Crystalluria

Question 1

Risk factors for drug crystallization:

Answer 1

supersaturation of drug level in urine
volume depletion (low urine flow)
urine pH
reduced levels of inhibitors of crystallization

Most drug-crystalluria-induced acute kidney injury (AKI) resolves with drug withdrawal and supportive therapy

Question 2

Sulfadiazine (used to treat toxoplasmosis):

Answer 2

Risks: high dose > 4 to 6 g/d, urine pH < 5.5, volume depletion

Crystals are strongly birefringent as “shocks of wheat” or “bow-tie” with an amber color and radial striation.

Treatment: volume repletion, urine alkalinization with sodium bicarbonate to pH > 7.15

Question 3

Ciprofloxacin:

Answer 3

Risks: alkaline urine (pH > 7.0), elderly patients, volume depletion

Typically crystallizes in high urine pH > 7.3, but may occur in acidic pH

Crystals may take forms as needles, stars, fan shaped; all with lamellar structures and are strongly birefringent under polarized light.

Preventive measures: volume repletion, avoid concurrent use of alkalinizing agents, use with caution in patients > 65 to 70.

Question 4

Acyclovir:

Answer 4

Risks: rapid intravenous bolus (500 mg/m2) for herpes simplex virus–associated encephalitis, volume depletion.

Crystals are birefringent and needle shaped

Preventive measures: use low dose, or slow infusion with normal saline support.

Acyclovir is dialyzable.

Question 5

Indinavir (HIV protease inhibitor):

Answer 5

Crystallizes at physiologic pH 5.5 to 7.0; soluble at pH of ≤3.5.

Crystals are pleomorphic and may range from plate-like rectangles, fan shaped, to start burst shaped.

Associated with tubular obstruction, chronic tubulointerstitial nephritis (CTIN)

Treatment: volume intake of at least 2 to 3 L/d is suggested while on indinavir; dose adjustment in liver disease; avoid concurrent use of trimethoprim–sulfamethoxazole as it can increase indinavir blood levels. Urine acidification difficult to achieve and not recommended.

Question 6

Methotrexate:

Answer 6

Risks: low urine pH, low volume

Question 7

Methotrexate:

Answer 7

May cause both tubular obstruction and direct tubular toxicity

Question 8

Methotrexate:

Answer 8

Treatment: urine alkalinization to pH > 6.0, volume repletion, leucovorin rescue.

Question 9

Triamterene:

Answer 9

Risks: urine pH < 5.5

Question 10

Triamterene:

Answer 10

Crystals are spherical shaped, brown in color, appear as maltese crosses under polarized light.

Question 11

Triamterene:

Answer 11

Preventive: use low dose, adequate volume intake, avoid concurrent nonsteroidal anti-inflammatory drugs (NSAIDS) use.

Question 12

Triamterene:

Answer 12

Treatment: volume repletion, urinary alkalinization

Question 13

Orlistat (inhibitor of gastric and pancreatic lipase, induces fat malabsorption):

Answer 13

Associated with calcium oxalate deposition within renal tubules and interstitium. Mechanism for calcium oxalate stone formation is thought to be similar to that seen in patients with inflammatory bowel disease.

Question 14

Orlistat (inhibitor of gastric and pancreatic lipase, induces fat malabsorption):

Answer 14

Risks: underlying kidney disease, volume depletion

Question 15

Orlistat (inhibitor of gastric and pancreatic lipase, induces fat malabsorption):

Answer 15

Preventive: avoid use in patients with underlying kidney disease, volume repletion

Question 16

Ampicillin:

Answer 16

Needle Shaped

Question 17

Oral sodium phosphate solution used as bowel preparation for colonoscopy:

Answer 17

Calcium phosphate precipitations in renal tubular cells as well as tubular lumen

Question 18

Oral sodium phosphate solution used as bowel preparation for colonoscopy:

Answer 18

Risks: underlying kidney disease, females, and possibly hypertension (HTN) with concurrent use of angiotensin-converting enzyme inhibitor (ACEI) or angiotensin-receptor blocker (ARB)

Question 19

Oral sodium phosphate solution used as bowel preparation for colonoscopy:

Answer 19

Preventive measures: volume repletion, appropriate dosing, avoid concurrent use with ACEI, ARB, diuretics, and/or NSAIDS; Exercise caution with use in older patients.

Question 20

Vitamin C

Answer 20

(converts to oxalate, calcium oxalate stones)

Question 21

Other drug crystalluria:

Answer 21

foscarnet, pseudoephedrine

Question 22

Natural sources:

Answer 22

star fruit (oxalate), rhubarb leaves (oxalate), cranberry juice (oxalate), ma huang (ephedra), djenkol beans (needle like)