title: An analysis of the interactions between individual comorbidities and their treatments--implications for guidelines and polypharmacy.
abstract: BACKGROUND
  With aging there is an increase in frailty and chronic disease leading to a potential increase in medication use. Most clinical trials have excluded old, frail individuals and have failed to take into account the effects of outcome interaction.
  
  
  RESULTS
  In this article we provide a mathematical model demonstrating that comorbidities, including old age, interact with therapies, reducing their effectiveness.
  
  
  CONCLUSIONS
  These findings question the validity of single disease guidelines in old persons or in persons with multiple chronic diseases.
authors.affiliation: Internal Medicine, Royal Adelaide Hospital, Australia. Stephen.Fitzgerald@health.sa.gov.au
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Fitzgerald
authors.forename: Nigel G
authors.initials: NG
authors.lastname: Bean
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging; D002908:Chronic Disease / Q000188:drug therapy; D015897:Comorbidity; D019468:Disease Management; D017408:Guidelines as Topic; D006801:Humans; D015233:Models, Statistical; D019338:Polypharmacy