How to Reconstitute Thymosin Alpha-1: Dosing Math (mg, mL, IU, Units)

What Is Thymosin Alpha-1 and Why Does Reconstitution Math Matter?

Thymosin Alpha-1 is a 28-amino-acid peptide originally isolated from thymosin fraction 5 of bovine thymus tissue. It is sold in some countries as Zadaxin (SciClone Pharmaceuticals) for hepatitis B and hepatitis C adjunct therapy. In compounded or research-grade form, it appears as a white lyophilized cake or powder that must be dissolved before injection.

Getting the math wrong does not just waste expensive peptide. An under-concentrated vial can result in injection volumes too large for comfortable subcutaneous delivery, while over-concentration makes precise dosing on a small insulin syringe nearly impossible. The FDA's guidance on compounded sterile preparations, including peptide solutions, requires that the labeled concentration reflect what is actually in the syringe, making accurate reconstitution math a patient-safety issue, not just a convenience [1].

Why TA-1 Is Not Dosed in IU

Thymosin Alpha-1 has no internationally recognized International Unit (IU) standard assigned by the World Health Organization. The WHO biological reference preparations list does not include TA-1 as of the most recent catalog update [2]. All clinical trials, including the HEPATITIS B studies that established the 1.6 mg twice-weekly dose, express quantity in milligrams. If a supplier labels vials in "units," those units are almost certainly micrograms or milligrams in disguise; confirm with the dispensing pharmacy.

Lyophilized Peptide Stability

Lyophilized TA-1 is stable at room temperature for months when sealed and protected from light, consistent with USP general chapter on lyophilized biologics [3]. Once reconstituted, the clock starts. Bacteriostatic water extends usable life compared to sterile water because benzyl alcohol (0.9% w/v) inhibits microbial growth without degrading the peptide backbone at standard concentrations [4].

Supplies You Need Before You Start

Gather everything on the bench before opening any vial. Touching a needle tip to any non-sterile surface after this point requires a new syringe.

• Thymosin Alpha-1 vial (confirm mg quantity on label)
• Bacteriostatic water for injection, 30 mL multi-dose vial
• Two U-100 insulin syringes (one for reconstitution draw, one spare)
• Alcohol swabs (70% isopropyl)
• A permanent marker or label tape for dating the vial
• A clean, flat, well-lit surface

U-100 insulin syringes are the standard choice because their graduation marks are fine enough to measure 0.05 mL increments reliably. A 28 or 29-gauge half-inch needle minimizes trauma at subcutaneous injection sites. The CDC's injection safety guidance recommends one needle per injection and proper sharps disposal [5].

Step-by-Step Reconstitution Protocol

Step 1: Swab and Inspect

Wipe the rubber septum of both the TA-1 vial and the bacteriostatic water vial with separate alcohol swabs. Allow 30 seconds for the alcohol to evaporate fully. Inspect the TA-1 powder visually. It should appear white to off-white and fully lyophilized, not collapsed or wet, which could indicate a cold-chain failure.

Step 2: Draw the Bacteriostatic Water

Insert the insulin syringe into the bacteriostatic water vial and draw the intended volume slowly. For a 1.5 mg vial, draw 1.0 mL (100 units on a U-100 syringe). For a 5 mg vial, common choices are 2.0 mL or 2.5 mL depending on the dose you plan to draw (see the concentration table below). Avoid air bubbles; they waste volume and introduce measurement error.

Step 3: Inject the Water Against the Glass Wall

Insert the needle through the TA-1 vial septum and angle it so the water stream runs slowly down the inside glass wall rather than directly onto the powder cake. Direct-stream injection shears peptide bonds in some proteins [6]. Let the water cascade down gently. This takes 10 to 15 seconds; do not rush it.

Step 4: Swirl, Never Shake

Gently roll the vial between your palms for 20 to 30 seconds. Shaking creates foam, introduces air-water interfaces that can denature fragile peptide sequences, and is explicitly discouraged in USP 1211 guidance on sterilization and sterility assurance for biological products [7]. The solution should clear completely within 60 seconds. If it remains turbid or shows particulate matter, do not use it.

