Evaluation of the inhibitory effects of itraconazole on letermovir.

AIMS: Letermovir, a cytomegalovirus (CMV) DNA terminase complex inhibitor, is a substrate of ABCB1 (P-glycoprotein; P-gp), organic anion transporting polypeptide (OATP)1B1/3, UDP-glucuronosyltransferase (UGT)1A1, UGT1A3 and possibly ABCG2 (breast cancer resistance protein; BCRP). A study was conducted to evaluate the effects of itraconazole, a prototypic ABCB1/ABCG2 inhibitor, on letermovir pharmacokinetics (PK) and the effects of letermovir on itraconazole PK. METHODS: In an open-label, fixed-sequence study in 14 healthy participants, 200 mg oral itraconazole was administered once daily for 4 days. Following a 10-day washout, 480 mg oral letermovir was administered once daily for 14 days (Days 1-14) and then coadministered with 200 mg itraconazole once daily for 4 days (Days 15-18). Intensive PK sampling was performed for letermovir and itraconazole. PK and safety were evaluated. RESULTS: Letermovir geometric mean ratio (GMR; 90% confidence interval [CI]) for area under the concentration-time curve from time 0 to 24 h (AUC0-24 ) was 1.33 (1.17, 1.51) and for maximum concentration (Cmax ) was 1.21 (1.05, 1.39) following administration with/without itraconazole. Itraconazole GMR (90% CI) for AUC0-24 was 0.76 (0.71, 0.81) and for Cmax was 0.84 (0.76, 0.92) following administration with/without letermovir. Coadministration of letermovir with itraconazole was generally well tolerated. CONCLUSIONS: The increase in letermovir exposure with coadministration of itraconazole is likely predominantly due to inhibition of intestinal ABCB1 and potentially ABCG2 transport. The mechanism for the decrease in itraconazole exposure is unknown. The modest changes in letermovir and itraconazole PK are not considered clinically meaningful.

Acute and Chronic Effects of Rifampin on Letermovir Suggest Transporter Inhibition and Induction Contribute to Letermovir Pharmacokinetics.

Rifampin has acute inhibitory and chronic inductive effects that can cause complex drug-drug interactions. Rifampin inhibits transporters including organic-anion-transporting polypeptide (OATP)1B and P-glycoprotein (P-gp), and induces enzymes and transporters including cytochrome P450 3A, UDP-glucuronosyltransferase (UGT)1A, and P-gp. This study aimed to separate inhibitory and inductive effects of rifampin on letermovir disposition and elimination (indicated for cytomegalovirus prophylaxis in hematopoietic stem cell transplant recipients). Letermovir is a substrate of UGT1A1/3, P-gp, and OATP1B, with its clearance primarily mediated by OATP1B. Letermovir (single-dose) administered with rifampin (single-dose) resulted in increased letermovir exposure through transporter inhibition. Chronic coadministration with rifampin (inhibition plus potential OATP1B induction) resulted in modestly decreased letermovir exposure vs. letermovir alone. Letermovir administered 24 hours after the last rifampin dose (potential OATP1B induction) resulted in markedly decreased letermovir exposure. These data suggest rifampin may induce transporters that clear letermovir; the modestly reduced letermovir exposure with chronic rifampin coadministration likely reflects the net effect of inhibition and induction. OATP1B endogenous biomarkers coproporphyrin (CP) I and glycochenodeoxycholic acid-sulfate (GCDCA-S) were also analyzed; their exposures increased after single-dose rifampin plus letermovir, consistent with OATP1B inhibition and prior reports of inhibition by rifampin alone. CP I and GCDCA-S exposures were substantially reduced with letermovir administered 24 hours after the last dose of rifampin vs. letermovir plus chronic rifampin coadministration. This study suggests that OATP1B induction may contribute to reduced letermovir exposure after chronic rifampin administration, although given the complexity of letermovir disposition alternative mechanisms are not fully excluded.

Clinical and translational pharmacology of the cathepsin K inhibitor odanacatib studied for osteoporosis.

Cathepsin K (CatK) is a cysteine protease abundantly expressed by osteoclasts and localized in the lysosomes and resorption lacunae of these cells. CatK is the principal enzyme responsible for the degradation of bone collagen. Odanacatib is a selective, reversible inhibitor of CatK at subnanomolar potency. The pharmacokinetics of odanacatib have been extensively studied and are similar in young healthy men, postmenopausal women and elderly men, and were qualitatively similar throughout Phase 1 development and in-patient studies. Following 3 weeks of 50 mg once weekly dosing the geometric mean area under the curve from 0 to 168 hours was 41.1 µM h, the concentration at 168 hours was 126 nM and the harmonic mean apparent terminal half-life was 84.8 hr. Odanacatib exposure increased in a less than dose proportional manner due to solubility limited absorption. It is estimated that approximately 70% of the absorbed dose of odanacatib is eliminated via metabolism, 20% is excreted as unchanged drug in the bile or faeces, and 10% is excreted as unchanged drug in the urine. The systemic clearance was low (approximately 13 mL/min). Odanacatib decreases the degradation of bone matrix proteins and reduces the efficiency of bone resorption with target engagement confirmed by a robust decrease in serum C-telopeptides of type 1 collagen (approximately 60%), urinary aminoterminal crosslinked telopeptides of type 1 collagen to creatinine ratio (approximately 50%) and total urine deoxypyridinoline/Cr (approximately 30%), with an increase in serum cross-linked carboxy-terminal telopeptide of type 1 collagen (approximately 55%). The 50-mg weekly dosing regimen evaluated in Phase 3 achieved near maximal reduction in bone resorption throughout the treatment period. The extensive clinical programme for odanacatib, together with more limited clinical experience with other CatK inhibitors (balicatib and ONO-5334), provides important insights into the clinical pharmacology of CatK inhibition and the potential role of CatK in bone turnover and mineral homeostasis. Key findings include the ability of this mechanism to: (i) provide sustained reductions in resorption markers, increases in bone mineral density, and demonstrated fracture risk reduction; (ii) be associated with relative formation-sparing effects such that sustained resorption reduction is achieved without accompanying meaningful reductions in bone formation; and (iii) lead to increases in osteoclast number as well as other osteoclast activity (including build-up of CatK enzyme), which may yield transient increases in resorption following treatment discontinuation and the potential for nonmonotonic responses at subtherapeutic doses.