Lec 6

Lecture 6

pharmacokinetics

pharmacokinetics

deals with the drug disposition; “what the body does to the drug”

absorption, distribution, biotransformation, excretion

bodily processes involved in drug disposition which influence drug levels in the body

enteral & parenteral

routes of drug administration

enteral

route of DA that initiate orally or rectally

parenteral

non-oral routes

absorption

passage of drug molecules from the site of administration into the blood circulation

systemic & local

types of drug effect

systemic

effect that occurs when a drug is absorbed into the blood circulation

local

effect that is not preceded by absorption

small intestine

usual site of absorption for orally administered medications

TRUE

T or F.

Absorption may begin in the mouth and stomach for some drugs

dissolution rate of drug

rate-limiting factor in absorption from the gut

rate of injection or infusion

rate-limiting factor in absorption from IV injections

blood flow

rate-limiting factor in absorption from all other routes

TRUE

T or F.

The sublingual route is both enteral and parenteral.

passive diffusion

it is the most important mechanism for passage of drugs; it requires the establishment of a concentration gradient across the membrane

small in size, lipophilic, non-ionized/nonpolar

characteristics of a drug in order for it to move through the cell membrane by passive diffusion

TRUE

T or F.

Aside from passive diffusion, a drug can also be transported across cell membrane via carrier mediated transport and pinocytosis.

bioavailability

a measure of how much drug is absorbed into the blood circulation; expressed as percent of the dose administered

50%

If 100 mg of a drug is administered orally and only 50 mg of the drug is absorbed unchanged, the bioavailability is:

minimum effective concentration (MEC)

minimum level of a drug that should be attained in the plasma in order to induce an effect

FALSE. there is none

T or F.

There is still slight pharmacological effect produced below MEC.

pharmaceutical, physiological, physicochemical

factors affecting GIT absorption

incorporation of excipients, micronization/nanonization

pharmaceutical factors that affect the dissolution of dosage forms

micronization or nanonization

process of reducing particle size to improve the rate of drug dissolution, thus resulting in greater GIT absorption of the drug

solution > suspension > capsule > tablet

arrange the following dosage forms based on their availability to be absorbed:

suspension, tablet, capsule, solution

Answer this way:

suspension > tablet > capsule > solution

length of GIT, presence of food in the stomach, GIT pH

physiologic factors that affect the transit time of drug along the GIT

TRUE

T or F.

Ruminants have more alkaline pH in the GIT while carnivores have more acdic pH in the GIT

drug solubility, the degree of ionization of a drug

physicochemical factors affecting the absorption of drugs in the GIT

oil/water partition coefficient

ration of drug solubility in oil to its solubility in water; reflects the lipid solubility of a drug

FALSE

T or F.

high oil/water partition coefficient means that the drug is less lipid soluble, and thus has lower absorbability

TRUE

T or F.

A drug tends to pass thru the membrane if it is uncharged.

FALSE

T or F.

Uncharged drugs are less lipid-soluble than charged drugs.

TRUE

T or F.

The degree of ionization of a drug is related to its acidic or basic properties.

TRUE

T or F.

Drugs are mostly weak acids or weak bases.

drug pH, pH of the medium, dissociation constant (pK)

factors affecting the degree of ionization

TRUE

T or F.

When a weak acid reacts in an acidic environment, it becomes lipophilic which is more absorbable in the body.

FALSE

T or F.

When a weak base reacts in an acidic environment, it transforms into a lipophilic form.

intestine

Weak bases are best absorbed from the ___

Weak acids

They are best absorbed from the stomach

TRUE

T or F.

The lower the pK, the stronger the weak acid.

FALSE

T or F.

The higher the pK, the stronger the weak acid.

Henderson-Hasselbach equation

demonstrates the effect of drug pH, drug pKa, and the pH of the medium on the degree of drug ionization

pH = pK + log [A-]/[HA]

Henderson-Hasselbach equation