Ra. Kennedy et Pj. Stewart, THE EFFECT OF PH AND IONIC-STRENGTH ON THE RELEASE OF QUININE ADSORBED ON TO AN INSOLUBLE SODIUM POLYPHOSPHATE, Drug development and industrial pharmacy, 22(7), 1996, pp. 713-719
The preparation and evaluation of a potential prolonged-release drug d
elivery system with the model drug quinine HCl adsorbed onto an insolu
ble sodium polyphosphate (Maddrell's phosphate type II) is described.
The delivery system was prepared by equilibration of the drug with a s
uspension of the polyphosphate and then compressing the dried adsorbed
complex into disks. It was shown that the extraction of the drug from
the loose powder was enhanced by increasing the sodium ion concentrat
ion and by reducing the pH. The effect of sodium ion concentration upo
n release of the drug from compressed disks depended upon the pH of th
e dissolution fluid. At low pH, which slowly dissolved the disks, the
zero-order release of quinine was reduced as the ionic strength of the
dissolution medium was increased. At near-neutral pH, the release of
quinine was first-order at sodium concentrations greater than 0.025 M
and was zero-order at sodium concentrations lower than 0.025 M. The re
lease was promoted by an increase in the ionic strength.