Using Potentiometric Free Drug Sensors to Determine the Free Concentration of Ionizable Drugs in Colloidal Systems

Abstract

The present study investigates the use of free drug sensors (FDS) to measure free ionized drug concentrations in colloidal systems, including micellar solutions, emulsions, and lipid formulations during in vitro lipolysis. Diphenhydramine hydrochloride (DPH) and loperamide hydrochloride (LOP) were selected as model drugs. Self-diffusion nuclear magnetic resonance studies were performed and confirmed the entrapment of drugs in micelles in Brij 35 and sodium taurodeoxycholate (TDC)/phosphatidylcholine (PC) micellar solutions. The FDS measurements indicated that with a constant level of drug, the percentage of free DPH and LOP decreased from 84% to 57% and from 51% to 18%, respectively, as the concentration of Brij 35 was increased from 4.7 to 22 mM; and from 99% to 46% and from 100% to 21%, respectively, as the concentration of TDC/PC was increased from 0.49/0.04 to 8.85/0.78 mM. During the in vitro lipolysis of a lipid formulation, free drug concentration decreased with lipolysis time. The percentage of free DPH was higher than for LOP in the same colloidal system because DPH is less lipophilic than LOP. The study showed that FDS can be used to monitor the free drug concentration in colloidal systems with fast response, no sample treatment and simple data analysis.

Detection and quantification of Covid-19 antiviral drugs in biological fluids and tissues

“…Recently, there has been a growing need for constructing chemical sensors for the fast and economical monitoring of drug compounds through potentiometric methods in pharmaceutical analysis. The potentiometric sensors are also known as ion-selective electrodes, where the electric potential created over the ion-selective membrane depends on the activity of the analyte and allows its quantification [ 109 ]. However, potentiometric methods to determinate antiviral drugs in biological matrices remain still limited because many common ions occurring in biofluids and tissues interfere with the measurement of the target analyte.…”