Routes Of Administration Flashcards
Define pharmacokinetics
What the body does to the drug
- relationship between drug administration and exposure to drug (conc, time)
Define pharmacodynamics
What drug does to the body
- relationship between exposure to drug (conc of drug) + response
- response: desired / adverse effect
Exposure
Area under the curve (conc of drug and time)
What are the 3 classes of routes of administration
- Enteral
- Parenteral
- Topical
Enteral administration
Administration via GI tract
Drugs becomes systemically available - gets into patients circulation and gets distributed
Parenteral administration
Administered via non-GI route that allows delivery into systemic circulation
Topical administration
Administrated directly to where desired therapeutic route would be
- no requirement for drug to enter the circulation
Factors to consider when choosing the route
- therapeutic considerations (rapid / sustained delivery)
- effects of disease on route (medicating a vomiting patient - no oral route)
- drug properties (e.g. drug not absorbed from GI tract / drug not stable in gastric acid)
- adverse events (e.g. drug toxic of systemically bioavailable)
- patient preference
More info on topical administration
- limited systemic exposure = not absorbed / or relatively small dose -> administered directly so conc low in patients when disturbuted
- anatomical sites can be used for topical and systemic administration e.g. skin
Adv + Disadv of topical administration
Adv
- fast (direct)
- local
- allows high local doses to be achieved with relatively small quantities
- avoids systemic side effects
Disadv
- skills required to administer inhalers & drops
- absorption may be affected by disease
- accessibility of site
Adv of enteral administration (oral route)
Adv
- convenient
- patient compliance good
- consistent absorption
Factors that needs to be considered for enteral administration (disadv)
- drug must survive gastric acid (solubility may be affected)
- ^ would affect absorption from small intestines
- absorption relatively slow (fastest with empty stomach) - as with food delay in drug reaching SI
- drug must be sufficiently lipophilic (because wall of SI are lipophilic membrane) or taken up by transporter
- first pass effect - drug passes through liver before entering systemic circulation
First pass metabolism
- happens when route is oral. So to prevent it administer drug via diff route
- occurs before entering systemic circulation and liver would be the site of metabolism for the drug
- ^ would mean prevents absorption of drug from SI in systemic circulation because lots of drug gets metabolised in the liver
First pass metabolism leads to
- reduced bioavailability p.o.
- drug specific
- saturable
- affected by liver disease (rate of metabolism reduced = rate of first pass metabolism reduced. Can be bad because of adverse effects, reduced meta = high conc. of drug in circulation = side effects
Enterohepatic recycling
- recirculating between liver and intestines
- liver produces bile which is excreted into SI via bile duct to help with absorption of cholesterol and provides a route to recycle drug.
- some drug from liver excreted into bile duct which are excreted back into SI = exposure to drug gets prolonged
What are the ways of enteral administration
- Oral
- Sublingual
- Buccal
- Rectal
Sublingual - enteral administration
Adv + disadv
- under tongue
- absorbed through mucosal membrane
- no first pass effect - enters systemic circulation before liver
Disadv
Some drugs aren’t absorbed by this route
Some drugs cause irritation
Buccal - enteral administration
- absorbed by mucosal membrane of cheek
- no first pass effect - enters systemic circulation before liver
Rectal - enteral administration
- useful in patients who are vomiting, unconscious or drug has unacceptable taste
- no first pass effect - absorbed into internal prudenal veins to inferior vena cava
Disadv
Absorption may be irregular + irrational of rectal mucosa
Parental administration
Routes that leads to systemic bioavailability without going through GI tract
Parental administration adv + disadv
[can control conc. of drug achieved in patient’s plasma]
Fast
slow infusion
I.m. Injection allows depot - drug slowly released into systemic circulation over a period of time
Disadv
- injection: inconvenient, requires asepsis, requires training
S.c. Only with non-irrational drug
Drug in plasma can be
Bind to serum proteins (in plasma)
- binds to drugs and limits distribution into tissues
- protein- large so traps drug to serum
ADME
A - absorption [needs to get into systemic circulation]
D - distribution
M - metabolism [chemical transformation of drug. Lost/gained pharmacological activity]
E - excretion [common via kidneys]
Elimination
By metabolism and excretion
-> both remove pharmacology active version of drug
Disposition
Everything that happens after drug absorbed - DME
- distribution and elimination
Whole blood
Uncoaggulated and contains red and white blood cells
Plasma
Uncoaggulated blood and red + white cells are removed
Serum
Coaggulated blood and red + white cells removed
kinetics of i.v drug administration
- Cmax of i.v reaches max conc. instantaneously and conc decrease as drug distributed into diff tissues + some drug gets eliminated via metabolised or excreted
Kinetics of p.o drug administration
- delay corresponded due to swallowing drug then to stomach then to SI. Drug absorbed, conc in plasma increases. When conc decrease less drug = less absorption
