General principles of pharmacology Flashcards by Kathleen Monahan

Pharmacodynamics

Mechanism of action, what drug does to your body

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Pharmacokinetics

Time course, how your body metabolizes drug

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Drug action

Change at the molecular level, biochemical event

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Drug effect

**Clinical practitioner more concerned with this

Change in physiological function

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MEC

Minimum effective concentration: concentration needed to start seeing drug effect

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Maximum tolerated concentration

Concentration above which toxicity occurs

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Effect of drugs is dose dependent

Some level before which no effect occurs
Some level above which no extra effect occurs
Ideal range of drug concentration between when drugs begin being effective and cutoff for toxicity

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Therapeutic window

Between MEC and max tolerated concentration

Depends on absorption, distribution, elimination, and drug action + effect

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Percutaneous administration

Slow and sustained absorption

Lipid soluble > water soluble

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Enteral

Via GI

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Sublingual administration

Rich blood flow

More rapid than oral

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Oral administration

Most common but slower
2 barriers to absorption
Intestine > stomach
Absorption highly variable among patients (gastric emptying, pH, food, other drugs)
Drug recall is possible
Lipid > water soluble
Some drugs (PROTEINS) inactivated in GI
First pass metabolism
GI irritation

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Rectal administration

For vomiting patient

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Parenteral

Non-oral

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No barrier to absorption - easier to control concentration
Rapid but NO recall
Needs to be aqueous solution
No big "chunks" due to possible embolism
Possible infection at injection site

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Intra-arterial

More diagnostic

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Subcutaneous injection

Barriers to absorption: Slower absorption and sustained action
Can be poorly water soluble
Allows for depot preparations

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Protein drugs

Most need to be delivered IV or SQ

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Intramuscular injection

Only barrier is capillary, high blood flow in muscle
Time is dictated by water solubility (water > lipid)
Can inject oily and particulate matter

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Lipid/oily drugs

Oral, SQ, IM, percutaneous

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Water soluble drugs

Better with IV, faster with IM

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Particulate drugs

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Depot preparations

Can release effective amounts of drug for weeks or months

SQ or IM

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Inhalation

Keep localized to minimize systemic effects
Large SA
Particle size important

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Intranasal

Lots of it swallowed

Absorption

Movement of drug into the blood Rate - how soon effects start Amount - intensity of effects

Rate of dissolution

Dissolved = free in solution, not bound, free to move into cells Smaller size and liquid are better

Concentration gradient

Drug always moves down gradient | Blood flow readily changes gradient

Lipid absorption

Faster | Can more easily cross the membrane (hydrophobic)

Charged molecules

CANNOT diffuse

Determine amount of drug that is ionized

Tissue condition

Damaged tissue less likely to absorb

Distribution

To all areas perfused with blood | Can move into interstitial fluid or within cells

Volume of distribution

Hypothetical volume of fluid into which the drug is distributed May calculate to be larger than 42L if drugs build up in tissues

Water compartments

Plasma: 4L Extracellular: 14L Total: 42L

Drug redistribution

Drugs are constantly moving along gradient into different compartments

Blood brain barrier

Lipid soluble, nonpolar, noncharged cross more easily

Drug elimination

In urine, breath, stool, or sweat | Unchanged or biotransformed (active, inactive, larger or smaller)

Major site of biotransformation

Liver

Major biotransformation pathway

Conjugation: larger and more water soluble

Metabolites that are too large

Secreted into bile

Major form of elimination

Urine Involves glomerular filtration of plasma Drugs may be reabsorbed

Free drug

Unbound drug in solution

Most common type of drug movement into cell

Diffusion | Function of lipid solubility, conc. gradient, size, and charge

Concentration of drug at site of action (cell) is function of

absorption, biotransformation, distribution, and elimination

Active transport

Special tissues: renal, choroid, hepatocytes

Rate of diffusion

Directly related to concentration gradient | Nonionized only

Maintain steep conc. gradient

High blood flow

Ionized and polar molecules

More water soluble | Harder to cross membrane

Nonionized and nonpolar molecules

More lipid soluble | Easier to cross membrane

Concentration of ionized and nonionized form

Influenced by pH

High lipid water partition coefficient (above 1)

Very lipid soluble

Low lipid water partition coefficient (below 1)

Very water soluble

Weak acid in more acidic environment (pH

NONIONIZED

Weak base in more acidic environment (pH

IONIZED

Strong acids and bases

Not effected by pH Always ionized Drugs are mostly weak electrolytes

Excretion of weak acids increases with

Basic urine | Less reabsorbed

Excretion of weak bases increases with

Acidic urine | Less reabsorbed

Plasma concentration at equilibrium of weak acid

Higher than intracellular

Plasma concentration at equilibrium of weak base

Lower than intracellular

Ionized with large hydrophobic structure

May diffuse easily if hydrophobic enough

Why is IV drug so concentrated near stomach?

Lots of H+ available to ionize drug and trap in there

Acidosis

Weak acid more nonionized and moves into tissues

Alkalosis

Weak base ionized, builds up in plasma, and is then readily excreted

Quaternary salts

Permanently charged Does not cross BBB Quickly excreted if given IV

Anion transport

Penicillins and related antibiotics

Cation transport

Quaternary ganglionic blocking drugs

Albumin

Primary binding protein in plasma | Favors weak acids and lipid soluble drugs

Drug bound to protein

Cannot be used, cannot be filtered in kidney, and cannot cross membrane

Protein binding affects

Loading dose, all binding proteins must be saturated before therapeutic concentrations can be achieved Elimination may be prolonger

Drug interactions and protein binding

More than one drug may compete for same binding protein | Most problematic when drug binds in excess, has low Vd, is eliminated slowly, and has low therapeutic index

Drugs may displace endogenous substances

Thyroxine, steroids, billirubin

Drugs can be pre-bound to protein

Slower release

Drug redistribution concerning brain

High lipid solubility allows to enter quickly and lots of blood flow changes gradient causing drug to leave quickly as well Ex. thiopental

General principles of pharmacology Flashcards

(74 cards)