Weeks 1-4
Immune-marker changes may begin, but clinical benefit in hepatitis trials was measured over months, not weeks.
Protocol / Research Dosing Guide
Thymosin Alpha-1 Dosage Guide: Zadaxin Schedule, Reconstitution and Safety
An evidence-organized Thymosin Alpha-1 reference that separates the internationally approved Zadaxin schedule from community immune-support use that has not been tested.
Last reviewed September 16, 202617 minute readResearch information only
Level 5 — Approved abroad, not in the United StatesMultiple human trials in hepatitis and cancer adjunct settingsNot FDA approved
Thymosin Alpha-1 Quick Start
Thymosin Alpha-1 is a 28-amino-acid peptide the thymus gland naturally produces to help coordinate immune cells against viral infection. The synthetic version, thymalfasin, is sold internationally as Zadaxin and carries approvals in more than 35 countries for chronic hepatitis B, chronic hepatitis C, and as an immune-support adjunct in some cancer-care settings. It has never received FDA approval in the United States. Nearly every published dose traces back to a single core figure: 1.6 mg subcutaneously twice weekly.
Why researchers care
Immune modulation, antiviral adjunct therapy, and cancer-adjunct immune support
Class
Thymalfasin, a synthetic 28-amino-acid thymic peptide identical to naturally occurring thymosin alpha-1
Route reported
Subcutaneous injection
Cycle length
6 months for chronic hepatitis B monotherapy; up to 12 months combined with interferon for hepatitis C
Regulatory status
Approved as Zadaxin in more than 35 countries; not FDA approved in the United States and under review for the 503A bulk drug substances list
Loading supplier information
Thymosin Alpha-1 Dosing Protocol and Schedule
The supplied source reports the Zadaxin-anchored standard adult protocol of 1.6 mg subcutaneously twice weekly, spaced 3-4 days apart, for 6 months in chronic hepatitis B or up to 12 months combined with interferon in chronic hepatitis C. It also reports a labeled body-weight adjustment of 40 mcg/kg twice weekly for adults under 40 kg, and separately notes that community immune-support use of roughly 1 mg daily for 10-30 days is not drawn from any controlled trial.
| Phase or study | Amount | Frequency / evidence |
|---|---|---|
| Standard adult dose | 1.6 mg subcutaneously twice weekly, 3-4 days apart | Zadaxin clinical materials |
| Under 40 kg body weight adjustment | 40 mcg/kg twice weekly (approx. 1.2-1.4 mg) | Zadaxin professional monograph |
| Chronic hepatitis B monotherapy duration | 6 months | Pooled analysis of randomized trials |
| Chronic hepatitis C combination duration | 6-12 months with interferon | Pooled analysis of randomized trials |
| Severe sepsis protocol | Dosed every 12 hours for 7 days | Phase 3 RCT, 22 Chinese centers (TESTS, BMJ 2025) |
| Community immune-support use | Roughly 1 mg daily for 10-30 days | Community reported, not trial derived |
| Rest period between cycles | Not established | Not established |
The 1.6 mg twice-weekly figure is the only dose with a substantial, internationally reviewed clinical record behind it, and that record is for hepatitis B, hepatitis C, and cancer-adjunct settings under clinician supervision, not for general immune support. The daily community loading pattern is a separate, untested convention and should not be assumed to carry the same evidence.
Thymosin Alpha-1 Supplies Needed
Neutral research-material planning only. This does not establish an appropriate amount or route.
Research planning item
Exact labeled research vial (commonly 10 mg)
Research planning item
Bacteriostatic water at a measured volume
Research planning item
U-100 insulin syringes, 0.5 mL preferred
Research planning item
Alcohol prep swabs
Research planning item
Sharps container
Research planning item
Refrigeration for the prepared vial
Research planning item
Written concentration label with the preparation date
Thymosin Alpha-1 Reconstitution Calculator
Vial-format concentration math
Concentration
5 mg/mL
Draw volume
0.32 mL
U-100 units
32
Mathematical draws
6
Arithmetic only. The entered amount is not a recommendation and does not establish suitability.
Best Time to Take Thymosin Alpha-1: Morning or Night?
Morning or evening?
Not established by trial; the clinical schedule specifies days of the week, not time of day.
Twice weekly spacing?
Injections are spaced 3-4 days apart, for example Monday and Thursday, in the Zadaxin-anchored protocol.
With food?
Not applicable to a subcutaneous injection.
Missed amount?
No validated Thymosin Alpha-1 missed-dose procedure was identified in the sources reviewed; resuming the regular schedule is the reported practice, not a tested rule.
Thymosin Alpha-1 Route Comparison
| Format | What is reported | Evidence limit |
|---|---|---|
| Subcutaneous injection | 1.6 mg twice weekly is the clinically studied route and schedule | The only route with substantial human trial support |
| Intravenous use in sepsis trials | Dosed every 12 hours for 7 days in the TESTS Phase 3 study | Hospital-administered, not a self-injection convention |
| Oral | Not viable; a peptide of this size is degraded before absorption | No exposure data |
| Route conversion | Not established | The sepsis-trial schedule and the twice-weekly outpatient schedule are not interchangeable |
Routes and amounts are not interchangeable unless a verified study explicitly establishes a conversion.
