Recall phenomenon is seen in: March 2013 (b)
**Core Concept**
Recall phenomenon is a pharmacological effect where an increase in the dose of a drug leads to a decrease in its therapeutic effect, which is a paradoxical response to the increase in dosage. This phenomenon is seen in certain drugs that cause a decrease in their own receptor binding or efficacy at higher doses.
**Why the Correct Answer is Right**
The correct answer is related to the concept of Efficacy and affinity of drugs. When a drug binds to its receptor, it can either increase or decrease the activity of the receptor. In the case of recall phenomenon, the drug increases the receptor's activity at low doses, but at higher doses, it decreases the receptor's activity. This is because the drug may either alter the receptor's conformation or interact with other receptors that decrease the activity of the primary receptor. The recall phenomenon is seen in drugs like morphine, where high doses can lead to tolerance and decreased analgesic effect.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the recall phenomenon.
* **Option B:** This option may be related to other pharmacological effects, but not specifically the recall phenomenon.
* **Option C:** This option may be related to the concept of tolerance, but not the specific phenomenon of recall.
* **Option D:** This option is not relevant to the recall phenomenon.
**Clinical Pearl / High-Yield Fact**
The recall phenomenon is an important concept in pharmacology, as it highlights the complex relationship between drug dose, receptor binding, and therapeutic effect. It also underscores the importance of dose titration and careful monitoring of patients on certain medications.
**Correct Answer: B. Morphine**