Absorption

Question 1

Describe PK VS PD.

Answer 1

1. PK = what the body does to the drug
   -fate of the drugs in systemic circ (blood)
   -absorption, distribution, metabolism, excretion
2. PD = what the drug does to the body
   -mechanism of action
   -effects/activity
   -systemic & local administration

Question 2

Describe what to do if a patient doesnt respond to management.

Answer 2

-reconsider differential diagnosis via problem orientated approach
-reconsider therapeutic (PK or PD)

Question 3

Define absorption.

Answer 3

-transfer of drug from site of administration into systemic circulation (regardless of route of administration)
*not absorbed in IV bc goes directly into blood

Question 4

Describe absorption parameters.

Answer 4

Cmax = peak (ug/mL)
tmax = time to reach Cmax (h)
Ka = absorption rate (h-1)
>speed of drug absorption

Question 5

Describe absorption bioavailability.

F calves > F pigs (compare same dosage & route)

Answer 5

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

Question 6

Describe the factors affecting drug absorption.

Answer 6

1. Route of administration
2. Drug
3. Patient

Question 7

Describe how route of administration affects absorption.

Answer 7

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

Question 8

Describe how a drug can affect absorption.

Answer 8

1. Chemistry (passage across membranes)
   -molecular size
   -degree of ionization
   -solubility
2. Enteral
   -drug interactions
   -transit time (motility/patient factor)
3. PD of drug (effect on blood flow)
   -epi -> local vasoconstriction -> decreased blood flow -> decreased absorption
4. PK of drug
   -bile elimination -> reabsorption = enterohepatic cycle
5. Drug formulation
   -dissolution: (best) liquid>gel>tab>coated tab (longer dissolution)
   -(+/-) dosage

Question 9

Describe how a patient can affect drug absorption.

Answer 9

1. Absorptive surface area
2. Blood flow
3. Species
4. Individual

Question 10

Describe absorptive surface area on drug absorption.

Answer 10

-transdermal absorption: correlated w amt of SA

Question 11

Describe blood flow affecting drug absorption.

Answer 11

1. increased blood flow -> inc drug absorption
   >heat/massage IM inj site
2. decreased blood flow -> dec absorption
   -hypovolemia
   -cardiovascular failure (+/- shock)
   -distributive disturbance (+/- shock)
   -CT
   >repeated infections in same place -> local tissue fibrosis
3. Sympathetic stimulation
   -inc blood flow to skeletal muscles
   -decrease blood flow to GIT & SQ
4. Parasympathetic stimulation
   -decrease blood flow to skeletal muscle
   -inc blood flow to GIT
   -motility of GI

Question 12

Describe how species & individuals can affect drug absorption.

Answer 12

1. Inter species (anatomy & physiology)
2. Intra species = individual factors
   -inter individual
   -intra individual
   -health status
   -age
   -behavior

Question 13

Describe the consequence of absorption from environmental contamination or local administration.

Answer 13

-doping in sports
-drug residues in food animals
-systemic side effects