What is bacteriostatic water and why is it used for peptides?

Bacteriostatic water (BAC water) is sterile water containing 0.9% benzyl alcohol, which prevents bacterial growth. It is the standard solvent for reconstituting lyophilised peptides because it keeps the solution safe for multi-dose use over several weeks, unlike plain sterile water which should be used within 24 hours.

How much bacteriostatic water should I add to a peptide vial?

The amount depends on the peptide quantity in the vial and your desired concentration. A common starting point is 1 mL of BAC water per 5 mg of peptide. Use a reconstitution calculator to determine the exact volume needed for your target dose per insulin unit.

Can I shake the vial to dissolve the peptide faster?

No. Never shake a peptide vial. Shaking can denature the peptide and break its molecular structure, reducing potency. Instead, gently roll the vial between your palms or let it sit in the refrigerator - most peptides dissolve fully within a few minutes.

How long does a reconstituted peptide last?

When reconstituted with bacteriostatic water and stored at 2–8°C (refrigerated), most peptides remain stable for 28–30 days. Some more stable peptides like BPC-157 can last longer. Always check for cloudiness or particles before use - discard if the solution is no longer clear.

What size syringe should I use for reconstitution?

Use a standard 1 mL (100 unit) insulin syringe with a 29–31 gauge needle for drawing and injecting. For adding BAC water to the vial, a larger 3 mL syringe can make it easier to measure the water volume accurately.

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How to Reconstitute Research Compounds

Lyophilised (freeze-dried) research compounds arrive as a delicate powder inside a sealed vial. Before they can be used, they need to be reconstituted, dissolved into a liquid solution using bacteriostatic water (BAC water). This guide covers everything you need to do it correctly, safely, and without degrading the compound.

What you'll need

Lyophilised vial The sealed vial containing your research-compound powder.

Bacteriostatic water Sterile water with 0.9% benzyl alcohol, the standard solvent for multi-use vials.

Insulin syringes 1 mL (100 unit), 29–31 gauge needles for precise measurement.

Alcohol swabs For sterilising vial tops before each needle insertion.

Clean workspace Flat, well-lit surface wiped with 70% isopropyl alcohol.

Important: Don't use normal saline or plain sterile water for vials you plan to store. BAC water's benzyl-alcohol content inhibits bacterial growth, keeping your reconstituted solution viable for up to 30 days refrigerated.

Step-by-step reconstitution

Prepare your workspace Wipe down your work surface with 70% isopropyl alcohol. Allow your vial and BAC water to reach room temperature if they've been stored cold, this takes about 10–15 minutes. Cold BAC water can still be used, but room-temperature water dissolves the powder more evenly.

Clean the vial tops Swab the rubber stopper of both the compound vial and the BAC water vial with an alcohol pad. Let them air-dry for a few seconds. This prevents introducing contaminants when you pierce the stopper.

Draw bacteriostatic water Insert the syringe needle into the BAC water vial and draw out the desired volume. The amount you add determines the concentration of your solution. Concentration formula: 1 mL of BAC water added to a 5 mg vial means each 0.1 mL (10 IU on an insulin syringe) contains 0.5 mg (500 mcg). Adding 2 mL would make each 0.1 mL contain 0.25 mg (250 mcg). Open the Reconstitution Calculator → Enter your vial size, water volume, and target dose to get exact syringe units.

Add water to the vial This is the most critical step. Insert the needle and aim the stream at the inside wall of the vial , not directly onto the powder. Let the water trickle down the glass slowly. Lyophilised compounds are fragile, a direct jet can damage molecular structures and reduce potency.

Dissolve gently Once all the water is in, gently roll the vial between your palms or tilt it back and forth slowly. Most compounds dissolve within 30–60 seconds. Never shake the vial , vigorous agitation can denature peptide bonds. The solution should become clear and colourless. If particles remain after 2–3 minutes of gentle swirling, let the vial sit in the refrigerator for 30 minutes, some compounds take longer to fully dissolve.

Store properly Refrigerate the reconstituted vial at 2–8°C (standard refrigerator temperature). Keep it away from light. A reconstituted compound in BAC water typically remains stable for up to 30 days . For longer storage, some researchers aliquot the solution into smaller vials and freeze them, though freeze-thaw cycles should be minimised.

Concentration quick reference

Use this table for common vial sizes with BAC water added:

Vial size BAC water added Per 0.1 mL (10 IU) 2 mg 1 mL 200 mcg 5 mg 1 mL 500 mcg 5 mg 2 mL 250 mcg 10 mg 1 mL 1000 mcg (1 mg) 10 mg 2 mL 500 mcg

Common mistakes to avoid

Squirting water directly onto the powder , always aim at the vial wall and let it run down gently.

Shaking the vial , this can break peptide bonds. Gentle rolling or swirling only.

Using plain sterile water for multi-use vials , without benzyl alcohol, bacteria can colonise the vial after the first puncture.

Storing at room temperature , reconstituted compounds degrade rapidly above 8°C. Always refrigerate.

Reusing syringes , always use a fresh, sterile syringe for each draw to prevent contamination.

Bacteriostatic vs sterile water

Both are pharmaceutical-grade, but they serve different purposes:

Bacteriostatic water

Contains 0.9% benzyl alcohol, prevents bacterial growth. Ideal for multi-use vials accessed with a syringe over days or weeks.

Sterile water

No preservative. Single-use only, once opened or punctured, bacteria can grow. Only appropriate if the entire vial is used in one session.

For research compounds stored in multi-use vials, BAC water is always the correct choice .

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Use the Reconstitution Calculator to see exactly how many units to draw. Then learn how to store your reconstituted vials.

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