Drug Interactions between letermovir and moxifloxacin / triamcinolone

MONITOR CLOSELY: Concomitant administration of corticosteroids may potentiate the risk of tendinitis and tendon rupture associated with fluoroquinolone treatment. The mechanism is unknown. Tendinitis and tendon rupture have most frequently involved the Achilles tendon, although cases involving the rotator cuff (the shoulder), the hand, the biceps, and the thumb have also been reported. Some have required surgical repair or resulted in prolonged disability. Tendon rupture can occur during or up to several months after completion of fluoroquinolone therapy.

MANAGEMENT: Caution is recommended if fluoroquinolones are prescribed in combination with corticosteroids, particularly in patients with other concomitant risk factors (e.g., age over 60 years; recipient of kidney, heart, and/or lung transplant). Patients should be advised to stop taking the fluoroquinolone, avoid exercise and use of the affected area, and promptly contact their physician if they experience pain, swelling, or inflammation of a tendon. In general, fluoroquinolones should only be used to treat conditions that are proven or strongly suspected to be caused by bacteria and only if the benefits outweigh the risks.

MONITOR: Coadministration with letermovir may increase the plasma concentrations of drugs that are substrates of CYP450 2C8, CYP450 3A4, and/or organic anion transporting polypeptide protein (OATP) 1B1 and 1B3. Letermovir has been shown to be a reversible inhibitor of CYP450 2C8 in vitro, although its effect on CYP450 2C8 substrates has not been evaluated clinically. Letermovir is also a time-dependent inhibitor and inducer of CYP450 3A4 in vitro. According to the product labeling, midazolam peak plasma concentration (Cmax) and systemic exposure (AUC) increased by an average of 1.7- and 2.3-fold, respectively, when a single 2 mg oral dose of midazolam was coadministered with letermovir 480 mg orally once daily. The Cmax did not change when midazolam 1 mg was administered intravenously with letermovir 240 mg orally once daily, but AUC increased by 1.5-fold and concentration at 24 hours postdose (C24hr) increased by 2.7-fold. The increased AUC of midazolam, a CYP450 3A4 probe substrate, indicates that net effect of letermovir on the isoenzyme is moderate inhibition. In addition, letermovir is an inhibitor of the hepatic uptake transporters, OATP 1B1 and 1B3. When a single 20 mg dose of atorvastatin, a CYP450 3A4 and OATP1B1/1B3 substrate, was coadministered with letermovir 480 mg orally once daily, atorvastatin Cmax, AUC and C24hr increased by an average of 2.2-, 3.3- and 3.6-fold, respectively. Additional use of cyclosporine is likely to further increase the magnitude of these interactions, since it is an inhibitor of CYP450 3A4 and a strong inhibitor of OATP 1B1 and 1B3.

MANAGEMENT: Caution is advised when letermovir is used concurrently with drugs that are substrates of CYP450 2C8, CYP450 3A4, and/or OATP 1B1 and 1B3, particularly those with a narrow therapeutic range. Dosage adjustments as well as clinical and laboratory monitoring may be appropriate for some drugs whenever letermovir is added to or withdrawn from therapy. Moreover, clinicians should be aware that the magnitude of CYP450 3A- and OATP1B1/3-mediated drug interactions with coadministered drugs may be different when letermovir is used with cyclosporine. The combined effect of the two drugs on CYP450 3A4 may be similar to that of a strong CYP450 3A4 inhibitor, hence clinicians should refer to the prescribing information for dosing recommendations of the CYP450 3A4 substrate with a strong CYP450 3A4 inhibitor. Similarly, letermovir and cyclosporine may demonstrate some additive effects on OATP1B1 inhibition, although cyclosporine by itself is already a strong OATP1B1/3 inhibitor.