Spironolactone

Mechanism

Both drugs are mineralocorticoid receptor antagonists. Concurrent use produces dual aldosterone blockade; renal potassium excretion stops. Severe hyperkalaemia (K+ above 6.5 mmol/L) develops with risk of fatal arrhythmia.

Symptoms

Muscle weakness, paresthesia, bradycardia. ECG shows peaked T waves, QRS widening; in severe cases asystole.

Management

Combination contraindicated. For resistant heart failure choose one: spironolactone if renal function is preserved, or eplerenone if gynaecomastia developed on spironolactone. Check potassium at weeks 1, 2 and 4, then monthly.

Mechanism

Both are potassium-sparing diuretics. Combined use produces dual potassium retention and severe hyperkalaemia with risk of fatal arrhythmia.

Symptoms

K+ above 6.5 mmol/L, muscle weakness, arrhythmia, ECG peaked T waves.

Management

Combination contraindicated. Choose one potassium-sparing diuretic.

Mechanism

Trimethoprim blocks ENaC in collecting ducts – potassium retention. With spironolactone dual aldosterone blockade. Sudden death increase reported in the elderly.

Symptoms

Hyperkalaemia within 3-7 days.

Management

Combination contraindicated in patients over 65. In younger patients check K+ at 3-5 days.

Mechanism

Aspirin suppresses renal prostaglandin synthesis that maintains glomerular perfusion. Diuretic and natriuretic effects of spironolactone diminish and potassium accumulates.

Symptoms

Oedema, weight gain, rising blood pressure. Weakness, paraesthesia, and arrhythmias from hyperkalaemia. Reduced diuretic effect emerges within 1–2 weeks of starting aspirin.

Management

At low aspirin doses (75–100 mg for cardioprotection), the clinical effect is minimal; co-prescription is acceptable with potassium and creatinine monitoring. At full anti-inflammatory doses, the diuretic response drops markedly – titrate spironolactone clinically.

Mechanism

Captopril (ACE-I) reduces aldosterone synthesis, while spironolactone directly blocks aldosterone receptors. Both retain potassium. In chronic kidney disease and older patients, severe hyperkalaemia risk reaches 10–15% in the first weeks.

Symptoms

Muscle weakness, paraesthesia in the limbs, slowed pulse, arrhythmias. ECG shows peaked T waves and widened QRS. Severe cases progress to cardiac arrest. Symptoms typically appear within 1–2 weeks of starting the combination.

Management

The combination is appropriate in heart failure. Check potassium and creatinine 1 week after start, then monthly. If potassium exceeds 5.5 mmol/L, reduce the spironolactone dose; above 6.0 mmol/L, stop one of the drugs.

Mechanism

Trimethoprim in co-trimoxazole blocks epithelial sodium channels in renal collecting ducts via the same mechanism as amiloride. Combined with spironolactone this produces dual potassium retention. In the elderly and in chronic kidney disease cohort studies show increased sudden death rates with the combination.

Symptoms

Hyperkalaemia within 1–2 weeks: weakness, paresthesia, arrhythmia. Detected on labs; symptoms appear late.

Management

Switch to an alternative antibiotic when possible (amoxicillin, cefalexin for urinary tract infection). If co-trimoxazole is required, check potassium and creatinine on days 3–5 and at end of course. Avoid the combination in patients over 65 with eGFR below 60 mL/min/1.73 m².

Mechanism

Spironolactone reduces digoxin clearance and prolongs its half-life, so digoxin levels rise (spironolactone SmPC), by about 25% according to the digoxin label. Spironolactone and its metabolites can also distort digoxin assays that cross-react with them (spironolactone labels).

Symptoms

Nausea, vomiting, loss of appetite, confusion, altered colour vision with yellow-green halos around lights, and heart rhythm disturbances such as bigeminy and atrioventricular block.

Management

Before starting spironolactone, measure the serum digoxin concentration with an assay that does not interact with spironolactone. Then reduce the digoxin dose by about 15–30% or give it less often and keep monitoring the concentration, as the FDA digoxin and spironolactone labels require. The Spanish spironolactone SmPC asks for caution with this combination (spironolactone SmPC). Spironolactone raises potassium, so check potassium and kidney function before starting and regularly during treatment (spironolactone SmPC).

Mechanism

Enalapril (an angiotensin-converting enzyme inhibitor, ACE-I) reduces aldosterone synthesis, while spironolactone directly blocks aldosterone receptors. Both retain potassium; hyperkalaemia develops in renal impairment or diabetes.

Symptoms

Muscle weakness, paraesthesia in the limbs, slowed pulse, arrhythmias. The electrocardiogram shows peaked T waves and a widened QRS complex. Severe cases progress to cardiac arrest. The risk is higher with renal impairment, diabetes mellitus, dehydration and age over 70.

