I - Basic Principles Flashcards by Grazielle Verzosa

Any substance that brings about a change in biologic function through its chemical actions

drugs

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Actions of a drug on the body

Pharmacodynamics

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Actions of the body on a drug

Pharmacokinetics

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Molecular Weight of most drugs

100-1000

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MW of Lithium

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MW of Altepase

50,000

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MW: rarely selective in their actions

< 100

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MW: poorly absorbed and poorly distributed

> 1000

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Bonds According to Strength

covalent > electrostatic > hydrophobic

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Movement of drug molecules into and within biologic environments

Permeation

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Passive movement of non-protein-bound drugs between the blood and extravascular space through small water-filled pores

Aqueous Diffusion

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Aqueous Diffusion happens in all organs except

brain, testes, eye, placenta

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Aqueus Diffusion is governed by

Fick’s Law of Diffusion

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Movement of drugs through lipid membranes separating body compartments and the ECF from the ICF

Lipid Diffusion

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Most important limiting factor for permeation

Lipid Diffusion

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Lipid Diffusion is governed by

Fick’s Law of Diffusion

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Lipid Diffusion is very important for the diffusion of

weak acids and weak bases

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Drugs that do not readily cross through membranes may be transported across barriers by mechanisms that carry

similar endogenous substances

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Transport by special carriers is _____ by Fick’s Law of Diffusion and is _____-limited

not governed by Fick’s Law of Diffusion, capacity-limited

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For large drugs to be endocytosed, they have to

bind with receptors

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Large drugs are internalized and released after

vesicle breakdown

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Small polar drugs combine with _____ to form _____ which undergo endocytosis.

special proteins, complexes

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Predicts the rate of movement of molecules across a barrier

Fick’s Law of Diffusion

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Rate = (C1-C2) x (permeability coefficient/thickness) x area

Fick’s Law of Diffusion

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Absorption is faster in organs with _____ surface area and _____ membranes.

larger surface area, thinner membranes

Aqueous solubility is _____ proportional to electrostatic charge.

directly

Lipid solubility is _____ proportional to electrostatic charge.

inversely

Many drugs are _____ acids and bases.

weak

Unprotonated acids are more _____-soluble and undergoes _____ clearance.

water-soluble, better clearance

Protonated acids are more _____-soluble and are _____ to cross biological membranes.

lipid-soluble, more likely to cross biological membranes

Unprotonated bases are more _____-soluble and are _____ to cross biological membranes.

lipid-soluble, more likely to cross biological membranes

Protonated bases are more _____-soluble and undergoes _____ clearance.

water-soluble, better clearance

pH below pKa: protonated __ unprotonated

pH at pKa: protonated __ unprotonated

pH above pKa: protonated __ unprotonated

Excretion of a weak acid may be accelerated by _____ the urine with _____.

alkalinizing urine, bicarbonate (HCO3-)

Excretion of a weak base may be accelerated by _____ the urine with _____.

acidifying urine, ammonium chloride (NH4Cl)

Transfer of a drug from its site of administration to the bloodstream

Absorption

Absorption is affected by

route of administration, blood flow, concentration

Route of Administration: offers maximum convenience

oral

Route of Administration: most common

oral

For the oral route, absorption is

slow, less complete

A significant amount of the drug is metabolized in the gut wall, portal circulation and liver before it reaches the systemic circulation

First-Pass Effect

Route of Administration: instantaneous, complete absorption, bypasses first-pass effect

intravenous

IV route is _____ dangerous than oral.

more dangerous

Route of Administration: faster absorption, more complete absorption than oral, large volume, less irritation

intramuscular

Anticoagulants cannot by given intramuscularly because they can cause

hematomas

IM Injections to Buttocks: superolateral

safe

IM Injections to Buttocks: superomedial

gluteus medius gait

IM Injections to Buttocks: inferomedial

sciatica

Route of Administration: slower absorption than IM, bypasses first pass effect

subcutaneous

Route of Administration: direct absorption into the systemic venous circulation, bypasses the first-pass effect

buccal, sublingual, IV

Route of Sublingual Administration

lingual vein → internal jugular vein → brachiocephalic vein → superior vena cava → right atrium

Route of Administration: partial avoidance of the first-pass effect, large amounts, drugs w/ unpleasant taste, vomiting patient

rectal (suppository)

Route of Rectal Administration: Superior Rectal Vein

IMV → PV (first-pass)

Route of Rectal Administration: Middle Rectal Vein

IIV → IVC

Route of Rectal Administration: Inferior Rectal Vein

IPV → IIV → IVC

Route of Administration: delivery closest to the target in respiratory diseases, rapid absorption with minimal systemic effects, gases at room temperature, easily volatilized

inhalational

Route of Administration: local effect, slowest

topical

Topical Drugs: Most to Least Evaporation

tinctures > wet dressings > lotions > gels > aerosols > powders > pastes > creams > foams > ointments

Topical Drugs: Acute Inflammation

drying agents: tinctures, wet dressings, lotions

Topical Drugs: Chronic Inflammation

lubricating agents: creams, ointments

Route of Administration: skin, systemic effect, slow, bypasses first-pass effect

transdermal

Drug reversibly leaves the bloodstream and enters the target organ

Distribution

Distribution is affected by

size of organ, blood flow, solubility, binding

Distribution: determines concentration gradient between blood and the organ

size of organ

Distribution: important determinant of the rate of drug uptake

blood flow

Distribution: influences the concentration of the drug in the extracellular fluid surrounding blood vessels

Solubility

Most barriers are _____ barriers.

lipid

Distribution: increases the drug's concentration in the compartment with macromolecules

Binding

Acidic drugs are bound to

albumin

Basic drugs are bound to

orosomucoid

Chemical alteration of a drug in the body

Metabolism

Metabolic Fates of Drugs

termination of drug action, drug activation, elimination without metabolism

Termination of a drug action

Elimination

Release of a drug and its metabolites

Excretion

Duration of drug action is determined by

dose, rate of elimination

Mode of elimination of drugs that are not metabolized

Excretion

Elimination: concentration decreases exponentially over time

First-Order

Elimination: concentration decreases by 50% for every half-life

First-Order

Elimination: most common

First-Order

Elimination: rate is proportionate to the concentration

First-Order

Elimination: rate is constant

Zero-Order

Elimination: concentration decreases linearly over time

Zero-Order

Elimination: occurs when drugs have saturated their elimination

Zero-Order

Drugs that follow Zero-Order Kinetics

warfarin, heparin, aspirin, tolbutamide, phenytoin, ethanol, theophylline