Question

What should be the log P value for an ideal drug candidate for transdermal permeation:

• A. Below 1
• B. 1-3
• C. 5-7
• D. Above 7

Answer 1

The Correct Option is B

The correct option is (B): 1-3.

Answer 2

The question asks about the ideal log P (octanol-water partition coefficient) range for a drug meant to cross the skin in a transdermal delivery system. Let's assess each range.

1. Below 1: A drug this hydrophilic struggles to cross the lipid-rich stratum corneum, the main barrier layer of the skin. Permeation through this outer layer would be very poor.
2. 1-3: A drug in this range is lipophilic enough to dissolve into and move through the lipid bilayers of the stratum corneum, yet still polar enough to partition out into the more aqueous viable epidermis and dermis beneath it and reach the blood supply. This balance is exactly what transdermal permeation needs.
3. 5-7: A drug this lipophilic tends to get trapped inside the stratum corneum itself. It partitions into the skin lipids so strongly that it resists moving further into the aqueous layers underneath, so overall permeation drops.
4. Above 7: This is even more extreme than the 5-7 range. Such a highly lipophilic drug would be almost insoluble in the aqueous tissue below the stratum corneum, making it a poor candidate for transdermal delivery.

A log P of 1-3 gives the balance of lipophilicity and hydrophilicity a drug needs to cross the stratum corneum and then move into the systemic circulation.

Therefore, the correct answer is 1-3.