5-Aminosalicylic Acid Distribution into the Intestinal Membrane Along the Gastrointestinal Tract After Oral...

Area of Science:

• Pharmacology
• Gastroenterology
• Drug Delivery

Background:

• 5-Aminosalicylic acid (5-ASA) is the primary treatment for ulcerative colitis.
• 5-ASA is a zwitterionic drug with poor solubility, and its absorption is believed to occur mainly in the small intestine.

Purpose of the Study:

• To investigate the pH-dependent solubility of 5-ASA in vitro.
• To examine the intestinal membrane distribution of 5-ASA and its metabolite (AC-5-ASA) in rats after oral administration.

Main Methods:

• In vitro solubility studies across a range of pH values.
• Oral administration of 5-ASA to fed rats in various vehicles (water, HCl, NaOH, NaHCO3) with or without lansoprazole pretreatment.
• Analysis of 5-ASA and AC-5-ASA distribution in intestinal membranes at 3 and 8 hours post-administration.

Main Results:

• 5-ASA solubility was higher at pH < 2 and pH > 7.
• In rats, 5-ASA and AC-5-ASA were primarily found in the small intestine at 3 hours and in the colon at 8 hours.
• Dosing vehicle and lansoprazole pretreatment did not significantly alter luminal pH or 5-ASA membrane distribution.

Conclusions:

• Intestinal membrane distribution of 5-ASA in the proximal region is constrained by luminal pH, low solubility, and saturable permeability.
• Unabsorbed 5-ASA from the proximal intestine is transported to the distal intestine.
• Increased oral 5-ASA dosage may enhance distal intestinal delivery due to limited proximal absorption, potentially benefiting ulcerative colitis treatment.