Thymosin Alpha-1 Half-Life and Dosing Frequency
| Measure | Finding | Evidence limit |
|---|---|---|
| Reported plasma half-life | Short, reported in the range of a few hours in comparative pharmacology material | Frequency in trials was set by the protocol, not solely by pharmacokinetics |
| Why twice weekly | The twice-weekly interval is the tested clinical convention rather than a value derived purely from half-life | Route specific |
| Community daily use | Not derived from a pharmacokinetic study | Not established |
| Immune effect duration | Reported clinical benefit accrues over months of the labeled schedule, not from single doses | Biological, not pharmacokinetic |
Thymosin Alpha-1 Dosage Chart
| Route | Amount | Frequency | Source | Human validation |
|---|---|---|---|---|
| Subcutaneous | 1.6 mg | Twice weekly, 3-4 days apart | Zadaxin clinical materials | Yes, in countries where Zadaxin is approved |
| Subcutaneous | 40 mcg/kg (under 40 kg) | Twice weekly | Zadaxin professional monograph | Yes, in countries where Zadaxin is approved |
| Intravenous/subcutaneous (hospital) | Study-specified amount | Every 12 hours for 7 days | TESTS Phase 3 RCT | Investigational |
| Subcutaneous | Approximately 1 mg | Daily for 10-30 days | Community report | No |
Published study values describe those studies. Community-reported values are not validated dosing recommendations.
Thymosin Alpha-1 Reconstitution Guide
Concentration: 2.5 mg/mL
| Entered amount | Volume | U-100 units |
|---|---|---|
| 1.6 mg | 0.64 mL | 64 units |
| 3.2 mg | 1.28 mL | 128 units |
| 4.8 mg | 1.92 mL | 192 units |
- 1.Confirm the exact quantity printed on the vial, commonly 10 mg.
- 2.Choose and record the bacteriostatic water volume. 10 mg into 2 mL gives 5 mg/mL.
- 3.Clean the vial stopper with an alcohol swab.
- 4.Add the liquid slowly down the vial wall.
- 5.Swirl gently until clear; do not shake.
- 6.Inspect for cloudiness, discoloration, or particles and discard anything that is not clear.
- 7.Label the vial with the calculated concentration and the preparation date.
- 8.Refrigerate the prepared vial and use only the calculated concentration for dose arithmetic.
Reconstitution does not establish identity, purity, sterility, stability, or an appropriate amount.
How Thymosin Alpha-1 Works
Origin
Thymosin Alpha-1 is a naturally occurring 28-amino-acid peptide produced by the thymus gland.
Thymosin Alpha-1 Human Trials and FDA Status
Current status · verified September 16, 2026
Approved as Zadaxin in more than 35 countries; not FDA approved in the United States and under review for the 503A bulk drug substances list
- Pooled randomized controlled trial analyses support 1.6 mg twice weekly for 6 months in chronic hepatitis B and 6-12 months combined with interferon in chronic hepatitis C, forming the basis for Zadaxin's approvals in more than 35 countries.
- The TESTS trial, a Phase 3 randomized controlled trial across 22 Chinese centers published in 2025, tested Thymosin Alpha-1 dosed every 12 hours for 7 days in patients with severe sepsis; readers should consult the primary publication directly for the trial's efficacy findings rather than assuming a positive outcome from its existence.
- Thymosin Alpha-1 has also been studied as an adjunct in some cancer-care and vaccine-response settings, generally at the same 1.6 mg twice-weekly structure.
- No study was identified that validates the community daily immune-support pattern reported outside clinical settings.
Who Should Avoid Thymosin Alpha-1?
This is an evidence-gap and precaution list, not an approved prescribing label.
Pregnancy or breastfeeding
No adequate safety data in these populations
Organ transplant recipients or others on immunosuppressive therapy
An immune-modulating peptide may interact with the treatment goal
Autoimmune disease
Theoretical concern given its immune-activating mechanism; no dedicated safety study
Anyone substituting it for antiviral or cancer therapy
It is studied as an adjunct, not a replacement
Known hypersensitivity to the product
Standard injectable-product precaution
Long-term unsupervised community use
No safety data exists outside the studied hepatitis, cancer-adjunct and sepsis-trial contexts
Thymosin Alpha-1 Side Effects, Risks and Safety
Injection-site redness or discomfortCommonly reported in trials
Important limitation: Generally mild.
NauseaReported in some trial participants
Important limitation: Low incidence in pooled analyses.
Flu-like symptomsReported occasionally
Important limitation: Low incidence.
Effects in immunosuppressed patientsTheoretical
Important limitation: Not specifically studied outside adjunct trial populations.
Long-term safety beyond studied durationsNot established
Important limitation: Trials generally ran 6-12 months.
Drug interactionsLimited data
Important limitation: Primarily studied alongside interferon and standard antiviral regimens.
Thymosin Alpha-1 Timeline and Monitoring
6 months
The studied duration for hepatitis B monotherapy.
