Wednesday, April 11, 2007

The week after Easter

In the run up to Easter normally sane people go a bit crazy, just because the GP surgery is going to be closed for four consecutive days. So it's fair to say that it's quite a busy week. Things normally calm down after easter - not for me though, this week has been even busier than last week.

Today has been interesting shall we say. Firstly I had to deal with a dispensing error made by one of the pharmacists who was covering me on my week off. Zispin 30mg had been given instead of 15mg, so the patient had been taking double the dose she should have been for about a week. Unsurprisingly she had been a bit drowsy, but I managed to sort things out for her. I then had a patient in with a subconjunctival haemorrhage. These look spectacular, but in most cases aren't anything to worry about. I've had one myself - I won't go into details but it involved contact lenses and alcohol.

I've also bent the rules a few times today. Firstly I did a medicines use review with the daughters of a patient. MURs are supposed to be done with the patient, but this patient was housebound and the daughters are in and out everyday anyway so are up to speed with what's going on. Next I dispensed some out of date medicines, intentionally. I had a prescription brought in for a lady who has not got too long left. It had diamorphine (heroin) and hyoscine on it. In terminally ill patients hyoscine is used to reduce respiratory secretions ('death rattle'). So it's something that is needed fairly quickly. I didn't have any in stock, but one of the other pharmacies near by did. The only problem was it went out of date a few days ago. Damn. I really didn't want to leave this lady overnight without the hyoscine. So I phoned the manufacturers who at least confirmed there were no toxic products produced when hyoscine degrades. Of course the manufacturer came out with their standard line of 'we don't recommend you use the product after the expiry date.' Well I know this, but I don't really have much choice at the moment do I?

Monday, April 09, 2007

Reporting of benefits

I had an interesting study week on the diploma course I'm doing. One of the things we did during the week was to pick a couple of papers to pieces and look at how they discussed the results.

There are several ways the results of a study can be discussed. Obviously you have the raw numbers, but they are difficult to compare between studies. The three main ways of reporting the benefits of a treatment are relative risk reduction (RRR), absolute risk reduction (ARR) and numbers needed to treat (NNT). Relative risk reductions sound impressive, and are loved by the press and drug companies but they don't actually tell you very much. So you see headlines such as 'aspirin cuts risk of dying by 25%' or 'schoolkids use of drugs doubles'. RRR tells you, as the name suggests, the relative difference between the experiemental arm and the control arm, but, to know if this matters or not you need to know the background incidence of the event. Advertising departments of drug companies and the media often either hide away the background incidence or don't tell you it at all.

Absolute risk reductions are often small, just a few percent, and don't sound particularly impressive, but they tell you infinitely more than RRRs. Again, as the name suggests the ARR tells you the absolute difference between the control and treatment arms. However it can be difficult to translate how an ARR benefits patients. This leads on to the number needed to treat. Now the NNT does what it says on the tin. It tells you how many patients need to be treated for one to benefit and NNTs are very useful in comparing treatments.

Now for some examples. What if I told you there was an easy way to double your chances of winning the lottery? It's easy, just buy two tickets instead of one. But because your chances (or risk, or probability -they all mean the same thing) are vanishingly small to start with, doubling your chances still means they are vanishingly small: they are now just 1 in 15 million compared to the 1 in 30 million before. So the ARR in this case would be absolutely tiny. But now think about a school raffle where one ticket has a 1 in 100 chance of winning. Again there is an easy way to double your chances of winning by buying two tickets instead of one, but in this case your chances have increased significantly from 1 in 100 to 2 in 100, an absolute increase of 1%. Now the NNT is easy to calculate: it's 100/ARR. So if the ARR was 2%, you would need to treat 50 patients for one to benefit.

Sounds straightforward enough? (Or maybe not, depending how well I've explained it.) Well consider the following scenario: your hospital is considering four different cardiac rehabilitation programmes. You must choose which one you will implement. Reliable evidence shows that, during a three year period:
- Programme A reduced the rate of deaths by 20%
- Programme B produced an absolute reduction in deaths of 3%
- Programme C increased patient survival from 84% to 87%
- Programme D meant that 31 people had to enter it to prevent one death.

Which one would you choose?

This was actually the basis of a study performed by Fahey et al The figures above actually relate to the same data, just presented in different ways. Unsurprsingly they found that the programme that reported the RRR was the one chosen most often for funding.

The moral of the story is this: if you want to sell a drug report the RRR. If you want to know whether the drug is actually worth the money then look at the ARR and NNT (or speak to your prescribing advisor or community pharmacist if they are good)

Ben Goldacre probably explains this kind of thing far better than I do, and there is plenty of information on his website and in his Guardian columns.

Too funny

A couple of recent stories that made me chuckle:
Holy water not that holy
Sign up to test condoms