drug absorption

Question 1

what is the pharmacokinetic process

Answer 1

getting the drug to the site of action

Question 2

what is the pharmacodynamic process

Answer 2

producing the correct pharmacological effect

Question 3

what are the 4 basic factors that determine drug pharmacokinetics
(ADME)

Answer 3

Absorption
Distribution
Metabolism
Elimination

Question 4

define pharmacokinetics

Answer 4

the science of the rate of movement of drugs within a biological system

Question 5

what does pharmacokinetics allow the understanding of

Answer 5

dosage, drug administration, drug handling, patient variability, potential for harm

Question 6

what do most drugs require to have biological action

Answer 6

enter the blood stream and be distributed to a site of action

Question 7

methods of administration of drugs

Answer 7

oral, IV (not absorbed), subcutaneous, intramuscular, other GI (sublingual, rectal), inhalation, nasal, transdermal

Question 8

define absorption

Answer 8

the process of movement of unchanged drug from the site of administration to the systemic circulation

Question 9

regarding absorption, what 2 factors is there always a correlation between

Answer 9

plasma concentration of the drug and the therapeutic response

Question 10

Tmax

Answer 10

time to peak concentration of the drug, depends on how acute the symptoms are to be treated

Question 11

Cmax

Answer 11

peak concentration of the drug

Question 12

AUC

Answer 12

area under the drug concentration-time curve, represents the amount of drug which reaches the systemic circulation and is used to work out bioavailability

Question 13

during which point do we want Cmax to occur within

Answer 13

the therapeutic window

Question 14

what would cause an earlier Tmax

Answer 14

a more rapid rate of absorption

Question 15

what impact does dose have on Tmax and Cmax

Answer 15

doesnt effect Tmax but does increase Cmax

Question 16

Define therapeutic range

Answer 16

the range of concentrations over which a drug is active
below this = insufficient or no pharmacological action
above this = toxicity

Question 17

what is the therapeutic index

Answer 17

a measure of the range at which a drug is safe and active

Question 18

what is the bioavailability of a drug given IV

Answer 18

100%

Question 19

what factors affect bioavailability

Answer 19

formultion, ability of the drug to pass physiological barriers, GI effects, route of administration, first pass metabolism

Question 20

how does formulation affect bioavailability

Answer 20

some medications are prepared in slow release preparations, capsules break down faster than tablets

Question 21

what can alter the ability of drugs to cross physiological barriers

Answer 21

particle size, lipid solubility (blood-brain/ovary barrier, placenta etc), pH, ionisation

Question 22

why can lipid soluble drugs have significant side effects

Answer 22

they can bypass lipid membranes e.g. cannabis

Question 23

how do GI effects alter bioavailability

Answer 23

motility: speed of gastric absorption affects the speed at which the drug reaches the side of aborption (most drugs are absorbed in small intestine), can be affected by other drugs, food/drink and illnesses
food: can enhance or impair absorption
illness: malabsorption can increase/decrease rate of absorption, migraine reduces rate of stomach emptying and therefore rate of absorption of analgesic drugs

Question 24

how does route of administration affect bioavailability

Answer 24

by mouth will get into the blood faster than rectally

Question 25

first pass metabolism and its effects on bioavailability

Answer 25

• Varies markedly between individuals and increases during pregnancy
  
  • Metabolism of drug prior to reaching systemic circulation, can be a limit on oral route for some drugs (oral route not useable - insulin), gut lumen (acid, enzymes), gut wall (metabolic enzymes), liver (hepatic enzymes). These factors can be changed by drugs and disease

Question 26

subcutaneous/intramuscular drug administration

Answer 26

can change the rate of absorption from these sites with different physical properties of formulation, depends on blood flow to site, needs small volume, avoids first pass metabolism, some drugs not well absorbed from this route (water soluble better)

Question 27

sublingual/buccal drug administration

Answer 27

sublingual absorption from the buccal mucosa bypasses first pass metabolism which will inactivate the drug, drugs given this way enter the circulation directly e.g. GTN for angina

Question 28

rectal drug administration

Answer 28

bypasses first pass metabolism, absorption tends to be slow, often used for drugs that cause stomach irritation or local conditions

Question 29

inhalation/nasal administration

Answer 29

absorption depends on the type of delivery system, particle size and patient technique. Better for volatile agents, can be metabolism in the lungs. Relatively rapid action, about 5-10% absorbed. Most commonly used for asthma, allows dosage to be reduces. Usually used for topical effect or to avoid problems of oral absorption e.g. nausea

Question 30

transdermal drug administration

Answer 30

avoids first pass metabolism, can provide controlled released, few substances well absorbed, need to be non-irritant

Question 31

what factors need to be taken into consideration when determining the mode of administration for a drug

Answer 31

• purpose and site of drug action (local, first pass metabolism)
• disease effects
• patient’s ability to take the medicine
• speed of action
• reliability of absorption