Dr.GastroMayo said:

Reconstitution tip for anyone mixing dosing arithmetic from lyophilized powder: use bacteriostatic water, NOT sterile water.

Coming at Dr.GastroMayo’s question from a different direction. They are two different exemptions from the same federal requirements and they buy different things. A 503A pharmacy is regulated primarily by the state board, needs a patient-specific prescription, is exempt from CGMP, and may use a bulk substance that has a USP monograph, is a component of an approved drug, or appears on the 503A bulks list — three independent doorways. A 503B outsourcing facility registers with the FDA, is inspected on a risk basis, must comply with CGMP, may compound for office stock without a patient-specific prescription, and has one doorway to a permitted bulk substance: the 503B bulks list, or the drug shortage list.

Dr.GastroMayo said:

Reconstitution tip for anyone mixing dosing arithmetic from lyophilized powder: use bacteriostatic water, NOT sterile water.

Bacteriostatic water quality matters for dosing arithmetic reconstitution. Not all BAC water is created equal:

• Should contain 0.9% benzyl alcohol as preservative
• Must be sterile and pyrogen-free
• Should come in a sealed, intact vial
• Check expiration date — yes, BAC water expires
• Store at room temperature, protected from light

I buy from a reputable medical supply company, not Amazon marketplace sellers. The $3 savings isn't worth the infection risk from unverified BAC water.

A narrower follow-up, since the general answer is now clear:

What would you measure differently if you were starting again?

Dr.PulmRoch said:

Bacteriostatic water quality matters for dosing arithmetic reconstitution.

Peptide calculator app recommendation for dosing arithmetic: I use ReconCalc to calculate reconstitution volumes and injection doses. Eliminates math errors completely.

Input: vial size (mg), desired concentration (mg/mL), prescribed dose (mg)
Output: BAC water volume (mL), injection volume (units on insulin syringe)

A math error with injectable medication can mean underdosing or overdosing. Use a calculator every time until the math becomes second nature.

Dr.PulmRoch said:

Bacteriostatic water quality matters for dosing arithmetic reconstitution.

Ongoing cost tracking for dosing arithmetic — transparency for the community:

Monthly medication cost: $110
Supplies (syringes, BAC water, alcohol swabs): ~$8/month
Janoshik testing: ~$10/month (amortized quarterly)
Lab work: ~$50/month (amortized quarterly)
Total: ~$210/month

Compare to brand Wegovy at $1250/month without insurance. Compounded is roughly 88% cheaper for what I have found to be clinically equivalent medication.