Basic Biopharmaceutics Chapter 10 Biopharmaceutics • The study of the factors associated with drug products and physiological processes, and the resulting systemic concentration of the drugs. How Drugs Work • Drugs produce either desired or undesired effects on the body. – Once the drug is in the blood, drugs are circulated throughout the body. – Both the drug and the body influence where the drug will go. – The place where the drug causes an effect to occur is called the site of action. How Drugs Work • The objective of drug therapy is to deliver the right drug, in the right concentration, to the right site of action, and at the right time to produce the desired effect. How Drugs Work • When a drug produces an effect, it is interacting at a molecular level with cellular material or structure. • Cellular material directly involved in the action of the drug is called a receptor. • The receptor is described as a lock into which the drug molecule fits as a key. • Drugs are selective in their action, they only act on specific targeted receptors and tissues. How Drugs Work • Pharmacological effects of these interactions are agonists (agonism) or antagontists (antagonism). – Agonist – drugs that activate receptors to accelerate or slow normal cellular function – Antagonists – drugs that bind with receptors but do not activate them. They block receptor action by preventing other drugs or substances from activating them ADME Process Blood concentration of a drug are the result of four simultaneously occurring processes: – Absorption – Distribution – Metabolism – Excretion – Besides the ADME process, an important factor of drug concentration is how drugs move through biological membranes by diffusion. Absorption • Once a drug is released from its dosage formulation, the process that transfers it into the blood is called absorption. • One of the primary factors affecting oral drug absorption is the gastric emptying time. – This the time that the drug remains in the stomach before it is emptied into the small intestine – Most absorption occurs in the small intestine. – Some factors increase the gastric emptying time, but most slow it. – If a drug remains in the stomach too long, it can be degraded or destroyed, and its effect decreased. Absorption • Gastric emptying time can be affected by: – Amount and type of food in the stomach – The presence of other drugs – The person’s body position – The person’s emotional state Distribution • Blood carries the drug throughout the body and to its sites of action. • Drugs are rapidly distributed to organs having high blood flow rates such as the heart, liver and kidneys. • Distribution to the muscle, fat, and skin is slower because they have lower blood flow rates. Metabolism • Drug metabolism refers to the body’s process of transforming drugs. • The transformed drug is called a metabolite. • The primary site of drug metabolism is in the liver. • When transformed in the liver a drug is broken down into inactive or active molecules. Inactive are excreted through the kidneys and active produce effects and excreted later. Excretion • Most drugs are excreted in the urine by the kidneys. The functional unit of the kidney is the nephron. • Some oral drugs that are difficult to break down can be excreted in the feces (poop). • The job of the kidney is to filter the blood and remove waste products.