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Small-molecule calcitonin gene–related peptide (CGRP) receptor antagonists have demonstrated therapeutic potential for the treatment of migraine. However, previously investigated CGRP receptor antagonists, telcagepant and MK-3207, were discontinued during clinical development because of concerns about drug-induced liver injury. A subsequent effort to identify novel CGRP receptor antagonists less likely to cause hepatotoxicity led to the development of ubrogepant. The selection of ubrogepant, following a series of mechanistic studies conducted with MK-3207 and telcagepant, was focused on key structural modifications suggesting that ubrogepant was less prone to forming reactive metabolites than previous compounds. The potential for each drug to cause liver toxicity was subsequently assessed using a quantitative systems toxicology approach (DILIsym®) that incorporates quantitative assessments of mitochondrial dysfunction, disruption of bile acid homeostasis, and oxidative stress, along with estimates of dose-dependent drug exposure to and within liver cells. DILIsym successfully modeled liver toxicity for telcagepant and MK-3207 at the dosing regimens used in clinical trials. In contrast, DILIsym predicted no hepatotoxicity during treatment with ubrogepant, even at daily doses up to 1000 mg (10-fold higher than the proposed clinical dose of 100 mg). These predictions are consistent with clinical trial experience showing that ubrogepant has lower potential to cause hepatotoxicity than has been observed with telcagepant and MK-3207.

Purpose This study investigated the effect of small manipulations in carbohydrate (CHO) dose on exogenous and endogenous (liver and muscle) fuel selection during exercise. Method Eleven trained males cycled in a double-blind randomised order on 4 occasions at 60% for 3 h, followed by a 30-min time-trial whilst ingesting either 80 g h −1 or 90 g h −1 or 100 g h −1 13 C-glucose- 13 C-fructose [2:1] or placebo. CHO doses met, were marginally lower, or above previously reported intestinal saturation for glucose–fructose (90 g h −1 ). Indirect calorimetry and stable mass isotope [ 13 C] techniques were utilised to determine fuel use. Result Time-trial performance was 86.5 to 93%, ‘likely, probable’ improved with 90 g h −1 compared 80 and 100 g h −1 . Exogenous CHO oxidation in the final hour was 9.8–10.0% higher with 100 g h −1 compared with 80 and 90 g h −1 (ES = 0.64–0.70, 95% CI 9.6, 1.4 to 17.7 and 8.2, 2.1 to 18.6). However, increasing CHO dose (100 g h −1 ) increased muscle glycogen use (101.6 ± 16.6 g, ES = 0.60, 16.1, 0.9 to 31.4) and its relative contribution to energy expenditure (5.6 ± 8.4%, ES = 0.72, 5.6, 1.5 to 9.8 g) compared with 90 g h −1 . Absolute and relative muscle glycogen oxidation between 80 and 90 g h −1 were similar (ES = 0.23 and 0.38) though a small absolute (85.4 ± 29.3 g, 6.2, − 23.5 to 11.1) and relative (34.9 ± 9.1 g, − 3.5, − 9.6 to 2.6) reduction was seen in 90 g h −1 compared with 100 g h −1 . Liver glycogen oxidation was not significantly different between conditions (ES < 0.42). Total fat oxidation during the 3-h ride was similar in CHO conditions (ES < 0.28) but suppressed compared with placebo (ES = 1.05–1.51). Conclusion ‘Overdosing’ intestinal transport for glucose–fructose appears to increase muscle glycogen reliance and negatively impact subsequent TT performance.

The characterization of brimonidine metabolites presents some challenges since brimonidine and its metabolites generate few structurally informative fragment ions in the LC-MS/MS spectra. The objective of the current study is to use on-line hydrogen/deuterium (H/D) exchange LC-MS/MS and stable-isotope tracer techniques to further characterize unknown brimonidine metabolites in vitro and in vivo. Brimonidine and D4-brimonidine were co-incubated in rat and human microsomes and rabbit aldehyde oxidase in vitro. In addition, the urine was collected from rats co-administered orally with brimonidine and D4-brimonidine. The hepatic microsomal and urinary metabolites were then characterized by H/D LC-MS/MS system. In addition to previously characterized 2-oxobrimonidine, 3-oxobrimonidine and 2,3-dioxobrimonidine, the results show that oxidation occurs at quinoxaline ring producing oxo-hydroxybrimonidine and hydroxyquinoxaline metabolites. The hydroxyquinoxaline metabolite was only observed in microsomal incubations with hydroxylation at the 7- or 8- position. The dehydro-hydroxybrimonidine metabolites were characterized as 2-oxo or 3-oxo -4', 5'-dehydrobrimonidine. A novel metabolite ((4-bromo-lH-benzoimidazol-5-yl)-imidazolidin-2-ylidene-amine) of benzimidazole derivative of brimonidine in rats in vivo was identified and confirmed with reference standard. In conclusion, on-line H/D exchange LC-MS/MS and stable-isotope tracer techniques are useful for the characterization of brimonidine metabolites.