Females present a higher risk of adverse drug reactions. Sex‐related differences in drug concentrations may contribute to these observations but they remain understudied given the underrepresentation of females in clinical trials. The aim of this study was to investigate whether anthropometric and socioeconomic factors and comorbidities could explain sex‐related differences in concentrations and dosing for metoprolol and oxypurinol, the active metabolite of allopurinol. We conducted an analysis of two cross‐sectional studies. Participants were self‐described “White” adults taking metoprolol or allopurinol selected from the Montreal Heart Institute Hospital Cohort. A total of 1007 participants were included in the metoprolol subpopulation and 459 participants in the allopurinol subpopulation; 73% and 86% of the participants from the metoprolol and allopurinol subpopulations were males, respectively. Females presented higher age‐ and dose‐adjusted concentrations of both metoprolol and oxypurinol (both p < 0.03). Accordingly, females presented higher unadjusted and age‐adjusted concentration:dose ratio of both metoprolol and allopurinol/oxypurinol compared to males (all p < 3.0 × 10−4). Sex remained an independent predictor of metoprolol concentrations (p < 0.01), but not of oxypurinol concentrations, after adjusting for other predictors. In addition to sex, age, daily dose, use of moderate to strong CYP2D6 inhibitors, weight, and CYP2D6 genotype‐inferred phenotype were associated with concentrations of metoprolol (all p < 0.01). Daily dose, weight, estimated glomerular filtration rate (eGFR), and employment status were associated with oxypurinol concentrations (all p < 0.01). Females present higher dose‐adjusted concentrations of metoprolol and oxypurinol than males. This suggests the need for sex‐specific dosing requirements for these drugs, although this hypothesis should be validated in prospective studies.

Objective: To conduct a review of studies evaluating the influence of body size and weight (WT) on the pharmacokinetics (PK) of drugs recommended for heart failure (HF) treatment. Data Sources: A systematic search of the MEDLINE (1946 to April 2023) and EMBASE (1974 to April 2023) databases was conducted for articles that focused on the impact of WT or body size on the PK of drugs of interest used in HF patients. Study Selection and Data Extraction: Articles written in English or French related to the aim of our study were retained for analysis. Data Synthesis: Of 6493 articles, 20 were retained for analysis. Weight was associated with the clearance of digoxin, carvedilol, enalapril, and candesartan as well as the volume of distribution of eplerenone and bisoprolol. There was no documented direct impact of WT on the PK of furosemide, valsartan, and metoprolol, although these studies were limited or confounded by the small sample size, adjustment of PK factors by WT, or the use of the Cockroff-Gault equation for the evaluation of creatinine clearance, which includes WT. Relevance to Patient Care and Clinical Practice: This review highlights and summarizes the available data on the importance of WT on the PK of HF treatment. Conclusion: Considering the significant impact of WT on most HF drugs in this review, it may be important to further investigate it in the context of personalized therapy, particularly in patients presenting extreme WTs.