Introduction & Pharmacokinetics Flashcards
Abbreviations
o. d.
b. d.
t. d.s
q. d.s
p. r.n
- o.d. Once daily
- b.d. Twice daily
- t.d.s Thrice daily
- q.d.s Four times daily
- p.r.n. As required
Lidocaine is used as a…
Antiarrhytmic drug
Time required for one arm-brain cycle
ca. 10 seconds
Phenytoin is used to manage…
Status epilepticus
Advantages of IV
- Rapid effects
- Absorption circumvented, i.e. not subject to bioavailabilty
- Permits titration of dosage
- Emergency use
Cons in use of IV route
- Increased risk of adverse effects
- Risk of embolism
- Not suitable for oily solutions or insoluble substances
- Requires IV access
Advantages of subcutaneous administration
- Slow sustained release from repository preparations
- Suitable for some insoluble suspensions
Cons of subcutaneous administration
- Not suitable for large volumes
- Somewhat incomplete bioavailability, varies from drug
Pros of intramuscular administration
- Slow sustained release from repository preparations
- Suitable for oily vehicles and some irritating substances
Cons of intramuscular administration
- Painful
- Less predictable absorption
- Danger from injection at incorrect site e.g. nerve damage
Pros of oral route
- Convenient
- Cheap
Cons of oral route
- Subject to 1st pass metabolism
- Propanolol, morphine, statins
- Varying bioavailability
- Effected by food in stomach
ADME
Absorption
Distribution; some drugs redistribute or pile up in certain areas e.g. brain
Metabolism; liver/kidney
Exrection
Drugs subject to first pass metabolism
Propanolol, morphine, statins
Describe first pass metabolism
• The first pass effect (also known as first-pass metabolism or presystemic metabolism) is a phenomenon of drug metabolism whereby the concentration of a drug is greatly reduced before it reaches the systemic circulation. It is the fraction of drug lost during the process of absorption which is generally related to the liver and gut wall. Notable drugs that experience a significant first-pass effect are imipramine, morphine, propranolol
Define zero-order eliminatin kinetics
“Elimination of a constant quantity per time unit of the drug quantity present in the organism.”
Define First order elimination kinetics
“Elimination of a constant fraction per time unit of the drug quantity present in the organism. The elimination is proportional to the drug concentration.”
Define bioavailability
the proportion of a drug or other substance which enters the circulation when introduced into the body and so is able to have an active effect.
Formula for working out Bioavailability
F=AUCoral/AUCiv
Aminophyline/Theophylline Salt factor
Aminophylline is 80% Theophylline
Define Volume of Distribution
The apparent volume in which a drug is distributed. Drugs with low Vd are predominantly in the circulation, while drugs with a high Vd are predominantly have diffused into the peripheral tissue compartment
Volume of Distribution formula
Define clearance
Volume of plasma cleared of the drug per unit time
Formula for clearance
