title: Patterns of Drug Use and Serum Sodium Concentrations in Older Hospitalized Patients: A Latent Class Analysis Approach.
abstract: BACKGROUND
  Several drugs may lower serum sodium concentrations (NaC) in older patients. However, distinguishing their individual effects is particularly difficult in this population because of the high prevalence of polypharmacy and disease states that are per se associated with hyponatremia.
  
  
  OBJECTIVE
  Our objective was to identify specific patterns of medication use in older hospitalized patients and determine whether these patterns were associated with serum NaC.
  
  
  METHODS
  We collected clinical and demographic data, pre-admission drugs, Drug Burden Index (DBI) score, and average NaC during hospitalization in a consecutive series of older medical patients (n = 101, mean ± standard deviation [SD] age 87 ± 6 years). We used latent class analysis (LCA) to identify specific patterns of drug use and multivariate regression to determine the associations between 14 separate drug classes, identified patterns of drug use, and NaC.
  
  
  RESULTS
  LCA revealed three patterns: lower overall drug use (class 1), anticoagulant use and higher drug use (class 2), and antiplatelet use (class 3). Mean (±SD) DBI score in each class was 2.7 ± 1.3, 3.3 ± 1.6, and 2.4 ± 1.5, respectively (p = 0.04). Mean (± SD) NaC in classes 1, 2, and 3 were 140.6 ± 6.8, 138.7 ± 5.3, and 136.5 ± 4.7 mmol/l, respectively (p = 0.006). After adjustment for age, sex, Charlson Comorbidity Index score, estimated glomerular filtration rate (eGFR), DBI score, and digoxin use, mean NaC in class 2 and class 3 was significantly lower than in class 1 (-3.9 mmol/l; 95% confidence interval [CI] -7.1 to -0.8, p = 0.01 and -5.2 mmol/l; 95% CI -7.9 to -2.5, p < 0.001, respectively). Mean serum NaC was not significantly associated with any of the 14 individually assessed drug classes. In addition to latent class, increasing age and higher eGFR were also independently associated with lower serum NaC (p = 0.002 and p = 0.03, respectively).
  
  
  CONCLUSIONS
  LCA enabled us to identify patterns of drug use associated with lower serum NaC in older inpatients. Our results suggest that older patients using antiplatelets or anticoagulants are especially at risk of lower serum NaC.
authors: Centre for Epidemiology and Biostatistics, School of Medicine, Flinders University, GPO Box 2100, Adelaide, SA, 5001, Australia.
authors: Richard J
authors: RJ
authors: Woodman
authors: School of Medicine and Dentistry, University of Aberdeen, Polwarth Building, Foresterhill, Aberdeen, AB25 2ZD, UK.
authors: Karen M
authors: KM
authors: Wood
authors: Centre for Epidemiology and Biostatistics, School of Medicine, Flinders University, GPO Box 2100, Adelaide, SA, 5001, Australia.
authors: Aline
authors: A
authors: Kunnel
authors: Department of Clinical Pharmacology, School of Medicine, Flinders University and Flinders Medical Centre, Flinders Drive, Bedford Park, SA, 5042, Australia.
authors: Maneesha
authors: M
authors: Dedigama
authors: Department of Pharmacy, Flinders Medical Centre, Flinders Drive, Bedford Park, SA, 5042, Australia.
authors: Matthew A
authors: MA
authors: Pegoli
authors: Department of Medicine for the Elderly, NHS Grampian, Aberdeen Royal Infirmary, Foresterhill, Aberdeen, AB25 2ZN, UK.
authors: Roy L
authors: RL
authors: Soiza
authors: Department of Clinical Pharmacology, School of Medicine, Flinders University and Flinders Medical Centre, Flinders Drive, Bedford Park, SA, 5042, Australia. arduino.mangoni@flinders.edu.au.
authors: Arduino A
authors: AA
authors: Mangoni