Exploring the unexpected behavior of HPMC matrix tablets in dissolution media with SDS

Abstract

In the case of poorly soluble drugs, a surfactant is often added to dissolution media to increase drug release. In this study, diclofenac sodium (DF-Na) release from hydroxypropyl methylcellulose (HPMC) matrix tablets was explored in dissolution media containing different sodium lauryl sulfate (SDS) concentrations. Drug release increased with increasing SDS concentration; however, an unexpected decrease in DF-Na release was noticed in the medium with pH 4 containing 0.03–0.08% SDS, which is just below the critical micelle concentration (CMC). In addition, an inverse correlation between swelling and release was noticed. Measurements of transmittance of multiple HPMC–SDS dispersions showed that with increasing HPMC concentration transmittances are lower at a wider SDS concentration interval. Thus, when using media with low SDS concentrations, especially those with concentrations lower than CMC (0.03–0.08%), DF-Na release from HPMC matrix tablets is decreased due to increased swelling and lack of SDS in the swelled layer, both possibly due to SDS binding to HPMC. However, when using media with a higher initial SDS concentration in the medium, there remains a high concentration of non-bound SDS in the bulk, which can solubilize incorporated drug and thus enhance its release from HPMC matrix tablets.