Pharmacokinetics 9-1-05
Terms
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- What does phamacokinetics mean?
- mathematical description of the disposition and fate of administered drugs
- What does ADME stand for?
-
Absorption
Distribution
Metabolism (biotransformation)
Excretion - Examples of dosage forms:
- tablets, caplets, volatile liquids, aerosols, gases
- Route of administration depends on :
-
convenience
physical drug properties
bioavailability (proportion of drug that reaches the systemic circulation)
Desired onset, duration, and intensity of action
patients condition - What is main goal of drugs?
- To get into the systemic circulation
- Topical/Local
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direct application of small quantity to site of intended action so only a LOCAL response produced
ointments, creams, lotions, powder, sprays
local may be desired in specific body cavities (ie corticosteroids into a joint or intrathecal injection)
Patch (transdermal/percutaneous not considered local) - Enteral Routes
- GI-by way of small intestine oral and rectal
- Oral
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per os PO, safest, economical, most convenient route.strong first pass effect in GI and liver. bioavail only 5-<100
absorption may be affected by stomach contents (pH or digestive enzymes may destroy drugs), drugs may alter digestive process. NOT USEFUL unconscious or vomiting patients - Rectal
-
fast absorption, local effect, good for when drugs that would be irritating to stomach, less first pass effect compared to PO, bioavail = 30-100
USEFUL in unconscious or vomiting patients - Inhalation
- gases, vapors, aerosols, absorbed very rapidly thru bronchial mucosa/aveolar surface into systemic circ to produce effects elsewhere (general anaesthetics, amyl nitrate for angina pectoris) Bioavail = 5-100. Can be used for local affect on bronchioles. USEFUL uncon or vomit.
- Parenteral routes
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IV
IM
subcutaneous
Transdermal
Intrathecal
Intra-arterial
(not in gut, painful, sterility, more rapid absorption, uniform, predictable, allows more accurate dosage selection, more expensive)USEFUL uncon vomiting - I.V.
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injected directly into vein,immediate and total absorption,bioavail = 100. may give as slow infusion (20min) lessen risk of irrevocable overdose,obtain constant drug levels, bc more difficult to undo if overdose inject too rapidly =too high local concentrations
must be in soluble, nonparticulate form. - IM
-
injected deep in muscle mass
faster absorption than oral
bioavail = 75-100
prolonged even absorption of drug depots dissolved in oil
strong acid/base cause sterile abscesses
irritation at injection site possible
painful in large volumes - Subcutaneous
-
drug under skin
absorption almost rapid as with IM, administration very slow,bioavail=75-100, suitable for small volume, can only use nonirritating drugs, pain/irritation at injection site - Transdermal
- convenient painless, slow steady release, very slow absorption, prolonged duration, no first pass, bioava = 80-100,
- Intrathecal
- used for chemo and diagnostic procedures,injected into lumbar or cisterna magna,must be nonirritating, and strict asepsis maintained
- Intra arterial
- small volume of highly concentrated drug to specific tissued/organs for minimize effects elsewhere dilution in general circulation
- Most drugs cross membranes by
- passive diffusion (concentration gradient)
- Physiochemical props
- lipid soluble high = can get thru membrane easier, molecular weight, product formulation, ionization degree
- rate of dissolution
- increases as drug particle size decreases. Reducing particle size increases area exposed to solution
- All equilibrium btw systemic circulation and Actionsite,other tissues, excretion, biotransformation
- Bound drug becomes free if exctreted and comes back from all other sources to replenish the equilibrium all over. Bound - reservoir