Drug Interactions between mebrofenin and Synalgos-DC

MONITOR: Prior administration of opioids may delay transit of Technetium Tc 99m mebrofenin due to opioid-induced contraction of the distal common bile duct, which may result in nonvisualization. In one study, a group of investigators reviewed the records of 198 emergency department patients who underwent nuclear hepatobiliary imaging, after excluding those with evidence for pathologic common bile duct (CBD) obstruction. Delayed CBD visualization occurred in 28.6% of subjects who had received opioids (n=56) and 12.0% of subjects who had not received opioids, while delayed imaging was performed in 77.8% and 53.5%, respectively. The relative risk of delayed CBD visualization was 1.46 for meperidine, 4.18 for morphine, and 2.38 for any opioid. Nonetheless, low-dose intravenous morphine has been used during cholescintigraphy to increase biliary pressure, thereby allowing for visualization of gallbladder when there is failure to visualize 60 minutes or more after Technetium Tc 99m mebrofenin injection. Compared to standard cholescintigraphy, morphine-augmented cholescintigraphy has been shown to reduce imaging time and the number of false-positive results.

MANAGEMENT: Nonvisualization may occur in patients who have been receiving opioids prior to cholescintigraphy.

One study has reported that coadministration of caffeine and aspirin lead to a 25% increase in the rate of appearance and 17% increase in maximum concentration of salicylate in the plasma. A significantly higher area under the plasma concentration time curve of salicylate was also reported when both drugs were administered together. The exact mechanism of this interaction has not been specified. Physicians and patients should be aware that coadministration of aspirin and caffeine may lead to higher salicylate levels faster.