Early Corrected QT Interval Changes Following First-dose Long-acting Injectable Antipsychotics: A Retrospective...

Long-acting injectable (LAI) antipsychotics improve adherence and reduce relapse, yet short-term cardiac effects during the initial dosing window remain insufficiently characterized. We examined early corrected QT (QTc) changes within 7-14 days after first LAI dose in psychiatric inpatients and tested whether changes vary by LAI type and common clinical modifiers.

We conducted a retrospective chart review of psychiatric inpatients who received their first LAI antipsychotic during admission. Electrocardiograms (ECG) obtained before LAI initiation and again 7-14 days after injection were analyzed. QTc intervals were calculated using Bazett's formula. The primary outcome was the within-patient QTc change (ΔQTc). Prespecified subgroup analyses examined differences across clinical subgroups.

Sixty-three patients had paired ECG recordings. Baseline QTc values were comparable across subgroups. Overall, QTc change after LAI injection was small and not statistically significant (418.7 ± 22.8 ms vs. 421.0 ± 25.0 ms; p = 0.323), and no patient exceeded QTc ≥ 500 ms. Modest QTc increases were observed with second-generation LAIs (p = 0.008), particularly paliperidone palmitate (p = 0.046), as well as with concomitant anticholinergic use (p = 0.024) and medical comorbidity (p = 0.034); however, absolute changes remained < 10 ms. In regression analysis (R² = 0.565), baseline QTc was the only independent predictor of post-injection QTc (β = 0.687, p < 0.001).

Early QTc changes after LAI initiation were small and not clinically meaningful. Post-injection QTc was mainly determined by baseline QTc, supporting guideline-concordant ECG monitoring without routine intensified cardiac surveillance in low-risk patients.