The stability of theophylline tablets with a hydroxypropylcellulose matrix

The behavior of 40:60 anhydrous theophylline/hydroxypropylcellulose (HPC) d irect compression tablets obtained using a variety of hydroxypropylcellulos es with low or medium-high degrees of substitution (L-HPCs and HPCs, respec tively) was determined immediately following their preparation and after st orage for 6 months at 20 degrees C and a relative humidity (RH) of either 7 0.4% or 93.9%. The lower relative humidity did not bring about hydration of the active principle in any formulation, but the higher relative humidity totally hydrated the drug in all except one L-HPC formulation, in which hyd ration remained incomplete. Both relative humidities caused significant tab let swelling, with L-HPC formulations being more affected than HPC formulat ions. Drug release was slowed by hydration of the active principle, but acc elerated with tablet swelling. The lower relative humidity caused significa nt alteration of drug release characteristics in only two L-HPC formulation s, release from which was accelerated, while the higher relative humidities only failed to cause such alterations in two HPC formulations, with releas e from all except one of the others slowed (in the exceptional formulation, which exhibited incompletely hydrated theophylline and the greatest swelli ng of all, release was accelerated).