title: Lithium dosing and serum concentrations across the age spectrum: from early adulthood to the tenth decade of life.
abstract: OBJECTIVE
  Little is known about how lithium should be dosed to achieve therapeutic but safe serum concentrations in older adults. In this paper, we investigate how the lithium dose-concentration ratio changes across the lifespan.
  
  
  METHODS
  This was a cross-sectional analysis of 63 current lithium users aged 20-95 years using data from McGLIDICS (the McGill Geriatric Lithium-Induced Diabetes Insipidus Clinical Study). Participants underwent blood and urine tests, including serum lithium concentrations. Multivariate analyses were conducted to evaluate potential correlates of the lithium dose-concentration ratio.
  
  
  RESULTS
  We found that between the ages of 40-95 years, the total daily dose of lithium required to achieve a given serum concentration decreases threefold (500 vs. 1,500 mg for 1.0 mmol/L). Greater age, once-daily dosing, and lower renal function (estimated glomerular filtration rate) were independently associated with a lower lithium dose-concentration ratio.
  
  
  CONCLUSIONS
  The lithium dose required to achieve a given serum lithium concentration decreases threefold from middle to old age, with this trend continuing into the ninth and tenth decades of life. In order to avoid lithium toxicity in aging patients, continued serum concentration monitoring and judicious dose reduction may be required, particularly in those patients with reduced renal function.
authors.affiliation: Department of Psychiatry, McGill University, Irving Ludmer Research and Training Building, 1033 Pine Avenue West, Montreal, QC, H3A 1A1, Canada, soham.rej@mail.mcgill.ca.
authors.forename: Soham
authors.initials: S
authors.lastname: Rej
authors.forename: Serge
authors.initials: S
authors.lastname: Beaulieu
authors.forename: Marilyn
authors.initials: M
authors.lastname: Segal
authors.forename: Nancy C P
authors.initials: NC
authors.lastname: Low
authors.forename: Istvan
authors.initials: I
authors.lastname: Mucsi
authors.forename: Christina
authors.initials: C
authors.lastname: Holcroft
authors.forename: Kenneth
authors.initials: K
authors.lastname: Shulman
authors.forename: Karl J
authors.initials: KJ
authors.lastname: Looper
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging; D018692:Antimanic Agents / Q000008:administration & dosage* / Q000097:blood; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008094:Lithium / Q000008:administration & dosage* / Q000097:blood; D008875:Middle Aged
chemical_list: D018692:Antimanic Agents; D008094:Lithium