Dear Bluesky,

for the calculation of the MACO there are two figures missing:

-The minimum daily dosage of the contaminant (of which you found 1,12 µg/100 cm², i will call it “A”). For the calculation i will assume that the minimum daily dosage of A is 5 mgA/day of a solid dosage form.

- The maximum daily takings (or the maximum daily dosage of its active) of the “next batch” product (I will call the next product “B”). I will assume that the posology of the product indicates a maximum of “three times a day” of the next product. (in case you have the maximum daily dosage of the active ingredient of B, the maximum daily takings are that dosage divided by the active content in each dosage unit of B).

As safety factor for solids 0,001 is currently used. So if the minimum daily dosage is 5 mg A/day, a “safe” contamination is 5 mg A/day x 0,001=0,005 mg A/day. This is the amount of active A that can be taken “safely” together with the product B, both per day. So, if you can take 3 dosage units of B per day, this is the amount of A in that 3 dosage units, or, per dosage unit, (0,005mgA/day)/(3 unitsB/day)=0,00167 mgA/unitB ≡ 1,67 µA/unit B.

The batch size of B is 360 kg and the dosage unit weight 500 mg, so batch size of B in units is (360 kg/Batch B x 1000000 mg/kg)/(500 mg/unit B)= 720000 units B/Batch B.

So, if 1,67 mg A were allowed in each unit B, in one batch of 720000 units B you can have (0,00167 mgA/unitB) x (720000 units b/Batch B)= 1202,4 mg A/Batch B, being this your MACO.

This figure assumes homogeneous distribution of contaminating A in the batch of B (which is only reasonable to assume until the last step with mixing action). This contamination is taken from the surfaces of the shared equipment (67500 cm²) by the product B, so the maximum allowed contamination per unit of surface is (1202,4 mg A/Batch B)/(67500 cm²/Batch B)=0,0178 mgA/cm² ≡ 17,8 µgA/cm², and this is the limit against which you compare the contamination of 1,12 µgA/100cm² ≡ 0,0112 µgA/cm² you found.

To compare this limit with the MaxRL: (1202,4 mg A/Batch B)/(360 kgB/Batch B) = 3,34 mgA/kgB=3,34 ppm < 10 ppm.

Hope this answered your question.

Best regards

Alfred