I have worked in a vet compounding pharmacy for the past 23 years and I make all of our master formulas, powders being my specialty. I’ll see if I can explain why you could have a variance as powder can be tricky as people have mentioned - they can settle and compact during transport and are not the most accurate dosing form which is why most human medications are not loose filled powder in a jar. If its a powder, they are in single dose packages like NeoCitran (we had a machine at our pharmacy that did this and it was the most accurate way to get a powder, but then vets complained about waste of packaging so we do not offer this anymore).
I can not speak about the pharmacy that you were speaking with, but that is an odd way of compounding a powder (and we do not have to put weights on our jars, and we do not as it can change from batch to batch and that info is irrelevant - you just need to know the dosing, which in your case is 60 scoops. If it was dosed by weight, as in you have to give 1g, then the weight of the jar would have to be on the label. I’m also in Canada and I know US laws are different and from State to State - we used to own a few pharmacies in the US as well and I did a lot of their formulations as well, so I am somewhat knowledgeable on some US laws/regulations - though we sold the company many years ago so I’m a tad out of touch now).
For any powder, you need what we call fill weights for each ingredient. You need to find out how much “room” each item takes up in a scoop. To use miso as an example, if 100% drug (API) in a tsp weighs 2.5g and 100% filler in a tsp weighs 5g, this is how we would determine how much of each ingredient is needed.
For 100 tsp of miso at 1000mcg/scoop:
100 tsp x 1000mcg = 100,000mcg or 0.1g (100,000mcg/1000 = 100mg/1000 = 0.1g - its easiest to work in g)
0.1 / 2.5 (so wt of API in g /full tsp wt of API) = 4% so the API (miso) takes up 4% of room in a tsp.
Then we try to figure out how much room is left in a tsp for the filler:
100 (so 100 % of a tsp) - 4% (room API takes up) = 96% (this tells us there is 96% of room left in the tsp for the filler)
100 tsp x 96% x 5g (wt of filler) = 480g of filler needed for 100 tsp.
So in this case a tsp of miso 1000mcg would weigh 4.801g (you take 480g of filler + 0.1g of API and divide that by 100 tsp to get 4.801g/tsp). Each final 100 tsp jar would weigh 480g + 0.1g = 480.1g
So technically these calculations can change from batch to batch depending on the fill weights. If you get a new API in and a tsp fill weight changes from 2.5g to 3g, it makes a difference and you would need more filler. We keep track of each manufacture lot # and perform new fill weights of each material as they come in. You would be surprised on how different each lot # can be. You could easily have a final fill weight of 100tsp jar be 480.1g one time and the next time you order, it an be 450g, all dependent on fill weights of the materials involved.
It also really depends on how each person “scoops” as well. I can take a light scoop and it can weigh 5g, but someone with a heavier hand and scoop of the same material can have a weight of 6g. We train at our pharmacy a similar way to scoop while obtaining fill weights, but its not a perfect system. It also depends on how you “scrape” off the final scoop. We have directions on our jars to show how to dose, but again, its dependent on so many things.
A tad confusing, but hope this helps!
