How exact are the times for how long to wait between pills?

Question

A 120mg pill of Sudafed (Pseudoephedrine hydrochloride), for example, lasts for 12 hours. You are not supposed to take another Sudafed pill before the 12 hours are up.**How exact is this 12-hour limit?** Do i have to wait at least exactly 43200 seconds between pills? How much leeway is there? Could i take the second pill a few minutes (5? 10? 30?) before the time is up?Note that Sudafed is used as an example here. The same should apply to any other drug with a time limit.

Answer 1

That is a great question, and the timing of the next dose of any medication depends on that medication's specific pharmacodynamics, including the duration of the action of the medication. This time is determined for every medication and is the length of time that the medication works in the body.

Some medications can have negative effects on the body if there is too much circulating, or acting on organs, at any time, so it is important to wait and take the next dose during the recommended window. Some patients take chronic (daily) medications, and it is important for them to maintain a "steady state", meaning they need to keep a certain concentration of their medication in their blood for it to be effective. These patients need to pay attention closely to the dosing and timing recommendations as well.

So, in short, being off by a few seconds or minutes is not likely to make any significant change in your outcome, but it is a good guide and should be followed as closely as possible.

It is variable for every medication, since every medication has a different onset, peak, duration of action and half-life, so the next dose is recommended based on these values.

I always be sure to review with my patients how long they should wait between dosages, and what to do if they miss a dose (whether it is safe to double-up and take it as soon as they remember, or if they should skip the missed dose), and this varies based on each medication.

I hope that helps!