Lab-quality (low tolerance) graduated cylinders / pipettes?
November 5, 2020 8:05 AM   Subscribe

Working with my psychiatrist, I'm continuing a years-long taper off of a psychiatric medication (in IR tablet form) that I have developed an extreme physiological dependence on. Compounding services aren't financially viable for me in the long term, so I am planning on preparing my own solutions of appropriate dosages. Because of the therapeutic dose of this medication, I am going to need to have the ability to accurately measure liquid in very small amounts. Any professional chemists (or the like) have suggestions for me?

I am totally and completely a lay person when it comes to this. I had to learn how to read a meniscus in AP Chemistry, but that was a long time ago...

I am willing to spend a good amount of money for good products, as this is an extremely serious endeavor.

I don't plan on threadsitting, but I am happy to answer any additional questions I may have neglected to address.
posted by vocativecase to Science & Nature (24 answers total) 1 user marked this as a favorite
 
You can compound at home: using a good gram scale, take 1 part medication, 99 part filler, mix together so that they are well dispersed and homogeneous. Now you have a 1% strength mix.

So for example, let's say you want to take 1/10 of a tablet. Let's say you weigh 10 tablets and they come up to 2 grams. Grind them up and add (2x99=) 198 grams of filler powder for a total of 200gm. Mix well. Now, 2 grams of the result will give you 1/10 of a tablet. You can now measure out 2 grams and put it in a gelatin capsule.

Depending on how the tablet was made, the modified-release properties may be lost as soon as you grind up the pill. It depends on if the modified-release is in the coating, or by micro-encapsulation. I would say keep it in powder form because liquid solutions are more problematic - the active ingredient can settle, it can chelate or react, and also it can affect the micro-encapsulation.
posted by dum spiro spero at 8:15 AM on November 5, 2020 [5 favorites]


I got some seriously sturdy vintage Pyrex labware from a professor emeritus at the ag science college where I used to work, but not in the small sizes you would require. But if you have any friends in academia, that might be an avenue to explore?
posted by The Underpants Monster at 8:18 AM on November 5, 2020


I think a typical method is to mix the medication with a carrier (applesauce, water, juice, etc) to make a known dilution, so you're handling larger quantities that are easier to measure.

Say you need to take 0.3 ml of your medication - Mix 1 ml of the medication with 9 ml of water and then take 3 ml of the mixture. The next day, you can taper down to 0.2 ml and take 2 ml of the mixture, etc etc. I would check with your doctor or probably better, your pharmacist first though, to get advice on things like shelf life and if there are better or worse things to mix it with.
posted by yeahlikethat at 8:22 AM on November 5, 2020 [1 favorite]


Can you be a little more specific about what quantities you need to measure and how much accuracy you need?
posted by en forme de poire at 8:28 AM on November 5, 2020 [4 favorites]


I know nothing about pharmacy in general. Diluting and working with more familiar quantities sounds to me, as a non-expert who has no real basis for evaluation, like it is probably best. But on the question of tools for working with very small quantities, what you might be looking for is microscale chemistry lab equipment.
posted by eviemath at 8:37 AM on November 5, 2020


For a layperson I’d strongly consider going by weight; I think it’d be pretty easy to mess up serial dilutions or mess up the med’s effectiveness if it’s not already in solution and you make up a batch at the start of the week. A scale that can go down to milligram quantities isn’t super pricey, and that’d be fine if you are crushing pills and going down by a percent or two at a time.

If you are stuck on measuring liquids (for example if the med is already in liquid) I’d lean toward using a micropipette, which can be purchased with a bunch of accuracy/volume levels, like this. You’d also need the disposable plastic tips, but you could squirt your measured dose right into your mouth or a glass of water.
posted by tchemgrrl at 8:41 AM on November 5, 2020 [5 favorites]


Note that micropipettes also need to be calibrated.
posted by en forme de poire at 8:51 AM on November 5, 2020 [3 favorites]


For liquids, you'd be better off using serological pipettes than a micropipette (which are expensive, need to be calibrated and require training in their correct use). Amazon sell them in a variety of sizes and you'll need a filler. This can be manual (something like this) or electronic (spendy though). None of those links are to anything I can personally recommend, but if you want to go that route, MeMail me for specifics.

