Influence of ionic strength and HPMC viscosity grade on drug release and swelling behavior of HPMC matrix tablets

Matrix tablets containing paracetamol and hydroxypropyl methylcellulose (HPMC 2906) of different viscosity grades (50, 400, 1500, and 4000 mPa·s) were evaluated for drug release and change in matrix tablet mass [Δ M (%)] after exposure to 0.09, 0.15, 0.31, and 0.52 M ionic strengths of dissolution media. At 0.09 and 0.15 M ionic strength, drug‐release profiles reflected the extended release characteristic; in addition the increase in Δ M was slow and continuous within first few hours. At 0.31 M the higher viscosity grade matrices showed extensive initial swelling and the loss of extended release whereas at 0.52 M a similar tablet performance is observed for the matrices of all viscosity grades. Notably, when extensive increase in Δ M occurs in the very beginning of exposure to medium the loss of extended release from the matrix is expected.