Fentanyl patches are used for chronic cancer pain but carry significant risks. The reason fentanyl is particularly suitable for transdermal delivery (unlike morphine) is:
- A Fentanyl is highly lipophilic and has low molecular weight, facilitating permeation across the stratum corneum ✓
- B Fentanyl has higher water solubility enabling aqueous gel formulations for faster skin penetration
- C Fentanyl undergoes less skin esterase metabolism than morphine preserving drug integrity
- D Fentanyl's low volume of distribution prevents extensive tissue distribution from the dermal depot
Correct answer: A. Fentanyl is highly lipophilic and has low molecular weight, facilitating permeation across the stratum corneum
Explanation
Effective transdermal delivery requires a drug to be highly lipophilic (for stratum corneum permeation), have relatively low molecular weight, and have sufficient aqueous solubility to partition from skin into dermal capillaries. Fentanyl is 600 times more lipophilic than morphine (logP ~4.05 vs –0.9 for morphine) with a molecular weight of 337 Da, making it ideal for transdermal delivery. Morphine's high polarity prevents meaningful transdermal absorption.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.