Objective: Triptans are highly effective in the treatment of migraine. Both central and peripheral mechanisms of action have been suggested. Until now, firm data about the passage of triptans into the CNS in humans have been lacking. The aim of the current study was to evaluate, using positron emission tomography (PET), the uptake and distribution of zolmitriptan into the CNS after intranasal administration.
Subjects and methods: Eight healthy volunteers, five males and three females (mean ages 23 and 26 years, respectively), were included. Radioactive [carbonyl-11C]zolmitriptan was infused intravenously for 5 minutes on two occasions: once alone, and once 30-40 minutes after intranasal administration of unlabelled zolmitriptan 5 mg. PET was used to measure the concentration of labelled zolmitriptan in the brain, from the start of the tracer infusion for 90 minutes. Regional cerebral blood volume was determined with [15O]carbon monoxide. In addition, an MRI scan was performed to obtain anatomical information. The PET images were analysed quantitatively for different areas of the brain, generating [11C]zolmitriptan time-activity data corrected for circulating tracer activity. The rate of uptake of intranasal zolmitriptan into the CNS was estimated by kinetic modelling using the PET data.
Results: PET data from this study demonstrate a rapid dose-proportional uptake of [11C]zolmitriptan into the brain. Significant concentrations of [11C]zolmitriptan were found in all brain regions studied. Calculated CNS concentrations after intranasal zolmitriptan administration showed a gradual increase, reaching about 2 nM (0.5 microg/L) 30 minutes after administration and 3.5 nM (1.0 microg/L), or one-fifth of the plasma concentration, 1 hour after administration. Five minutes after zolmitriptan administration, the mean CNS concentration had already reached 0.5 nM, which is higher than in vitro values for initiation of the agonistic action on 5-HT(1B/1D) receptors.
Conclusion: This study demonstrates by direct measurements that zolmitriptan enters the brain parenchyma in humans, achieving an uptake rate and concentration compatible with a central mode of action.