To describe prescription patterns, dosing and persistence of guideline-directed medical therapy (GDMT) among patients with heart failure with reduced ejection fraction in Singapore, and to identify factors associated with the use of quadruple therapy (ACE inhibitor (ACEi)/angiotensin II receptor blocker (ARB)/angiotensin receptor-neprilysin inhibitor (ARNI), β-blocker, mineralocorticoid receptor antagonist (MRA) and sodium-glucose cotransporter-2 (SGLT2) inhibitor).

Retrospective, observational cohort study.

Secondary and tertiary care settings across seven public hospitals in Singapore.

3999 adults hospitalised from 2020 to 2022 with a first heart failure-related admission and left ventricular ejection fraction ≤40%. Patients with absolute contraindications to specific GDMT classes were excluded from eligibility calculations.

Primary outcomes were the proportions of eligible patients prescribed each GDMT class and quadruple therapy at discharge. Secondary outcomes were 6-month prescription patterns, dose attainment and predictors of quadruple therapy use.

Among eligible patients, 80%–99% met criteria for each GDMT drug class, yet only 29% received quadruple therapy at discharge in 2022. Prescription rates for ACEi/ARB/ARNI (67%), beta-blockers (89%), MRAs (40%), and SGLT2 inhibitors (46%) remained suboptimal despite high eligibility. At discharge, over 90% of patients on ACEi/ARB/ARNI and beta-blockers received ≤50% of target doses. By 6 months, prescription rates declined by 16% for ACEi/ARB/ARNI, 26% for beta-blockers and 7% for MRAs, while SGLT2 inhibitor use increased. Older age (OR 0.97, 95% CI 0.96 to 0.98) and chronic kidney disease stage 3a–4 (OR 0.65 to 0.04) were associated with lower odds of receiving quadruple therapy, while significant institutional variation was observed.

Despite high eligibility, uptake and optimisation of GDMT remain poor in Singapore, with substantial treatment gaps driven by underprescription, inadequate dosing and discontinuation. Interventions targeting clinician awareness, postdischarge support and institutional practice variation may improve adherence to guideline-recommended therapy.