routes of administration - pharmacokinetics Flashcards
pmp103 instead oops
What is absorption?
Movement of a drug from the site of administration to the bloodstream.
What is distribution?
Movement of drug
around different
tissues in the body.
What is metabolism?
Change of drugs into
compounds which are
easier to eliminate
What is excretion?
irreversible loss of
(unchanged) drug
from the body
What are metabolism and excretion known as?
elimination
Where is Bioavailability the best?
*IV administration means the entire dose reaches the
systemic circulation, i.e. 100% bioavailability (F)
* Bioavailability will be lower via other routes
What does bioavailability depend on?
- Can depend upon permeability of the
biological membrane, drug properties,
and other route-dependent factors,
e.g. stomach contents for oral route
What is included in the first-pass (presystematic) metabolism?
- 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
What is an example of a drug that undergoes first pass metabolism?
Naloxone:
* Used to combat opiate overdose
* Rapid onset required
* Undergoes first pass metabolism
What is the bioavailability of the first-pass metabolism to the liver?
0.9-2%
Where does metabolism typically take place?
- Metabolism predominantly takes place in the liver but can
also happen elsewhere, e.g. skin, plasma, kidneys
What is phase I metabolism?
- Simple chemical changes, e.g.
oxidation, reduction, hydrolysis - Cytochrome P450 isoenzyme
particularly important - Products are likely to be inactive
and more water-soluble
What is phase II metabolism?
- Involves the conjugation (or
addition) of groups to the drug to
increase its solubility - Conjugates include glucuronates
and sulphates
What are some examples of oral administration routes? +exact drugs
- Solid (tablets, capsules) or liquid
(suspensions, solutions) dosage forms
*paracetamol
*amoxiccilin
*omeprazole
Describe what oral drugs must do to reach absorption sites
- Dosage form travels to the main sites of
absorption – stomach and small
intestines - Drug must cross lipophilic barriers to
be absorbed
What are some examples of the parenteral route of administration and example drugs?
- Parenteral formulations include:
̶Injections (intravenous, intramuscular,
subcutaneous…)
̶Infusions
*insulin
*adrenaline
*benzylpeniccilin Na
What are the advantages to the parenteral route?
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
What are some examples of the inhalation route? + some example drugs
- Drug is delivered directly to the lungs typically via an inhaler
or a nebuliser
+saltbutamol
+beclometasone
+colistimethane Na
What are the advantages to the inhalation route?
-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
What is the transdermal route + examples of drugs used for this?
*application of the drug to the surface of the skin with the intention of receiving a systematic effect
*estradiol
*fentanyl
*nicotine
What are the pharmacokinetic advantages of the transdermal route?
*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
What is the rectal route used for and example drugs?
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
What are the advantages of the rectal route for systematic delivery?
-Suitable if patient cannot easily swallow a solid
oral dosage form, e.g. unconscious, child
̶Drug not suited for oral delivery
What are the typical dosage forms of the rectal route and why?
- Drug usually incorporated into a suppository
which dissolves or melts within the rectum - Foam formulations which expand to fill the
rectum are also available
What are the downsides to the rectal route?
*issue with pharmacokinetics and cultural acceptability
