Bioavailability of single and multiple doses of a new oral formulation of 5-ASA in patients with inflammatory bowel disease and healthy volunteers.
An oral multiparticulate coated formulation of 5-aminosalicylic acid (5-ASA: mesalazine) has been developed to provide a controlled release of the drug, in a pH-dependent fashion, in the distal ileum and colon. The purpose of the present study was to assess the systemic availability of the drug and its metabolite, acetyl-5-ASA, following single (800 mg) and multiple (2400 mg for 56 days) oral dose administration. Three groups were investigated: six healthy volunteers, six patients with ulcerative colitis, and nine patients with Crohn's disease in remission. In the single oral dose study (800 mg) all three groups participated, whereas in the multiple oral dose study (2400 mg/day for 56 days) only the patients with inflammatory bowel disease took part. Plasma and urine 5-ASA and Ac-5-ASA were measured for 48 h. In the single oral dose regimen, systemic absorption of 5-ASA and Ac-5-ASA were low and did not differ between the three groups. Only about 20% of the 5-ASA given was absorbed, with more than 80% of the drug being available in the terminal ileum and colon for therapeutic activity. The multiple oral dose regimen in patients with inflammatory bowel disease produced a significantly higher plasma concentration and urine excretion of both 5-ASA and Ac-5-ASA by the end of the treatment, in comparison to the first dose. There was a statistically higher systemic absorption of 5-ASA in patients with ulcerative colitis than in patients with Crohn's disease. After 56 days of dosing, no adverse event was reported and laboratory screening tests remained within normal ranges. The new oral 5-ASA formulation is gradually released throughout the small and large intestine, reflected by a low plasma concentration of the drug and its metabolite, with about 80% of the drug being available for ileum-colon therapeutic activity.