– Why does body weight matter with certain drugs?



Wondering why body weight matters with certain drugs. It’s never made sense to me considering that drugs act on receptors in the brain, so I don’t see why body weight would matter if the drug is only affecting the brain receptors

In: Biology

As drugs travel through your system, they can be absorbed by other cells in your body. If they absorb too much, those cells can die, so by knowing your body weight, you can estimate how much of a drug your body can absorb before it becomes potentially lethal

Body weight matters with all drugs because of bioavailability. Drugs are dosed by weight per kg from the manufacturer. Your BMI or BMA for infants, is what determines the amount of drug you are given based on it’s half-life (how long it’s active/stays in your system), it’s strength, route of administrationand frequency. Your weight directly correlates to the dose to avoid a low dose or an overdose. Also contrary to popular belief pharmacy tech and pharmacists do the dosage calculations for a lot of prescriptions.

If you aren’t given the correct dose based on weight, your “receptors” do not respond. If you use too much, they may shut down completely. It’s like finding the sweet spot in a manual car. No too are exactly the same, but each one has a perfect balance to perform how it’s expected. Two different cars with the same workings may need two separate approaches to get it going.

Let’s start with the fact that many many many medications target receptors that aren’t situated in the brain. Neurons, synapses, epithelial cells, muscle cells, sex organs, lung tissue, liver, kidneys, etc.

Most drugs become distributed through your bloodstream. Overall weight correlates well with total circulating volume, so basing dosages on weight corresponds well to concentration of drug at any one time. Concentration is critical to activity at receptor sites, so it is important to have a suitable dose for the overall circulating volume.

Off the top of my head – tolerance levels, body fat absorption, and retention of the toxin in the system.

Having a larger body means that the drug has more places to stop,and it reaches the brain slower.the drug can start being broken down in the blood by the specific enzymes,even before it reaches the liver.