Spironolactone and Apixaban Interaction: What Patients and Clinicians Need to Know

Does spironolactone change apixaban levels?

On their labels, the two drugs are handled by different routes.

Apixaban is eliminated mainly by CYP3A4 metabolism, with P-gp and BCRP transport, and about 27% of its clearance is renal [2][3]. The drugs that change apixaban exposure are the ones that hit those pathways hard. In 18 healthy subjects, ketoconazole 400 mg/day raised apixaban AUC by 99% and peak concentration by 62%; diltiazem 360 mg/day raised AUC by 40% and peak concentration by 31% [5]. In the other direction, rifampin 600 mg/day cut oral apixaban AUC by 54% in 20 healthy participants [6]. The Eliquis label says to cut the apixaban dose by 50% (for patients taking 5 mg or 10 mg twice daily) with combined P-gp and strong CYP3A4 inhibitors such as ketoconazole, itraconazole or ritonavir, and to avoid the combination in patients already on 2.5 mg twice daily. It also says to avoid combined P-gp and strong CYP3A4 inducers such as rifampin, carbamazepine, phenytoin and St. John's wort [2].

Spironolactone is rapidly and extensively metabolized. Its label describes the metabolites canrenone, 7-alpha-thiomethylspironolactone (TMS) and 6-beta-hydroxy-7-alpha-thiomethylspironolactone (HTMS) without naming any cytochrome P450 enzyme, and it lists no CYP-based interactions [1].

Real-world data shows how much a genuine P-gp/CYP3A4 interaction can matter. In a Belgian nationwide observational cohort of 193,072 patients with atrial fibrillation on DOACs, concomitant P-gp/CYP3A4 inhibitors were associated with more major bleeding (adjusted HR 1.24, 95% CI 1.18-1.30), and in apixaban users specifically the adjusted HR was 1.27 (95% CI 1.16-1.39) [7]. Amiodarone, diltiazem, verapamil, ticagrelor and clarithromycin were among the individual drugs linked to significantly higher major bleeding [7].

What does the spironolactone label warn about?

Hyperkalemia. Spironolactone blocks aldosterone at the sodium-potassium exchange site in the distal tubule, so sodium and water are excreted while potassium is retained [1]. The label says risk rises with impaired renal function, potassium supplements, potassium-containing salt substitutes, ACE inhibitors and angiotensin receptor blockers, and it also names NSAIDs, heparin and low molecular weight heparin, and trimethoprim as drugs that can raise potassium [1][10].

The Aldactone label lists hyperkalemia, Addison's disease and concomitant use of eplerenone as contraindications [10]. It says to check serum potassium within 1 week of starting or changing the dose and regularly afterward, and to recheck it when ACE inhibitor or ARB therapy is changed [10].

Where the two drugs actually meet

Kidney function matters for both drugs, for different reasons. Apixaban has a labeled dose reduction for atrial fibrillation: 2.5 mg twice daily instead of 5 mg twice daily when at least two of age 80 or older, body weight 60 kg or less, or serum creatinine 1.5 mg/dL or more apply [2]. Spironolactone carries a higher hyperkalemia risk when kidney function is reduced, and renal dysfunction including renal failure is among its reported adverse reactions [1].

NSAIDs and heparin appear on both labels, for different reasons: the spironolactone label lists them among drugs that can raise potassium [1], and the Eliquis label lists them among drugs that add to bleeding risk [2].

Bleeding risk comes from apixaban's side. The Eliquis label names aspirin and other antiplatelets, other anticoagulants, heparin, thrombolytics, SSRIs, SNRIs and NSAIDs as drugs that add to it [2]. In ARISTOTLE, aspirin use raised the bleeding rate on apixaban from 1.8% to 3.4% per year [2]. Spironolactone is a potassium-sparing diuretic and aldosterone antagonist, not an antiplatelet or anticoagulant, and it is not on that list [2]. The spironolactone label does list gastritis and gastric bleeding among reported digestive adverse reactions [1].

The Eliquis boxed warning covers two things: stopping the drug early raises the risk of thrombotic events unless it is stopped for pathological bleeding or completion of therapy, and spinal or epidural hematomas can occur with neuraxial anesthesia or spinal puncture, with risk increased by indwelling epidural catheters, concomitant NSAIDs, platelet inhibitors or other anticoagulants, traumatic or repeated punctures, and spinal deformity or surgery [2]. The label also says serious, potentially fatal bleeding can occur; that andexanet alfa is the specific reversal agent available for adults; and that the drug's effect persists at least 24 hours after the last dose [2].

If spironolactone is being taken for acne

Acne is not a labeled indication for spironolactone; the labeled uses are heart failure, add-on hypertension, edema and primary hyperaldosteronism [10]. The best randomized evidence in acne is the SAFA trial: 410 women aged 18 and older with facial acne persisting at least 6 months, randomized to spironolactone 50 mg/day to week 6 then 100 mg/day to week 24, or placebo [4]. Investigator's Global Assessment success at week 12 was 18.5% versus 5.6% (adjusted OR 5.18, 95% CI 2.18-12.28); headache was reported by 20.4% versus 12.0%, with no serious adverse reactions [4].

Hyperkalemia in healthy young women is rare. A retrospective study of 974 healthy young women taking spironolactone for acne found 13 abnormal potassium values in 1,802 measurements (0.72%), equal to a 0.76% baseline rate in 1,165 comparison women. The study excluded women with cardiovascular disease, renal failure, or use of drugs acting on the renin-angiotensin-aldosterone system [11]. The Aldactone label itself still says to monitor potassium [10].