A friend calls you from the bar. He had 6 x 12 oz beers (5.7% ABV) over 2 hours. He feels steady on his feet and not altered. He wonders if he is legally safe to drive home. If not, he wonders how long he should wait at the bar. He is a 38 yo M that weighs 80 kg. He is average weight for his height. Is there anyway to help us calculate expected blood alcohol level? Is there any standard clearance rate for alcohol? What do you tell him?
There are numerous online calculators that help us to predict expected alcohol levels:
These calculators help incorporate different factors such as person’s weight, age, and gender.
They are typically based off the Widmark formula for calculating BAC. They however are not perfect models. It is impossible to fully model how each individual person tolerates and metabolizes alcohol.
Metabolism rates typically range from 10-20 mg/dl/hr, however are not predictable. Chronic drinkers can have higher clearance rates. Large variation between individuals exist.
For this patient, his estimated BAC is 146 mg/dl. He is likely above the legal limit and should not drive. Given the inaccurate nature of these numbers and unclear clearance rates, he likely should call a cab or you could pick him up.