Thymosin alpha-1: approved dosage in Italy
Not a recommendation, not treatment guidance. This page shows only the dosing in the official product information, with sources. The dose is always decided by the doctor who prescribes the medicine. Fimea warns against using injectable peptides bought online: Fimea warning.
Source of the dosing: Zadaxin (thymosin alpha-1), summary of product characteristics (AIFA, Italy) (AIFA), date of the text 26 Feb 2026 [1]official
Zadaxin (thymosin alpha-1) is a prescription medicine authorised in Italy. According to the summary of product characteristics, its only indication is to boost the effect of flu vaccination in adults whose immune defence is weakened [1]official.
According to the summary of product characteristics, the strength of the product is 1.6 mg of thymosin alpha-1, and the medicine is given into a muscle or under the skin [1]official.
Dosing in the product information
| Product and step | Indication | Dose | Frequency | Duration | Source and level |
|---|---|---|---|---|---|
| Zadaxin (thymosin alpha-1), first vaccination | Add-on to flu vaccination in adults whose immune defence is weakened | 1.6 mg into a muscle or under the skin | Twice a week | Four weeks from the first vaccination | [1]official |
| Zadaxin (thymosin alpha-1), second vaccination | Add-on to flu vaccination in adults whose immune defence is weakened | The same dose into a muscle or under the skin | Twice a week | From week 8 (second vaccination) to week 12 | [1]official |
Evidence levels: official = official product information · A = randomised human trial or meta-analysis · B = observational human study or case series · C = animal study · D = cell or laboratory study · E = not peer-reviewed
Units: µg = microgram, written mcg in the calculator. A milligram (mg) is a thousand times larger.
Notes
According to the summary of product characteristics, the dose is calculated from body surface area, 900 µg per square metre. Its table gives doses of 1.32-1.87 mg by height and ideal body weight [1]official.
According to the summary of product characteristics, Zadaxin (thymosin alpha-1) must not be used in children [1]official.
What points the other way or is uncertain
The randomised placebo-controlled TESTS trial did not show that thymosin alpha-1 reduced deaths in 1,106 patients with sepsis. It studied a different use than the summary of product characteristics, so it says nothing about boosting vaccines [2]A.
- Thymosin alpha-1: the full substance page
- Thymosin alpha-1: why no calculator preset
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- All dose pages and calculators
Read the research yourself: sources
- Agenzia Italiana del Farmaco (AIFA). ZADAXIN 1,6 mg/ml polvere e solvente per soluzione iniettabile (timosina alfa-1), Riassunto delle caratteristiche del prodotto. AIC 028364026, SciClone Pharmaceuticals Italy. Documento reso disponibile da AIFA il 26/02/2026. AIFA
- Wu J, Pei F, Zhou L, et al. The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial. BMJ. 2025;388:e082583. PMID 39814420
- Carraro G, Naso A, Montomoli E, et al. Thymosin-alpha 1 (Zadaxin) enhances the immunogenicity of an adjuvated pandemic H1N1v influenza vaccine (Focetria) in hemodialyzed patients: a pilot study. Vaccine. 2012;30(6):1170-1180. PMID 22178096
Thymosin alpha-1 has no central EU marketing authorisation (EMA list, checked on 12 Oct 2026), so the dosing is from the summary of product characteristics published by the Italian medicines agency AIFA. It has no revision date, so the date is the one on which AIFA published it (26 Feb 2026). The document is in Italian; the translation is ours.
Content is general information about research, not medical advice. If you have symptoms, contact a healthcare professional.