Drug Interaction Report

MONITOR: Coadministration with asciminib may increase the plasma concentrations of drugs that are substrates of the P-glycoprotein (P-gp) transporter. In vitro, asciminib is a substrate and inhibitor of P-gp, an efflux transporter expressed in the gastrointestinal tract, liver, and kidney. However, drug interaction studies with P-gp substrates have not been conducted.

MANAGEMENT: Caution is advised when asciminib is used concomitantly with drugs that are substrates of P-gp, particularly sensitive substrates or those with a narrow therapeutic range. Dosage adjustments as well as clinical and laboratory monitoring may be appropriate for some drugs whenever asciminib is added to or withdrawn from therapy. The prescribing information recommends closely monitoring for the development of adverse reactions in patients receiving asciminib therapy with certain P-gp substrates where minimal concentration changes may lead to serious or life-threatening toxicities. In addition, the prescribing information for concomitant medications should be consulted to assess the benefits versus risks of coadministration of a P-gp inhibitor like asciminib and for any dosage adjustments that may be required.

ADJUST DOSING INTERVAL: Food may reduce the oral bioavailability of asciminib. When a single 40 mg dose of asciminib was administered with a low-fat meal (400 calories; 25% fat) in healthy volunteers, asciminib peak plasma concentration (Cmax) and systemic exposure (AUC) decreased by 35% and 30%, respectively, compared to asciminib administered in the fasted state. Administration with a high-fat meal (1000 calories; 50% fat) decreased the Cmax and AUC of asciminib by 68% and 62%, respectively.

MANAGEMENT: To ensure adequate asciminib exposures, food consumption should be avoided for at least 2 hours before and 1 hour after taking asciminib.

Administration of digoxin with a high-fiber meal has been shown to decrease its bioavailability by almost 20%. Fiber can sequester up to 45% of the drug when given orally. Patients should be advised to maintain a regular diet without significant fluctuation in fiber intake while digoxin is being titrated.

Grapefruit juice may modestly increase the plasma concentrations of digoxin. The mechanism is increased absorption of digoxin due to mild inhibition of intestinal P-glycoprotein by certain compounds present in grapefruits. In 12 healthy volunteers, administration of grapefruit juice with and 30 minutes before, as well as 3.5, 7.5, and 11.5 hours after a single digoxin dose (0.5 mg) increased the mean area under the plasma concentration-time curve (AUC) of digoxin by just 9% compared to administration with water. Moreover, P-glycoprotein genetic polymorphism does not appear to influence the magnitude of the effects of grapefruit juice on digoxin. Thus, the interaction is unlikely to be of clinical significance.