definitions t1/2 tmax cmax auc 1st order kinetics
DESCRIPTION
DEFINITIONS T1/2 & Tmax Cmax AUC 1st order kinetics Zero order kinetics Steady state (enteric coated, longer T1/2) Loading doses Therapeutic indexTRANSCRIPT
DEFINITIONS• T1/2 & Tmax
• Cmax
• AUC• 1st order kinetics• Zero order kinetics• Steady state (enteric coated, longer T1/2)• Loading doses• Therapeutic index
Maximum plasma concentration achieved
Time to maximum peak plasma concentration
Area of plasma concentration to fall by halfOnly applies to drugs with first order kinetics
Amount of drugs in plasma = Bioavailability
Distribution leads to a fall in plasma concentration / achieving equilibrium within different compartments.Vd=Q/C. When Vd is high = high affinity for lipophilic tissues seen in psychotropic drugs
1-Applies to most drugs2-Rate of elimination depends of the amounts of the drug present3-Amount of the drugs eliminated in each half-life differs
1-Rate of elimination independent of the amount of drug present2-e.g fixed IV infusions, alcohol, absorption from depot 3-There is no fixed half-life
ELIMINATION• Excretion by kidneys most important• Li+: most important; What is the effect of Na+
• Urinary pH: important for barbiturates• Age• Renal impairment• Also through bile or through skin
Steady state: after repeated dosage leading to an equilibrium between absorption and elimination
Depends on dose, time between dose and elimination half lifeAchieved after 4-5 half lifeLoading dosage can be given to achieve therapeutic plasma concentrationTherapeutic Index: Is the minimum plasma drug concentration causing toxic effect to that causing therapeutic effect
PHARMACODYNAMICS• Mechanism of action of drugs “The effect of the drug on the body”• Usually there is a neurotransmitter or various involved. The therapeutic effect appears to depend on the
neurotransmitter that is involved (also the Side effects)
•Effect can occur at various levels
Level of actions ExamplesRe-uptake TCA, SSRI, Cocaine
Pre synaptic Lofexidine at alpha 2
Post synaptic D2 blockers antipsychotics
Partial agonist Aripiprazole / Buprenorphine
antagonist Flumazenil
Full agonist Bzd at GABA complex
Second messenger Lithium at inositol level