Alternatively, you could just use sterile disposable syringes (widely available), again assuming you're measuring liquids.
posted by car01 at 9:02 AM on November 5, 2020


If it's liquid you might also consider syringes. You can get sizes as small as 1ml and that will have 0.05ml marks on it.

Edit: jinx
posted by zengargoyle at 9:07 AM on November 5, 2020


> I am going to need to have the ability to accurately measure liquid in very small amounts

This doesn't sound like a good strategy to me. As others have stated, you should probably dilute your medication with some other carrier (maybe water?), and then work with larger quantities of liquid. Working with very small volumes is difficult and error-prone.
posted by alex1965 at 9:10 AM on November 5, 2020 [2 favorites]


Sorry I wasn't more specific about quantities. The lowest weight tablets made by the manufacturer are 10 mg. I will need to be confident about measurements down to around .1 mg.

I am totally prepared to work with larger quantities of liquid as carrier, but I encounter a problem with larger quantities of liquid with this medication, unfortunately: If I have more than a glass of water in the couple hours before or after my dose, which is taken exactly at 8PM, I experience hours where I am unable to sleep due to extreme, hallucinatory night terrors and sleep paralysis. It's as fun as it sounds. My psychiatrist is supportive of my plan to taper slowly, but, like many psychiatrists, is seemingly totally unaware of severe discontinuation symptoms that necessitate a slow taper schedule.
posted by vocativecase at 9:16 AM on November 5, 2020


A note: it sounds crazy, but he is the only psychiatrist in a 400+ mile radius that takes my insurance. Now that I'm thinking about it, it would be definitely be worth it to pay out of pocket to see a psychiatrist that has expertise in this area, which I'm going to plan on doing ASAP. In the meantime, I welcome any suggestions you may have!
posted by vocativecase at 9:18 AM on November 5, 2020 [2 favorites]


Yeah, doing this with solids is going to be far easier. The important things you need to know are
a) how much does each tablet weigh (NOT the weight of active ingredient per pill), and
b) what is the smallest fraction of a tablet that you will need to take (on preview, answered as 1/100th)

Those two things set the minimum accuracy of the scale needed. So if your pill weighs 1 g, you need a scale accurate to 0.01 g (and preferably 0.001 g). Make sure you get some calibration weights in the same range. These amounts are readily measurable by a non-specialist, given the right scale and setup. Note: if you can be prescribed a lower dose pill, say a 1 mg tablet, that'll help you out.

Storage and pre-prep are another thing to think about. Mashing up a pill into powder drastically increases the surface area. Any oxidation that could be a problem will happen much faster (same thing would happen in water). Plus if it absorbs water from the air, this will happen much faster, and throw your weights off if it's sitting around.

If it's not a restricted substance, or absurdly expensive, I'd be asking for a pill per dose. Do the grinding in a mortar and pestle, measure your dose, throw the rest of the pill out.
posted by Jobst at 9:25 AM on November 5, 2020 [5 favorites]


Note: if you can be prescribed a lower dose pill, say a 1 mg tablet, that'll help you out.

Unfortunately 10mg is the lowest dose tablet available :(
posted by vocativecase at 9:32 AM on November 5, 2020


Another vote for weight.

Above serological pipettes were suggested as alternative to micro pipettes (« pipettemen »), which need calibration. But serological pipettes have quite a wide tolerance (or allowed range of error).

Even in the lab, with many options available, we often measure liquids by weight for best precision. So surely, measuring solids by weight is going to be a better route than say, dissolving and measuring volumetrically in many cases.
posted by Tandem Affinity at 10:21 AM on November 5, 2020 [1 favorite]


My chemistry teacher said if you want to weight a pea, do it on the back of an elephant.

If I were going to do this at say 10 mg pill to 0.1 mg pill, I would use a gram scale like this, crush up one pill with mortar and pestle, add water to 200 g, then pour off 2 g, that is the dose. I'd estimate that gets you +/- half a gram of solution or +/- 0.025 mg of active ingredient. Is that good enough?
posted by muddgirl at 10:24 AM on November 5, 2020




As a person who owns a scale in her lab that cost as much as a car .... I defer to liquid dilutions wherever possible. I have much more confidence in our ability to measure and, crucially, transfer 0.5 mL than I do 0.5 mg. We routinely dilute a few mg of a substance into a known quantity of water (like 10 mg into 100 mL) then aliquot / mete out smaller amounts of that. That's the strategy I'd recommend here.