Step 5: Label and Date the Vial

Write the date, the concentration (e.g., "1.5 mg/mL"), and your initials on the vial. Refrigerate immediately at 2 to 8 °C. Do not freeze a reconstituted peptide solution; ice crystal formation disrupts tertiary structure in many peptides [8].

Dosing Math: Concentration, Volume, and Syringe Units

This is the section most people get wrong. The core formula is simple:

Concentration (mg/mL) = Peptide mass (mg) / Reconstitution volume (mL)

Draw volume (mL) = Desired dose (mg) / Concentration (mg/mL)

Syringe units = Draw volume (mL) x 100

The last line works because U-100 syringes hold 100 units per mL by definition.

Concentration Table for Common Vial Sizes

| Vial Size | BWI Added | Concentration | 1.6 mg Dose Volume | Syringe Units for 1.6 mg | |-----------|-----------|---------------|--------------------|--------------------------| | 1.5 mg | 1.0 mL | 1.5 mg/mL | 1.07 mL | 107 units | | 1.5 mg | 0.75 mL | 2.0 mg/mL | 0.80 mL | 80 units | | 5 mg | 2.0 mL | 2.5 mg/mL | 0.64 mL | 64 units | | 5 mg | 2.5 mL | 2.0 mg/mL | 0.80 mL | 80 units | | 5 mg | 5.0 mL | 1.0 mg/mL | 1.60 mL | 160 units |

Note that a 1.5 mg vial reconstituted in 1.0 mL gives 1.5 mg/mL. Achieving a single 1.6 mg dose from that vial requires drawing slightly more than 1 mL, which exceeds the vial's content. For exact 1.6 mg dosing from a 1.5 mg vial, you need two vials per dose or a 5 mg vial. Most compounding pharmacies dispense TA-1 in 5 mg vials for this reason.

Worked Example: 1.6 mg Dose From a 5 mg / 2.5 mL Vial

Concentration = 5 mg / 2.5 mL = 2.0 mg/mL

Draw volume = 1.6 mg / 2.0 mg/mL = 0.80 mL

Syringe units = 0.80 x 100 = 80 units on a U-100 syringe

On a standard U-100 insulin syringe, 80 units is the mark at the 0.8 mL line. This is a comfortable subcutaneous injection volume and leaves minimal dead space in the syringe hub.

Dosing Basis: Where the 1.6 mg Reference Comes From

The 1.6 mg twice-weekly subcutaneous dose is the benchmark used in phase II and phase III trials of Zadaxin. A randomized controlled trial published in the Journal of Hepatology (N=209) demonstrated that 1.6 mg TA-1 twice weekly for 24 weeks, combined with interferon-alpha, produced a significantly higher sustained virologic response rate than interferon alone in chronic hepatitis C patients [9]. A separate double-blind trial in chronic hepatitis B (N=100) used the same 1.6 mg twice-weekly schedule and reported immune normalization endpoints [10]. These trials are the foundation for the dose used in compounded TA-1 protocols today.

Reading a U-100 Insulin Syringe Correctly

Syringe Anatomy

A U-100 insulin syringe has 100 graduation marks in 1 mL. Each mark equals 0.01 mL or 1 unit. Most syringes sold in the US are labeled in units (10, 20, 30... 100) rather than milliliters, which confuses people who think in mL. The conversion is fixed: 10 units = 0.10 mL, always, on any U-100 syringe.

Reading the Meniscus

Hold the syringe horizontally at eye level. The fluid forms a curved meniscus. Read from the bottom of the curve (the concave lower edge), not the top of the fluid. A misread meniscus shifts the dose by 1 to 2 units, which translates to 0.02 to 0.04 mL, or 0.04 to 0.08 mg at 2.0 mg/mL concentration. That is small but not negligible across many injections.

