How do I model twelve months of dulaglutide across supply routes?

This is a first order from this supplier, so I have no track record to reason from.

The units are where I keep going wrong, so please be explicit about them.

I have sanity-checked the order of magnitude and it seems right, which is not the same as being right.

How many significant figures are actually justified here?

Twelve months is 52 weekly administrations across 365 days, and on a four-week ladder from the bottom of the range about 5 steps — so roughly 20 of the 52 doses are escalation doses and 32 are at maintenance. Model it in that order and the routes become comparable: doses per year first, milligrams per dose second, cost per milligram third. Anything quoted per vial hides the second of those, which is the one that changes most between the first 20 doses and the last 32. Then add what each route charges that the other does not. A prescription route carries consultation and dispensing fees, spread across the 52 doses rather than paid once. A research route carries testing, shipping, and the material lost between them. Testing is the line most sheets omit. At one lot a quarter, a test-every-lot policy is 4 assays a year; at one lot a month it is 12. That difference is usually larger than any difference in price per milligram, and it is a policy you choose rather than a cost you are quoted. Put doses per year in the top row and derive everything under it, and the twelve-month totals compare on arithmetic instead of on presentation.

To be exact about it, this is a spreadsheet question and doing it properly changes conclusions more often than people expect.

Worked example. Supplier A: £60 for a 10 mg vial, content 96 per cent, so 9.6 mg for £60, or £6.25/mg before carriage. Supplier B: £52 for the same nominal vial, content 88 per cent, so 8.8 mg for £52, or £5.91/mg. B still wins here, but the gap has narrowed from thirteen per cent on the label to five per cent in reality.

Mechanically, carriage amortises across the order. Twenty-five pounds of carriage on one vial is £2.50/mg on a 10 mg vial; on ten vials it is £0.25/mg. That single term explains most of the case for larger, less frequent orders.

Nothing here is medical advice, and research-use compounds are not approved for human use.

Fixed-needle syringes save more peptide than most price differences do.

Put another way, wastage from expired reconstituted vials is a real line item and nobody includes it.

Independent testing costs roughly the price of one to two vials at the services this community uses. On a two-vial order that is a fifty to a hundred per cent surcharge; on a twenty-vial order it is five per cent.

To be exact about it, wastage from a reconstituted vial discarded at the end of its in-use period is a genuine cost, and it is a function of the diluent volume chosen at reconstitution rather than of anything the supplier did.

Carriage on international consignments scales sub-linearly with weight, which is the quantitative basis for order consolidation.

Larger orders are cheaper per milligram and concentrate lot risk. Price both.

edited 20 Sept 2024 by dead_volume — clarified the distinction between purity and content

The honest answer is that the cheapest headline price is frequently not the cheapest outcome.

The full calculation: (unit price + carriage share + testing share) ÷ (nominal mg × measured content fraction × (1 − dead-space and wastage fraction)). Every term after the first is routinely omitted.

Cost per milligram is the wrong metric entirely if you are optimising for confidence rather than price, and it is worth saying which one you are doing before you build the spreadsheet.

Include carriage and testing as per-milligram terms. They dominate small orders.

Testing cost per milligram falls sharply with order size, which is the main argument against very small repeat orders.

Dead-space loss is small with fixed-needle insulin syringes — a few microlitres per draw — and substantial with detachable-needle luer syringes at 35 to 100 microlitres. Across twenty draws that is up to two millilitres of solution.

Larger orders reduce cost per milligram and increase exposure to a single lot, which is a real trade rather than a free win.

Decide whether you are optimising cost or confidence before you build the model.

The short version: unit price, carriage, testing, dead-space loss and wastage. The first is the one everybody compares and rarely the one that decides it.

Change one number and it reverses: if B assays at 82 per cent, that is 8.2 mg for £52, or £6.34/mg, and the cheaper vial is now the more expensive peptide.

Independent testing prices at the services this community uses are published and are stable enough to model.

The caveat is that optimising cost per milligram optimises for the wrong thing if documentation and consistency are what you actually need.

Divide by measured content, not by label claim. That is the whole correction.

edited 22 Jul 2024 by esben_lykke — expanded the table to cover the lower concentration