An economic evaluation of enteric-coated and standard formulations of naproxen from a gastrointestinal perspective

Abstract

An economic evaluation was conducted to determine the direct costs associated with managing severe gastrointestinal (GI) adverse events occurring during treatment with either Naprosyn-EC or uncoated, 'standard' naproxen. The study combined data from two double blind, randomised controlled clinical studies of six weeks duration in which the two formulations were compared. The GI adverse events included in the model were described as severe: abdominal pain, dyspepsia, nausea/vomiting, diarrhoea and constipation. The clinical studies had shown that overall there were significantly fewer GI adverse events associated with Naprosyn-EC than with standard naproxen. Detailed information regarding how general practitioners (GPs) would treat severe GI adverse events was obtained from an independent survey with a sample of 105 GPs throughout the UK. The pattern of investigation for those patients referred to hospital was obtained from three consultants. Costs were combined with these data and the adverse event incidence rates, to calculate the 'hidden costs' of treatment with standard naproxen and Naprosyn-EC, ie. the cost of treating adverse events. In this model, from a general practice perspective, the average hidden cost to the NHS of treating/investigating adverse events for each patient prescribed standard naproxen over a six-week period was £12.74 compared with £3.67 for Naprosyn-EC. Adding the drug cost of six weeks' treatment, the average total shadow costs were £19.72 and £23.84, respectively. The mean difference was £4.12, in favour of standard naproxen. Modelling the direct cost of treating these five severe GI adverse events therefore shows that Naprosyn-EC costs on average £0.69 per week more than generic standard naproxen. Extensive sensitivity analyses were conducted, including varying the GP information, using Scottish instead of English prices and allowing for future inflation. A best and worst case scenario, using the extremes of the 90% confidence interval for the adverse event rates, was also used. Substantial proportions of rile extra cost of Naprosyn-EC were saved due to its lower side effect profile. In conclusion, this economic evaluation investigated the average overall cost of treating a patient with either standard naproxen or Naprosyn-EC. The drug acquisition cost of standard naproxen is less, at generic prices, than the enteric-coated formulation. However, due to the direct costs associated with treating the greater number of severe GI side effects caused by standard naproxen, the total shadow costs for the two formulations are broadly equivalent. Indirect patient costs such as patient discomfort, loss of work or inconvenience were not included in this evaluation. The cost difference between generic, standard naproxen and Naprosyn-EC would therefore appear to be a small premium to pay since the overall well-being of the patient is the main concern.