DEFINITIONS T1/2 Tmax Cmax AUC 1st order kinetics
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Transcript of DEFINITIONS T1/2 Tmax Cmax AUC 1st order kinetics
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DEFINITIONS• T1/2 & Tmax
• Cmax
• AUC• 1st order kinetics• Zero order kinetics• Steady state (enteric coated, longer T1/2)• Loading doses• Therapeutic index
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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
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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
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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
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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
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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
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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
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