The Lancet SEPTEMBER 19, 2015

Spironolactone versus placebo, bisoprolol, and doxazosin to determine the optimal treatment for drug-resistant hypertension (PATHWAY-2): a randomised, double-blind, crossover trial

Bryan Williams, Thomas M MacDonald, Stephanie Morant, David J Webb, Peter Sever, Graham McInnes, Ian Ford, John K Cruickshank, Mark J Caulfield, et al.

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Bottom Line

The PATHWAY-2 trial demonstrated that spironolactone is the most effective fourth-line add-on therapy for patients with resistant hypertension, significantly lowering home systolic blood pressure compared to placebo, an alpha-blocker (doxazosin), and a beta-blocker (bisoprolol).

Key Findings

1. Spironolactone significantly reduced mean home systolic blood pressure compared to placebo by -8.70 mm Hg (95% CI, -9.72 to -7.69; P < 0.0001).

2. Spironolactone was superior to the mean of the two other active treatments (doxazosin and bisoprolol), providing an additional systolic blood pressure reduction of -4.26 mm Hg (95% CI, -5.13 to -3.38; P < 0.0001).

3. Compared to individual active agents, spironolactone showed superior efficacy, reducing home systolic blood pressure by -4.03 mm Hg more than doxazosin and -4.48 mm Hg more than bisoprolol.

4. The BP-lowering effect of spironolactone was inversely related to plasma renin concentration, supporting the hypothesis that resistant hypertension is predominantly a salt-retaining state.

5. Adverse events were generally well-tolerated, with only 2% (six of 285) of patients on spironolactone experiencing a single episode of serum potassium exceeding 6.0 mmol/L.

Study Design

Design

RCT

Double-Blind

Sample

335

Patients

Duration

12 weeks per cycle

Median

Setting

Multicenter, UK

Population Patients aged 18–79 years with resistant hypertension (clinic systolic BP ≥140 mm Hg or ≥135 mm Hg for diabetics) despite at least 3 months of maximally tolerated triple therapy.

Intervention Spironolactone (25-50 mg daily)

Comparator Placebo, bisoprolol (5-10 mg daily), and doxazosin (4-8 mg daily) in a randomized, crossover sequence.

Outcome Mean difference in home systolic blood pressure between spironolactone and placebo, then compared against active agents.

Study Limitations

• The study was a crossover design without formal washout periods between treatment cycles, though carry-over effects were analyzed and considered unlikely to bias the primary conclusions.

• The patient cohort primarily consisted of individuals with normal renal function, limiting the generalizability to patients with severe chronic kidney disease.

• The trial duration for each cycle was relatively short (12 weeks), providing information on immediate blood pressure efficacy but not long-term cardiovascular outcomes or safety data.

• The study focused on hypertension control as a physiological surrogate marker, not clinical hard endpoints such as cardiovascular morbidity or mortality.

Clinical Significance

This landmark study provides robust evidence confirming spironolactone as the preferred fourth-line agent for patients with resistant hypertension. It shifts clinical practice by validating the physiological mechanism of resistant hypertension as a sodium-retaining state and establishing spironolactone as more efficacious than alternative adrenergic-based treatment strategies.

Historical Context

Prior to PATHWAY-2, the optimal pharmacological management for patients failing conventional three-drug regimens (ACEi/ARB, CCB, and diuretic) was poorly defined, often resulting in heterogeneous treatment approaches and the use of second- or third-line agents as add-ons. The trial was designed to address this uncertainty, directly testing the pathophysiology of resistant hypertension and providing a definitive comparative analysis of available fourth-line options.

Guided Discussion

High-yield insights from every perspective

Med Student

Medical Student

The PATHWAY-2 trial demonstrated that spironolactone is the most effective fourth-line drug for resistant hypertension. Based on the RAAS pathway, what is the physiological rationale for using a mineralocorticoid receptor antagonist when a patient is already failing a combination of an ACE inhibitor/ARB, a calcium channel blocker, and a thiazide diuretic?

