Transcript Basic-Pharm-161-Presentation-pharmacokinetics1

Pharmacokinetics
Study of process of drug absorption,
metabolism and excretion, distribution,
biotransformation, excretion and halflife
Absorption
o Process by which drug is made
available for use in the body.
 Transfer drug from the body fluids to
the tissue sites-
Absorption (Cont)
 Factors that influence the rate of
absorption:
 Route of administration
o IV- most rapid- immediate onset
o IM- short onset w/in minutes- about
20 min
o SubQ- rapid- e.g. insulin
o Oral- takes 30-60 minutes before
absorption from GI tract… onset of
drug action thus delayed
Absorption (Cont)
 Solubility of drug
o More soluble, more rapidly absorbed
o Most drugs are Water-sol (most readily
absorbed)- and partially lipid soluble
 Law of Diffusion- drug molecules pass
from an area of high concentration to
an area of low concentration –
– Concentration of drug on each side
differs… so will equal out with
transport
Absorption (Cont)
 Drugs pass through cell membranes
through
 Filtration
 Passive transport- most pass this
way
 Active transport
Absorption (Cont)
 Presence of certain body
conditions:
o Development of lipodystrophy
o Orally, food delays drug absorption
o Some drugs irritate stomach
Absorption (Cont)
 Factors that influence distribution:
 Systemic circulation distributes
drugs to various body tissues or
target sites (receptor sites)
o Interact w/ specific receptors during
distribution
o Some bind to protein or albumin in the
blood plasma
Absorption (Cont)
 Blood levels must be maintained for drug
to be effective… Therapeutic level
 Blood flow needs to be adequate
 Blood-brain barrier: lipid barrier
 Blood-brain barrier: lipid barrier
o Drugs need to be lipid soluble to get
into brain cells.
Biotransformation
o Metabolism
 Process by which drug is converted to a
substance that can be eliminated
 Drug is converted by the liver to inactive
compounds
 DMMS- drug microsomal metabolizing
system
 Drugs such as barbiturates and sedatives
stimulate the DMMS when taken frequently
Excretion
o Inactive compounds of drugs excreted
by the kidneys- must be water- soluble
o Some drugs excreted w/o being
changed by the liver
o Caution for pts w/ kidney disease
o lower doses in infants and children as
immature kidney function…. And in
older age pts w/ diminished kidney
function
Half-life
o Time required for body to eliminate
50% of drug or for the concentration in
blood to fall to half of the original level.
o Affects timing/frequency of drug
dosage
 Drug w/ short half-life of 2-4 hours need
freq adm
 Drug w/ long half-life (20-24 hrs) req less
freq dosing.
 Rate of metabolism and excretion affects
half-life.
Drug Reactions /
Interactions
• Adverse drug reactions:
o Undesirable drug effects which may
be common or infrequently occurring
o May be mild, severe or life
threatening.
o May occur after first dose, after
several doses, or after many
Drug Reactions /
Interactions (Cont)
• Reporting adverse drug reactions:
o Drugs used, studied for many yrs…
and may take that long for adv rxns
to become known.
o Reporting mechanisms to help ID adv
rxns
Allergic drug reactions
o Allergic reaction
 Hypersensitivity reaction
 Allergy to drug begins to occur after more
than one dose given.
 Occ may occur the first time a drug is
given e.g. penicillin so need to monitor pt
carefully w/ first dose.
Allergic drug reactions
(Cont)
 immune system views drug as an antigen
or foreign body which then stimulates the
antigen-antibody response that prompts
body to produce antibodies and release
histamine from the cell against the drug.
• Allergy SXS: itching, skin rashes, hives
(urticaria), incr nasal secretions, diff
breathing and wheezing due to broncoconstriction, cyanosis, sudden loss of
consciousness, swelling of eyes, lips or
tongue.
Allergic drug reactions
(Cont)
o Anaphylactic shock- extreme serious
allergic drug rxn occurs shortly after
adm of drug w sensitivity
 TX raise BP, improve breathing, restore
cardiac function, tx symptoms as arise.
Allergic drug reactions
(Cont)
 Angioedema – angioneurotic edema…
collection of fluid in subq tissue.
 Eyelids, mouth, lips, throat.
 Dangerous when mouth affected.
Swelling may block airway and result in
asphyxia or difficult breathing or inability
to breath
Drug idiosyncrasy
o Any unusual or abnormal rxn to a
drug different from the one expected.
o Cause due to genetic deficiency
making pt unable to tolerate certain
drugs and chemicals.
