Implications of dose rounding of chemotherapy to the nearest vial size

There are practical implications of preparing cytotoxic doses calculated to the exact milligram. The objective here was to explore the magnitude of the effect of dose rounding to the nearest whole vial strength for some newly marketed expensive cytotoxic chemotherapy agents.

Body surface areas (BSA) of 2838 adult patients presenting for chemotherapy at the Peter MacCallum Cancer Centre between May 1996 and December 2000 were calculated by using the DuBois and DuBois linear equation to two decimal places. Each individual dose of docetaxel, liposomal doxorubicin, gemcitabine, oxaliplatin and vinorelbine was calculated from the actual BSA based on the dose recommended in the approved drug product information. This calculated dose was then rounded upwards to the full next vial if the calculated dose exceeded above 50% of the next appropriate vial strength and was rounded downwards to the full previous vial if the calculated dose did not exceed above 50% of the next appropriate vial strength. Potential impacts on cost were calculated in Australian dollars for each drug for both the calculated and rounded dose on those instances where the difference was no greater than +/-5%.

The proportion of patients in whom the dose rounded to the nearest vial strength varied by not more than +/-5% was 89.5% for docetaxel, 60.4% for liposomal doxorubicin, 99.4% for gemcitabine, 34% for oxaliplatin and 56.3% for vinorelbine. The implications of dose rounding in financial terms are significant and project savings of 4-14.2%.

The judicious application of dose rounding of chemotherapy agents is possible without any negative clinical effect. It is feasible to dose round to the nearest vial for those cytotoxic agents that are available in multiple vial sizes.