One study found no link between prescribing characteristics and self-reported reliance on promotion. Hemminki117 found no differences in observed frequency of prescribing psychotropic drugs between doctors who chose journals, textbooks or commercial sources as their main information source.
However most studies have found links. Mapes99 found that doctors who reported relying on pharmaceutical industry literature were more likely to prescribe three or more drugs that frequently cause side-effects. Conservative doctors, who did not endorse the industry as a source of post-graduate knowledge, prescribed drugs that were newer, more effective and safer. This study used prescribing data routinely collected by the Department of Health in the UK. Bower and Burkett100 found that family physicians who reported relying less on sales representatives for information were likely to prescribe more generic medicines, as were residency trained doctors, and regular readers of the New England Journal of Medicine. The self-assessed ability to recognise generic drug names was also highest amongst these doctors, those who relied least on journal advertising, and regular readers of the Medical Letter. Caudill et al.101 found, among primary care doctors in Kentucky, USA, that those who rated information provided by sales representatives highly (as credible, available, and applicable) and reported using it more, chose more expensive prescribing options in response to three clinical vignettes. This study had a low response rate. The study reported in Becker et al.102 and Stolley et al.103 used self-report data on attitudes to and reliance on promotion; expert ratings of responses to questions about prescribing for certain conditions, and knowledge about certain drugs; and analysis of actual prescribing of chloramphenicol (an antibiotic that should not be widely used). They found that doctors who relied on journal articles and tended to be disdainful of journal advertisements, sales representatives and retail pharmacists as sources of information received higher ratings from the experts and prescribed less chloramphenicol. Better prescribers were more positive about generics, and gave other indications of a less positive attitude towards the industry and promotion than other doctors. A single question, about whether sales representatives were good sources of prescribing information about new medicines, produced the highest correlation with prescribing appropriateness. Berings et al.118 found that Belgian doctors in their study who felt that commercial sources of information were more important, prescribed more benzodiazepines than those who rated these sources as less important. Their prescribing was observed through the use of special prescription forms provided by the researchers.
In the Netherlands, Haayer104 presented eight case studies of hypothetical patients to GPs and asked them if they would prescribe medication for this patient, and if so, what they would prescribe. An expert panel assessed the rationality of their prescriptions. The GPs were later interviewed and asked about their use of different sources of information about medicines. Less than half (48%) of the prescribing decisions made were rated as ‘entirely rational’.
Differences between doctors accounted for more variance than differences between cases: that is, doctors seem to be more or less rational prescribers, over a range of different conditions. Haayer found that reliance on information provided by the pharmaceutical industry was negatively associated with prescribing rationality. That is, doctors who relied on promotional information wrote less rational prescriptions for the case studies than those who reported relying less on promotion.
Cormack and Howells105 surveyed GPs in the UK before and after they attended a course on benzodiazepine prescribing. Their prescribing, adjusted by their number of patients (‘list size’) and the number over 65 years of age, was also analysed using Prescription Pricing Authority data. This produced a very wide range of scores. Doctors were classified as high or low prescribers of benzodiazepines. In interviews low prescribers rated information from pharmaceutical companies more sceptically than high prescribers.
Williams and Cockerill106 in Ontario found that doctors who reported writing higher numbers of prescriptions per week had more contact with the industry (i.e. interacting with sales representatives, receiving benefits such as meals or conference fees) and were more likely than others to rate sales representatives and industry-sponsored seminars as important sources of drug information. The first result may have been partly due to higher prescribers being likely to spend more time in medical practice per week than lower prescribers. However Williams et al. note that high volume prescribers reported writing more prescriptions per patient, which adds weight to the idea that these are doctors who prescribe heavily. Another possible explanation for these findings is that sales representatives selectively target doctors who are already known to be heavier prescribers. These results are also presented in Williams, Cockerill and Lowy119.
There is also evidence that those who rely more on promotion may be older, and are earlier adopters of new drugs. Stross107 investigated the reasons for changes in the management of chronic airways obstruction between 1978 and 1983 in small community hospitals. Using chart audits he identified a significant change in management of the condition during this period. He interviewed doctors who had treated patients at these hospitals in the study years. Older doctors reported relying more on sales representatives as a source of information for changing patient management. Stross looked at decisions to adopt three types of medicines (single-agent bronchodilators, beta-sympathomimetic agents and corticosteroid aerosols). For the last two, around 35% of doctors said sales representatives were their most important source of information in decisions to adopt the drugs. Early adopters of the changes were more likely than late adopters to list sales representatives as a major source of information. This study is useful in that it relies on significant observed changes in prescribing, which the researcher identified.
Strickland-Hodge and Jepson108 compared the characteristics of the first and last 100 doctors to prescribe cimetidine in one area in the UK. Although their response rate was only 50%, they found that earlier prescribers rated commercial sources of information (sales representatives, advertisements in medical journals, direct mail, MIMS and controlled circulation journals) significantly higher as information sources than late prescribers. Early prescribers reported reading more of their direct mail than late prescribers and reading fewer journals.
Together these studies provide convincing evidence that doctors who regard promotion more highly, and report relying on it more as a source of information about drugs, prescribe more drugs, prescribe less rationally and prescribe new drugs earlier than other doctors. However they can only provide circumstantial evidence for a causal link between promotion and individual prescribing. Other doctor characteristics, such as attitudes to risk, beliefs about clinical experience and evidence, views of new technologies, and academic inclination or ability may be behind these results. For example, doctors who believe that their clinical experience is more important than scientific evidence may be less likely to respond to evidence presented in journals, therefore be more dependent on other sources of information such as promotion, and less likely to prescribe rationally (i.e., according to the evidence). Alternatively less academically inclined doctors may not read journals, may rely on advertising because it is very accessible, and may also prescribe in less than optimal ways. The main problem with these studies is that they cannot show that doctors who report relying on promotion would prescribe differently or more rationally, if they did not rely on promotion.
CONCLUSION: Doctors who report relying more on promotion prescribe less appropriately, prescribe more often, or adopt new drugs more quickly.