Management

The combination is used deliberately and with potassium monitoring. The enalapril SmPC does not recommend combining enalapril with spironolactone because of the risk of hyperkalaemia; if the combination is indicated, use it with caution and frequent potassium checks (enalapril SmPC). Such an indication exists: the European Society of Cardiology (ESC) recommends a mineralocorticoid receptor antagonist such as spironolactone, together with an angiotensin-converting enzyme (ACE) inhibitor and a beta-blocker, for all patients with heart failure with reduced ejection fraction (ESC 2021). In heart failure, start spironolactone at 25 mg once daily if potassium is no higher than 5.0 mmol/L and creatinine no higher than 2.5 mg/dL, and do not exceed 50 mg a day (spironolactone SmPC). Check potassium and creatinine within a week of starting or increasing the dose, then monthly for the first 3 months, every 3 months until the end of the first year and every 6 months after that; stop spironolactone temporarily or permanently if potassium is above 5 mmol/L or creatinine above 4 mg/dL (spironolactone SmPC). Take particular care in impaired renal function and when potassium is 5.0 mmol/L or higher (ESC 2021). Potassium supplements are usually stopped when heart failure patients start spironolactone (US spironolactone label, FDA). Do not add an angiotensin II receptor blocker to an ACE inhibitor plus spironolactone because of the risk of renal dysfunction and hyperkalaemia (ESC 2021).

Mechanism

Losartan (angiotensin II receptor blocker, ARB) suppresses the renin-angiotensin-aldosterone system and reduces aldosterone release. Spironolactone directly blocks aldosterone receptors. Both retain potassium.

Symptoms

Muscle weakness, paraesthesia in the limbs, slowed pulse, arrhythmias. ECG shows peaked T waves and widened QRS. Severe cases progress to cardiac arrest. Symptoms typically appear within 1–2 weeks of starting the combination.

Management

The combination is appropriate in heart failure. Check potassium and creatinine 1 week after start, then monthly. If potassium exceeds 5.5 mmol/L, reduce the dose of one agent; above 6.0 mmol/L, stop one of them.

Mechanism

Spironolactone retains potassium via aldosterone receptor blockade. Tacrolimus reduces renal potassium secretion via a distal tubular inhibitory effect. Additive hyperkalaemia.

Symptoms

Muscle weakness, paraesthesia, slowed pulse, arrhythmias. ECG: peaked T waves, widened QRS. Severe cases progress to cardiac arrest.

Management

Avoid the combination in transplant patients. Alternative diuretics: furosemide (loop, removes potassium) or hydrochlorothiazide. If spironolactone is needed, check potassium and creatinine every 1–2 weeks.

Mechanism

Additive hyperkalaemia. Both drugs retain potassium: spironolactone directly blocks aldosterone receptors; telmisartan (ARB) reduces aldosterone synthesis.

Symptoms

Muscle weakness, paraesthesia, slowed pulse, arrhythmias. ECG: peaked T waves, widened QRS. Severe cases progress to cardiac arrest.

Management

The telmisartan SmPC (EMA) lists potassium-sparing diuretics, spironolactone included, under combinations that are not recommended. If the combination is needed, check serum potassium often. It is most often used in heart failure with reduced ejection fraction, where a mineralocorticoid receptor antagonist is part of core therapy (ESC 2021). Per the spironolactone SmPC, check potassium and creatinine within the first week after starting or increasing the dose, then monthly for 3 months, quarterly until the end of the first year and every 6 months after that. Stop spironolactone temporarily or permanently if potassium exceeds 5 mmol/L or creatinine exceeds 4 mg/dL (354 µmol/L). Do not give potassium supplements when potassium is above 3.5 mmol/L.

Mechanism

Valsartan (ARB) suppresses the RAAS, while spironolactone blocks aldosterone receptors. Dual aldosterone blockade raises hyperkalaemia risk.

Symptoms

Muscle weakness, paraesthesia in the limbs, slowed pulse, arrhythmias. ECG shows peaked T waves and widened QRS. Severe cases progress to cardiac arrest. Symptoms typically appear within 1–2 weeks of starting the combination.

Management

The combination is appropriate in heart failure with reduced ejection fraction. Check potassium and creatinine 1 week after start, then monthly. If potassium exceeds 5.5 mmol/L, reduce the spironolactone dose.

Mechanism

No direct pharmacokinetic interaction. In chronic kidney disease, spironolactone causes hyperkalaemia and apixaban exposure rises (partly renally cleared). Cumulative adverse event risk in reduced renal function.

Symptoms

Weakness, fatigue, arrhythmia (from hyperkalaemia), bleeding and bruising without trauma (from apixaban). Symptoms are more pronounced with creatinine clearance below 50 mL/min.

Management

With normal renal function, no dose change needed. At creatinine clearance 30–50 mL/min, check potassium and creatinine every 2–4 weeks. In severe CKD (clearance below 30 mL/min), stop spironolactone or switch to eplerenone with careful potassium monitoring.

Mechanism

Standard combination in heart failure with reduced ejection fraction – additive antihypertensive effect. Spironolactone retains potassium, reducing arrhythmia risk on a beta-blocker.

Symptoms

Lower blood pressure, postural dizziness, fatigue. Older patients: fall risk.

