Skin can act as a barrier and prevent deep penetration of drug molecules. Percutaneous absorption of most drugs is a passive diffusion process that can be described by Fick’s first law of diffusion. In the initial diffusion stage, drug molecules may penetrate the skin along the hair follicles or sweat ducts and then be absorbed…
The existence of different ionic forms of amino acids can be more easily understood by the titration curves as shown in Figure 3.1. At low pH, leucine exists in a fully protonated form as cation. As titration proceeds with NaOH, leucine loses its proton, and at isoelectric pH (pI), it blames a zwitterion. Further titration results…
On topical application of a semisolid drug, the drug diffuses passively out of its vehicle and partitions into either the stratum corneum or the sebum-filled ducts of the pilosebaceous glands. Inward diffusive movements continue from these locations to the viable epidermal and dermal points of entry. Thus, a concentration gradient develops across the skin up…
Isoelectric point (pI) is defined as the pH at which a molecule exists as zwitterion or dipolar ion and carries no net charge. Example: pI for leucine is 6.
Learning Objectives Semisolid dosage forms are mainly meant for external application on the skin or mucous membrane. They are traditionally used for treating topical ailments. They are also used for treating ophthalmic, nasal, buccal, rectal and vaginal ailments. Semisolid dosage forms may be used for therapeutic, cosmetic or protective properties. Examples are ointments, pastes, creams,…
The amino acids differ in their physical chemical properties, which ultimately determine the characteristics of proteins.