Push-Pull Controlled Drug Release Systems: Effect of Molecular Weight of Polyethylene Oxide on Drug Release.

First, an elementary osmotic pump (EOP) with a simple structure was prepared using polyethylene oxide (PEO) and NaCl as an excipient, and the influence of the molecular weight (Mw) of PEO on drug release was investigated. In the dissolution test of EOP, it was observed that the gelated core tablet was pushed out through the orifice. The dissolution profile of EOP was sigmoidal, and despite the short time, a zero-order release region was observed. The gel swelling rate in the zero-order region was independent of the Mw of PEO. It was also found that higher the Mw of PEO, the larger the saturated swelling amount. Next, a push-pull pump (PPP) with almost identical formulation to that of EOP was prepared, and its drug release characteristics were investigated. PPPs were prepared by varying the combination of Mws of PEO in both layers, and their dissolution profiles were compared. It was found that PPP using a low-Mw PEO for the drug layer and PEO with a high-Mw in the push layer showed the longest dissolution profile of the linear region. The obtained findings suggested that the properties of PEO and its hydrogel play a crucial role in the drug release of PPP.