Microspheres prepared with NaOH-pretreated

The release profile of a batch of microspheres prepared with NaOH-pretreated polymer is shown in Figure 5. For comparison, release curves for microspheres prepared in the usual manner, with and without NaOH, are also included in this figure. If there was some interaction between the polymer and NaOH, one would expect that the release characteristics of this batch of microspheres would be similar to those prepared in the usual manner with NaOH, as represented by the dotted line. Instead, the release pattern of the microspheres prepared with the NaOH-pretreated polymer, represented by the solid circles, almost coincides with the solid line, which corresponds to microspheres prepared without NaOH. This indicates that drug release was not enhanced by pretreating the polymer with NaOH prior to preparing the drug-loaded microspheres. 

Two experiments were conducted in an attempt to understand why drug release was enhanced by the addition of NaOH. The first experiment involved the preparation of microspheres using polymer which was pretreated with NaOH. The second experiment is concerned with posttreating the microspheres with NaOH. 

Figure 5. Effect of NaOH pretreatment on thioridazine release from poly(DL-lactide) microspheres. Key (o ) prepared in usual manner with no NaOH, 15-85 pm ( ) polymer pretreated with 0.14 mole NaOH/mole lactic acid, 15-55 pm ( ) prepared in usual manner with 0.14 mole NaOH/mole lactic acid, 10-75 pm. Drug loading, 46%. Emulsifier, sodium oleate.

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