Background: Curcuminoids, major ingredients of turmeric crude extract, have shown P-glycoprotein [P-gp] inhibitory properties in both in vitro and in vivo studies. However, their potential interaction with drugs known as P-gp substrates in humans is not characterized.

Objective: To investigate the effect of turmeric crude extract on P-gp activity in healthy subjects.

Materials and Methods: This preliminary, open-label, randomized, two-period, crossover study was conducted in 12 healthy male volunteers. Pharmacokinetic [PK] parameters of digoxin, a P-gp probe, were measured following a single oral dose of 0.5 mg digoxin administered without and with concurrent use of turmeric extract (equivalent to 500 mg of curcuminoids, given twice daily for four days prior and three days after a single dose of digoxin).

Results: Considering ±25% change of maximum plasma concentration [C_max] of digoxin in each individual subject to be of clinical relevance, three categories of interaction between turmeric extract and digoxin were observed. With concurrent use of turmeric extract, C_max of digoxin increased, remained unchanged, and decreased in six, four, and two subjects, respectively.

Conclusion: These findings suggest that medical professionals should be aware of possible divergent interactions between turmeric crude extract and P-gp substrates for the proper monitoring of their individual patients.

Keywords: Turmeric extract, Digoxin, Pharmacokinetics, Drug interactions, P-glycoprotein, Healthy volunteers