{"id":1794,"date":"2026-08-11T09:00:00","date_gmt":"2026-08-11T16:00:00","guid":{"rendered":"https:\/\/vistaralabs.ca\/pt-141-reconstitution-bacteriostatic-water\/"},"modified":"2026-09-21T17:33:49","modified_gmt":"2026-09-22T00:33:49","slug":"pt-141-reconstitution-bacteriostatic-water","status":"publish","type":"post","link":"https:\/\/vistaralabs.ca\/fr\/pt-141-reconstitution-bacteriostatic-water\/","title":{"rendered":"How Much Bacteriostatic Water for a PT-141 10 mg Vial?"},"content":{"rendered":"

A 10 mg vial of PT-141 reconstituted with 2 mL of bacteriostatic water gives a concentration of 5 mg\/mL; with 1 mL it gives 10 mg\/mL. The calculation depends only on the quantity in the vial and the volume of water added, so the figures below apply to any 10 mg vial.<\/p>\n

There is no single correct volume. Adding more water does not change how much is in the vial. It spreads the same quantity through a larger volume, which changes how many syringe units correspond to a given amount. The tables on this page use volumes that produce round numbers on a U-100 syringe; other volumes work identically as long as the resulting concentration is written on the vial.<\/p>\n

Concentration by water volume<\/h2>\n

Concentration is the quantity in the vial divided by the water volume. A 10 mg vial holds 10 mg whether it receives 1 mL or 5 mL; only the mg\/mL figure moves. The right-hand column converts each concentration into the number of U-100 units that contain 1 mg.<\/p>\n\n\n\n\n\n\n\n\n
Vial<\/th>\nBacteriostatic water added<\/th>\nConcentration<\/th>\nUnits containing 1 mg<\/th>\n<\/tr>\n<\/thead>\n
10 mg PT-141<\/td>\n1 mL<\/td>\n10 mg\/mL<\/td>\n10 units<\/td>\n<\/tr>\n
10 mg<\/td>\n2 mL<\/td>\n5 mg\/mL<\/td>\n20 units<\/td>\n<\/tr>\n
10 mg<\/td>\n3 mL<\/td>\n3.33 mg\/mL<\/td>\n30 units<\/td>\n<\/tr>\n
10 mg<\/td>\n5 mL<\/td>\n2 mg\/mL<\/td>\n50 units<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Before choosing a larger volume, check that the vial has headspace for it. A 10 mL vial of bacteriostatic water reconstitutes five 10 mg vials at 2 mL each.<\/p>\n

Reading the concentration on a U-100 syringe<\/h2>\n

A U-100 insulin syringe is graduated in units, and 100 units equal 1 mL. Units are therefore millilitres multiplied by 100: 0.1 mL is 10 units and 0.25 mL is 25 units. A 0.5 mL syringe carries 50 units and a 0.3 mL syringe carries 30 units on the same scale, with finer markings that make small volumes easier to read.<\/p>\n

To find the volume that contains a given amount, divide the amount by the concentration. At 5 mg\/mL (a 10 mg vial with 2 mL of water), the volume that contains 1 mg is 1 divided by 5, which is 0.2 mL, or 20 units. The table below runs the same calculation for four arbitrary amounts. They illustrate the arithmetic and nothing else.<\/p>\n\n\n\n\n\n\n\n\n
Amount (illustrative)<\/th>\nVolume at 5 mg\/mL<\/th>\nU-100 units<\/th>\n<\/tr>\n<\/thead>\n
0.25 mg<\/td>\n0.05 mL<\/td>\n5 units<\/td>\n<\/tr>\n
0.5 mg<\/td>\n0.1 mL<\/td>\n10 units<\/td>\n<\/tr>\n
1 mg<\/td>\n0.2 mL<\/td>\n20 units<\/td>\n<\/tr>\n
2 mg<\/td>\n0.4 mL<\/td>\n40 units<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

At 10 mg\/mL, which the same vial gives with 1 mL of water, every volume in the table moves in proportion: a 1 mg draw measures 10 units instead of 20. Volumes below about 0.1 mL are hard to read accurately on a 1 mL syringe. Either move to a 0.3 mL or 0.5 mL syringe, or reconstitute with more water so that the same mass occupies a larger, more legible volume.<\/p>\n

\n

PT-141 is supplied by Vistara Labs as a lyophilised material for research use. The quantities on this page illustrate the arithmetic of dilution and measurement only.<\/p>\n<\/div>\n

