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dromaeovet t1_j6gl154 wrote

Reply to comment by TheRedLob in Can you (roughly) determine the dosage of a drug taken based off of the blood concentration? by bynarie

As a vet, the question of “why aren’t human medications doses based on weight” has always baffled me! We dose nearly everything in mg/kg because patient sizes are so different. We have some rules of thumb for species with a fairly standard size (mg/cat is a common one!) but I typically double check the mg/kg dose anyway.

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sat1vum t1_j6hhp3y wrote

In humans small differences in weight are usually not that big of a deal. Other factors like liver function or wether you take an oral drug with or without food introduce much more variability. Even if weight varies greatly between subjects, it’s often because of a higher fat mass. Most drugs don’t distribute into fatty tissue that well and so in those cases a weight based dose might over dose someone. Fat free mass is sometimes used but often not really needed. In children we do use a weight based dose though.

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