Abstract
Using a model system oj Ca(II)-phosphate and Al(lll)-phosphate.the precipitation behavior of Ca(ll) and Al(111) was studied on the basis of the time (lag-time) between sample preparation and the appearance of obvious precipitation In the Al(lll)-phosphate system, the lag-time was not affected by various experimental conditions such that crystal form or particle size was changed. In the Ca(ll)-phosphale system, the lag-time increased in the presence of citric acid or EDTA and, simultaneously, precipitates with high crystallinity were formed. From the crystal form and solubility behavior of the precipitates obtained. it was suggested that the lag-time might be further increased by adsorption of complexing agents to the precipitate nuclei. By determining the metal (Al and Ca), phosphate, and citric acid content of the precipitates. a mechanism was proposed by which complexing agents can chemically adsorb as Ca(ll) or Al(lll) complex to precipitates. In view of the fact that apparent lag-time increase and crystal growth of the precipitates were not observed in the Al(Ill)-phosphate system. regardless of significant adsorption of citric acid to the precipitates . the lag-time in the presence of complexing agents in phosphate buffer solutions was considered to be greatly dependent on the changes of Ca(ll) and Al(III) arrangement in the precipitates by the complexes adsorbed, Further. from metal/phosphate molar ratios of the precipitates, it was found that the possible complex composition (metal ion, citric acid molar ratio) may be 1:1 for Ca(ll)-citric acid complex, while it ranged from 0.2 to 11 for Al(111)-citric acid complex. On the basis of these results, prevention conditions against precipitation after filling solutions for parenteral use were proposed, particularly, in view of the greater contribution of Ca(11) to the lag-time in phosphate buffer solutions containing complexing agents.
- Received October 1, 1982.
- Accepted December 15, 1982.
- Copyright © Parenteral Drug Association. All rights reserved.
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