DEFINITIONS T1/2 Tmax Cmax AUC 1st order kinetics

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