**Question:** The newer aminosalicylate with side effect of watery diarrhea caused by increased secretion of fluid in the small bowel is:

A. Sulfasalazine
B. Mesalazine
C. Salicylic acid
D. Salicylic acid

**Correct Answer:** B. Mesalazine

**Core Concept:** Aminosalicylates are a class of medications derived from salicylic acid, which are commonly used as anti-inflammatory agents in inflammatory bowel diseases such as ulcerative colitis and Crohn's disease. They exert their therapeutic effect by inhibiting the production of pro-inflammatory mediators, including prostaglandins, leukotrienes, and cytokines, in the gastrointestinal tract.

**Why the Correct Answer is Right:** Mesalazine (5-aminosalicylic acid) is the correct answer because it is the aminosalicylate drug with the least potential for causing watery diarrhea due to increased fluid secretion in the small bowel. Mesalazine is selectively absorbed in the large intestine (colon) and has a lower systemic bioavailability compared to other aminosalicylates like Sulfasalazine, which is absorbed in both the small and large intestine, leading to potential systemic side effects.

**Why Each Wrong Option is Incorrect:**

A. Sulfasalazine: This drug is absorbed not only in the small intestine but also in the large intestine, leading to higher systemic bioavailability and potential side effects such as watery diarrhea due to increased fluid secretion in the small bowel.

B. Salicylic acid: Salicylic acid is the parent compound from which aminosalicylates are derived. It is not a medication in itself but a precursor for their synthesis.

C. Salicylic acid: Similar to option B, salicylic acid is a precursor for the synthesis of aminosalicylates. It is not a medication that can cause watery diarrhea due to increased fluid secretion in the small bowel.

**Clinical Pearl:** When treating patients with inflammatory bowel disease, it is essential to consider the pharmacokinetic properties of different aminosalicylates to minimize systemic side effects and improve patient outcomes.