Assessing Drug Interaction Potential of Herbal Medicine Liv.52, Smokeless Tobacco Snuff and Edible Camphor using Human Liver Microsomes

Cytochrome P450 inhibition potential of Liv.52, snuff and camphor was assessed using human liver microsomes for any clinical consequences if taken together with other medications. They were screened for potential to inhibit 9 drug metabolizing cytochrome P450 (CYP 450) isoforms. Samples were analyzed by liquid chromatography mass spectrometry (LC-MS/MS) using stable labeled internal standards of metabolites. Liv.52 did not inhibit CYP2A6, CYP2D6, and CYP2E1 up to the highest tested concentration of 1.13 mg/mL. Its IC50 value ranged from 0.08 mg/mL to 0.160 mg/mL with CYP1A2, CYP2B6, CYP2C8, and CYP2C19. With CYP2C9, the IC50 value was 0.32 mg/mL, with CYP3A4 using midazolam as substrate, the mean IC50 value was 0.63 mg/mL and 0.86 mg/mL with testosterone as substrate. Snuff did not inhibit any of the tested CYPs up to the highest tested concentration of 500 μg/mL, except CYP2B6 and CYP2C8 with mean IC50 values of 381 μg/mL and 399 μg/mL, respectively. Camphor did not inhibit CYP1A2, CYP2C8, CYP2C9, CYP2D6, CYP2E1, and CYP3A4 up to the highest tested concentration of 100 μg/mL. Camphor inhibited CYP2A6 and CYP2C19 with mean IC50 values of 60 μg/mL and 74 μg/mL, respectively. It showed the most potent inhibition with CYP2B6 with mean IC50 of 3.2 μg/mL. Generally, test items with IC50 values below 0.5 μg/mL are considered as potent CYP inhibitors and liable for further drug interaction studies. Liv.52 showed the lowest IC50 of 80 μg/mL with various CYPs, snuff showed IC50 values greater than 350 μg/mL with all the tested CYPs confirming no major CYP interaction liabilities. As not many marketed drugs are substrates of CYP2B6, the liability of camphor as CYP2B6 inhibitor is limited.