Doses per vial: theoretical vs. actual

[JustSomeGuy050]

My RS has been using Reta for several months. Something I’ve picked up on: the expected count of doses in a vial doesn’t match what actually comes out. Take 10mg mixed with 1.0mL Bac; at a 2mg dose that math says 5 doses at 20 units. In practice, though, I only get 3-4 doses from that same setup.

I’ve double-checked my numbers with a ton of reconstitution and dosing calculators, so I don’t think I’m making an error there.

A 4mm filter is part of my process.

On the most recent recon, I had 12mg. I added 1mL bac and purged with 0.5mL, so the result was 12mg/1.5mL, meaning a 2mg dose lands at 25 units.

Yet after 3 shots, my RS’s vial appears to have just 1 dose remaining.

Where might I be going wrong? Or is this just how it goes?

 

[Sasquatch]

For the dilution, what's the reason for switching between units and millilitres like that?

 

[CNCCurrency]

JustSomeGuy050 said:

My RS has been using Reta for several months. Something I’ve picked up on: the expected count of doses in a vial doesn’t match what actually comes out. Take 10mg mixed with 1.0mL Bac; at a 2mg dose that math says 5 doses at 20 units. In practice, though, I only get 3-4 doses from that same setup.

I’ve double-checked my numbers with a ton of reconstitution and dosing calculators, so I don’t think I’m making an error there.

A 4mm filter is part of my process.

On the most recent recon, I had 12mg. I added 1mL bac and purged with 0.5mL, so the result was 12mg/1.5mL, meaning a 2mg dose lands at 25 units.

Yet after 3 shots, my RS’s vial appears to have just 1 dose remaining.

Where might I be going wrong? Or is this just how it goes?

There's no reason to have RS on this platform.

 

[Mood]

Which kind of syringe do you use when you reconstitute and when you inject? With Luer lock syringes, dead space can reach 0.1ml (10iu). That means dead space alone could cost you 20 units, which works out to one dose. One option is to take the needle off, pull some air in, and air purge so that part of that dead space gets cleared.

 

[bada bing]

Whenever a solution gets transferred using a syringe and needle, a bit of it stays behind. Splitting one vial into a large number of doses, instead of just 1 or 2, makes those losses add up, since each pull of the syringe leaves something behind. Even so, with good technique the amount lost should stay small, roughly 1 or 2 units across a whole vial.

 

[Mood]

bada bing said:

Whenever a solution gets transferred using a syringe and needle, a bit of it stays behind. Splitting one vial into a large number of doses, instead of just 1 or 2, makes those losses add up, since each pull of the syringe leaves something behind. Even so, with good technique the amount lost should stay small, roughly 1 or 2 units across a whole vial.

That holds true with a fixed needle syringe, but dead space is bigger in luer lock syringes/needles. Should you put bac into a vial, then draw out the reconstituted peptide and filter it into a different vial, and switch needles several times without purging with air, the loss could approach 20 units. A small amount is still lost even when you do an air purge, though far less.

For my trt injections I reach for luer loc syringes and keep an air bubble of 5-10 units inside the syringe (let the bubble rise to the plunger side before you begin injecting), which clears most of that dead space.

 

[CNCCurrency]

jsc1980 said:

bada bing said:

Whenever a solution gets transferred using a syringe and needle, a bit of it stays behind. Splitting one vial into a large number of doses, instead of just 1 or 2, makes those losses add up, since each pull of the syringe leaves something behind. Even so, with good technique the amount lost should stay small, roughly 1 or 2 units across a whole vial.

That holds true with a fixed needle syringe, but dead space is bigger in luer lock syringes/needles. Should you put bac into a vial, then draw out the reconstituted peptide and filter it into a different vial, and switch needles several times without purging with air, the loss could approach 20 units. A small amount is still lost even when you do an air purge, though far less.

For my trt injections I reach for luer loc syringes and keep an air bubble of 5-10 units inside the syringe (let the bubble rise to the plunger side before you begin injecting), which clears most of that dead space.

