Cost-utility analysis
The decision tree shows the expected cost for the 6-week period as £120.07 for the co-amoxiclav arm and £193.96 for the placebo arm. Moreover, the expected utility of those in the co-amoxiclav arm was 0.986, compared to 0.969 in the placebo cohort.
\begin{equation} ICER=\ \frac{\text{COST}\left(\text{Antibiotic}\right)-COST(Placebo)}{\text{QoL\ }\left(\text{Antibiotic}\right)-QoL(Placebo)}=\ \frac{\pounds 120.07-\pounds 193.96}{0.986-0.969}=-\pounds 4403.14\ \text{per\ QoL}\nonumber \\ \end{equation}
The ICER calculated was -£4404.14 per QOL. An assumption can be made that patients’ QOL will remain stable over the course of 1 year, this gives an ICER of -£4404.14/QALY. As shown in Figure 2, the results of the analysis indicate that the activity (co-amoxiclav prophylaxis) dominates the current practice of providing no antibiotic prophylaxis (placebo). It provides greater benefit at a lower cost; thus, making it a cost-effective intervention, considerably lower than the cost-effectiveness threshold of £30,000/QALY.
Net Monetary Benefit (NMB) and Net Health Benefit (NHB): calculation of the NMB and NHB provides a means of expressing the ICER in terms of a monetary or health unit, catering for simpler interpretation. Using the NICE threshold of £30,000/QALY, the NMB is £577.34 and the NHB is 0.019 QALYs. As these values are greater than 0, the intervention is deemed to be cost-effective, subject to sensitivity analysis. The NHB of 0.019 QALYs indicates that co-amoxiclav results in a gain of 0.019 QALYs, where each QALY is valued at £30,000.