: What is the advantages (for patients) in delayed and extended release drugs? What are the advantages for patients between extended and delayed release drugs? i understand the difference between these two drugs, but i want

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To understand the advantages of Extended Release (ER) and Delayed Release (DR) formulations, the primary differences between them should be highlighted. Taken from "A Clinician's Guide to Oral Extended-Release Drug Delivery Systems in Epilepsy" (italics are mine):

Delayed-Release (DR) Formulations. The US Pharmacopeia (USP) defines DR as a dosage form that does not release the medication promptly after administration. In other words, once a certain amount of time has lapsed, the drug is immediately and completely released. The delayed release may be time sensitive or dependent on the environment (e.g., gastrointestinal pH). For example, an enteric coating can be used to intentionally delay drug release until after the tablet has passed through the stomach. This may reduce drug irritation of the gastric mucosa or prevent gastric juices from inactivating an acid-labile drug.
Extended-Release (ER) Formulations. The USP defines ER as a dosage form designed to release the medication in a controlled manner during an extended period of time, at a predetermined rate, duration, and location following administration. At steady state, the rate of absorption is approximately equivalent to the rate of elimination due to metabolism and excretion.

It is evident that these are essentially two different profiles of a drug, as each type of formulation gives the drug a distinct behavior, which gives the drug better chances for efficacy:

The advantage in delayed-release formulations is not exactly an advantage for the patient. Rather, it's an advantage for the treatment, because using such formulations enables the doctor to treat the patient with drugs that could not be taken orally otherwise, such as acid-labile drugs (e.g. omeprazole for heartburn).
The advantage in extended-release formulations is more direct for the patient, because it allows the patient to take the drug less frequently, which is always preferable, as it increases the chances of adherence to the treatment (compare taking a tablet 6 times a day to once a day. It is obviously a lot easier to take a tablet once a day and be done with it, than having to stop what you are doing every few hours and take a tablet).

This figure from the above-cited paper demonstrates this discussion very clearly:

In the top figure, you can see that the pharmacokinetic profile for IR (immediate release) and DR are identical, only the DR profile occurs later, since it is only "postponed" as discussed above. ER, however, demonstrates a profile of a different shape, since the peak is lower, but higher concentrations are maintained for a longer period of time compared to the IR and DR formulations, which give only a short strong peak.
The advantage of ER formulations is even better elucidated in the bottom figure, where it is seen that taking an ER formulation once a day (compared to taking an IR formulations three times a day) provides desired serum concentrations throughout the day and with lower chances for side effects (the peak does not cross the top of the therapeutic range, as opposed to the sharp peaks of IR formulations), and lower chances for dropping to subtherapeutic concentrations (the peak does not cross the bottom of the therapeutic range, as opposed to the sharp peaks of IR formulations).