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Section 1: Sulfonamide Pharmacology & Crystalluria
I. Multiple Choice Questions (40 Total)
Questions 1-20
1. What biochemical property of sulfonamide metabolites primarily
drives crystalluria?
A) High solubility in lipids
B) Low solubility in acidic urine
C) Strong protein-binding affinity
D) Rapid glomerular filtration
Answer: B
Rationale: Sulfonamides are acetylated in the liver into metabolites
like N-acetyl-sulfamethoxazole, which exhibit poor solubility in acidic
environments (pH < 5.5). These metabolites precipitate as needle-shaped
crystals in renal tubules, causing mechanical obstruction and acute
kidney injury. This pH-dependent insolubility is distinct from other
nephrotoxins and underscores the need for urine alkalinization per
Katzung’s Pharmacology (15th ed., Ch. 46).
2. Which patient is at HIGHEST risk for sulfonamide crystalluria?
A) A 25-year-old athlete on TMP-SMX with urine pH 7.2
B) A 70-year-old with heart failure (on fluid restriction) and urine pH 5.0
C) A 40-year-old taking sodium bicarbonate with urine output 2L/day
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D) A 30-year-old with asthma using albuterol
Answer: B
Rationale: Advanced age, dehydration from fluid restriction, and acidic
urine (pH 5.0) synergistically increase crystalluria risk. Reduced urine
volume concentrates sulfonamide metabolites, while low pH promotes
precipitation. IDSA UTI Guidelines (2021) flag elderly patients with
comorbidities as "high-risk," requiring aggressive hydration and pH
monitoring. Neither asthma (D) nor alkalinization (C) confers significant
risk.
3. Urine alkalinization with sodium bicarbonate prevents crystalluria
by:
A) Increasing the ionization of sulfonamide metabolites
B) Enhancing renal blood flow
C) Inhibiting hepatic acetylation
D) Chelating calcium in urine
Answer: A
Rationale: Alkalinization (target pH 7.0–7.5) ionizes sulfonamide
metabolites, converting them into water-soluble forms that resist
precipitation. This does not alter hepatic metabolism or renal perfusion
but directly enhances solubility. Rang & Dale’s Pharmacology (2023)
notes that sodium bicarbonate is preferred over citrate in renal
impairment due to no potassium load.
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4. Which sulfonamide is MOST associated with crystalluria?
A) Sulfasalazine (for IBD)
B) Sulfadiazine (for toxoplasmosis)
C) Sulfamethoxazole (in TMP-SMX)
D) Acetazolamide (for glaucoma)
Answer: B
Rationale: Sulfadiazine has the lowest solubility of common
sulfonamides, especially in acidic urine, and is used in high doses for
CNS infections. Its acetylated metabolite rapidly forms stable crystals,
necessitating strict hydration (>3L/day) and alkalinization.
Sulfamethoxazole (C) has higher solubility, while non-antibiotic agents
(A, D) rarely cause crystalluria (Katzung’s, 15th ed.).
5. A patient develops sulfonamide crystalluria. Urine microscopy would
MOST likely show:
A) Hexagonal crystals
B) Rhomboid crystals
C) Needle-shaped crystals
D) Amorphous crystals
Answer: C
Rationale: Sulfonamide metabolites (e.g., acetyl-sulfadiazine) form
needle-shaped or sheaf-like crystals under microscopy, distinct from uric
acid (rhomboid) or cystine (hexagonal) crystals. This morphology is
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Section 1: Sulfonamide Pharmacology & Crystalluria
I. Multiple Choice Questions (40 Total)
Questions 1-20
1. What biochemical property of sulfonamide metabolites primarily
drives crystalluria?
A) High solubility in lipids
B) Low solubility in acidic urine
C) Strong protein-binding affinity
D) Rapid glomerular filtration
Answer: B
Rationale: Sulfonamides are acetylated in the liver into metabolites
like N-acetyl-sulfamethoxazole, which exhibit poor solubility in acidic
environments (pH < 5.5). These metabolites precipitate as needle-shaped
crystals in renal tubules, causing mechanical obstruction and acute
kidney injury. This pH-dependent insolubility is distinct from other
nephrotoxins and underscores the need for urine alkalinization per
Katzung’s Pharmacology (15th ed., Ch. 46).
2. Which patient is at HIGHEST risk for sulfonamide crystalluria?
A) A 25-year-old athlete on TMP-SMX with urine pH 7.2
B) A 70-year-old with heart failure (on fluid restriction) and urine pH 5.0
C) A 40-year-old taking sodium bicarbonate with urine output 2L/day
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D) A 30-year-old with asthma using albuterol
Answer: B
Rationale: Advanced age, dehydration from fluid restriction, and acidic
urine (pH 5.0) synergistically increase crystalluria risk. Reduced urine
volume concentrates sulfonamide metabolites, while low pH promotes
precipitation. IDSA UTI Guidelines (2021) flag elderly patients with
comorbidities as "high-risk," requiring aggressive hydration and pH
monitoring. Neither asthma (D) nor alkalinization (C) confers significant
risk.
3. Urine alkalinization with sodium bicarbonate prevents crystalluria
by:
A) Increasing the ionization of sulfonamide metabolites
B) Enhancing renal blood flow
C) Inhibiting hepatic acetylation
D) Chelating calcium in urine
Answer: A
Rationale: Alkalinization (target pH 7.0–7.5) ionizes sulfonamide
metabolites, converting them into water-soluble forms that resist
precipitation. This does not alter hepatic metabolism or renal perfusion
but directly enhances solubility. Rang & Dale’s Pharmacology (2023)
notes that sodium bicarbonate is preferred over citrate in renal
impairment due to no potassium load.
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4. Which sulfonamide is MOST associated with crystalluria?
A) Sulfasalazine (for IBD)
B) Sulfadiazine (for toxoplasmosis)
C) Sulfamethoxazole (in TMP-SMX)
D) Acetazolamide (for glaucoma)
Answer: B
Rationale: Sulfadiazine has the lowest solubility of common
sulfonamides, especially in acidic urine, and is used in high doses for
CNS infections. Its acetylated metabolite rapidly forms stable crystals,
necessitating strict hydration (>3L/day) and alkalinization.
Sulfamethoxazole (C) has higher solubility, while non-antibiotic agents
(A, D) rarely cause crystalluria (Katzung’s, 15th ed.).
5. A patient develops sulfonamide crystalluria. Urine microscopy would
MOST likely show:
A) Hexagonal crystals
B) Rhomboid crystals
C) Needle-shaped crystals
D) Amorphous crystals
Answer: C
Rationale: Sulfonamide metabolites (e.g., acetyl-sulfadiazine) form
needle-shaped or sheaf-like crystals under microscopy, distinct from uric
acid (rhomboid) or cystine (hexagonal) crystals. This morphology is
