Cost Utility Study Shows Value of Aggressive Antiemetic Use

LONG BEACH, Calif-Cost utility studies are in their infancy and can yield very different results if incorrect assumptions about utility scores are made. For example, two different analyses of the same cost utility data suggested that the cost of a 5-HT3 antagonist in patients receiving emetic chemotherapy is either $4,000 per quality-adjusted life year (QALY), or 10 times that much.

Speaking at the 1995 Quality of Life symposium, sponsored by St. Mary Medical Center, Steven Grunberg, MD, explained how these two disparate figures were reached, with a step-by-step review of the specific calculations that were involved.

Zbrozek et al, through a literature review, estimated a 25% reduction in vomiting with use of ondansetron (Zofran), compared with metoclopramide, at an estimated additional cost of $56 per chemotherapy cycle for a 70-kg patient (Am J Hosp Pharm 51:1555-1563, 1994).

In their cost utility analysis, they made two assumptions with which Dr. Grunberg disagreed. They assumed that the 25% decrease in emesis with use of ondansetron accounted for only a 0.05 unit improvement in utility score (utilities are measured on a scale of 0 to 1 with 0 representing death and 1 representing perfect health).

In calculating QALY, they compounded this error, in his view, by assuming that the period of risk for change in utility was just the single day that chemotherapy was administered (0.05 × 1/365 = 0.00014 QALY), leading to an unacceptably high cost utility ratio of about $400,000 per QALY ($56/0.00014).

Using $80,000 per QALY as a benchmark for a worthwhile intervention, the cost of ondansetron calculated in this way would be too expensive, he said.

Dr. Grunberg and his colleagues at the Univerity of Vermont College of Medicine, Burlington, came up with a much lower figure using data they presented at the ASCO meeting in Los Angeles.

They studied 31 patients coming to their clinic for a cycle of chemotherapy later than the first cycle. "We wanted patients who could look back on a previous cycle of chemotherapy for comparison," he said.

They asked only two questions, to be answered using a visual analogue scale (1 to 100 mm): Considering the 1 month since your last chemotherapy, how would you rate your overall quality of life during that time (1) if you had had no nausea or vomiting (ie, antiemetic protection) or (2) if you had had three vomiting episodes on day 1, followed by 3 days of nausea (ie, antiemetic failure)?

The researchers found a median score for quality of life without vomiting of 88 mm vs 20 mm with vomiting--a better than fourfold improvement with effective antiemetic therapy. When the visual analogue score range (0 to 100 mm) was converted to a utility score range (0 to 1), they found an incremental improvement without vomiting of 0.68 unit.

Assuming that ondansetron reduces vomiting by 25%, an appropriate incremental utility score for this study would be 0.17 unit (0.68 unit × 25%), rather than the 0.05 unit improvement in Zbrozek's study. For the time period, Dr. Grunberg used an entire 6-month chemotherapy cycle, rather than a single day of chemotherapy once a month. The appropriate calculation would then show 0.085 QALY (0.17 × 0.5 year).

Using this estimate of incremental improvement in quality of life, the incremental cost for the use of ondansetron in the Vermont study population would only be about $4,000 per QALY ($56 × 6 months = $336/0.085), "an amount that would be considered extraordinarily inexpensive for this level of gain and would suggest significant value for aggressive antiemetic intervention," he said.