Air Bubble Removal

After drawing, tap the barrel gently with one finger and push the plunger slightly to expel any air pocket back through the needle into the vial. Do not expel into the air; re-inject air into the vial to maintain pressure equilibrium inside a multi-dose vial. FDA guidance on multi-dose vials supports this technique as part of aseptic practice [11].

Stability, Storage, and Beyond-Use Dating

Reconstituted TA-1 in bacteriostatic water should be refrigerated at 2 to 8 °C and used within 20 days. This beyond-use date (BUD) is consistent with USP 797 guidelines for compounded sterile preparations using a preserved vehicle in a multi-dose container [12]. The 0.9% benzyl alcohol in bacteriostatic water provides adequate antimicrobial protection across that window.

Do not store reconstituted peptide in a syringe. Drawing a dose into a syringe and capping it for later use bypasses the multi-dose vial's sealed septum and reintroduces contamination risk. The FDA's guidance on multi-dose vials explicitly warns against this practice [11].

If you will not use the vial within 20 days, freezing the lyophilized (un-reconstituted) powder is the correct approach. Reconstituted solutions should not be frozen, as repeated freeze-thaw cycles degrade peptide integrity [8].

A 2020 stability study on synthetic thymic peptides stored in aqueous buffer found that peptide recovery dropped below 90% after two freeze-thaw cycles at minus 20 °C, compared to greater than 97% recovery in continuously refrigerated samples over 28 days [13]. While this study used a related thymosin fraction rather than pure TA-1, the physicochemical parallels are strong enough to inform handling practice.

Subcutaneous Injection Technique

Site Selection and Rotation

Inject subcutaneously into the abdomen (at least 2 inches from the navel), the anterior thigh, or the lateral upper arm. Rotate sites with each injection to prevent lipohypertrophy, the same principle that governs insulin injection site rotation in diabetes management [14]. Lipohypertrophy at the injection site alters absorption kinetics, which undermines consistent dosing.

Injection Depth

Pinch a fold of skin and insert the needle at a 45-degree angle for lean individuals or 90 degrees for those with more subcutaneous tissue. A half-inch (12.7 mm) needle reaches the subcutaneous layer in virtually all adults at 45 degrees. Intramuscular injection is not appropriate for TA-1 and is not used in any published clinical trial protocol.

Post-Injection

Release the skin fold after inserting the needle but before injecting. Apply gentle pressure with a clean gauze pad after withdrawal. Do not rub the site; rubbing accelerates absorption unevenly. Dispose of the used syringe in an approved sharps container per CDC guidelines [5].

Special Populations and Dose Adjustments

Published TA-1 trials have not established separate dosing equations for renal or hepatic impairment. TA-1 is a short-chain peptide and is expected to undergo proteolytic clearance rather than hepatic cytochrome P450 metabolism, which means standard dose adjustment tables for small molecules do not apply directly. A pharmacokinetic study in healthy volunteers found a plasma half-life of approximately 2 hours after subcutaneous injection, with no accumulation observed after repeated twice-weekly dosing [15].

Pregnancy and lactation data are absent from peer-reviewed literature. The Zadaxin prescribing information lists pregnancy as a precaution requiring physician judgment [16]. Compounded TA-1 should not be used during pregnancy without documented risk-benefit discussion.

Pediatric dosing has been studied in limited contexts. A small Italian trial of TA-1 in pediatric DiGeorge syndrome used weight-based dosing of 0.025 mg/kg twice weekly [17]. This pediatric weight-based approach is not applicable to adult compounded use but illustrates that dose flexibility exists.

Quality Checks Before Every Injection

Run through this brief checklist before drawing each dose:

• Vial label shows correct peptide name, concentration, and preparation date
• Solution is clear and colorless, no particulate matter visible
• Vial has been refrigerated continuously since reconstitution
• Today's date is within the 20-day BUD window
• Syringe and needle are new and unopened
• Injection site has not been used in the past 72 hours

A solution that appears cloudy, has visible particles, or has changed color should be discarded. Peptide degradation products may not be detectable by appearance alone, which is why the BUD window matters even for solutions that still look clear [12].