Nonionic surfactants are strong inhibitors of cytochrome P450 3A biotransformation activity in vitro and in vivo.

Nonionic surfactants are commonly used as excipients in pharmaceutical formulation, but recent studies demonstrate that the ingredients affect the pharmacokinetics of the active drugs. However, the mechanisms are largely unknown. Here, we examined the effects of four common nonionic surfactants polysorbate 20, polyoxyl 35 castor oil, polyoxyl 40 stearate and poloxamer 188, on cytochrome P450 3A in vitro and in vivo using midazolam as a probe. We first examined the effects of these surfactants on the 1'-hydroxylation of midazolam in isolated rat liver and intestinal microsomes. All the surfactants tested inhibited midazolam 1'-hydroxylation in a concentration-dependent manner and presented a mixed competitive inhibitory model with decreased V(max) and increased K(m) values in vitro. Among the tested nonionic surfactants, polysorbate 20 was the most potent inhibitor of midazolam 1'-hydroxylation with an IC(50) of 2.06 and 0.39mgml(-1) in the liver and intestinal microsomes, respectively. These surfactants were also tested in vivo as we investigated their effects on the pharmacokinetics of midazolam in rats. These four surfactants displayed different inhibitory patterns in terms of the AUC of midazolam and 1'-hydroxymidazolam. Polysorbate 20 significantly increased both AUC(0-4h) and AUC(0-infinity) of midazolam and decreased the AUC(0-4h) of 1'-hydroxymidazolam to about 40% (p<0.05) in both single- and multiple-treated rats, along with a significant decrease of the metabolic ratio of 1'-hydroxymidazolam/midazolam to 25%. Polyoxyl 35 castor oil, polyoxyl 40 stearate and poloxamer 188 displayed complicated inhibition on the 1'-hydroxylation of midazolam dependent on the administration formula. These results confirmed that effects of these surfactants would have potential inhibitory effects on cytochrome P450 3A and altered midazolam bioavailability. Therefore, caution is needed when selecting nonionic surfactants in drug formulation.