Key Response

Resistant hypertension is frequently characterized by concealed volume expansion and a low-renin state. Even while on ACE inhibitors or ARBs, 'aldosterone escape' can occur. Spironolactone addresses this by directly blocking the mineralocorticoid receptor, counteracting the sodium retention and volume expansion that typically drive resistance to standard triple-therapy regimens.

Resident

In a patient meeting the PATHWAY-2 criteria for resistant hypertension (uncontrolled BP despite treatment with maximum tolerated doses of an ACEi/ARB, CCB, and thiazide), what are the specific biochemical monitoring requirements and clinical thresholds for initiating and maintaining spironolactone therapy?

Key Response

Residents must monitor serum potassium and creatinine. Per the trial's safety considerations and general clinical practice, spironolactone should typically be avoided or used with extreme caution if the eGFR is <45 mL/min/1.73m² or if baseline potassium is >4.5 mmol/L, due to the high risk of life-threatening hyperkalemia when combined with other RAAS inhibitors.

Fellow

PATHWAY-2 identified that the blood pressure response to spironolactone was inversely related to baseline plasma renin activity (PRA). How does this finding influence the contemporary understanding of 'primary aldosteronism' versus 'low-renin hypertension' in the resistant hypertension phenotype?

Key Response

The trial suggests that many patients with resistant hypertension have a physiological state of primary sodium retention, evidenced by low PRA. The fact that spironolactone's efficacy was highest in those with the lowest renin levels supports the theory that resistant hypertension is often a spectrum of mineralocorticoid excess, whether or not the patient meets strict biochemical criteria for primary aldosteronism.

Attending

Given that spironolactone outperformed both doxazosin (an alpha-blocker) and bisoprolol (a beta-blocker) in PATHWAY-2, how should this evidence change the hierarchy of 'add-on' therapy in your clinical teaching, and what are the limitations of applying these findings to patients with advanced chronic kidney disease (CKD)?

Key Response

The hierarchy should shift from 'any fourth-line agent' to a clear preference for MRAs (spironolactone or amiloride) as the definitive fourth step. However, since PATHWAY-2 excluded patients with significant renal impairment, the attending must emphasize that in CKD Stage 4+, the evidence for MRAs is less robust and the risk of hyperkalemia may necessitate using the alternatives (doxazosin or bisoprolol) despite their lower comparative efficacy in the trial.

Scholarly Review

Critical appraisal through the lens of expert reviewers and guideline development

PhD

The PATHWAY-2 trial employed a double-blind, randomized, crossover design. Discuss the statistical and methodological advantages of using a crossover design in this context compared to a parallel-group trial, specifically addressing the concept of 'within-patient' versus 'between-patient' variability.

Key Response

A crossover design allows each patient to serve as their own control, significantly reducing the impact of inter-individual variability (noise) and increasing statistical power. This allowed the researchers to definitively demonstrate the superiority of spironolactone with a relatively small sample size (n=335), as it directly compared the same biological system's response to four different interventions.

Journal Editor

While PATHWAY-2 is a landmark trial, a critical reviewer might note the potential for 'carry-over effects' in a crossover design. How did the investigators mitigate this risk, and does the 6-week treatment cycle provide sufficient duration to assess the 'true' steady-state blood pressure lowering effect of these medications?

Key Response

Reviewers would flag the 6-week cycle as potentially short. However, the investigators utilized a 'washout' period or relied on the fact that most antihypertensive effects stabilize within 4 weeks. Editors must determine if the lack of a prolonged washout between active cycles could bias the results in favor of the more potent, long-acting agent (spironolactone), though the randomized sequence of the crossover helps mitigate systematic bias.

Guideline Committee

Based on the PATHWAY-2 findings, should clinical guidelines for resistant hypertension be updated to specify MRAs as the mandatory fourth-line agent (Class I, Level A), and how does this evidence reconcile with the 2017 ACC/AHA guidelines regarding 'Step 4' therapy?

Key Response

The 2017 ACC/AHA guidelines already recommend spironolactone as the preferred fourth-line agent (Class I, Level B-R). PATHWAY-2 provides the high-quality, randomized evidence to potentially elevate this to Level A. The committee must decide if the trial's specific population (mostly European) and the use of home BP monitoring are generalizable enough to mandate this across all demographics and clinical settings.

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