We investigated the drug and fatty acid binding capacity of Pluronic-based microemulsions through simple turbidity experiments. Pluronic-based oil-in-water microemulsions of various compositions were synthesized and titrated to turbidity with concentrated amitriptyline, an antidepressant drug. The BASF Pluronic grid was used to select two series of Pluronic surfactants: (1) those having the same number of ethylene oxide (EO) groups, with an increasing number of propylene oxide (PO) groups and (2) those having the same number of propylene oxide groups with an increasing number of ethylene oxide groups. We observed that the binding of sodium caprylate fatty acid and amitriptyline drug increases with increasing hydrophobicity (i.e., increasing number of PO groups). This is attributed to the greater number of binding sites for the sodium caprylate, which results in more charge on the microemulsion, subsequently leading to increased drug binding. We also determined that when the number of PO groups was held fixed and the number of EO groups was increased, there is no direct correlation to the binding behavior of fatty acid and drug. This is due to the fact that the hydrophilic groups (EO) do not play a direct role in the binding of fatty acid molecules. In fact, when there are a significantly large number of EO groups present, they can act to inhibit binding of fatty acid and hence, drug, to the microemulsion.

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