I have recently spent some time in the Hazardous Drug space and have encountered another instance in which it seems to me that we pretend to achieve levels of precision which seem unlikely. Specifically, I have looked at dosing per square meter of Body Surface Area (BSA).
There is a BSA Calculator that shows my BSA (ok... I'm old... and a bit overweight) from 8 different formulas that range between 1.93 m2 and 2.1 m2. That doesn't seem like much until you start looking at the dosing. If you take the standard dosing for Fluorouracil (2400 mg/m2), that means that a dose for me ranges somewhere between 4,632 mg and 5,040 mg (over 400 mg difference) depending on which formula you use.
This isn't original with me, by the way. Back in 2012 I had the opportunity to meet the person from Scotland (it may have been James Baker) who had published on dose banding, and he informed me that his thinking was driven first and foremost by the ranges of doses that could arise for the same patient depending on the BSA estimation formula being used. The resulting dose banding generated improved throughput in the outpatient clinics and a reduction in waste. That meeting was in Belfast, Northern Ireland, and we sat at the same table on the (mocked up) deck of the Titanic.
It gets even more interesting if one then tries to talk about measurability. These highest and lowest doses for me represent 92.64 mL and 100.8 mL of 50 mg/mL Fluorouracil, respectively. Presuming that one could convince oneself that they had accurately measured these doses (we don't have any manual tools that will measure these amounts to two places behind the decimal), the syringes we use measure at best at ±4% which means that we are somewhere between 88.9 mL and 98.2 mL for the lower number and between 96.7 mL and 104.8 mL for the larger number. One wonders if the outcome would be different if the dose was 4800 mg (96 mL) which is at least more reliably measurable and well within the range of doses that might occur based on calculations to the last digit.
This isn't really about dose banding, though it is probably a derivative of the issue. I just continue to wonder why we push ourselves to artificial levels of precision when we do not know that such precision is required or effective or even achievable.
What do you think?
As always, the thoughts in this blog are my own, and not necessarily those of anyone else, including ASHP.
Dennis A. Tribble, PharmD, FASHP
Retired
Ormond Beach, FL
tribbledennis@gmail.com