The PT-141 vial<\/h2>\n

PT-141, also called bremelanotide, is a cyclic heptapeptide of the melanocortin family and a metabolite of Melanotan II. Vistara Labs supplies it as a 10 mg lyophilised vial. The same arithmetic covers Melanotan II<\/a>. Certificates of analysis for the catalogue are published on the Lab Results<\/a> page.<\/p>\n

PT-141 is the melanocortin peptide in this catalogue that went on to become a medicine: as bremelanotide it was approved in the United States in 2019 under the name Vyleesi, supplied as a ready-to-use autoinjector rather than a powder. The research vial here is a lyophilised laboratory material and is a separate product. Its origin in the Melanotan II trials is covered in Melanotan II: the clinical history and the PT-141 connection<\/a>.<\/p>\n

Reconstitution technique<\/h2>\n

Let the vial reach room temperature, swab both stoppers, and run the measured water slowly down the inside wall of the vial rather than onto the powder. Swirl or tilt gently until the cake dissolves, never shake, and give any remaining powder a few minutes to settle into solution. Label the vial with the date and the concentration, then keep it refrigerated at 2 to 8 °C and protected from light. The full method, with the reason behind each step, is in how to reconstitute peptides with bacteriostatic water<\/a>.<\/p>\n

Why the solution should look clear<\/h2>\n

Properly reconstituted PT-141 forms a clear, colourless solution. Cloudiness, strands or a gel that will not disperse usually mean the water went in too fast or the vial was shaken; haze that appears later points to warm or bright storage. The causes are covered in why peptides gel or go cloudy<\/a>.<\/p>\n

Bacteriostatic water, not sterile water<\/h2>\n

Bacteriostatic water is sterile water with 0.9% benzyl alcohol, a preservative that allows a refrigerated vial to be accessed more than once; plain sterile water is intended for single access. The difference is explained in bacteriostatic water explained<\/a>.<\/p>\n

Frequently asked questions<\/h2>\n

How much bacteriostatic water do I add to a 10 mg vial of PT-141?<\/h3>\n

There is no single correct volume. With 2 mL of bacteriostatic water a 10 mg vial of PT-141 gives 5 mg\/mL; with 1 mL it gives 10 mg\/mL. Adding more water does not change the quantity in the vial, it spreads it through a larger volume, so write the concentration you chose on the vial.<\/p>\n

How many 10 mg vials does a 10 mL vial of bacteriostatic water cover?<\/h3>\n

A 10 mL vial of bacteriostatic water reconstitutes five 10 mg vials at 2 mL each. Check that the peptide vial has headspace for the volume before choosing a larger one.<\/p>\n

How many units on a U-100 syringe contain 1 mg at 5 mg\/mL?<\/h3>\n

At 5 mg\/mL (a 10 mg vial with 2 mL of water), the volume that contains 1 mg is 1 divided by 5, which is 0.2 mL, or 20 units. Units are millilitres multiplied by 100, so 0.1 mL is 10 units. The amounts on this page illustrate the arithmetic only.<\/p>\n

What should reconstituted PT-141 look like?<\/h3>\n

Properly reconstituted PT-141 forms a clear, colourless solution. Cloudiness, strands or a gel that will not disperse usually mean the water went in too fast or the vial was shaken; haze that appears later points to warm or bright storage. More on the causes in why peptides gel or go cloudy<\/a>.<\/p>\n

Can I use sterile water instead of bacteriostatic water?<\/h3>\n

Only for a vial that will be accessed once. Bacteriostatic water is sterile water with 0.9% benzyl alcohol, a preservative that allows a refrigerated vial to be accessed more than once; plain sterile water is intended for single access. Details in bacteriostatic water explained<\/a>.<\/p>\n

How should a reconstituted PT-141 vial be stored?<\/h3>\n

Refrigerated at 2 to 8 \u00b0C, protected from light and labelled with the date and the concentration. Unopened lyophilised vials are kept cold and dark until they are needed. The full storage guide is how to store research peptides<\/a>.<\/p>\n

Work it out for a different vial or concentration<\/h2>\n

Our peptide calculator<\/a> opens pre-set for a 10 mg vial with 2 mL of water and marks the 1 mg draw of 20 units on a syringe diagram. Change the vial size, water volume, amount or syringe and it recalculates.<\/p>\n

Products: PT-141 10 mg<\/a> and bacteriostatic water 10 mL<\/a>.<\/p>\n

Related reading.<\/strong> Melanotan II and PT-141: the clinical history<\/a>.<\/p>\n