Pharmacokinetics

Question 1

What is the definition of pharmacokinetics?

Answer 1

What the body does to drugs/how drugs move through the body

Question 2

What are the three classes of routes for giving medications?

Answer 2

1. Parental 2. Enteral & 3. Topical

Question 3

What are the different routes for administering medication?

Answer 3

Oral, intramuscular (IM), intravenous (IV), intraosseous (IO), subcutaneous, sublingual, bucal, rectal, topical & percutaneous

Question 4

What are the four stages of the ADME process?

Answer 4

Absorption;
Distribution;
Metabolism;
& Excretion.

Question 5

What are some of the factors that affects drug absorption?

Answer 5

. Physical nature of the dosage form
. Presence of food in the stomach
. GI contents and their composition
. Gastric and/or interstitial pH
. Mesenterio blood flow
. Concurrence administration of other drugs

Question 6

What happens during passive diffusion?

Answer 6

Small drug particles pass through the cell membrane from a stronger solution to a weaker one. (Energy neutral)

A lot of the drug is lost though the GI system - high dose required.

Question 7

What happens during facilitated diffusion?

Answer 7

Lipid solubles cross with the help of a carrier molecule, passively, as a concentration gradient is required. (No energy expended)

Question 8

What happens during active transport?

Answer 8

Drugs that resemble substances in the body require absorption against the concentration gradient, therefore, require carrier molecules. (Energy expended via respiration)

Question 9

Define bioavailability.

Answer 9

The proportion of the administered dose that reaches the system circulation.

e.g. IV drugs are 100% bioavailable as they are given directly into the blood stream.

Question 10

What factors affect distribution?

Answer 10

. Blood flow
. Displacement
. Protein binding
. Blood brain carrier
. Placental barrier
. Storage sites

Question 11

Explain protein binding.

Answer 11

Most drugs entering the circulation are not very soluble and are carried by plasma proteins.

Drug molecules are either free, or bound to these plasma proteins.

Only free drugs can cross plasma membranes as bound drugs are too large.

Question 12

What do acidic drugs and alkaline drugs bind to?

Answer 12

. Acidic drugs bind to Albumin
. Alkaline drugs bind to glycoproteins

Question 13

What is the therapeutic index?

Answer 13

If more than one drug that burns to a plasma protein is present at one time, they will fight for the same site.

I don’t have to find a balanced state where the drugs have space to work.

Clinically important to know that one drug can displace another.

Question 14

Define volume of distribution.

Answer 14

The extent that a drug is distributed throughout the body and bound to other tissues.

Question 15

What kind of drugs can pass the blood brain barrier?

Answer 15

Only highly lipid soluble drugs can cross the blood brain barrier.

The brain has higher blood perfusion that fats or muscles enabling a quicker action.

Question 16

What kind of drugs can pass across the placental barrier in pregnancy?

Answer 16

Highly lipophilic drugs can cross this barrier.

E.g. morphine and ethanol (alcohol).

Question 17

What is first pass metabolism?

Answer 17

A defensive effect where a body system or organ removes the drug prior to any therapeutic effect.

E.g. GTN - which is why we administer sublingually or transdermally.

Question 18

What effect does metabolism have on drugs?

Answer 18

It alters the chemical composition of the drug to make them more water soluble and remove the effect of the drug - easier to excrete.

Question 19

What are some examples of drugs that become active in Phase 1 and remain active in Phase 2 or metabolism?

Answer 19

Phase 1 - Diamorphine (e.g. heroin) is made active by metabolising to morphine, becoming pharmacologically active.

Phase 2 - Morphine attaches to a glucoronate compound and still exerts some level of analgesia.

Question 20

What are some factors that affect metabolism?

Answer 20

. Age
. Genetic/racial/community/health
. Smoking
. Other drugs taken including food/herbs e.g. ginseng and charcoal)
. Liver/kidney function
. Heart failure
. Endocrine disorders

Question 21

Where are drugs mainly excreted?

Answer 21

Most drugs are excreted via the kidneys.

Also excreted via
. Sweat
. Tears
. Saliva
. Breath
. Breast milk

Question 22

What happens with drugs via renal excretion?

Answer 22

Drugs bound to plasma proteins are too large to pass through and can be reabsorbed through the blood stream.

Free or unbound drugs can pass through.

Question 23

What is the enterohepatic cycling?

Answer 23

Mechanism that excretes drugs via the liver in bile - through to small intestine - reabsorbed into blood stream.

E.g. aspirin, benzodiazepines, morphine and oral contraceptives.

Not many drugs are excreted in bile.

Bad gut health means the cycle won’t work well. (E.g. if you have diarrhoea or vomiting, your oral contraceptive level won’t be as high).

Question 24

What is the definition of a drug half life?

Answer 24

The amount of time needed for the plasma concentration to fall to half of its original value - measured in hours.

Concentration will drop based in metabolism and excretion.

This is why some drugs are given as losers doses initially then maintenance doses. E.g. doxycycline.