Thymosin alpha-1, thymalfasin by its non-proprietary name, is a 28-amino-acid peptide first isolated from calf thymus and made synthetically since the 1980s. It is the unusual case on this site: a research-market peptide that also exists as a licensed medicine, Zadaxin, sold in more than 30 countries, with a label that states a dose, a reconstitution volume and a concentration. It has no United States approval. The research vial, in 5 mg and 10 mg sizes on this site's calculator preset, holds three to six label-sized doses, and the arithmetic that converts one into the other is the subject of this page.
This page reports the label, the trials and the circulating figures with their sources and dates, and converts the sourced amounts into syringe units at every research-vial concentration. It recommends nothing. The thymosin alpha-1 calculator runs the same sums for any vial and volume, and the dosage hub indexes every compound this site covers.
What the label states
| Item | Zadaxin label |
|---|---|
| Dose | 1.6 mg, stated as 900 mcg per m² of body surface |
| Route and frequency | subcutaneous, twice a week |
| Duration | 6 to 12 months (chronic hepatitis B, alone or with interferon; chronic hepatitis C with interferon) |
| Under 40 kg | 40 mcg/kg |
| Vial | 1.6 mg lyophilized powder with 50 mg mannitol and phosphate buffer |
| Reconstitution | 1.0 mL of the sterile water supplied, immediately before use; final concentration 1.6 mg/mL |
| Storage | 2 to 8 °C before reconstitution; used immediately after |
| Not for | intravenous use |
Sources: the Singapore National Drug Formulary entry for Zadaxin injection (SIN07483P, licence holder SciClone Pharmaceuticals International (SG), manufacturers Patheon Italia and Alfa Wassermann, Italy) and the prescribing information reproduced on RxList, both read 2026-09-18. The two agree on every figure.
Two arithmetic checks sit inside the label. The dose is the whole vial: 1.6 mg in 1.0 mL is 1.6 mg/mL, and 1.0 mL is 100 units on a U-100 syringe. And the surface-area figure reproduces the flat dose: 900 mcg/m² for an adult of 1.8 m² is 1.62 mg.
Where the label applies, and where it does not
SciClone's annual report for 2004 stated that Zadaxin was approved for sale in over 30 countries, primarily in Asia, the Middle East and Latin America, that 2004 sales were $22.8 million, 91% of them to China, and that two US phase 3 hepatitis C trials of 1.6 mg twice a week for 48 weeks were fully enrolled, with a new drug application planned for 2006 (SEC filing, read 2026-09-18). No US approval followed: a DailyMed search for thymalfasin and for thymosin alpha 1 returned no record on 2026-09-18. The same report describes a 12-week dose-ranging study in 31 hepatitis C non-responders that used 0.8, 1.6 and 3.2 mg twice a week with pegylated interferon, the only published range around the label figure.
What the trials used
| Source | Amount | Route and frequency | Duration | Population and result |
|---|---|---|---|---|
| Zadaxin label (read 2026-09-18) | 1.6 mg | subcutaneous, twice a week | 6 to 12 months | chronic hepatitis B and C; a licensed dose, not a trial |
| SciClone dose-ranging study (annual report for 2004) | 0.8, 1.6, 3.2 mg | subcutaneous, twice a week | 12 weeks | 31 hepatitis C non-responders with pegylated interferon; early virologic response 20 to 36% |
| SciClone US phase 3 trials (annual report for 2004) | 1.6 mg | subcutaneous, twice a week | 48 weeks | over 500 hepatitis C non-responders per trial; no US approval followed |
| TESTS (BMJ, 2025-01-15, PMID 39814420) | 1.6 mg in 1 mL sterile water | subcutaneous, every 12 hours | 7 days | 1,106 adults with sepsis; 28-day mortality 23.4% vs 24.1%, not significant |
The counts around those rows: ClinicalTrials.gov listed 64 studies with thymalfasin as an intervention, and PubMed held 884 records with 64 tagged as randomised controlled trials, on 2026-09-18. A 2025 meta-analysis of eleven sepsis trials found a mortality benefit overall that disappeared in the high-quality and multicentre subgroups (Frontiers in Cellular and Infection Microbiology, 2025-09-03, PMID 40969554). The sepsis regimen is fourteen times the hepatitis frequency for a week; the two are different uses of the same 1.6 mg vial.
