: What is the blood level evolution of a intramuscular injection? Suppose an intramuscular injection of a substance is done on a patient. What would be the form of the graph of the blood concentration of this substance over

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This is taken from a paper on Science Direct.

The intramuscular route is used where effects are desired over a
longer period of time than can be expected after intravenous
injection, for drugs that are too irritant to be given subcutaneously,
or for oily solutions, which cannot be given intravenously. Drugs in
aqueous solution are often absorbed rapidly from intramuscular sites.
Drugs dissolved in oil (‘depot’ injections) are absorbed more slowly
and absorption can continue for weeks after injection.

Generally, the intramuscular (IM) route results in slower absorption and a longer duration of action than intravenous (IV) injections.

However, there is a wide variability depending on the preparation and the drug involved.

Here is a qualitative graph showing a comparison of plasma concentration against time.

The branch of pharmaceutical science concerned with the absorption and elimination of drugs is called pharmacokinetics.