Lecture 6 Chapter III physico chemical properties in relation to biological activity

Nội dung text: Lecture 6 Chapter III physico chemical properties in relation to biological activity

1. LECTURE 6 CHAPTER III PHYSICO CHEMICAL PROPERTIES IN RELATION TO BIOLOGICAL ACTIVITY Recapturing
2. DEFINITION:  The ability of a chemical compound to elicit a pharmacological/ therapeutic effect is related to the influence of various physical and chemical (physicochemical) properties of the chemical substance on the bio molecule that it interacts with. 1)Physical Properties Physical property of drug is responsible for its action 2)Chemical Properties The drug react extracellularly according to simple chemical reactions like neutralization, chelation, oxidation etc.
3. Various Physico-Chemical Properties are, ✓Solubility ✓Partition Coefficient ✓Ionization ✓Hydrogen Bonding ✓Chelation ✓Surface activity ✓Isosterism
4. ROUTES OF ADMINISTRATION  The choice of appropriate route in a given situation depends upon both drug as well as patient related factors.  Drugs administered locally or systematically.  The drugs administered through systemic routes is intended to be absorbed into blood & distributed all over.
5. Different Routes Of Drug Administrations Oral/ Oral/ Rectal Epithelial Inhalation Parentral Swallowed Sublingual Topical: local effect, substance is applied directly where its action is desired. ❖ Epicutaneous (application onto the skin), e.g. allergy testing, typical local anesthesia ❖ Inhalational, e.g. asthma medications ❖ Enema, e.g. contrast media for imaging of the bowel ❖ Eye drops (onto the conjunctiva), e.g. antibiotics for conjunctivitis ❖ Ear drops - such as antibiotics and corticosteroids for otitis externa
6. ABSORPTION:  The process by which the drug is released in the body from its dosage form is known as absorption.  Drug absorption is the movement of a drug into the bloodstream.  The factors which effect the rate of absorption are ◦ Concentration of the drug ◦ Route of administration ◦ Solubility of the drug ◦ Dissolution rate for solid dosage form
7. ◦ Blood circulation to the site of application and the area of the absorbing surface in local applications. ◦ Physico-chemical parameters of the drug.  To reach he site of action the drug has to cross one or more membrane barriers .  The main process by which a drug molecule cross the neutral barrier is, ◦ Simple diffusion ◦ Facilitated diffusion ◦ Pore transport ◦ Diffusion of the ion across the membrane ◦ Active transport ◦ phagocytosis 7
8. DISTRIBUTION:  Once the drug has been absorbed into the blood ,it distributed around the body. It get distributed throughout the blood supply , with in a minute. As the blood recirculates, the drug moves from the bloodstream into the body's tissues.  Drug is evenly distributed through out the blood supply, this does not mean the drug is evenly distributed around the body . Since he blood supply is rich in some areas of the body than the other. 8
9.  Drugs penetrate different tissues at different speeds, depending on the drug's ability to cross membranes. For example, the anesthetic thiopental, a highly fat-soluble drug, rapidly enters the brain, but the antibiotic penicillin, a water-soluble drug, does not. In general, fat- soluble drugs can cross cell membranes more quickly than water-soluble drugs can.  Distribution of a given drug may also vary from person to person. For instance, obese people may store large amounts of fat-soluble drugs, whereas very thin people may store relatively little. Older people, even when thin, may store large amounts of fat-soluble drugs because the proportion of body fat increases with aging. 9
10. METABOLISM:  Drug metabolism is the chemical alteration of a drug by the body.  metabolism is what the body does to the drug, Some drugs are chemically altered by the body (metabolized). The substances that result from metabolism (metabolites) may be inactive, or they may be similar to or different from the original drug in therapeutic activity or toxicity. Some drugs, called prodrugs, are administered in an inactive form, which is metabolized into an active form. 10