Ok, so how does pain medication work. I don’t mean, how it understands where the pain is and then acts on it. I mean, how do doctors prescribe a certain dosage?
If I have a prescription for 500mg of ABC painkiller, what does 300mg or 650mg do? does it become more/less effective?
How does 500mg of ABC painkiller become more effective than 500mg of XZY painkiller? (Ibuprofen vs Paracetamol)
I know this is a weird question and I feel like the answer is in the question somehow. But, I’d like someone to ELI5.
In: Biology
It doesn’t know where the pain is.
In a very simplified way: You have nerves that have “sensors” for pain, they receive pain signals from from other nerves. There are two main outcomes from using pain medications: you lower the frequency/likelihood/amount of pain signals, and/or you block the pain sensors themselves. Either outcome usually results in you feeling less pain.
Painkillers can be dose-dependent: up to a safe limit, the more you add, the more it’s able to act on pain signals and sensors. But painkillers can be dangerous depending on the type and dose, and the ideal amount to give is *just enough* so that you’re in an acceptable amount of pain. Given that pain is a very subjective thing, there isn’t a set point/dosage that works for everyone. However, you can make an educated guess based on past data. This usually causes x/10 on the pain scale, using y amount usually brings it down to a z/10 on the pain scale for most people, so we’ll start with y amount and adjust from there. Opioid-based painkillers are addictive, it’s best to use them very sparingly.
As for ibuprofen and acetaminophen, they block pain in similar ways. Ibuprofen blocks the chemicals that trigger pain, inflammation, etc.–these are essentially the “signals” mentioned above. Acetaminophen does something similar. Usually what dictates whether to use one, the other, both, or neither, comes down to the patient’s other conditions: for example, Ibuprofen affects blood clotting, so if you’re on blood thinners, you usually wouldn’t also be given Ibuprofen. If you’re a trauma patient who just got an arm ripped off in a combine, they’re gonna give you a shit ton of morphine, probably. If you have a headache, it’s probably going to be Advil or something similar. And so on.
High doses of ibuprofen or acetaminophen can damage your liver as well, so that’s also something to consider. While there isn’t an exact dosage that causes liver damage, we know that it’s caused liver damage in some patients at some dosages, and eventually, death at some higher dosages. So you can’t give someone, say, 100,000mg of intravenous acetaminophen in place of morphine, since that would definitely kill the patient, which is sub-optimal.
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