19F Nuclear Magnetic Resonance Spectrometric Determination of the Partition Coefficients of Flutamide and Nilutamide (Antiprostate Cancer Drugs) in a Lipid Nano-Emulsion and Prediction of Its Encapsulation Efficiency for the Drugs.

To design a useful lipid drug carrier having a high encapsulation efficiency (EE%) for the antiprostate cancer drugs flutamide (FT) and nilutamide (NT), a lipid nano-emulsion (LNE) was prepared with soybean oil (SO), phosphatidylcholine (PC), and sodium palmitate, and the partition coefficients (K ps) of the drugs for the LNE were determined by 19F nuclear magnetic resonance (NMR) spectrometry. The 19F NMR signal of the trifluoromethyl group of both drugs showed a downfield shift from an internal standard (trifluoroethanol) and broadening according to the increase in the lipid concentration due to their interaction with LNE particles. The difference in the chemical shift (Δδ) of each drug caused by the addition of LNE was measured under different amounts of LNE, and the K p values were calculated from the Δδ values. The results showed that FT has higher lipophilicity than NT. The total lipid concentration (SO + PC) required to encapsulate each drug into LNE with an EE% of more than 95% was calculated from the K p values as 93.3 and 189.9 mmol/L for FT and NT, respectively. For an LNE prepared with the total lipid concentration of 215 mmol/L, the predicted EE% values were 98 and 96% for FT and NT, respectively, while the experimental EE% values determined by a centrifugation method were approximately 99% for both drugs. Thus, the 19F NMR spectrometric method is a useful technique to obtain the K p values of fluorinated drugs and thereby predict the theoretical lipid concentrations and prepare LNEs with high EE% values.