Medical history data was frequently redacted in the trial datasets to maintain patient confidentiality, and even when provided, different terminologies were used. In contrast, all the trials providing data on concomitant medication used the World Health Organization Anatomic Therapeutic Chemical (WHO-ATC) system, the de facto standard for drug coding in clinical trials [24 ]. We therefore used concomitant medication data to identify 21 comorbidities in both the trial and community datasets.
Trials either reported the ATC codes directly or reported preferred terms often along with the drug route. In the latter case, we used RxNorm (the US drug metathesaurus) [25 ], the UK British National Formulary [21 ] and manual review to assign ATC codes. Trial concomitant medications were defined as any drug started on or before the randomisation date.
For the community sample, we used the NHS Business Authority ATC to Read code lookup table (as processed by the OpenPrescribing project) [26 ]. For drugs not found in the lookup table, we manually mapped Read code-defined drugs to ATC codes. Any drug prescribed during 2011 was included.
The following comorbidities (detailed in Additional file4 ) were identified based on medication use: cardiovascular disease, chronic pain, arthritis, affective disorders, acid-related disorders, asthma/chronic obstructive pulmonary disease, diabetes mellitus, osteoporosis, thyroid disease, thromboembolic disease, inflammatory conditions, benign prostatic hyperplasia, gout, glaucoma, urinary incontinence, erectile dysfunction, psychotic disorders, epilepsy, migraine, parkinsonism and dementia. These drug-based definitions were developed in consultation with a steering committee comprising clinicians, epidemiologists and statisticians and were finalised before the analysis of the primary care data.
For each patient/participant, and within each index condition, we summed the number of individual comorbidities, not including the index condition, to obtain a comorbidity count.
Trials either reported the ATC codes directly or reported preferred terms often along with the drug route. In the latter case, we used RxNorm (the US drug metathesaurus) [25 ], the UK British National Formulary [21 ] and manual review to assign ATC codes. Trial concomitant medications were defined as any drug started on or before the randomisation date.
For the community sample, we used the NHS Business Authority ATC to Read code lookup table (as processed by the OpenPrescribing project) [26 ]. For drugs not found in the lookup table, we manually mapped Read code-defined drugs to ATC codes. Any drug prescribed during 2011 was included.
The following comorbidities (detailed in Additional file
For each patient/participant, and within each index condition, we summed the number of individual comorbidities, not including the index condition, to obtain a comorbidity count.
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