# A 78-year-old client with HFrEF on lisinopril and spironolactone is prescribed trimethoprim-sulfamethoxazole for a UTI. Baseline potassium is 4.6 mEq/L and creatinine is 1.4 mg/dL. Which is the most appropriate nursing action?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=375241&lang=en  
> language: en  
> subject: Medical Emergencies  
> category: PA

## Question

A 78-year-old client with HFrEF on lisinopril and spironolactone is prescribed trimethoprim-sulfamethoxazole for a UTI. Baseline potassium is 4.6 mEq/L and creatinine is 1.4 mg/dL. Which is the most appropriate nursing action?

## Option

1. Administer the TMP-SMX as prescribed, as the potassium level of 4.6 mEq/L is within normal limits and no other labs require intervention; continue to monitor for UTI symptom resolution and encourage fluid intake to prevent further kidney stress, as this is the standard of care for an elderly client with a UTI.
2. Contact prescriber and pharmacist; TMP-SMX + ACEi + aldosterone antagonist + reduced renal function in elderly carries high hyperkalemia risk (TMP acts like amiloride); plan baseline/follow-up K and renal labs, propose alternative (nitrofurantoin if CrCl>30, fosfomycin, cephalexin), teach high-K food limits, ECG if K rises. **✔ Correct answer**
3. Add a potassium supplement such as oral potassium chloride 20 mEq daily, since the baseline potassium of 4.6 mEq/L may drop with antibiotic therapy and spironolactone, which can cause potassium loss; this will prevent hypokalemia and maintain cardiac function in this elderly heart failure client.
4. Increase spironolactone to 50 mg daily to offset any potential potassium loss from the antibiotic and provide additional heart failure management; monitor serum potassium and creatinine levels daily for the first 72 hours of treatment, as spironolactone is known to counteract the renal effects of sulfonamides.

**Correct answer: 2**

## Explanation

TMP-SMX is widely effective for UTI, but trimethoprim has a structure similar to amiloride and inhibits the epithelial sodium channel in the distal nephron, decreasing potassium excretion. The combination with ACE inhibitors or ARBs (which suppress aldosterone), aldosterone antagonists (spironolactone, eplerenone), potassium supplements, NSAIDs, beta-blockers, or pre-existing renal impairment markedly increases the risk of severe hyperkalemia, with documented cases of arrhythmia, hospitalization, and death especially in older adults. Combined nursing/care-coordination action: (1) baseline and follow-up labs — potassium, creatinine, BUN — typically within 3 to 5 days of starting; (2) communicate with the prescriber and pharmacist about the risk and propose an alternative antibiotic when culture allows — nitrofurantoin if creatinine clearance over 30 mL/min, fosfomycin single dose, cephalexin, or other narrow-spectrum agents; (3) teaching about high-potassium foods (bananas, oranges, tomatoes, potatoes, salt substitutes containing KCl) to limit intake during therapy; (4) report symptoms of hyperkalemia — weakness, paresthesias, palpitations; obtain ECG if K rises showing peaked T waves, prolonged PR, widened QRS; (5) follow standard sulfa cautions for SJS, photosensitivity, hydration, and folate; (6) document allergies and review home meds for any other potassium-elevating drugs. Administering without checks, increasing spironolactone, or adding K supplement are unsafe.

## In-depth explanation

TMP-SMX + ACEi/spironolactone + elderly with reduced renal function = high hyperkalemia risk. Communicate, monitor labs, propose an alternative antibiotic.

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