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Friday, February 6, 2009

Pharmacokinetics Lecture notes


Pharmacokinetics Lecture notes

Four basic pharmacokinetic processes are

¬Drug movement throughout the body
¬Absorption – movement of drug from its site of administration into blood
¬Dissolve – must dissolve before being absorbed
¬Surface area – the larger the faster
¬Blood flow – most rapid where blood flow is high
¬Lipid solubility - the higher the faster
¬pH partitioning

Absorption - Routes
IV – no barriers to absorption
Intramuscular – good for poorly soluble drugs, "time released"
Subcutaneous – again no significant barriers
Oral – must pass through cells of epithelium, enteric coating
Safer but highly variable absorption – enteric, sustained-release, tablets

Factors Affecting Drug Absorption
Rate of dissolution
Surface area
Blood flow
Lipid solubility
pH partitioning

Blood flow to tissues
Exiting the vascular system once it has been delivered – pass through pores in capillary wall
Protein - binding
Drugs can bind with proteins
Parts of drugs will be bound during any given time period
Impedes drug’s ability to reach sites of action, metabolism, or excretion

Drug Distribution
Factors influencing distribution are
Blood flow to tissue
– Exiting the vascular system
– The blood-brain barrier
– Placental drug transfer

Enzymatic alteration of drug structure
Consequences of metabolism
Accelerated renal excretion – kidney cannot excrete highly lipid soluable
Drug inactivation
Increased therapeutic action
Activation of prodrugs
Increased or decreased toxicity

Drug Metabolism

Liver—primary site of drug metabolism
P450 system (cytochrome P450)

Drug Metabolism—Implications
Therapeutic consequences are
Accelerated drug excretion
Drug inactivation
Increased therapeutic action
Activation of prodrugs
Toxicity variations

Routes of Administration
Two major groups
Via gastrointestinal tract
Outside the gastrointestinal tract
Usually referred to as "by injection"
Common routes—intravenous, subcutaneous, intramuscular

Special Considerations in Drug Metabolism
Induction of drug-metabolizing enzymes
First-pass effect
Nutritional status
Competition between drugs

Drug Excretion
Removal of drug from the body
Kidney—via three processes
Glomerular filtration
Passive tubular reabsorption
Active tubular secretion

Time Course of Drug Responses
Plasma drug levels
Minimum effective concentration (MEC)
Toxic concentration
Therapeutic range
Drug half-life
Loading dose
Maintenance dose

Achieving and Maintaining Therapeutic Concentrations

•Repeated dose scheduling
•Drug accumulates in blood stream
•Plateau reached
•Amount administered = amount excreted

Differentiate between Loading Dose and Maintenance Dose

•Loading Dose
–Higher amount of given drug

•Maintenance Dose
–Doses administered at intermittent (scheduled) times

Drug Half-life
The time for the amount of drug in the body to decrease by 50%

Glomerular filtration – blood to tubular urine
Tubular reabsorption
Active tubular secretion – pumps for organic acids and organic bases – to urine

Monitoring drug levels
Plasma drug levels
Therapeutic range

Drug Half-life
Time requires for the amount of drug in the body to decrease by 50%
Will determine dosing requirements

Goal - plateau

Loading doses – when plateau must be achieved quickly
Routine smaller doses – maintenance doses
Peak and trough levels

Maximal efficacy – largest effect a drug can produce

Potency – one that produces its effects at lower dosages

Drugs bind to receptors to produce effects

All that drugs can do is mimic the physiological activity of the body’s own molecules
Block the physiological activity of the body’s own molecules

Mimic the body’s own regulatory molecules

Drugs that block the actions of endogenous regulators

Partial agonists
Mimic the actions but with reduced intensity

Drug Interactions
Can have varying effects
Direct chemical or physical – IV preparation
Drug – Food Interactions
Frequently decreased rate of absorption
Grapefruit juice can inhibit metabolism
"with food" – with or shortly after meal
"empty stomach" – one hour prior to meal or two hours after


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Welcome to my blog!I am a nursing student in an accelerated BSN nursing program. This is where i review my nursing classes by putting down nursing lecture notes. I hope you find it useful and thanks for visiting.