Therapeutic dose is based on allowing a certain fraction of a daily dose to carry over to a daily dose of a following product.
That fraction (for example, 1/100th, 1/1000th, or 10,000th of the original daily dose) is called the safety factor.
The result of the calculation is called the Maximum Allowable Carryover (MAC or MACO).
MACO
MACO = (allowable carryover into a single daily dose of next product) x (number of daily doses in complete batch of next product)
or
MACO = (allowable carryover into a single daily dose of next product) x (batch size of next product)/daily dose of next product)
where:
TD = a single therapeutic dose
BS = the batch size of the next product to be manufactured in the same equipment
SF = the safety factor
LDD = the largest daily dose of the next product to be manufactured in the same equipment
(PDA 29)