routes of administration - pharmacokinetics

Question 1

What is absorption?

Answer 1

Movement of a drug from the site of administration to the bloodstream.

Question 2

What is distribution?

Answer 2

Movement of drug
around different
tissues in the body.

Question 3

What is metabolism?

Answer 3

Change of drugs into
compounds which are
easier to eliminate

Question 4

What is excretion?

Answer 4

irreversible loss of
(unchanged) drug
from the body

Question 5

What are metabolism and excretion known as?

Answer 5

elimination

Question 6

Where is Bioavailability the best?

Answer 6

*IV administration means the entire dose reaches the
systemic circulation, i.e. 100% bioavailability (F)
* Bioavailability will be lower via other routes

Question 7

What does bioavailability depend on?

Answer 7

• Can depend upon permeability of the
  biological membrane, drug properties,
  and other route-dependent factors,
  e.g. stomach contents for oral route

Question 8

What is included in the first-pass (presystematic) metabolism?

Answer 8

• Drugs absorbed from the stomach, small
  intestines and upper colon pass into the hepatic
  portal system → liver
• Some drugs are metabolised extensively through their “first-
  pass” through the liver

Question 9

What is an example of a drug that undergoes first pass metabolism?

Answer 9

Naloxone:
* Used to combat opiate overdose
* Rapid onset required
* Undergoes first pass metabolism

Question 10

What is the bioavailability of the first-pass metabolism to the liver?

Answer 10

0.9-2%

Question 11

Where does metabolism typically take place?

Answer 11

• Metabolism predominantly takes place in the liver but can
  also happen elsewhere, e.g. skin, plasma, kidneys

Question 12

What is phase I metabolism?

Answer 12

• Simple chemical changes, e.g.
  oxidation, reduction, hydrolysis
• Cytochrome P450 isoenzyme
  particularly important
• Products are likely to be inactive
  and more water-soluble

Question 13

What is phase II metabolism?

Answer 13

• Involves the conjugation (or
  addition) of groups to the drug to
  increase its solubility
• Conjugates include glucuronates
  and sulphates

Question 14

What are some examples of oral administration routes? +exact drugs

Answer 14

• Solid (tablets, capsules) or liquid
  (suspensions, solutions) dosage forms
  *paracetamol
  *amoxiccilin
  *omeprazole

Question 15

Describe what oral drugs must do to reach absorption sites

Answer 15

• Dosage form travels to the main sites of
  absorption – stomach and small
  intestines
• Drug must cross lipophilic barriers to
  be absorbed

Question 16

What are some examples of the parenteral route of administration and example drugs?

Answer 16

• Parenteral formulations include:
  ̶Injections (intravenous, intramuscular,
  subcutaneous…)
  ̶Infusions
  *insulin
  *adrenaline
  *benzylpeniccilin Na

Question 17

What are the advantages to the parenteral route?

Answer 17

Useful if drug labile in GI tract
̶Fast-acting
̶Prolonged effect possible with IM
̶Localised effect, e.g. intra-articular
̶Drugs can be administered to unconscious patients
̶100% bioavailability for IV

Question 18

What are some examples of the inhalation route? + some example drugs

Answer 18

• Drug is delivered directly to the lungs typically via an inhaler
  or a nebuliser
  +saltbutamol
  +beclometasone
  +colistimethane Na

Question 19

What are the advantages to the inhalation route?

Answer 19

-Smaller doses can be used (salbutamol oral dose =
4 mg; inhaled dose 0.2 mg)
̶Reduces the chance of unwanted systemic (side)
effects
̶Fast onset because drug delivered to the site of action
̶Avoids first pass metabolism

Question 20

What is the transdermal route + examples of drugs used for this?

Answer 20

*application of the drug to the surface of the skin with the intention of receiving a systematic effect
*estradiol
*fentanyl
*nicotine

Question 21

What are the pharmacokinetic advantages of the transdermal route?

Answer 21

*avoids first pass metabolism
*controlled rate of drug delivery (avoids the peaks and troughs found with oral delivery)
*reduces dosage frequency which can increase compliance

Question 22

What is the rectal route used for and example drugs?

Answer 22

Typically used for the local delivery of drugs to
the rectum, e.g. haemorrhoids, but can also be
used for systemic delivery
*astringents
*glycerol
*prednisone

Question 23

What are the advantages of the rectal route for systematic delivery?

Answer 23

-Suitable if patient cannot easily swallow a solid
oral dosage form, e.g. unconscious, child
̶Drug not suited for oral delivery

Question 24

What are the typical dosage forms of the rectal route and why?

Answer 24

• Drug usually incorporated into a suppository
  which dissolves or melts within the rectum
• Foam formulations which expand to fill the
  rectum are also available

Question 25

What are the downsides to the rectal route?

Answer 25

*issue with pharmacokinetics and cultural acceptability