PT-141 Reconstitution Calculator

Enter your vial size, bacteriostatic water, and dose to get your exact draw in insulin syringe units.

Reconstitution calculator

Enter your peptide amount, diluent volume, and target dose to see your draw.

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Units
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Target Dose
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Syringe Fill
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Doses per compound

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Draw 0.05 ml (5 units on a U-100 insulin syringe) for a 250 mcg dose.

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Mixing PT-141: What to Know Before You Reconstitute

PT-141, also known as bremelanotide, is sold as a lyophilized powder, most commonly in 5 mg and 10 mg vials. Its defining practical feature is cadence: unlike peptides run on a daily or weekly schedule, PT-141 is typically used occasionally rather than on a fixed calendar. That single difference drives most of the reconstitution questions people have about it, because a vial mixed today may see its second draw weeks later, and the discard clock does not pause in between.

  1. Bacteriostatic water vs. sterile water

    Bacteriostatic water contains 0.9% benzyl alcohol, which inhibits bacterial growth after the vial has been punctured. Sterile water has no preservative and is generally treated as single use. For a compound used occasionally across an extended period, bacteriostatic water is the conventional choice, since the vial will sit in the refrigerator between draws rather than being consumed steadily.

  2. How much water to add

    Water volume changes concentration, not content. A 10 mg vial holds 10 mg whether you add 1 mL or 3 mL. PT-141 doses fall in the milligram range, so draws are larger than with microgram peptides, and the concentration you choose determines whether a dose fits comfortably in the syringe.

    VialWaterConcentrationPer unit1 mg draw2 mg draw
    5 mg1 mL5.0 mg/mL50 mcg20 units40 units
    5 mg2 mL2.5 mg/mL25 mcg40 units80 units
    10 mg2 mL5.0 mg/mL50 mcg20 units40 units
    10 mg3 mL3.33 mg/mL33.3 mcg30 units60 units

    Because a vial is often not finished before its discard window closes, the water volume decision here carries a consideration the other compounds do not have: a more concentrated mix produces smaller draws but leaves more unused solution behind when the window arrives. Some people mix less water for that reason. The calculator above shows the doses per vial figure, which is the number that makes this trade visible.

  3. Mixing technique

    Angle the needle so the water runs down the inside wall of the vial rather than onto the powder directly, then swirl gently or let it stand until dissolved. Do not shake. The finished solution should be clear with no visible particles, and a vial that stays cloudy after gentle swirling is one most people will not use.

  4. Storage before and after mixing

    Unopened lyophilized vials keep cool and dark. Once mixed, the vial is refrigerated and the same roughly 28 day convention applies, drawn from the discard window for punctured bacteriostatic water. This is the step that matters most with PT-141 specifically. On an occasional use pattern, weeks can pass between draws, and the vial's expiration is governed by the date it was mixed rather than by how much is left in it. Writing the mix date on the vial, or letting PepKit count it down, is the difference between knowing and guessing when a vial has been sitting for a month.

  5. The syringe

    U-100 insulin syringes, where 100 units equal 1 mL and each unit is 0.01 mL. Milligram doses produce draws in the twenties to forties of units at common concentrations, so the 1 mL 100 unit syringe is the usual choice, though a 0.5 mL syringe can hold most doses at higher concentrations.

  6. Common mistakes worth avoiding

    The recurring ones: losing track of when a vial was mixed because draws are far apart, assuming a vial is still good because it is still mostly full, mixing more water than the use pattern justifies and discarding most of the vial, confusing mg and mcg in conversion, and reusing a previous unit count after mixing a new vial at a different volume.

FAQ

How much bacteriostatic water do I mix with 10 mg of PT-141?
Commonly 2 mL to 3 mL. At 10 mg in 2 mL the concentration is 5 mg/mL, so a 1 mg draw is 20 units. Water volume changes only the concentration, so choose one that gives a comfortable draw for your dose.
How long does reconstituted PT-141 last in the fridge?
About 28 days refrigerated is the widely followed convention, based on the discard window for punctured bacteriostatic water. This matters more with PT-141 than with daily compounds, because occasional use means a vial can reach that date while still mostly full.
My PT-141 vial is still full but it has been over a month. Is it still good?
The convention is based on time since the vial was punctured, not on how much solution remains. A vial mixed more than about 28 days ago has passed the usual window regardless of its fill level, which is why the mix date is the number people record.
Should I mix less water if I only use PT-141 occasionally?
Some people do, because a more concentrated mix means fewer doses left unused when the discard window closes. The trade is smaller draws. The doses per vial figure in the calculator above makes this comparison easy to see.
What size syringe do people use for PT-141?
Usually a 1 mL 100 unit U-100 insulin syringe, since milligram doses commonly land between 20 and 40 units. A 0.5 mL syringe can also work at higher concentrations.

PepKit's calculator is an arithmetic tool for reconstitution math. It does not provide dosing recommendations or medical advice. Follow the guidance of your provider or protocol.