Medical or Surgical Therapy for Erosive Reflux Esophagitis: Cost-Utility Analysis Using a Markov Model

Joseph Romagnuolo, MD, FRCP(C), MSc, (Epid); Michael A. Meier, MD, FRCS(C); Daniel C. Sadowski, MD, FRCP(C)

Disclosures

Annals of Surgery. 2002;236(2) 

In This Article

Results

In our base case analysis, LNF was less expensive than omeprazole. Over the 5-year time horizon of the model, the per-patient cost of LNF was $3,519.89, compared to $5,464.87 for medical therapy. This represents an incremental cost of $1,944.98 per patient for medical therapy. QALY estimates were not significantly different among treatment arms: 4.335 and 4.350 for LNF and medical therapy respectively, which equates to a difference of less than 1 "healthy day" over 5 years ( Table 4 ). This corresponds to an incremental cost for medical therapy of $129,665 per QALY gained. We performed sensitivity analyses to test the robustness of the baseline assumptions and to determine thresholds (Figure 2, Figure 3, Figure 4). One-way sensitivity analysis demonstrated that the model's conclusions were most dependent on the values of three variables: the cost of medical therapy, the cost of surgery, and time.

A one-way sensitivity analysis comparing the two treatment options as they vary with the cost of omeprazole (medical therapy: dashed line; surgery: solid line). The threshold (point at which both therapies have equal expected costs) is $38.60/mo. The vertical dotted line represents the cost used in the model ($68.65).

A one-way sensitivity analysis comparing the two treatment options as they vary with the cost of surgery (medical therapy: dashed line; surgery: solid line). The threshold is $5,296.40. The vertical dotted line represents the cost used in the model ($3,091).

A one-way sensitivity analysis comparing costs of the two treatment options as they vary with time (medical therapy: dashed line; surgery: solid line). The threshold is 3.1 years or 12.2 cycles. At 5 years, surgery is the less expensive option.

The results of the Monte Carlo simulation based on 10,000 patients are summarized in Table 5 and Figure 5. Using the Monte Carlo simulation, the 95% interpercentile range for the cost of the medical therapy strategy was $1,912 to $8,628, and the distribution was trimodal, with the largest mode between $4,000 and $5,000, a second smaller one between $7,000 and $8,000, and the smallest between $1,000 and $2,000. This likely reflects the three maintenance dosing possibilities modeled (20, 40, or 60 mg/day omeprazole). which over time have diverging cost trends. The corresponding interval for the surgical arm was $3,091 to $9,548; this distribution was skewed toward lower values, with outliers (a second mode in fact) corresponding to those patients who suffered complications, at $9,000 to $10,000. For utilities, the 95% interpercentile range for medical therapy was 1.48 to 4.73 QALYs; for the surgical arm, it was 1.23 to 4.73 QALYs.

This histogram displays the distribution of possible 5-year costs, using the Monte Carlo simulation of 10,000 hypothetical patients, of the two arms of the model.

The intervals resulting from Monte Carlo simulations must be interpreted with caution as they are a result of a mathematical simulation taking into account the variables and ranges included in the model, for which the distributions are not well known, and may not accurately represent the true variability in the general population. However, based on the results of this analysis, surgical therapy appeared less costly than medical therapy. There was no clinically important difference in quality of life, estimated by QALYs.

Figure 2 depicts the results of a one-way sensitivity analysis on the cost of medical therapy. The monthly cost of omeprazole would have to be reduced to less than $38.60 before medical therapy would become the cheaper option, and to $38.80 before it became cost effective. Likewise, our analysis of the surgical arm suggested that the cost of LNF would have to rise higher than $5,296.40 before the medical option would be the less expensive strategy and $5,273.70 before it became cost effective (see Fig. 3). Because the predominant cost driver of surgical procedures in Canada is the length of hospital stay, we performed a separate one-way analysis on this variable. As the length of stay rose beyond 4.2 days, or the cost of one day in the hospital rose above $1,857, medical therapy became the superior option. A one-way analysis using time as the dependent variable demonstrated that the initial costs of the surgical procedure were recouped after 3.1 years when compared to the medical arm (see Fig. 4), and the cost-effectiveness ratio began to become superior after 3.3 years.

Figure 6 presents a two-way sensitivity analysis illustrating simultaneously the relationship between time and monthly medical costs. This allows one to plot local drug costs and expected maintenance time. For example, if the drug costs were expected to be $40/month and 2 years of medical maintenance therapy were anticipated, medical therapy would then be less expensive than LNF. Other variables, including the cost of endoscopy, office visits, and drug dispensing fees, appeared to affect both strategies equally and therefore did not influence the conclusions of the model.

A two-way sensitivity analysis, simultaneously examining the effects of omeprazole costs and anticipated duration of medical therapy on overall costs of the two strategies. The shaded area under the line highlights the coordinates that correspond to conditions where medical therapy would be the less expensive option. Coordinates falling above the line correspond to conditions for which surgery is the less expensive option.

As LNF is a relatively new therapeutic intervention, the long-term efficacy has yet to be firmly established. In our base case analysis, we assumed a failure rate of 5.5% over 5 years (failure defined as the return of reflux symptoms requiring the use of maintenance omeprazole therapy at any dose). However, several other reports have suggested that the failure rate may be as high as 5% to 10% per year (see Table 1 ).[69,74,75] Therefore, our sensitivity analysis used a maximal failure rate of up to 10% per year. At this rate, the 5-year costs for LNF would be $4,030.16. Nevertheless, the annual failure rate for LNF would have to rise above 37% per year before medical therapy became the less expensive option. However, as one would expect, at this failure rate, the utilities for LNF drop approximately linearly to 4.24 QALY. As expected, the utilities associated with quality of life were most sensitive to the long-term effects of postoperative symptoms and daily medication use. A rise above 3% in the annual LNF failure rate would cause the quality of life utilities to become correspondingly less favorable.

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