mg per kg dosing · Peak Physique

mg per kg dosing

Drug dosing is often simplified into three main methods: fixed dosing, weight-based dosing, and body surface area dosing. Today, I want to focus on weight-based dosing, where the dose is calculated as milligrams per kilogram of body weight. At first glance, it makes sense—larger individuals would need a higher dose than smaller individuals because their bodies are bigger.

However, this assumption has limitations.

The assumption behind weight-based dosing is that all pharmacokinetic parameters, like how the body absorbs, distributes, metabolizes, and excretes a drug, scale proportionally with body weight. Essentially, doubling someone’s body weight would require doubling their dose. But the body doesn’t work that way. For example, enzymes which are responsible for metabolizing drugs, don’t increase in number or efficiency just because someone weighs more. Similarly, processes like filtration in the kidneys aren’t directly proportional to body size either.

Take oxandrolone, for instance. A clinically studied dose for an 80 kg male is 20 mg, or 0.25 mg per kilogram. Using this formula, a 100 kg male would receive 25 mg, but this assumes that every extra kilogram of body weight increases the drug demand proportionally, which isn’t true. The liver enzymes processing the drug don’t multiply with weight, and neither do the androgen receptors the drug interacts with.

So, what’s the takeaway? Weight-based dosing is a convenient tool, but it oversimplifies the complexities of human physiology. Drug metabolism depends on far more than body weight, and assuming a linear relationship can lead to inappropriate dosing.

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