An analysis of the interactions between individual comorbidities and their treatments--implications for guidelines and polypharmacy.
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.
Fitzgerald
Stephen P
SP
Internal Medicine, Royal Adelaide Hospital, Australia. Stephen.Fitzgerald@health.sa.gov.au
Bean
Nigel G
NG
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