Basic Biopharmaceutics Chapter 10 Pgs. 290- 312

How Drugs work Drugs produce either desired or undesired effects in the body. When producing an effect, interacting at molecular level with cellular material. Receptors are located on surfaces of cell membranes and inside cells. When molecules bind with a receptor, can cause a reaction that stimulates or inhibits cell growth. Number of receptors available to interact with a drug will directly influence the effect. Receptors can be changed by drug use.

Concentration & effect One problem is that many factors influences a drug’s movement from site of administration to site of action. Can be physically impossible to measure the drug at the site of action because of unknown location or small size. Ways to monitor amount of drug in body: dose-response curve blood concentration levels

Adme processes & diffusion Blood concentrations are the results of four simultaneously occurring processes: A: absorption D: distribution M: metabolism E: excretion

Transfer of drug into the blood from an administered drug product. absorption Transfer of drug into the blood from an administered drug product.

Factors affecting oral drug absorption: Factors affecting oral drug absorption: *gastric emptying time amount and type of food in stomach presence of other drugs person’s body position emotional condition *bile salts and enzymes from intestinal tract *rate of movement through intestines Most of these will slow time; but some can increase.

distribution Movement of a drug within the body once the drug has reached the blood.

Distribution will be affected by physiological functions and the drugs properties. Blood flow rates have significant effect on distribution (heart vs. muscle). Permeability of tissue membranes. Protein bindings.

Body’s process of transforming drugs Metabolism Body’s process of transforming drugs

Primary site for metabolism is the LIVER Primary site for metabolism is the LIVER. With chronic administration of certain drugs, liver will increase enzyme activity Liver may secrete drugs or their metabolites into bile. ****Know First-Pass Metabolism****

excretion Most drug and their metabolites are excreted in the urine by the kidneys.

Drugs are also excreted through feces and bile Drugs are also excreted through feces and bile. Urinary excretion is fastest ( may be excreted within hours). Factors affecting excretion: impaired kidney function drug affect urine pH Amount of drug excreted in urine = filtered + amount secreted – amount reabsorbed.

bioavailability Amount of drug delivered to the site of action and the rate at which it becomes available.

Measured using data from blood concentration – time profile Measured using data from blood concentration – time profile. To determine extent must compare patient profile to drug standard profile. Need to know difference between absolute and relative bioavailability.

bioequivalence Comparing bioavailabilities of one drug to another. Required by the FDA before manufacturers can have products approved for marketing. Also used to compare between different dosage forms ( capsules, tablets, etc.). Exact bioequivalence between drug products does not occur and is not expected.

REVIEW

The place where a drug causes an effect to occur is called: Site of action Site of administration Therapeutic window Minimum toxic concentration (MTC) (A)

The amount of drug excreted in the urine is the amount: Filtered + secreted + reabsorbed Filtered + secreted – reabsorbed Filtered - secreted + reabsorbed Filtered - secreted – reabsorbed (B)

Drug action can be determined by the: Number of receptors occupied Number of receptors present Sensitivity of the receptors All of the above (D)

Blood concentrations are the result of ____ simultaneously occurring processes. Two Four Three Five (B)

The transfer of a drug out of a dosage form and into the blood is called: Absorption Dissolution Metabolism Elimination (A)

Which processes can influence the absorption of drugs given orally? First – pass metabolism Intestinal transit time Gastric emptying All of the above (D)

Elimination is: Absorption and metabolism Metabolism and excretion Distribution and excretion Distribution and metabolism (B)

Which drug would not typically be monitored with peak and trough blood levels? Vancomycin Valproic Acid Promethazine Phenytoin (C)