Management

Standard combination. Check potassium and creatinine 1 week after start, then monthly. If potassium exceeds 5.5 mmol/L, reduce spironolactone.

Mechanism

Spironolactone is a weak P-glycoprotein inhibitor and may slightly raise colchicine levels. Clinically significant toxicity is described in chronic kidney disease and on long-term combination.

Symptoms

Nausea, vomiting, diarrhoea, muscle weakness, paraesthesias. With severe toxicity: myopathy, neuropathy, bone marrow suppression.

Management

With normal renal function, no dose adjustment needed. With creatinine clearance below 50 mL/min, halve the colchicine dose. Check creatinine, CK, and CBC every 3 months. In gout flares, a short colchicine course (0.5 mg 2–3 times daily for 1–3 days) is better tolerated than long-term use.

Mechanism

Opposing effects on potassium: furosemide depletes it via the loop of Henle, spironolactone retains it by blocking aldosterone in collecting ducts. Target combination in heart failure, resistant hypertension, and ascites.

Symptoms

With a balanced combination, no specific symptoms. In chronic kidney disease, hyperkalaemia may occur: Weakness, fatigue, paraesthesias, arrhythmia. Symptoms develop at potassium above 5.5 mmol/L; life-threatening above 6.5 mmol/L.

Management

Check potassium and creatinine at 1 and 4 weeks after starting, then every 3 months. With creatinine clearance below 30 mL/min, do not prescribe spironolactone, or cap at 25 mg every other day. In dehydration, temporarily stop both until volume is restored.

Mechanism

Opposing effects on potassium: thiazide depletes it, spironolactone retains it. Combination in resistant hypertension and ascites. In CKD, hyperkalaemia risk rises.

Symptoms

With a balanced combination, no specific symptoms. Weakness, fatigue, paraesthesias, arrhythmia. Symptoms develop at potassium above 5.5 mmol/L; life-threatening above 6.5 mmol/L.

Management

Check potassium and creatinine at 2 and 4 weeks after starting, then every 3 months. With creatinine clearance below 30 mL/min, do not prescribe spironolactone. In older patients, watch for dehydration, especially in heat or acute illness.

Mechanism

Ibuprofen blocks prostaglandin synthesis in the kidney, which weakens the diuretic, natriuretic and blood-pressure-lowering effect of spironolactone (spironolactone labels). Spironolactone blocks aldosterone, so the kidneys keep potassium; nonsteroidal anti-inflammatory drugs (NSAIDs) given with potassium-sparing diuretics raise the risk of hyperkalaemia (both SmPCs). NSAIDs reduce renal blood flow, and taken with a diuretic they raise the risk of kidney damage, especially in older or dehydrated patients and in those with heart, kidney or liver disease (ibuprofen SmPC).

Symptoms

Hyperkalaemia often causes no symptoms and shows only in blood tests. At higher potassium levels, the patient may have tingling and numbness, muscle weakness and cramps, flaccid paralysis and heart rhythm disturbances (spironolactone SmPC). Worsening kidney function shows as rising creatinine and urea and reduced urine output. If the diuretic effect weakens, oedema increases and weight and blood pressure go up.

Management

Use the combination with caution and check serum potassium while the patient takes both drugs (ibuprofen SmPC). Check potassium within 1 week of starting or increasing spironolactone and regularly after that (spironolactone label, US Food and Drug Administration, FDA). With nonsteroidal anti-inflammatory drugs, more frequent checks may be needed (spironolactone FDA label). Keep the patient well hydrated and check renal function, volume status and the diuretic effect of spironolactone after starting the combination and periodically (ibuprofen SmPC, spironolactone labels). In patients with heart, liver or kidney disease, keep the ibuprofen dose as low and the course as short as possible (ibuprofen SmPC). If hyperkalaemia occurs, reduce the spironolactone dose or stop it (spironolactone FDA label). In severe heart failure, interrupt spironolactone if potassium is above 5 mmol/L or creatinine above 4 mg/dL (spironolactone SmPC). Ibuprofen is contraindicated when the glomerular filtration rate is below 30 mL/min and in New York Heart Association class IV heart failure, and spironolactone in hyperkalaemia or acute renal failure (both SmPCs).

Mechanism

No direct interaction. Mild additive hypotension and fall risk in older patients during hypovolaemia or on starting the combination.

Symptoms

Possible mild morning hypotension and sedation. In older patients: fall risk.

Management

No dose adjustment needed. In older patients, start alprazolam at 0.125 mg at bedtime. In dehydration or acute illness, temporarily stop spironolactone.

Mechanism

No direct interaction. Additive orthostatic hypotension possible in older patients during hypovolaemia: spironolactone via diuresis, amitriptyline via α1-blockade.

Symptoms

Possible postural dizziness, fatigue. In older patients: fall risk.

Management

Begin amitriptyline at 10 mg at bedtime. In older patients, do not exceed 25 mg/day. Check standing/sitting BP at 1–2 weeks. With pronounced orthostatic hypotension, consider neuropathic-pain alternatives: gabapentin or pregabalin.