Polyuria and Medications Quiz

Approach for Polyuria and Medications that Cause Polyuria

I. Introduction

• Polyuria is excessive urination (>3 liters/day for adults)
• Main causes include diabetes insipidus (DI), diabetes mellitus (DM), primary polydipsia (PP), and drug-induced polyuria

II. Initial Assessment

• Full history and physical exam, including vital signs, cardiac, respiratory, abdominal, and fluid status
• Pelvic exam if concerns of incontinence or urogynecologic issues
• Current medical conditions
• Investigations, including urine dipstick, blood glucose measurement, serum electrolytes, osmolality and creatinine, urine electrolytes and osmolality

III. Urine Analysis

• Urinalysis to assess for glucosuria or proteinuria
• Low specific gravity (<1.005) is indicative of DI or PP
• Glucosuria and high specific gravity (>1.015) is suggestive of DM

IV. Water Deprivation Test

• Purpose is to differentiate between DI and PP
• Conducted by withholding fluids for 8 hours and measuring plasma and urine osmolality
• Precautions should be taken due to dehydration risk

V. Additional Testing

• Serum glucose for DM, serum calcium for hypercalcemia, renal function tests, hormone levels, and imaging
• Desmopressin test to observe urine osmolality change to differentiate central and nephrogenic DI

VI. Treatment

• Desmopressin for DI, insulin therapy or oral hypoglycemic agents for DM, fluid restriction and addressing underlying psychiatric issues for PP, and adjusting or changing medication for drug-induced polyuria

Medications that Cause Polyuria: I. Furosemide

• Type: Loop diuretic
• Mechanism of action: inhibits Sodium-Potassium-Chloride co-transporter in the Loop of Henle, reduces water resorption
• Effects: polyuria, urinary frequency, loss of sodium, chloride, and potassium in urine
• Dose adjustment considerations: maintain the patient on the smallest dose possible to achieve euvolemia, decrease the dose if the patient is euvolemic and shows no signs of heart failure

II. Spironolactone

• Type: Aldosterone antagonist
• Mechanism of action: competitive binding of receptors at aldosterone-dependent potassium exchange in the distal convoluted renal tubule
• Effects: polyuria (less likely than furosemide), urinary frequency (less likely than furosemide), increase in serum potassium
• Dose adjustment considerations: continue the current dose or higher to see benefits for heart failure

III. Levothyroxine

• Type: Thyroid supplement
• Mechanism of action: can cause polyuria and urinary frequency when it causes hyperthyroidism (e.g. toxicity), downregulation of aquaporin 1 and 2, increased blood pressure and food and water intake, increased distal delivery of sodium, resulting in increased urine flow
• Effects: polyuria, urinary frequency
• Dose adjustment considerations: perform lab work for thyroid-stimulating hormone (TSH), if TSH is suppressed (suggesting oversupplementation), reduce the levothyroxine dose.