unit 1- concepts Flashcards
drug
•any chemical that can affect living processes
pharmacology
- study of drugs and their interactions with living systems
- physical/chemical properties
- physiologic/biochemical effects
- knowledge of history, sources, uses
- knowledge of absorption, distribution, metabolism, excretion
clinical pharmacology
•study of drug interactions in humans
therapeutics
- use of drugs to dx, prevent, tx disease or to prevent preggo
- medical use of drugs
Factors influencing intensity of drug responses
- ) administration- dose, route, time
- ) pharmacokinetics
- ) pharmacodynamics
- ) individual pt variation
pharmacodynamics
•processes that, once the drug reaches site of action, determine nature and intensity of response
- ) receptor interaction
- ) pt functional state
- ) placebo effects
how do you classify propofol (Diprivan)
- general anesthetic
- CNS sedative
- suppresses respiratory system
pharmacokinetics
•movement of drugs within the body
- ) absorption
- ) distribution
- ) metabolism
- ) excretion
many penicillins have to be given on an empty stomach b/c…
•presence of food in stomach can interfere with absorption
aspirin absorption
- acidic molecule
- remains nonionized in stomach -> absorbed
- ionizes in intestine -> little absorbed
absorption
- drug movement from site of administration into blood
* amount absorbed determines intensity of effects
factors affecting drug absorption
- rate of dissolution (faster)
- surface area (high)
- blood flow (high b/c [] gradient)
- lipid solubility (lipid soluble faster)
enteral administration
•via gastrointestinal tract
parenteral administration
- injection
- outside GI tract
- IV
- subQ
- IM
Intravenous administration
- no barriers to absorption
- instantaneous and complete absorption
- rapid onset of action
advantages IV administration
- allows for precise control
- large fluid volumes
- use of irritant drugs (diluted in blood)
- eliminates need for absorption
disadvantages IV administration
- high cost
- irreversible
- risk for fluid overload
- risk for infection
- risk for embolism
advantages IM route
- ideal for poorly soluble drugs
* ideal for depot preps (drugs absorbed slowly over time)
disadvantages IM route
- discomfort/inconvenience
* bleeding risks, so not ideal for pt on anticoagulant therapy
oral (PO) administration
- drugs absorbed through stomach, intestine, or both
- barriers of cells lining GI tract and capillary wall
- absorption determined by solubility/stability, pH, gastric emptying, food, coadministration, drug coating
- drugs must go through liver before general circulation
advantage PO route
- easy, convenient, cheap
- safer than injection
- reversible and able to be sped up
disadvantages PO route
- effectiveness variability among pts
- potential for enzymatic inactivation
- requires pt cooperation
- risk for local irritation
what occurs first when an oral drug is absorbed
•drugs molecules move from small intestine into portal venous system
distribution
•drug moment form blood to interstitial space of tissues and into cells
•determined by:
1.) blood flow to tissues
2.) ability of drugs to exit vascular system
3.) ability of drugs to enter cells
abscesses
- impedes blood flow at tissue
* lack blood supply, so drugs can’t get to bacteria within
solid tumor
- impedes blood flow at tissue
* limited blood supply, esp. at core, which makes them resistant to drug therapy
how drugs exit vascular system
- ) capillary beds
- ) blood brain barrier
- ) placental transfer
- ) protein binding
drug exit via capillary bed
- through pores in wall
* BETWEEN cells
blood brain barrier (BBB)
- tight junction caps. in CNS
- drugs must pass THRU and must be lipid soluble or have transporter
- protects, but also limits drug access
membranes of placenta
•separate maternal circulation from fetal
•do NOT constitute absolute barrier to drugs
•lipid soluble pass thru
•non-ionized, polar, or protein bound don’t pass
*best to assume that ALL drugs pass thru
protein binding of drugs
- many drugs travel thru bloodstream by binding to albumin
- % active and able to perform, be metabolized/excreted is % not bound to protein
- bound drug may act as a reservoir from which drug is slowly released as unbound form (maintaining equilibrium when previous unbound metabolized)
- albumin most abundant and important b/c never leave bloodstream (large/no transporter)
- percentage of drug binding determined by binding attraction
free drugs
- unable to bind to saturated protein
* go to target tissue
multiple drug therapy
- compete with each other on albumin binding sites
- on drug can displace another, causing [free] to rise
- more free drug increases intensity of drug responses and may lead to toxicity
which drug is most likely to increase metabolism of other drugs
•barbiturates (ex: phenobarbital) b/c known to increase NZ activity in liver
•stimulates induction
•important b/c other drugs are metabolized faster in liver, so decreased therapeutic effect of the other drugs
*barbiturates are used for seizures
metabolite
- metabolized drug
- can be active or inactive
- Ex: Demerol converted into active metabolite, which results in adverse affects
metabolism (biotransformation)
- enzymatically mediated alteration of drug structure
- most occurs in liver
- performed by hepatic microsomal NZ system (P450 system)
- includes breakdown and synthesis
- nutritional status plays a key role
P450 system
- performs drug metabolism
* hepatic NZ that are capable of catalyzing rxns using drug substrates
therapeutic consequences of drug metabolism
- ) accelerated renal excretion
- ) drug inactivation (most common)
- ) increased therapeutic action
- ) activation of prodrugs (inactive -> active)
- ) increased/decreased toxicity
factors that affect metabolism
- ) age
- ) induction of drug-metabolizing NZ
- ) first-pass effect
- ) nutritional status
- ) competition b/t drugs
first pass effect
- rapid inactivation of certain oral drugs, resulting in no therapeutic effects
- drugs at risk are administered parenterally to bypass liver temporarily
excretion
- movement of drugs and their metabolites out of the body
- kidney most important organ (urine)
- also excrete via bile, sweat, saliva, breast milk, expired air
factors that modify excretion
- urinary pH- ionized at pH of urine, remain in tubule and excreted
- competition for tubular transport sites
- age
plasma drug levels
- concentration of drug in blood
- measured to regulate drug responses in regards to dosing/timing
- remain higher for longer period of time in children
minimum effective concentration (MEC)
- plasma drug level below which therapeutic effects will not occur
- effective drugs must be at or above MEC
toxic concentration
•plasma level at which toxic effects begin
therapeutic range
- range of plasma drug levels between MEC and toxic concentration
- enough drug to be effective, but not so much to be toxic