Drug tolerance/
dependence
o Body adapts to presence of certain
drugs
o Also sign of drug dependence
o Some users experience discomfort
when drug w/drawn- with physical or
psychological symptoms
Drug Reactions /
Interactions
• Cumulative drug effect:
o Seen most commonly w/ liver or
kidney disease as organs are major
sites of detox and excretion.
o Body is unable to metabolize and
excrete a normal dose of drug before
next dose occurs. Serious as can lead
to toxic effects.
Drug Reactions /
Interactions (Cont)
• Toxic reactions:
o Levels build up to toxic when lgr
doses given.
o Some drugs such as digoxin have
very, very narrow margin of safety
before toxic
Drug Reactions /
Interactions (Cont)
o Can be reversible or irreversible
 Liver damage reversible as liver cells can
regenerate.
 Hearing loss due to damage to 8th cranial
nerve permanent- due to streptomycin or
gentimicin.
 Can reverse w/ administration of
antidote, digitalis toxicity can give
Digibind, Narcan for narcotic overdose.
• monitor blood level for certain drugs:
gentimicin, theophylline, digitalis
Drug Reactions /
Interactions (Cont)
• Drug Interactions
o Drug-drug interactions and food-drug
interactions.
o Occurs when one drug interacts w/
action of another.
 antacids interact w drugs like tetracycline
 Know interactions:
 oral anticoagulants
 anti-infectives, antiarrhythmics,
alcohol
Drug Reactions /
Interactions (Cont)
 Additive drug reaction= when combined
effect of the two drugs equal to sum of
each drug given alone
• Synergistic drug reaction= drugs interact
w/ each other and produce effect greater
than sum of separate actions.
• Antagonistic drug reaction= one drug
interferes w/ action of another and
neutralizes or decreases effects
Drug Reactions /
Interactions (Cont)
 Drug-food interaction= food impairs or
enhances drug given orally.
 Some req food
 Some antibiotics
Factors influencing drug
response
o Age
 Infants and children req smaller doses
 Dose varies for age and wt.
 Elderly also need lower doses
o Polypharmacy- taking numerous
drugs that can potentially react.
Factors influencing drug
response
(Cont)
o Weight= based on wt of 150 # average wt
o Gender= women in general require smaller
dose of some drugs as smaller ratio of body
fat and water
o Genetic variations- some inherit protein or
enzyme patterns that influence absorption
o Emotional state
o Patient expectations… placebo affect
Factors influencing drug
response
(Cont)
o Disease = presence of disease may
influence action
 Liver disease= alters ability to metabolize
or detoxify drugs.
 Kidney disease = impairs excretion.
Route of administration
 Local and systemic effects
• LOCAL: topical application affects the
skin, eye, ear, mucous membranes –
creams, ointments, suppositories
 SYSTEMIC: absorbed and distributed
throughout system via blood stream
Route of administration
(Cont)
oOral- slowest, and most convenient
oParenteral= any route that does
not involve GI tract or inhalation
oIV- most rapid drug absorption
oIM- into muscles
• SubQ- into the subcutaneous
tissues of the skin
Nursing Implications
• Many factors influence drug action:
 Need to know routes, factors,
dosages, other drugs, if oral can be
give w/ or w/o food.
 Observe reactions, responses, adv
rxns drug tolerance.
 Report and record observations.
 Know when to w/hold drug and notify
MD.
Drug legislation / regulations
o Federal legislation- describes
conditions under which certain
meds may be given and
distributed.
o State legislation- describes who
may prescribe, dispense and
administer certain drugs and under
what conditions.
Drug legislation / regulations
(Cont)
o Pure Food and Drug Act (FDA)= first
act passed in 1906,
o Harrison Narcotic Act= 1914
o Pure Food, Drug and Cosmetic Act=
1938
o Comprehensive Drug Abuse Prevention
and Control Act= 1970
o Drug Enforcement Agency (DEA)
Pregnancy Categories
 Drugs carry risk of causing birth defects
o Teratogen= any substance that
causes abnormal development of the
fetus leading to a severely deformed
fetus.
o Five categories of potential for
causing birth defects.
Drug Development
o FDA approval required for use,
monitoring for adverse or toxic
reactions
o Investigational new drugs/ release of
drugs for use.