ampholytic derivatives were able to generate monolithic tablets by direct compression and allowed 60% loading of acidic (Acetylsalicylic acid), basic (Metformin), zwitterion (Mesalamine) or neutral (Acetaminophen) as drug models. The in vitro dissolution tests followed for 2 h in SGF and then in SIF, showed that the mentioned starch derivatives were stabilized by self-assembling and generated matrices able to control the release of drugs for about 24 h. The addition order of reagents has an impact on ampholytic starch properties offering thus a high versatility of this new class of starch excipients that can be tailored for challenging formulations with high dosages of several drugs.