Why Reta-B1 contains a proposed 20 mg thiamine component

A development strength, not a clinical prescription

Twenty milligrams is the strength at which Panacea is developing the thiamine layer — large enough to be a meaningful weekly replenishment quantity for a water-soluble vitamin with limited body reserves, small enough to sit inside a 0.5 mL reconstitution volume as a distinct lyophilised layer. It is a formulation-engineering decision that must earn its continuation through evidence, exactly like every other element of the specification.

The salt qualification

20 mg thiamine—vitamin B1—with the precise pharmaceutical salt and thiamine-equivalent basis to be declared in the final analytical specification.

Thiamine exists in several pharmaceutical salt forms with different molecular weights and properties. Until the final analytical specification is locked, this site does not equate “20 mg” with any particular salt: the number refers to the development target, and the specification will state the weighed form and the thiamine-equivalent basis explicitly.

How the inclusion must be justified

Three workstreams decide whether 20 mg survives development. Dose justification: the quantity must be argued from thiamine physiology, intake modelling and the weekly administration rhythm — not inherited from oral-supplement conventions. Route-specific safety evaluation: a subcutaneous presentation of a thiamine salt must be evaluated for the route it will actually take, including local tolerance. Measurements of thiamine status: whole-blood thiamine pyrophosphate by LC-MS/MS (healthy-adult reference intervals 101–189 nmol/L) and erythrocyte transketolase activity provide the readouts against which any replenishment claim stands or falls.

The 20 mg question, worked

A recurring skeptic question — is 20 mg injected once a week meaningful next to an inexpensive daily tablet? — has a three-part answer, and each part is stated with its limit.

• Oral, low dose. At ordinary supplement doses thiamine crosses the gut by a saturable active transporter; the pharmacokinetic literature puts the absorbed yield at roughly 4.5 mg from a 50 mg oral dose, so much of a low-dose tablet never reaches the blood.
• Oral, high dose. A passive uptake route opens at high doses and absorption rises approximately linearly up to about 1,500 mg per day, so a motivated daily oral regimen can deliver more than 20 mg per week. The oral route is therefore not capped in principle; it is capped at ordinary doses and depends on daily adherence through dosing periods in which nausea and vomiting are the signature adverse events of this drug class.
• Parenteral. Injected thiamine bypasses the gut transporter entirely, so availability is essentially complete: 20 mg per week by injection averages about 2.9 mg per day, delivered with no absorption step. Acute clinical repletion uses far larger parenteral quantities — 100 mg-class doses three times daily in the standard clinical references — but those are treatment regimens for established deficiency, not weekly maintenance. No published study has measured thiamine status on a weekly 20 mg parenteral pulse.

What would decide the question is a three-arm comparison — weekly 20 mg parenteral versus daily oral versus no supplementation — tracking whole-blood thiamine pyrophosphate against the 101–189 nmol/L reference interval together with erythrocyte transketolase activity over a full dosing course. Until such measurements exist, 20 mg remains what this page states at the top: a formulation-development strength, not an established clinical requirement.