Some studies have investigated whether promotion affects overall consumption or sales of medicines. There are several ways to do this. Some studies have simply observed changes that occurred before, during or after promotional activities96,126-129. These studies are relatively simple and inexpensive but can provide quite convincing evidence if appropriate study periods are chosen and sales or consumption data are available. Other studies have used econometric modelling to investigate the relationship between promotion and sales over time130-132. These methods are so complex and sophisticated that it is hard for non-econometricians to judge whether the models are appropriate. Some studies in this area look at levels of promotion and sales of a range of drugs133-134. These cannot separate effects of promotion on sales from effects of sales on promotion.
That is, they ignore the fact that companies may heavily promote their most popular drugs because the robust sales have enabled them to pay for more promotion. In theory it is more likely that the relationship between promotion and sales is not a one-way causation link but a two-way negative feedback loop - more promotion leads to higher sales which leads to more promotion.
Cleary’s small study126 looked at what happened when the level of promotion varied naturally over time, when a sales representative was away on a sales training course. He examined trends in numbers of new prescriptions for three third-generation antibiotics in one hospital. He found that when the sales representative was away the numbers of new prescriptions for this product dropped. This did not happen to the other products studied, and there was no correlation between the pattern in this hospital or regional or national sales. This study has the advantage of avoiding any effect of sales on promotion: i.e., the change in level of promotion was not a result of changes in the level of sales. Similarly Dieperink and Drogemuller127 report their investigation of the reasons for a dramatic increase in the use of an atypical antipsychotic agent in their Minneapolis hospital. The most plausible explanation for this was a Grand Rounds presentation sponsored by the manufacturer of the product.
A small study reported in a letter to the Lancet by Suresh et al.135, suggests that useful medicines may be relatively under-utilised if they are not promoted. They describe the under-use of adenosine, an effective first-line treatment for supraventricular tachycardia, until it started to be marketed commercially in 1991. The medicine was available and cheap, and there was good evidence of its usefulness, but it was underused until an advertising campaign was carried out.
Stern128 examined the number of visit to doctors where topical tretinoin was prescribed, and the number of articles in the popular press and medical publications discussing its use. In 1988 a highly publicised study suggest that topical tretinoin improved the appearance of aged skin, and it was prescribed at an increasing number of consultations in the USA after this. Most of these prescriptions were probably for the unlabelled unapproved use of tretinoin to treat the effects of aging. Stern’s time series data are sporadic but, like Cleary’s and Suresh’s work, the paper suggests a link between promotion and overall sales.
Eichner and Maronick129 analysed correlations between sales, expenditure on DTCA and patient visits to doctors for four groups of medicines between 1996 and 1998. They concluded that DTCA campaigns had variable success, and that factors other than DTCA (such as product characteristics and other marketing efforts) were important in determining sales levels. However, that DTCA did seem to increase patient visits to doctors for advertised conditions.
Mackowiak and Gagnon130 used econometric modelling to investigate the relationship between promotion and demand for medicines. They looked at diuretics and benzodiazepines from 1977 to 1981, to investigate how overall expenditure on promotion, and individual company promotional expenditure affected demand for a group of medicines (i.e. overall market size), and how individual company promotional expenditure affected demand for a particular drug (i.e. market share). They used IMS data on the extent of sales representative activity and the extent of journal advertising, and converted these into estimates of expenditure. Advertising agency fees were not included and this seems a significant omission. IMS also provided data on the number of new prescriptions for the products studied. Using ARIMA (Auto Regression Integrated Moving Average) modelling, they could find no relationships between promotional expenditure and demand in any of the three areas outlined above. They suggest that this may be due to limitations of the methodology, or it could suggest that companies are spending so much on advertising that they are getting little marginal return for extra dollars spent. Although this study clearly has methodological limitations (such as the choice of two drugs whose markets were not very dynamic in the period studied), it seems to make a minimum of unwarranted assumptions.
In another econometric study, Basara131 looked at the impact of a campaign of DTCA on sales of a new medicine. She used a quasi-experimental, interrupted time-series research design, comparing the number of new prescriptions before, during and after a real-life DTCA campaign. The paper includes a very long description of the complex analytical method used. Basara concluded that the campaign significantly increased the number of new prescriptions for the product. This effect appeared immediately and then tapered off over the campaign. The number of new prescriptions decreased after the campaign ended. Basara is an employee of Rhone-Poulenc Rorer Pharmaceuticals.
Similarly, using data on expenditure on advertising (from Competitive Media Reporting) and prescribing (from the National Ambulatory Medical Care Survey), Zachry et al.132 found positive correlations for some medicines and classes, but not for others. They based quasi-experimental time-series techniques. There were significant positive relationships between advertising expenditure and the number of prescriptions written for Zocor and Claritin, but a negative relationship between advertising for acid-peptic disorder medications and prescriptions for Zantac.
Krupka and Vener133 compared advertising in the New England Journal of Medicine and the Journal of the American Medical Association (JAMA) in 1972, 1977 and 1982, with the number of prescriptions filled for the 15 most advertised drugs in 1972, 73, 77, 78, and 82. They found that about a fifth of the 15 most advertised drugs were also one of the leading 15 drugs in terms of the number of prescriptions filled for the five years analysed. Ten of the 15 most advertised drugs in 1972 had advanced their ranking in terms of prescription numbers between 1972 and 1973, and two were in the same position. Dajda134 plotted the number of advertisements received in three GP practices in Swansea by therapeutic group, and the number of prescriptions written for drugs in these groups. He found a high correlation.
The ideal way to investigate this area would be, as Mackowiak and Gagnon suggest130, to ask manufacturers to experimentally vary promotion over regions and times, monitor the effect of this and publish the results. It is possible that pharmaceutical companies have done many such studies but not published them. In the absence of such data, the published studies do provide considerable circumstantial evidence for a positive, but not always consistent, association between promotion and overall sales.
CONCLUSION: Increased promotion is usually associated with increased sales.