SUMATRIPTAN ABSORPTION FROM DIFFERENT REGIONS OF THE HUMAN GASTROINTESTINAL-TRACT

Sumatriptan exhibits low oral bioavailability partly due to presystemi c metabolism, which may vary with regional differences in metabolic ac tivity throughout the gastrointestinal tract. This study evaluated sum atriptan absorption in humans after administration orally and by oroen teric tube into the jejunum and cecum. Because the site of cecal admin istration varied, pharmacokinetic parameters for sumatriptan and its m ajor metabolite were compared statistically only after oral and jejuna l administration. One-half of the oral dose was recovered in the urine as parent (3%) and metabolite (46%). Sumatriptan was absorbed through out the gastrointestinal tract; absorption was similar after oral and jejunal administration, and less after cecal administration. The metab olite AUC and the AUC ratio (metabolite/parent) were significantly low er after jejunal compared to oral administration; the AUC ratio was tw o-fold lower after cecal administration. Results suggest that presyste mic metabolism of sumatriptan varies throughout the gastrointestinal t ract and/or regional differences exist in the absorption of metabolite formed within the gastrointestinal tract.