Looks like you can buy graduated dropper pipettes, or a pipettor (still need tips for it. If you're going below 10 uL, then worry about calibration).

Pick up some weigh paper while you're at it (fold before use, the crease helps you slide stuff off it).
posted by Dashy at 11:09 AM on November 5, 2020


I am totally prepared to work with larger quantities of liquid as carrier, but I encounter a problem with larger quantities of liquid with this medication,

As a reminder: you don't need to do it at the same strength the entire time you're tapering. If your setup enables you to feel confident at the 1mL level, and eventually you want 0.5mg doses, at that point you might dissolve 10mg in 1L and take 50mL. But at the start, you could go from 10 mg to 9 mg by dissolving 10mg in 100mL and taking 90mL. You could even combine the two if needed; get 9.2mg by dissolving 10mg in 100ml and taking 90mL of that, plus dissolving 10mg in 1L and taking 20mL of that for the 0.2mg.
posted by Superilla at 11:30 AM on November 5, 2020 [3 favorites]


Please don't dissolve it in a liquid without knowing exactly what the pharmacologic reactions are with water and anything else you use.

If for some reason you feel so compelled, then spend the $150 and get the USP Compounding Compendium for precise information on solubility, interactions, degradation, etc.
posted by dum spiro spero at 2:58 PM on November 5, 2020 [4 favorites]


Yes. Dissolving in liquid is potentially problematic. You may get better answers if you list the drug.

I will also add that if you use the (preferable in my non-expert opinion) dry powder dilution methods, please make sure you mix very, very well. Practice with some dyed flour (food coloring/drying) and plain flour to get a feel for how (surprisingly) much you have to mix.
posted by SaltySalticid at 4:37 PM on November 5, 2020 [2 favorites]


I work in inorganic chemistry, and I'd recommend buying the book dum spiro spero mentioned to check you've got the chemistry right, as I know nothing of the potential pitfalls of diluting pharmaceuticals.

For equipment, a good balance is probably the easiest way to do this. Take it up in x ml of solvent, weigh. Then you can weigh out 1/100th of that weight to get 0.1mg of the original. Some plastic bottles and some disposable plastic pipettes would be enough, if you can find a good enough balance. You'd need it to be able to weigh a range of about 10000, e.g 0.01g to 100 g, to get the accuracy needed at the low weight, and it would have to be calibrated.

Glassware can work, if you can't get access to a balance. Class A is I think the highest accuracy, about 1%, which I assume would be accurate enough for your needs. A 100mL and a 1mL from somewhere like here would satisfy your needs. Or you could get a 100mL volumetric flask and a 1mL pipette. You'll also need a pipette bulb, and some disposible pipettes to add the last bit of water to the volumetric flask.

Everything needs to be clean and dry when you use it, but you can't heat the glassware to dry it, or you'll void the calibration. Watch some youtube videos on how to pipette and use a volumetric flask.

Storage may be an issue, if you're planning on keeping the bulk solution around for days. Make up new solutions regularly, and triple check your maths. It's really easy to be out by an order of magnitude.
posted by kjs4 at 4:59 PM on November 5, 2020 [1 favorite]


Seconding that if dissolving in water is okay you’re looking for a Class A volumetric flask and probably a couple Class A volumetric pipettes, at least a 1 mL for a measuring a .1 mg dose (assuming a 100 mL flask and a 10 mg tablet) and a 10 mL for a 1 mg dose, and use those in combination to get the dose you want. Anything that gives you a range a volume like a serological pipette is going to be far less accurate. You’ll want to read up on quantitative transfer techniques to makes sure you’re getting all of the tablet into that flask as well (basically you’re using distilled water the wash all of the ground tablet into the flask, and then adding more to fill to the marked line). Practice accurate pipetting and filling of the flask a bit before you start working with your actual medication, it does take some skill (in both instances the accurate measurement is when the bottom of the meniscus (the curve of liquid in a tube) is level with the line (at 20 degrees Celsius if you want to be truly accurate).

Good lab glassware is far cheaper than a precision balance.
posted by Jawn at 10:15 PM on November 5, 2020


I totally forgot about solubility, but dum spiro spero is entirely correct -- making sure you have the right solvent and making sure you've got drug dissolved is definitely an issue here. Even the smallest particles can be quite stubbornly not actually in solution.
posted by Dashy at 2:30 PM on November 6, 2020


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