pharmacology

Question 1

Define bioavailability

Answer 1

Fraction of an administered dose of unchanged drug that reaches systemic circulation and is available for clinical effect

or

The proportion of ingested drug available to take clinical effect (amount of drug that actually affects patient)

Question 2

Describe first pass metabolism

Answer 2

Drug gets metabolized at a specific location in the body that results in a reduced concentration of the active drug in systemic circulation upon reaching its site of action or the systemic circulation

• Concentration of drug is greatly reduced before it reaches the systemic circulation
• Fraction of a drug lost during the process of absorption in the gut and metabolism in the liver

or

• When a drug is broken down and metabolised (in liver) too quickly; before it has had a chance to take effect.
• Liver metabolises orally-administered drugs and INACTIVATES them

Question 3

How would you overcome first pass metabolism problem?

Answer 3

• Dissolve tablet under tongue,
• Give drug via injection
• Use drug in spray form sublingually
  –> drug delivered directly into bloodstream (avoids being metabolised by liver)

Question 4

advantages and disadvantages Oral medication: e.g. IBUPROFEN

Answer 4

Advantages:
* Socially acceptable

Disadvantages:
* First pass metabolism effect reduces the amount of drug that is passed to the systemic circulation
* Risk of drug causing gastric irritation & ulceration (NSAIDs par example)

Question 5

IV medication: e.g. MIDAZOLAM

Answer 5

Advantages:
* Rapid, immediate onset of drug
* Avoids first pass metabolism: nearly 100% bioavailability
* Some drugs are poorly absorbed
* Continuous, closely monitored administration

Disadvantages:
* Requires IV access: painful and can be difficult to obtain
* Increased infection risk

Question 6

Subcutaneous: e.g. INSULIN, HEPARIN

Answer 6

Advantages:
* Avoids first pass metabolism, therefore higher bioavailability in body
* Constant, slow & prolonged absorption by fatty tissue

Disadvantages:
* Needle breaks protective barrier against infection

Question 7

Intramuscular: e.g. GLUCAGON, ADRENALINE

Answer 7

Advantages
* Rapid onset, shorter duration
* Muscle can absorb liquid better than subcutaneous layer

Disadvantages:
* Neurovascular (nerve) damage
* Bleeding, painful & infection risk
* Dependent on blood flow: delayed absorption in shock

Question 8

Transdermal: e.g. GLYCERYL TRINITRATE PATCH

Answer 8

Advantages
* Avoids first pass metabolism, therefore higher bioavailability in body
* Controlled & continuous release

Disadvantages
* Skin is an effective barrier: only small molecule medications can work

Question 9

first pass metabolism

Answer 9

drug only reaches the systemic circulation AFTER passing through the liver once

can inactivate or activate proportion of the drug

Question 10

bioavailability

Answer 10

proportion of an ingested drug that is available for clinical effect

modified by dosage and route of administration

Question 11

conjugation

Answer 11

the process of covalently linking drugs or prodrugs to various natural or synthetic molecule carriers for specific applications, e.g. polymers, polypeptides or proteins, lipids, and carbohydrates

Question 12

zero order kinetics

Answer 12

Drug metabolism is at a FIXED rate – ACTIVE process
* Irrespective of drug concentration
* Can lead to the drug accumulation if saturation exceeded
* E.g. paracetamol

Question 13

agonist drugs

Answer 13

bind to specific receptors to activate the cascade for physiological response

e.g. opioids, beta-agonists, dopamine agonists

Question 14

first order kinetics

Answer 14

Drug metabolism increases as drug concentration increases
* Excretion is by PASSIVE DIFFUSION only

Question 15

antagonist drugs

Answer 15

bind to receptors to block or inhibit their normal physiological activity

e.g. beta-blockers, antihistamines, antipsychotics