What is the Origin of Lipophilic Drug Partitioning?

This principle is derived from classical physical chemistry, specifically Nernst's distribution law, and is a fundamental concept applied in pharmaceutical science to predict and optimize drug absorption across biological barriers. The oil-water partition coefficient, typically expressed as the logarithm of the partition coefficient (log P), serves as the quantitative measure of a compound's lipophilicity. This concept underpins the rational formulation of most steroid hormonal agents.

What is the Mechanism of Lipophilic Drug Partitioning?

A therapeutic hormone requires a finely tuned balance of lipophilicity and hydrophilicity to partition effectively out of the application vehicle and into the lipid-rich stratum corneum. Simultaneously, it must retain enough aqueous solubility to exit the stratum corneum and diffuse into the more aqueous viable epidermis and dermis. Excessive lipophilicity can lead to drug retention in the skin barrier, while insufficient lipophilicity hinders the initial membrane crossing. Optimizing this partitioning ensures maximal systemic drug uptake.

Lipophilic Drug Partitioning ∞ Area

Lipophilic Drug Partitioning

Meaning

The physicochemical principle describing the unequal distribution of a lipophilic, or fat-soluble, drug between two distinct, immiscible phases, such as an aqueous formulation vehicle and the lipid-rich stratum corneum. In the context of transdermal delivery, optimal partitioning from the application vehicle into the skin barrier is a necessary first step for efficient absorption. This critical balance dictates the thermodynamic driving force for the compound’s movement into the underlying tissue.