Question

Crystalluria, hematuria, and renal tubule blockage in the glomerular filtrate of the kidney can occur owing to precipitation of the:

• A. Sulfonamide
• B. Azithromycin
• C. Amoxicillin
• D. Ampicillin

Hint:

To prevent sulfonamide-induced crystalluria in veterinary patients (especially dogs and cats):
1. Maintain adequate hydration.
2. Supplement with urinary alkalizers (like sodium bicarbonate) to increase sulfonamide solubility in urine.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Renal clearance of drugs involves glomerular filtration, active tubular secretion, and passive tubular reabsorption.
When certain drugs or their metabolic products have low water solubility in acidic or concentrated urine, they can precipitate out of solution, leading to mechanical damage and blockage in the renal tubules.

Step 2: Detailed Explanation:
Let us review the renal safety profiles of the listed antimicrobials:
- Sulfonamides: These are weak organic acids that are metabolized primarily by acetylation in the liver.
Both the parent drug and its acetylated metabolites have poor solubility in acidic urine (which is typical of carnivores).
When they undergo glomerular filtration and concentrated tubular fluid becomes acidic, sulfonamides precipitate to form crystal aggregates (crystalluria).
These crystals mechanically damage the epithelial lining (causing hematuria) and can physically block the renal tubules, leading to acute post-renal injury.
- Amoxicillin and Ampicillin: While beta-lactams are excreted primarily in the urine, they are highly soluble and do not typically precipitate to cause mechanical crystalluria.
- Azithromycin: This macrolide is cleared primarily via biliary excretion, and very little is excreted in the urine.

Step 3: Final Answer:
Therefore, the precipitation leading to crystalluria, hematuria, and tubule blockage is a characteristic adverse effect of Sulfonamides.