Hyperkalemia and Worsening Renal Function During Heart Failure Titration

Ranked by likely magnitude and modifiability:

1. Trimethoprim-sulfamethoxazole (most modifiable, highest yield). Trimethoprim blocks the epithelial sodium channel in the distal nephron - pharmacologically it behaves like amiloride. Potassium rises within 3–5 days of starting, and the effect is magnified by RAAS inhibition and CKD. Trimethoprim also inhibits tubular creatinine secretion, so part of the creatinine jump is a pseudo-rise, not a true GFR loss. This single drug explains both lab abnormalities.
2. Spironolactone - a direct aldosterone-receptor blocker; with an eGFR near 30 its potassium-retaining effect is substantially amplified, especially in combination with an ARNI.
3. Sacubitril/valsartan - RAAS blockade lowers aldosterone; contributory but not the lead actor here.
4. Aggressive diuresis (80 mg IV BID → 2.5 L/day) now producing euvolemia - reduced distal sodium delivery plus intravascular depletion drives both prerenal azotemia and potassium retention.
5. Underlying CKD 3b - sets the baseline risk; not modifiable in the short term.
6. Dapagliflozin - a small, usually early, and clinically minor potassium effect.

Note what is not responsible: carvedilol has no meaningful potassium effect, and there is no evidence of hemolysis, acidosis, or adrenal insufficiency in the data given - but check a venous blood gas and CK if the potassium does not fall after removing the obvious causes.

No - do not reflexively stop the ARNI. It is carrying a mortality benefit that is not replaced by anything else, and an eGFR decline of up to 30% and a potassium of 5.5 mmol/L are within the range guidelines say to manage around therapy rather than abandon it.

Order of operations today:

1. Stop trimethoprim-sulfamethoxazole and substitute an agent chosen by culture and susceptibilities (e.g., cephalexin, amoxicillin-clavulanate, or fosfomycin; nitrofurantoin is not appropriate at an eGFR of 30).
2. Hold spironolactone - the correct first casualty among the heart failure drugs. Restart at 12.5 mg once K ≤5.0 and eGFR is stable.
3. Reduce furosemide - she is euvolemic with a 2.5 L/day output; ongoing 80 mg IV BID is now causing prerenal injury. Convert to a lower oral dose or hold.
4. Continue sacubitril/valsartan and carvedilol unless K exceeds 6.0, she becomes hypotensive/symptomatic, or eGFR falls more than 30% from baseline attributable to the ARNI.
5. Treat the potassium actively: dietary review, stop any potassium-containing supplements or salt substitutes, consider a potassium binder (patiromer or sodium zirconium cyclosilicate) if needed to permit MRA re-initiation rather than accepting MRA omission.
6. Recheck BMP in 48 hours and again at one week; treat the ECG if there are changes (the ECG is the urgent triage tool, not the number alone).

Discharge targets and sequencing (over roughly 2–4 weeks):

• ARNI: continue 97/103 mg BID if SBP permits; do not down-titrate for a creatinine bump that is explained by diuresis and trimethoprim.
• Beta-blocker: continue carvedilol 12.5 mg BID; tolerate HR in the 60s.
• MRA: restart spironolactone at 12.5 mg daily once K ≤5.0 and eGFR ≥30; check K and SCr at 1 week, then at 4 weeks, then quarterly. Pair with a potassium binder if that is what it takes to keep her on the drug - MRA withdrawal is a real outcome loss.
• SGLT2 inhibitor: continue dapagliflozin 10 mg daily; counsel on genital mycotic infection, volume depletion, and sick-day holding.

Safety infrastructure:

• Written avoid list: trimethoprim-sulfamethoxazole, NSAIDs, potassium supplements/salt substitutes, and over-the-counter 'renal' products.
• Sick-day plan for vomiting, diarrhea, or dehydration.
• Explicit note in the chart that TMP-SMX caused hyperkalemia, so the next prescriber does not repeat it.
• Pharmacist follow-up call at 72 hours and again at 2 weeks to verify labs were actually drawn and the MRA was restarted.
• Address the UTI recurrence risk (hydration, voiding habits) and consider whether the AF rate/rhythm strategy needs revisiting, since amiodarone and other antiarrhythmics bring their own interactions.