Studying co-medication patterns: the impact of definitions.
OBJECTIVE
To show the necessity of distinguishing several patterns of drug prescribing that may lead to co-medication. It is demonstrated how these different patterns can be investigated using large databases containing pharmacy data or reimbursement data.


METHODS
Two examples illustrate how the particular pattern of co-medication studied will influence the reported proportion of patients having co-medication, the use of antidepressants among people using anticonvulsants, and the use of antihistamines among people receiving penicillines.


RESULTS
Depending on definition and period considered, the percentage of anticonvulsant users co-medicated with antidepressants ranged from 5.8% (95%CI 5.0%, 6.8%) to 14.5% (95%CI 13.2%, 15.9%) in 2000. Comparing 2002 with 2000, the ratio of proportions ranged from 1.3 to 2.1. The percentage of people who received penicillines and were co-medicated with antihistamines ranged from 0.5% (95%CI 0.4%, 0.6%) to 9.7% (95%CI 9.3%, 10.2%) in 2000. Comparing 2002 with 2000, the ratio of proportions ranged from 1.2 to 1.6.


CONCLUSIONS
The co-medication patterns investigated yielded clinical as well as statistically significant different estimates. The estimates differed up to a factor 2.5 for the drugs usually prescribed for long periods, and a factor 12 for drugs prescribed for short periods. Hence, we propose to distinguish the patterns 'co-prescribing', 'concomitant medication,' and 'possibly concurrent medication.' The research question determines the co-medication pattern of interest, and the drug and disease under study determine the time window.
Tobi
Hilde
H
Department of Social Pharmacy, Groningen University Institute for Drug Exploration, Pharmacoepidemiology and Pharmacotherapy, Groningen, The Netherlands. hilde.tobi@wur.nl
Faber
Adrianne
A
van den Berg
Paul B
PB
Drane
J Wanzer
JW
de Jong-van den Berg
Lolkje T W
LT
D000293:Adolescent; D000328:Adult; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D000927:Anticonvulsants / Q000627:therapeutic use; D000928:Antidepressive Agents / Q000627:therapeutic use; D002648:Child; D003157:Community Pharmacy Services / Q000706:statistics & numerical data*; D011307:Drug Prescriptions / Q000706:statistics & numerical data; D004363:Drug Utilization / Q000706:statistics & numerical data / Q000639:trends; D005240:Feasibility Studies; D006634:Histamine H1 Antagonists / Q000627:therapeutic use; D006801:Humans; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D010406:Penicillins / Q000627:therapeutic use; D017891:Pharmacoepidemiology / Q000379:methods / Q000592:standards*; D019338:Polypharmacy; D010818:Practice Patterns, Physicians' / Q000706:statistics & numerical data / Q000639:trends*; D009626:Terminology as Topic; D013997:Time Factors
D000900:Anti-Bacterial Agents; D000927:Anticonvulsants; D000928:Antidepressive Agents; D006634:Histamine H1 Antagonists; D010406:Penicillins