Similar to why you can’t just drink a whole lifetimes worth of water at once and never have to drink again (assuming you survived). Your body can only use so much, and the rest doesn’t get “stored” for later use, it just gets filtered out.
Plus, antibiotics can mess with your gut biome if you take too much at once.
Pharmacist here. When thinking about why you have to do something for a medication the answer is almost always safety and efficacy.
Medications are studied and certain protocols are followed for the study. Your doctor knows a treatment is likely to be effective if that particular protocol is followed. This means the medication will be effective.
All medications can cause side effects. If you have too much of a medication it’ll be more likely to cause side effects. You will naturally filter out all medications in your body eventually, but if you take too much of something your body have a harder time doing so. This means there’s a lot of medication in your body which means you’re more likely to experience side effects. That’s the safety aspect of it.
Two problems with that idea: the first is that many antibiotics are toxic at high doses, and you’d cause damage to your body if you took them all at once; the second is that you want to be sure you kill all of the infection, and sometimes that requires exposing it to the antibiotics over a longer period of time.
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