The arithmetic per research vial
Concentration in mg/mL is the vial amount divided by the water volume; units on a U-100 syringe are the amount divided by the concentration, times 100, because a U-100 syringe holds 100 units in 1 mL and each small notch on a standard 1 mL insulin syringe is 1 unit (MedlinePlus, reviewed 2024-07-21). The columns are the three published amounts.
| Vial and water | mg/mL | 0.8 mg | 1.6 mg | 3.2 mg | 1.6 mg doses in the vial |
|---|---|---|---|---|---|
| 5 mg in 1 mL | 5 | 16 units | 32 | 64 | 3, with 0.2 mg left |
| 5 mg in 2 mL | 2.5 | 32 | 64 | 128 | 3, with 0.2 mg left |
| 5 mg in 3 mL | 1.67 | 48 | 96 | 192 | 3, with 0.2 mg left |
| 10 mg in 1 mL | 10 | 8 | 16 | 32 | 6, with 0.4 mg left |
| 10 mg in 2 mL | 5 | 16 | 32 | 64 | 6, with 0.4 mg left |
| 10 mg in 3 mL | 3.33 | 24 | 48 | 96 | 6, with 0.4 mg left |
The label's own presentation, 1.6 mg in 1 mL, is the most dilute row of all at 1.6 mg/mL, where the dose is 100 units. Every research-vial mix is more concentrated than the licensed product, so every reading is shorter; only 3.2 mg at 2 or 3 mL of water in a 5 mg vial exceeds a syringe.
The figures that circulate
Clinic and vendor pages read on 2026-09-18 cited 1.6 mg subcutaneously twice a week, most often in cycles of 8 to 12 weeks with a rest of four to six weeks between them, and attributed the figure to the Zadaxin label. The amount and the frequency are the label's; the cycle is not, since the label's courses run 6 to 12 months and name no rest. A patent text quoted on some pages gives 0.5 to 4.5 mg, with 1.6 to 3.2 mg preferred, for twice-weekly use. Peptifact's thymosin alpha-1 page reads the same sources from the journalism side.
What the figures omit
The label figure carries an indication (chronic viral hepatitis), a duration (6 to 12 months), a co-treatment in one indication (interferon) and a population (adults, with a per-kilogram rule for children under 40 kg). The sepsis figure carries an intensive-care setting, a seven-day course and a null result on its primary outcome. Neither says anything about the uses the circulating pages describe, none of which appears on a label or in a registered trial that could be found on 2026-09-18. The mechanism, the evidence file and the sourcing belong to Medibact's Thymosin Alpha-1 guide.
Status in the United States
FDA placed thymosin alpha-1 in Category 2 of its section 503A bulk-substance list, the category for substances FDA says raise significant safety risks, on 2023-09-29 (list read 2026-09-18). Its Pharmacy Compounding Advisory Committee considered thymosin alpha-1 and its acetate on 2024-12-04 (Federal Register notice 2024-24828, published 2024-10-25); trade reports of that meeting, read 2026-09-18, put the committee's vote at 4 to 17 against adding the substance to the compounding list. The vote is advisory. As of 2026-09-18 no thymosin alpha-1 product is approved in the United States, and the substance was not among the seven peptides FDA sent to the same committee in July 2026 (Federal Register, 2026-04-16).
Sources and dates
Opened 2026-09-18: the Singapore National Drug Formulary entry SIN07483P; the Zadaxin prescribing information on RxList; SciClone Pharmaceuticals' Form 10-K for the year ended 2004-12-31 (SEC EDGAR); DailyMed (no record); PubMed, with the abstracts of PMIDs 39814420 and 40969554 read in full; the full text of the TESTS paper at PMC11780596 for the dose per injection; ClinicalTrials.gov v2 API (64 interventional registrations); PubChem CID 16130571 for the molecular weight; FDA's 503A category list dated 2023-09-29; Federal Register documents 2024-24828 and 2026-07361; MedlinePlus, "Giving an insulin injection" (reviewed 2024-07-21); clinic and vendor pages for the circulating figures. Vial sizes are the ones the calculator preset uses.
This page does not recommend a dose, a route, a frequency or a schedule, and it does not say what any figure means for a particular person. It reports a non-US label, two trials and a filing, and converts their milligrams into syringe units, which is the whole of what it can honestly do.