In a healthy adult taking 100 mg losartan, how much potassium will be excreted in the urine after consuming a 16.9‑oz bottle of coconut water (~979 mg potassium)?

Urinary Potassium Excretion in Healthy Adults

In a healthy adult with normal kidney function, approximately 90% of ingested potassium is excreted in the urine, with the remaining 10% lost through feces. 1

Baseline Urinary Potassium Excretion

• Under normal physiological conditions, urinary potassium excretion closely matches dietary intake, typically ranging from 40–120 mEq/day (1,560–4,680 mg/day) depending on consumption patterns. 2
• The kidneys maintain serum potassium within a narrow range (3.5–5.0 mEq/L) through highly regulated distal nephron secretion, with approximately 90% of filtered potassium reabsorbed in the proximal tubule and loop of Henle. 1, 2
• The recommended adequate dietary potassium intake for adults is 4,700 mg/day (120 mEq/day), though actual urinary excretion is typically lower, reflecting lower dietary intake in most populations. 3, 4

Effect of Losartan on Potassium Excretion

• Losartan 100 mg daily reduces renal potassium excretion by blocking angiotensin II-mediated aldosterone release, which normally stimulates potassium secretion in the distal nephron. 5, 6
• Angiotensin II receptor blockers like losartan decrease urinary potassium losses, potentially eliminating the need for potassium supplementation in patients on diuretics. 1
• Losartan may cause hyperkalemia when combined with potassium-sparing diuretics (spironolactone, triamterene) due to additive effects on reducing renal potassium excretion. 7

Coconut Water Potassium Load Response

• After consuming 979 mg (25 mEq) of potassium from coconut water, a healthy adult on losartan 100 mg would excrete approximately 70–85% of this load in urine over 24 hours (roughly 680–830 mg or 17–21 mEq). 2
• The remaining 15–30% would be redistributed into intracellular space via Na+/K+-ATPase pumps stimulated by insulin and catecholamines, with minimal fecal excretion (<10%). 1, 2
• Losartan's potassium-retaining effect would reduce urinary excretion by approximately 10–20% compared to a patient not on RAAS inhibition, meaning slightly more potassium remains in the body. 5, 6

Critical Factors Affecting Urinary Potassium

• Only 2% of total body potassium exists in extracellular fluid, while 98% is intracellular, so serum potassium changes poorly reflect total body potassium balance. 4, 2
• Renal potassium excretion depends on multiple factors: prior potassium intake, distal sodium chloride delivery, urine flow rate, aldosterone levels, and tubular cell integrity. 2
• Losartan increases uric acid secretion and lowers plasma uric acid levels, which may lead to uric acid stone formation with chronic use. 6

Monitoring Recommendations

• For patients on losartan 100 mg daily, check serum potassium and renal function within 7–10 days after starting therapy, then at 3 months and every 6 months thereafter. 8
• Avoid potassium supplements, potassium-sparing diuretics, and salt substitutes in patients on losartan unless specifically indicated for documented hypokalemia. 8, 7
• Target serum potassium of 4.0–5.0 mEq/L to minimize both cardiac arrhythmia risk from hypokalemia and hyperkalemia complications. 8

Common Pitfalls

• Do not assume patients on losartan need potassium supplementation—RAAS inhibitors reduce renal potassium losses and supplementation may cause dangerous hyperkalemia. 1, 8
• Avoid NSAIDs in patients on losartan, as they impair renal potassium excretion and dramatically increase hyperkalemia risk. 1
• Pregnant women and breast-feeding mothers should not receive losartan, as it may disturb fetal growth or harm the newborn. 7