Impact of Rifabutin on the Pharmacokinetics of Elexacaftor/Tezacaftor/Ivacaftor

Trikafta (Elexacaftor [ELX], Tezacaftor [TEZ], Ivacaftor[IVA]) is contraindicated with concomitant use of strong inducers as co-administration of rifampin decreased the area-under-the concentration time curve (AUC) of IVA by 89%, creating a therapeutic challenge to the treatment of non-tuberculosis mycobacteria (NTM) infection in people with cystic fibrosis (CF). While rifabutin also induces CYP3A4 activity, its effects appear to be more moderate when compared with rifampin. Therefore, we hypothesize that rifabutin can be co-administered with an adjusted dose of ELX/TEZ/IVA in patients being treated for NTM pulmonary disease.

Inclusion criteria

• Able and willing to sign informed consent prior to any study-related activities.
• Male or female participants between 18 and 65 years of age inclusive.
• Healthy subjects as determined by no clinically significant deviation from normal in medical history, physical examination findings, and clinical laboratory test results
• Body mass index (BMI) of 17.5 to 30.5 kg/m2, inclusive; and a total body weight >50kg (110 lbs).
• Willing to stop using any herbal or natural health products for 2 weeks prior to and during the study including: Grapefruit, grapefruit juice, St. John's Wort.
• Participant must use a reliable method of birth control while they are participating in the study; for instance an intrauterine device (IUD), condom with spermicidal gel or foam, diaphragm with spermicidal gel or foam, vasectomy, tubal ligation, hysterectomy or abstinence or female must be post-menopausal for at least one year.

Exclusion criteria

• Female subjects of childbearing potential with positive urine pregnancy test at screening.
• Female subjects who are breastfeeding.
• Use of CYP3A modulators (e.g., rifampicin, phenobarbital, carbamazepine, phenytoin, azole drugs, telithromycin, clarithromycin, erythromycin)
• Any significant acute or chronic medical illness that might confound the results of the study or pose an additional risk in administrating study drugs to the subject, as determined by the investigator.
• Any condition that could affect drug absorption (eg, gastrectomy, pancreatitis).
• Any major surgery within 4 weeks of study drug administration.
• Blood donation of approximately 1 pint (500 mL) within 56 days before study drug administration.
• Known hypersensitivity to rifamycins
• Patients with hepatic impairment (Child-Pugh Class B or C) and/or with history of hepatobiliary disease or liver function test elevations.
• Renal insufficiency (eGFR < 60 mL/min)
• History of uveitis and/or current eye or vision problems with the exception of corrective lenses.
• Contact lens use during study drug administration.