In the news recently has been the new drug evolocumab (a PCSK9 inhibitor for the doctors amongst us which is sold as a monthly injection under the brand name Repatha) with most of the focus on the Number Needed to Treat (“NNT”) figure. Evolocumab is the next iteration of the statin type drugs designed to reduce the prevalence of heart attacks and strokes which still cause around 22% of deaths.
The NNT shows how many people the scientists need to treat in order to prevent one of the incidences. For evolocumab this amounts to one less heart attack or stroke for every 74 people over two years. This initially does not sound that impressive. Until we find out that the NNT for statins is 400 and we know that the increased prevalence of statins has contributed significantly to recent mortality improvements in the UK.
Around 40% of pensioners in the UK are currently prescribed statins. Heart attacks are particularly deadly with around 30% of people who have a heart attack every year dying.
A “typical” male pensioner aged 71 would have a probability of dying in the next year of around 1.4%.
Were the NNT for evolocumab to be correct, we could assume that 40% of all pensioners to be prescribed evolocumab (i.e. the same prevalence as statins - likely to be a significant exaggeration) and if 30% of heart attack or stroke victims to die then this would lead to a 6% improvement in the pensioner mortality rate. Were such an improvement to be observed then the cost of pensions would increase by 2%. A massive change from a single drug.
Of course it is most likely that the prevalence of evolocumab will be lower than for statins not least because most people in the UK rely on the NHS and evolocumab is expected to cost around £10 per day per person (compared to 10p a day for statins). The cost to the NHS of each death prevented is, at a £10 per day cost and on an NNT of 74 for two years, unfortunately around £1.8 million.
Mortality improvements have slowed in recent years based on population data with a total reduction in mortality rates of around 5% over the past five years. If only 35% of pensioners end up on evolcumab this adoption rate would generate the same level of mortality improvement for the typical pensioner as the improvement in population mortality over the last 5 years. Of course if very few of the population end up on evolocumab (due to the cost) or it tends to prevent the “less fatal” heart attacks then obviously the impact could be quite small.
Unfortunately this uncertainty about the impact of new medical discoveries on mortality rates only serves to demonstrate the high level of uncertainty with mortality improvement rates and the ultimate cost of any pension promises that have been made.