CSM thioridazine advice

Michael Wilcock

Wright and colleagues report on the impact on GP prescribing of thioridazine as a result of advice issued in December 2000 by the Committee on Safety of Medicines.1 They conducted a time series analysis and showed a significant reduction in the monthly number and cost of thioridazine prescriptions. Their paper is accompanied by a commentary on this type of before-and-after study, which does not really help the non-statistician to understand the method of analysis used. Although not subject to the same robust, high scientific standards as their paper, I prefer the interocular test (when data hit you in between your eyes).2 This test, if applied to data for GP prescribing in Cornwall and Isles of Scilly (Figure 1), tells us all we need to know about how GPs acted following this CSM urgent cascade fax. The prescribing of thioridazine dropped dramatically from over 4000 items per quarter down to less than 1000 in the space of two quarters.

Figure 1

Number of items prescribed by GPs per quarter.

References

↵
1. Wright NMJ,
2. Roberts AJ,
3. Allgar VL,
4. et al.
(2004) Impact of the CSM advice on thioridazine on general practitioner prescribing behaviour in Leeds; time series analysis. Br J Gen Pract 54:370–373.
↵
1. Erill S
(2002) Is it clinically significant? Lancet 359:1708.