I filter with them too, and I either put in a bit more bac water to make up for it or do a flush.

 

[BrightCandle]

Liquid gets retained by the filter, and the syringe too, so getting all of it out of the vial is tough, and each extra pull on the syringe pin also throws a bit away. Deadspace traps fluid in every component, and the filter in particular keeps a fair amount. With 1mg and 0.2mg doses, you really only get 4 doses, because the losses have to be factored in, and those losses are quite large once you count 1+4 syringe actions plus the filter.

Reconstituting with more BAC can cut the loss, since it is a fixed cost per "syringe action" and filter, so switching to 2ml or 3ml would keep the liquid loss the same while giving you more units of the 5 pin. That is also why many people go with reusable pens that take a cartridge: you draw from the vial just once and take about a 15 unit loss inside the cartridge, but you avoid losing the 5-10 units per pin from the syringe. My sense is the break-even sits around 4 pins a month; above that, cartridge pens preserve a lot of liquid, but below it they often do not save much.

I think you basically always have to calculate on the assumption that you lose at least something like 20 units of liquid from a vial.

 

[CNCCurrency]

BrightCandle said:

Liquid gets retained by the filter, and the syringe too, so getting all of it out of the vial is tough, and each extra pull on the syringe pin also throws a bit away. Deadspace traps fluid in every component, and the filter in particular keeps a fair amount. With 1mg and 0.2mg doses, you really only get 4 doses, because the losses have to be factored in, and those losses are quite large once you count 1+4 syringe actions plus the filter.

Reconstituting with more BAC can cut the loss, since it is a fixed cost per "syringe action" and filter, so switching to 2ml or 3ml would keep the liquid loss the same while giving you more units of the 5 pin. That is also why many people go with reusable pens that take a cartridge: you draw from the vial just once and take about a 15 unit loss inside the cartridge, but you avoid losing the 5-10 units per pin from the syringe. My sense is the break-even sits around 4 pins a month; above that, cartridge pens preserve a lot of liquid, but below it they often do not save much.

I think you basically always have to calculate on the assumption that you lose at least something like 20 units of liquid from a vial.

To make up for it, I put in a bit more bac or use it to flush.

 

[eidos]

This isn't about doing arithmetic — it comes down to technique.

Each time you handle the vial, small inaccuracies creep in. Syringes aren't micropipettes with calibration, and product gets left behind.

Want to cut those losses? Use a greater dilution. Drop the concentration while holding the volume steady, and the amount you lose shrinks. That's straightforward chemistry: C = q/V.

At the end, look at what remains in the vial. Injection pens make this simple, since they typically come with a graduated scale.

 

[TazaTaza]

My RS has been using Reta for several months. Something I’ve picked up on: the expected count of doses in a vial doesn’t match what actually comes out. Take 10mg mixed with 1.0mL Bac; at a 2mg dose that math says 5 doses at 20 units. In practice, though, I only get 3-4 doses from that same setup.

I’ve double-checked my numbers with a ton of reconstitution and dosing calculators, so I don’t think I’m making an error there.

A 4mm filter is part of my process.

On the most recent recon, I had 12mg. I added 1mL bac and purged with 0.5mL, so the result was 12mg/1.5mL, meaning a 2mg dose lands at 25 units.

Yet after 3 shots, my RS’s vial appears to have just 1 dose remaining.

Where might I be going wrong? Or is this just how it goes?

The dose you're not getting shows up during filtration — it can remain trapped inside the filter, the luer lock needle hub, or similar spots. Those parts hold a larger dead volume compared to an insulin syringe.

To check whether this is a technique problem on your end (which I doubt), grab an empty vial, a waste container for catching liquid, and tap water, then practice. Fill a test vial with 1 mL of water. Using an insulin syringe, pull 20 units 5 times, then do the same thing with a luer lock.

Even when no filter is involved, the deadspace in a luer lock can cost you a fair number of units.