Xeljanz (tofacitinib citrate) can interact with other medications, including certain antibiotics and antifungal medications. In some cases the interaction means that it is not recommended to take Xeljanz and the other drug at the same time, while in other cases it simply means that the dose of Xeljanz you take will need to be reduced.

Xeljanz is primarily metabolized - processed by the body - by CYP3A4, an enzyme in the liver.
Taking Xeljanz with other drugs that inhibit or induce CYP3A4 is likely to affect the way your body breaks down Xeljanz, meaning that you could get too much or too little of the drug. Xeljanz is also metabolized to a lesser extent by another enzyme called CYP2C19.

Taking Xeljanz and strong inducers of CYP3A4 is not recommended

Rifampin (Rifadin, Rimactane) is an antibiotic used to treat and prevent tuberculosis (TB). It is also a strong inducer of CYP3A4. It is not recommended to take Xeljanz and rifampin together because rifampin may reduce how well Xeljanz works as it decreases your exposure to the drug.

Adjusting your dose of Xeljanz is recommended when taking it with moderate or strong CYP3A4 inhibitors

The antifungal drugs itraconazole (Sporanox, Tolsura) and ketoconazole (Nizoral) are strong inhibitors of CYP3A4. Fluconazole is a moderate inhibitor of CYP3A4, but also a strong inhibitor of CYP2C19. The antibiotics clarithromycin (Biaxin XL) and erythromycin (E.E.S, Eryc, Erythrocin, Eryped) are also examples of strong inhibitors of CYP3A4.

Taking these drugs at the same time as Xeljanz can increase your exposure to the drug, meaning that the amount of Xeljanz you receive is increased, along with your risk of side effects.

It is recommended that you reduce your dose of Xeljanz while taking moderate or strong inhibitors of CYP3A4. Check with your doctor about what dose of Xeljanz you should take.

Xeljanz’s prescribing information recommends the following dosage adjustments (see table below) for patients taking strong CYP3A4 inhibitors, such as ketoconazole, or moderate CYP3A4 inhibitors that are also strong inhibitors of CYP2C19, such as fluconazole.