For the newly bred and nearly dead dosing is heavily dependent on rate of metabolism. This is why kidney and liver function are so important to dosage. If a person can’t metabolize and clear out metabolites at a steady rate then it increases the bioavailability of a drug in the person’s system and can lead to overdoses. I used to tell my lab students that there’s no guaranteed way to tell how young kids are going to react to a medication just because their little systems are doing so much at wildly different rates.