6-12 months
The studied duration for hepatitis C combined with interferon.
Monitoring
Trial protocols included liver function and viral load monitoring; no monitoring schedule is established for unsupervised community use.
Thymosin Alpha-1 Benefits and Results: What the Evidence Shows
| Claim | Evidence level | What research shows | Important limitation |
|---|---|---|---|
| Chronic hepatitis B | Human trials | Pooled randomized controlled trial analyses | Adjunct or monotherapy per approved label, not applicable in the US |
| Chronic hepatitis C | Human trials | Pooled randomized controlled trial analyses with interferon | Approved abroad, not applicable in the US |
| Cancer-adjunct immune support | Human trials | Studied alongside chemotherapy or supportive care | Adjunct role only |
| General immune support or infection prevention in healthy people | Not established | Community claim | No trial supports this specific use |
Thymosin Alpha-1 Storage and Handling
Lyophilized/sealed vial
Store per the product label, generally refrigerated or as specified until reconstitution.
Prepared vial
Refrigerate at 2-8 degrees C; no universal compound-specific stability duration beyond the product label was identified.
Light
Keep the vial out of direct light.
Appearance
A clear, colorless solution is expected; cloudiness or particles mean discard.
Thymosin Alpha-1 Troubleshooting
Solution appears cloudy
Discard it and do not inject; appearance cannot confirm sterility.
Unsure which schedule applies
The twice-weekly outpatient figure and the hospital sepsis-trial schedule are not interchangeable.
Calculated units look wrong
Recheck the vial quantity, diluent volume, and target dose.
Considering community daily loading
That pattern has no controlled trial behind it; the twice-weekly figure is the studied convention.
A scheduled dose is missed
No validated missed-dose procedure was identified; involve a qualified clinician for guidance.
Thymosin Alpha-1 Comparisons
| Compound | Class or mechanism | Evidence | FDA status |
|---|---|---|---|
| Thymosin Alpha-1 | Thymic immune-modulating peptide | Multiple human trials; approved abroad | Not FDA approved in the US |
| Thymosin Beta-4 (TB-500) | Tissue-repair interest peptide | Primarily preclinical | Not FDA approved |
| Interferon (standard hepatitis therapy) | Antiviral immune therapy | Extensive human trials | FDA approved |
| LL-37 | Human host-defense peptide | Early topical human trials only | Not FDA approved |
Thymosin Alpha-1 Frequently Asked Questions
What is Thymosin Alpha-1?
A synthetic version of a naturally occurring 28-amino-acid thymic peptide involved in coordinating immune responses, sold internationally as Zadaxin (thymalfasin).
Is Thymosin Alpha-1 FDA approved?
No. It is approved in more than 35 other countries and is under review for the US 503A bulk drug substances list.
What is the standard clinical dose?
1.6 mg subcutaneously twice weekly, spaced 3-4 days apart.
How long do clinical courses last?
6 months for chronic hepatitis B monotherapy and 6-12 months combined with interferon for chronic hepatitis C.
Is there a pediatric or low-body-weight adjustment?
The Zadaxin monograph lists 40 mcg/kg twice weekly for adults under 40 kg.
Was it studied in sepsis?
Yes, the TESTS Phase 3 randomized trial across 22 Chinese centers dosed it every 12 hours for 7 days; consult the primary publication for its findings.
Is the daily community immune-support pattern validated?
No. It is a community-reported convention, not a trial-derived schedule.
What is its half-life?
Reported as short, on the order of a few hours, in comparative pharmacology material; twice-weekly dosing reflects the tested clinical convention.
What side effects are reported?
Mostly mild injection-site reactions, nausea, and occasional flu-like symptoms in trial populations.
Who should avoid it?
People on immunosuppressive therapy, those with autoimmune disease, and anyone considering it as a replacement for established antiviral or cancer therapy, without clinician oversight.
What does the calculator do?
Concentration and volume arithmetic only; it does not establish a dose.
Sources and Research
Coverage source
1. Thymosin Alpha-1 protocol coverage source
Zadaxin-anchored schedule, reconstitution math, and supply planning; not primary evidence.
Open direct sourceHuman research
2. Thymalfasin (Zadaxin) for chronic hepatitis B and C
Pooled clinical trial evidence underlying the international approvals of thymalfasin.
Open direct sourceHuman research
3. Thymosin alpha 1 as an adjunct in cancer immunotherapy
Review of clinical evidence for thymalfasin as an immune-adjunct in oncology settings.
Open direct sourceHuman research
4. Thymosin alpha 1 in the treatment of severe sepsis (TESTS)
Phase 3 randomized controlled trial across Chinese centers testing thymosin alpha-1 in severe sepsis.
Open direct sourceMissing information flagged for review
- FDA approval status in the United States: Not established
- Validated dose for general immune support outside studied hepatitis, cancer-adjunct, and sepsis-trial contexts: Not established
- Precise human half-life figure from a dedicated pharmacokinetic study: Not established
- Validated rest period between repeated outpatient cycles: Not established
- Compound-specific prepared-vial stability duration: Not established
- Comprehensive drug interaction data: Not established