 - Treatment with clinically significant enzyme-inducing drugs, including known P-glycoprotein inducers including St Johns wort and rifampicin should be used only if absolutely necessary and considered to be the best available choice for the patient. If possible, it is recommended that alternatives to known substrates, inhibitors or inducers of P-glycoprotein be considered. Cases should be discussed with the principal investigator, and may be allowed as per hisher discretion. 