1 Routes of Administration Flashcards
Define Pharmacokinetics
what the body does to the drug
Define Pharmacodynamics
what the drug does to the body
What are the classes of Routes of administration
• Enteral
– via the gastro-intestinal tract
• Parenteral
– via a non-GI route that allows delivery into the systemic circulation
• Topical
– local administration: no requirement for drug to enter the circulation
Define route
– the site through which the drug is administered
– should allow access to the desired site of action!
Overview of circulation diagram
Draw
How is the route chosen?
• Goal – deliver the drug to site of action and achieve the desired therapeutic outcome while avoiding adverse events.
• Therapeutic considerations
– Eg rapid delivery (eg glycerol trinate) or sustained delivery (eg nicotine patch)
• Effect of disease on route
– Eg medicating a vomiting patient p.o.
• Drug properties
– Eg the drug may not be absorbed from the GI tract
– Eg drug may not be stable in gastric acid
• Adverse events
– Eg Drug may be toxic if systemically bioavailable eg Nystatin (treats fungal infection in GI tract)
• Patient preference
– paracetamol: p.r. or p.o. ?
What is topical administration
• Direct application to site of action
• Isn’t going to lead to large conc of drug present in plasma (Limited systemic exposure)
– relatively small dose absorbed, as its absorbed at site of active
• Note that some anatomical sites can be used for both topical and systemic administration
– Epicutaneous vs Percutaneous
topical administration - define epicutaneous
Epicutaneous (applied to the surface of the skin)
Eg. local anaesthesia, eczema medications
topical administration - define percutaneous
Percutaneous (through the skin)
Eg. subcutaneous, IV, IM
Examples of topical administration
• Epicutaneous – e.g. local anaesthesia, eczema medications • Inhalation – e.g. asthma medications • Ocular (eye drops) • Auricular (ear drops) • Intranasal (nose drops) • Rectal – e.g. laxatives • Vaginal – e.g. anti-infectives • Intrathecal
Properties of topical administration
• Fast
• Local
– Allows high local doses to be achieved with relatively small quantities
– Avoids systemic side-effects
• BUT:
– Skill required to administer inhalers & drops – Absorption may be affected by disease
Where is most of the drug absorbed
Small intestine
Enteral administration - advantages and disadvantages
By the gastrointestinal (GI) tract
• Oral (p.o.)
– several advantages: convenient; patient compliance good; usually consistent absorption
–BUT:
– drug must survive gastric acid (solubility may be affected)
– absorbed from small intestine
– delays in stomach emptying delay drug reaching small intestine
– absorption relatively slow (fastest with empty stomach)
– drug must be sufficiently lipophilic or taken up by transporter
– first pass effect – drug passes through liver before entering systemic circulation
What is first pass metabolism
- Reduces bioavailability p.o. •Drug specific
- Saturable
- Affected by liver disease
draw diagram
Enterohepatic recycling
draw diagram
