Methocel k4m premium cr

Hypromellose (Methocel™ K4M Premium CR, Colorcon GmbH Germany) and/or glyceryl behenate (Compritol® 888 ATO, Gattefossé France) were used as the controlled release agents forming matrix system. Prosolv® SMCC 90 (JRS PHARMA, GmbH & Co. KG, Germany) was used as a co-processed dry binder and magnesium stearate (Acros Organics, USA) was used as a lubricant. Tramadol hydrochloride and pentoxifylline (both European Pharmacopoeia Reference Standard, Sigma Aldrich Chemie GmbH, Germany) were chosen as the model highly water soluble drug and non-ionizing drug, respectively. Ethanol (96% v/v, 0.81 g/cm³) according to specification ph. eur. (Lach-Ner s.r.o., Neratovice, Czech Republic) was used to prepare the alcoholic dissolution medium (20 and 40% v/v).
For the preparation of dissolution media and standard solution of Tramadol hydrochloride or pentoxifylline, redistilled water and chemicals of analytical grade (Lach-Ner s.r.o., Neratovice, Czech Republic) were used.

The following active principle and excipients were used: Pal (Apotex Pharmachem, Bangalore, India), lactose (FlowLac^® 100; Meggle, Wasserburg am Inn, Germany), physical mixture of polyvinyl acetate and povidone (8:2) – Kollidon RS, HPC, (LH21; Shin-Etsu, Tokyo, Japan), HPMC (METHOCEL™ K4M Premium CR; Colorcon, Dartford, UK), CMCS (Fluka Chemie GmbH, Buchs, Switzerland), silicon dioxide, (Aerosil^®; Evonik), and magnesium stearate (Union Derivan, Barcelona, Spain).