1. Absorption Flashcards
what is PHARMACOKINETICS the STUDY OF
what the BODY DOES TO A DRUG
only SMALL PORTION of the DRUG reaches the SITE OF ACTION. what happens to the rest?
either METABOLISED or ELIMINATED
drug by ORAL ADMINISTRATION passage to SYSTEMIC CIRCULATION:
drug in solution
released in INTENSTINES lumen, passes intestines wall to the LIVER
(to systemic circulation)
drug by ORAL ADMINISTRATION passage to SYSTEMIC CIRCULATION:
DIRECTLY to Systemic Circulation
- BYPASSES other organs etc
an understanding of PHARMACOKINETICS should help us to:
- design DOSAGE Regimens
- PERSONALISE/STRATIFT DOSAGE Regimen based on PATIENT’S CHARACTERISTICS
- DETERMINE what is wrong when a patient FAILS to RESPOND to TREATMENT
- find out why a Drug has CAUSED TOXICITY
- Understand the MECHANISMS of DRUG INTERACTIONS
ROUTE of DRUG ADMINISTRATIONS:
(dependent on DRUG and TARGET AREA)
- ORAL
- SUBLINGUAL
- RECTAL
- other Epithelal surfaces:
SKIN, CORNEA, VAGINA, NASAL MUCOSA - INJECTION
- INHALATION
what is TOPICAL ADMINISTRATION
ON TO the SKIN
what is SYSTEMIC ADMINISTRATION
INTO the BODY
what is SYSTEMIC ADMINISTRATION: ENTERAL administration
GI TRACT ROUTE
what is SYSTEMIC ADMINISTRATION: PARENTAL administration
NON-GI TRACT ROUTE
eg. injection, inhalation
ORAL administration: what is Fa
Fraction of the dose AVAILABLE FOR ABSORPTION
ORAL administration: what is Fg
Fraction of the dose ESCAPING INTESTINAL METABOLISM
(ability to permeate intestinal wall)
ORAL administration: what is Fh
Fraction of the dose ESCAPING HEPATIC FIRST PASS METABOLISM
(penetration through first pass metabolism)
what is FIRST PASS METABOLISM
The degree of metabolic breakdown of an orally administered drug that occurs in the INTESTINE or LIVER BEFORE it reaches the SYSTEMIC CIRCULATION
How is PENETRATION and Cmax (max plama conc.) after INTRAVENOUS ADMINISTRATION
IMMEDIATE
Cmax at 0 Hours
what is HALF LIFE of a drug
Time taken for DRUG CONC to DECLINE by HALF
how to CALCULATE FRACTIONAL BIOAVAILABILTY (F)
= AUC (ORAL) / AUC (IV)
AUC - area under the curve
what is Drug BIOAVAILABILITY
FRACTION of the administered DOSE that ENTERS the SYSTEMIC CIRCULATION and so reaches SITE OF ACTION
why can ABSORPTION be DELAYED
due to FOOD
- causes DECREASED GASTRIC EMPTYING RATE
Why might you have DECREASED ABSORPTION:
- drug UNSTABLE in Gastric Fluids
- DECREASED SOLUBILITY due to CHANGES in pH
- INCREASED FIRST PASS METABOLISM
(GI Enzymes / Transporters can be INDUCED by Food / Concomitant Drugs)
why might there be INCREASED or DECREASED FIRST PASS METABOLISM
INDUCTION or INHIBITION of GI ENZYMES or TRANSPORTERS
by FOOD or CONCOMITANT (accompanying) DRUGS
why might you have INCREASED ABSORPTION
- INCREASED SOLUBILISATION of poorly soluble drug due to CHANGES in pH
- DECREASED FIRST PASS METABOLISM
(Inhibition of GI Enzymes/Transporters by Food or Concomitant drugs)
what can cause CHANGES in DRUG SOLUBILITY
PH CHANGES
ORAL ADMINISTRATION is a RESULT of Multiple Processes:
Fa, Fh, Fg
