When developing and testing a new medication/drug, how do they know what the “right” dosage should be? What do they use as a starting point to determine safe clinical trials?

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Also, for treatments that require multiple doses over a period of time (i.e. the Hep B series, or other treatments that require several visits over a period of time), how do they know how far apart the doses should be?

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Testing in mice and occasionally monkeys. Then they use the data there to extrapolate a range of dosages per kg of body weight, and move on to human testing. They’ll test dosages in that range through human trials to see which one has the most effectiveness with the least severe side effects.

Clinical trials are the **last step** in drug development. You do experiments on cells in the lab and loads of animals before you even propose experiments in humans.

Initial trials are safety based, giving small amounts to healthy people without the condition in question to see how much is absorbed into the bloodstream. This checks for toxic reactions, side effects, and absorption/removal rates. These facts let you figure out how much to give at what rate (once a day, every 4 hours, …) to give the drug to maintain a level.

Then you start trials with people who would actually benefit from the drug, to measure effective doses (again starting very small) and look for effect over time relative to side effects.

Only when all these tests are favorable do you propose a controlled trial with a statistically significant number of actual patients.