Duration of action for pain medication can differ extremely among individuals.
When my wife (chronic pain patient) wanted to switch from one pain med to another because of diminishing effect, I helped her neurologist review literature on the equianalgesia properties of various options.
For several meds, blood concentration vs. time varied by one order of magnitude among patients who were otherwise well-matched subjects. Some metabolized/eliminated a med to non- therapeutic levels in a day, others took nearly two weeks. Same dose, same route of administration. Probably different P450 enzyme activities [1] among other things.
I came away from the experience appreciating how incredibly difficult it is to construct a good pain management plan. It takes more time and info than many doctors can bring to bear on each patient.
When my wife (chronic pain patient) wanted to switch from one pain med to another because of diminishing effect, I helped her neurologist review literature on the equianalgesia properties of various options.
For several meds, blood concentration vs. time varied by one order of magnitude among patients who were otherwise well-matched subjects. Some metabolized/eliminated a med to non- therapeutic levels in a day, others took nearly two weeks. Same dose, same route of administration. Probably different P450 enzyme activities [1] among other things.
I came away from the experience appreciating how incredibly difficult it is to construct a good pain management plan. It takes more time and info than many doctors can bring to bear on each patient.
[1] https://en.wikipedia.org/wiki/Cytochrome_P450