2- pharmacokinetics pharmakodynamics Flashcards
things that can affect PK
Renal function Stress Pyrexia Liver function Albumin Cardiovascular function
bioavalibility
The ability of a drug or other substance to be absorbed and used by the body.(F)
what affecrs bioavalibility
Absorption - Formulation - Age (luminal changes) - Food (chelation, gastric emptying) - Vomiting/malabsorption (Crohn’s) - Previous surgery (bariatric) • First pass metabolism - metabolism before reaching systemic circulation (gut lumen, gut wall, liver and even lungs)
bioavalibility equation
F = mass of the drug delivered to the plasma ÷ total mass of the drug administered
Vd equation
Vd = total amount of drug in the body ÷ plasma drug concentration
what affects distribution
Protein binding
Albumin – acidic drugs – common!
Globulins – hormones Lipoproteins – basic drugs
Glycoproteins – basic drugs
Blood flow, capillary structure – think about poorly vs. well- perfused tissues
can protein bound drugs have effect
no
when is drug binding important
- highly protein bound
- narrow therapeutic index
- Low V
what does small Vd mean
drug is confined to plasma, higher theraputic effect, lower dose needed
what affects renal excretion
Affected by:
1 GFR and protein binding (gentamicin)
2 Competition for transporters such as OATs (penicillin)
3 lipid solubility, pH, flow rate (aspirin)
clearance
- Volume of blood cleared per unit time (mL/min)
rate of elimination/ drug concentration in plasma
half life equation
half life = 0.693 x Vd/ clearahce
when is steady state reached
4-5 half lives
maintenance dose equation
(clearance x plasma concentration wanted / bioavalibility ) / dose interval
loading dose equation
constant steady state x volume distribution