Gauging a drug size

For the sake of proper representation – and entertainment! – picture for yourself a … NEEDLE. Yeah, the common, average sewing needle you’ll go buy if you’d need to fix a button that just fell of your favored dress shirt. The thing would perhaps measure just about 3 to 4cm (1 to 1.5inches) in length and roughly 1mm in diameter. Naturally, the tip would be much smaller than the diameter. In theory, that sharp tip could get as little as an atom – but that is unrealistic to mass produce. So, the actual commercialized sewing needles have a quite bulkier tip. To be specific, according to the standards of the needle-making industry, the sewing needle tip must be 10 times smaller than the actual needle diameter – thus ~0.1mm.

Simple thus far, right?

If the tip diameter is 0.1mm, then its radius is 0.05mm. Knowing this, we can calculate the volume of the sphere representing the tip of the needle. Picture it as a ballpoint pen. That little sphere gliding your ink on the paper is the equivalent representation (only a lot bigger). The volume of a sphere is V=(4/3)*π*r^3. For a radius of 0.05mm, the volume of the sewing needle tip will be ~5.24×10-4mm3. If we do the same calculation for a hydrogen atom whose radius is 53 picometers (5.3×10-8mm), its volume will be to the tip of the needle about the same as what an elephant would be to the Indian Ocean if they would all for a swim at the same time.

With that in mind, let’s go figure how big a drug molecule is comparing to a needle tip!

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Dr. Alice

I teach people how drugs work, when they are needed, and why. My expertise as a pharmacist and researcher allows me to determine whether taking or not taking a drug will pose any risk given all current circumstances that apply at this moment. Many times we don't know unless we try, but other many times walking the extra mile pays off giving in return more wonderful moments and more to give to others.

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