Describe PK VS PD.
- PK = what the body does to the drug
-fate of the drugs in systemic circ (blood)
-absorption, distribution, metabolism, excretion - PD = what the drug does to the body
-mechanism of action
-effects/activity
-systemic & local administration
Describe what to do if a patient doesnt respond to management.
-reconsider differential diagnosis via problem orientated approach
-reconsider therapeutic (PK or PD)
Define absorption.
-transfer of drug from site of administration into systemic circulation (regardless of route of administration)
*not absorbed in IV bc goes directly into blood
Describe absorption parameters.
Cmax = peak (ug/mL)
tmax = time to reach Cmax (h)
Ka = absorption rate (h-1)
>speed of drug absorption
Describe absorption bioavailability.
AUC = (ug.h/mL)
>total drug exposure to drug
>depends on: absorption, dosage, elimination
1. Bioavailability (F)
-represents proportion of drug absorbed from the site of administration in the systemic circ
*IV: no bioavailability, no Ka, no Tmax, no Cmax
*SQ: straight line, 0
Describe the factors affecting drug absorption.
- Route of administration
- Drug
- Patient
Describe how route of administration affects absorption.
review the fastest to slowest
1. PO (drugs & patient factors)
-food interaction
-pH interaction
>hydrolysis (inactivation)
>ionization
-drug interaction
-motility (gastric emptying)
2. First pass effect: (decrease bioavailability)
A) hepatic portal system
-PO -> liver clearance
-rectal: distal rectum venous drainage to vena cava
B) renal portal system (reptiles)
-inj in cd part -> kidney clearance
by pass hepatic first pass effect = administered orally
Describe how a drug can affect absorption.
- Chemistry (passage across membranes)
-molecular size
-degree of ionization
-solubility - Enteral
-drug interactions
-transit time (motility/patient factor) - PD of drug (effect on blood flow)
-epi -> local vasoconstriction -> decreased blood flow -> decreased absorption - PK of drug
-bile elimination -> reabsorption = enterohepatic cycle - Drug formulation
-dissolution: (best) liquid>gel>tab>coated tab (longer dissolution)
-(+/-) dosage
Describe how a patient can affect drug absorption.
- Absorptive surface area
- Blood flow
- Species
- Individual
Describe absorptive surface area on drug absorption.
-transdermal absorption: correlated w amt of SA
Describe blood flow affecting drug absorption.
- increased blood flow -> inc drug absorption
>heat/massage IM inj site - decreased blood flow -> dec absorption
-hypovolemia
-cardiovascular failure (+/- shock)
-distributive disturbance (+/- shock)
-CT
>repeated infections in same place -> local tissue fibrosis - Sympathetic stimulation
-inc blood flow to skeletal muscles
-decrease blood flow to GIT & SQ - Parasympathetic stimulation
-decrease blood flow to skeletal muscle
-inc blood flow to GIT
-motility of GI
Describe how species & individuals can affect drug absorption.
- Inter species (anatomy & physiology)
- Intra species = individual factors
-inter individual
-intra individual
-health status
-age
-behavior
Describe the consequence of absorption from environmental contamination or local administration.
-doping in sports
-drug residues in food animals
-systemic side effects
