Comparative absorption, excretion, and storage of oily and aqueous preparations of vitamin A

Indirect-acting cholinergic agonists, or anticholinesterases, enhance the body's cholinergic activity by inhibiting acetylcholine's breakdown. They are categorized as reversible or irreversible agents based on their mechanism of action. They are further classified into short-acting, intermediate-acting, and long-acting agents based on their duration of action.
Reversible agents containing quaternary amines, such as neostigmine and edrophonium, are not easily absorbed orally because they are...

Dietary triglycerides from chyme in the duodenum are mixed with bile salts produced by the liver to emulsify fats. As a result, large droplets are broken down into smaller ones, increasing the surface area for enzymatic action. Once emulsified, pancreatic lipases hydrolyze the triglycerides into free fatty acids and monoglycerides.
These breakdown products bind with bile salts and lecithin to form micelles, which quickly pass between microvilli to come in close contact with the apical...

In vitro experiments are crucial for understanding the transport and absorption of drugs through biological materials. These studies employ varied methods such as the diffusion cell method, the everted sac technique, and the everted ring technique.
The diffusion cell method uses a two-compartment cell, including a donor compartment with the drug solution, which simulates the environment where the drug is applied, and a receptor compartment with a buffer solution, which simulates the environment...

Fats and lipids are crucial components in the human body. Some lipid-derived compounds, such as fat-soluble vitamins, eicosanoids, lipoproteins, and glycolipids, also play unique roles to support various  biological processes .
Fat-soluble Vitamins
Fat-soluble vitamins, including vitamins A, D, E, and K, are required in minimal quantities, but their deficiencies can lead to severely abnormal physiological conditions. For example, vitamin A deficiency can cause night blindness, dry skin, delayed...

Non-oral extravascular routes, which encompass sublingual, buccal, topical, intramuscular, and inhalation methods, primarily utilize passive diffusion to transport drugs into the systemic circulation. The absorption rates and effectiveness of these routes depend on the drug's physicochemical properties, as well as the patient's anatomical and pathophysiological state.
Lipophilic drugs that are stable at salivary pH (6) and exhibit minimal binding to the oral mucosa are absorbed more effectively...

The physicochemical characteristics of drugs play a crucial role in formulating stable and bioavailable drug products. The solubility of a drug, governed by the varying pH along the GI tract and its dissociation constant (pKa), is pivotal in determining its ionization state and absorption rate. Notably, weak acids and bases remain unionized and are absorbed more rapidly.
Enhanced drug absorption can be achieved by reducing particle sizes and increasing surface areas, thereby facilitating...