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137 Cards in this Set
- Front
- Back
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what are the 4 factors involved with pharmakokinetics
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1. Absorption
2. Distribution 3. Metabolism 4. Excretion |
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are all phases of pharmacokinetics occuring simoultaneously (ADME)
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yep, but obviously after we first take a drig absorption and distribution will prevail (plasma conc increases) whereas some time after taking the drug there will be more metabolism and excretion going on
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how can we represent pharmacokinetic profile of a drug? what can this curve tell us?
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by the plasma conc of a drug (if its excreted by kidney we can also use urine)
**from this we can determine -[plasma] at time 0 -Vd, volume of distribution -t1/2, half life -CL, clearance -AUC, area under curve |
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what are some ways a drug can be absorbed
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1. GI from oral drugs
2. Lungs from inhaled drugs 3. Blood from IV drugs |
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what about some ways the drug can be distributed
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from the liver (if the drug was abs orally and went to GI) and BV
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what are some ways drug can be excreted
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poo
pee lungs, breath it out |
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are K channels open or closed
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always open
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can drugs just enter cells?
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nope (well some can, lipid soluble)
1. Water soluble drugs passively diffuse in ion channels 2. Lipid soluble passively diffuse across PM 3. Carrier proteins can do active and passive transport |
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how does the composition of the cells in the GI and BV affect how drugs can enter/exit these areas. where are the larges pores
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int eh GI we have TJ so only super super small drugs will pass
in BV we have large fenestrea so drugs can pass much more readily largest pores in glomeruli, important for drug excretion **areas in brain with pores: pineal, pituitary, choroid plexus, median eminence, area postrema |
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we know most of the brain has BBB, are there areas where this is less than perfect and drugs can get to the brain
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large pores in...
1. pitutary 2. pineal 3. medium eminence 4. area postrema 5. choroid plexus |
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what are some ways drug can be excreted
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poo
pee lungs, breath it out |
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are K channels open or closed
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always open
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can drugs just enter cells?
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nope (well some can, lipid soluble)
1. Water soluble drugs passively diffuse in ion channels 2. Lipid soluble passively diffuse across PM 3. Carrier proteins can do active and passive transport |
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how does the composition of the cells in the GI and BV affect how drugs can enter/exit these areas. where are the larges pores
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int eh GI we have TJ so only super super small drugs will pass
in BV we have large fenestrea so drugs can pass much more readily largest pores in glomeruli, important for drug excretion |
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we know most of the brain has BBB, are there areas where this is less than perfect and drugs can get to the brain
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large pores in...
1. pitutary 2. pineal 3. medium eminence 4. area postrema 5. choroid plexus |
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wht is the anatomy that allows drugs to be excreted in the kidney
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the large pores in the glomeruli
**largest pores are here |
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what are the 4 mechs of membrane transport
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1. aqueous diffusion
2. carrier mediated: facilitated diffusion/active transport 3. lipid diffusion 4. Vesicular transport/Transcytosis **bottom line in order for the drug to do its job it needs to penetrate the membrane and enter the cell |
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describe lipid diffusion
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simple diffusion of lipid soluble drugs
**driven by conc grad **slow **non saturable **weak acids cross best in acidic environemnts **weak bases cross best in basic **drug neds to have some water solubility to get to the membrane in the first place |
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in what tissues is active transport used
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1. hepatocytes
2. neurons 3. renal tubule 4. choroid plexus **specific, saturable, competition, energy requirement, agaisnt gradient, fast |
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describe active transport
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fast
uses E to move things against its conc grad specific saturable can be competition for binding **seen in hepatocytes, neruons, choroid plexus, renal tubule |
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describe facilitated diffusion
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passive movement with the help of a carrier, goes with conc grad
**sugar, aa, purines, pyrimidines, and Ldopa transported this way |
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how is L dopa transported across a cell membrane
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facilitated diffusion
**carrier mediated passive |
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describe vesicular transport
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used for really big drugs
**cell engulfs the protein |
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what mode of transport is used to get big drigs into a cell
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endocytosis/vesicular transport
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whats the key principal behind all of these cellular transprort mechs
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the drug has to permiate many barriers to reach its receptor
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if you take L dopa and it works in the brain how does it get there?
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has to pass:
- GI cells (water layer, TJ, cell walls) -capillary cells of the gut -BBB -capillaries of the brain **lots of barriers to pass throuhg |
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what equation describes the extent of ionization of a drug
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henderson hasselbach
pH= pKa + log (A-/HA) pKa= pH where 50% disassociated |
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what is pKa
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its the pH when 50% of drug is disassociated
can use henderson hasselbach pH=pKa + log (A-/HA) **important bc we know drugs pass membranes more readily when they are NOT ionized |
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so drugs are either acids or bases and will have different degrees of ionization as they pass through the fluids of the body which are at dif pH's. how can we determine the extent of ionization
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Henderson Hasselbach
pH= pKa + log (A-/HA) pka= pH when 50% ioized |
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we know the HH is pH= pKa + log (A-/HA) this works really nice for acids, what about bases
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pH= pKa + log (B/BH+)
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what sthe pH
Gastric Juice Duodenum Ileum Lg Intestine Plasma CSF Urine |
Gastric Juice: 1-3
Duodenum: 5-6 Ileum: 8 Lg Intestine: 8 Plasma: 7.4 CSF: 7.3 Urine: 4-8 |
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what are some weak acid drugs
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1. asprin
2. Ampicillin 3. Acetemenophen 4. Sulfadiazine 5. Phenobarbital 6. Furosemide 7. Warfarin **they will be less ionized when they are in an acid and so are more lipid soluble in an acid |
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what are some weak base drugs
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1. Amphetamine
2. Clonidine 3. Coccaine 4. Codeine 5. Diazepam 6. Ergotamine 7. Epinepherine 8. Lidocaine **these will be non ionized in a base and so are more lipid soluble |
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how does pH affect the distribution of drugs
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each drug has its own pKa and pH and so will be more or less soluble in the differnt environemnts of the body
**an acidic drug will be more soluble inthe stomach and a basic will be more soluble in the intestines |
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a weak acid drug in a weak acid environment is ____ lipid solible and so it ____ absorbed
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highly
readily |
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what happens to a basic drug that is in an acidic environment
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it will become ionized and unable to pass membranes and so is trapped
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what can be said about drugs that are strong acids or strong bases
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they are always ionized and so arent lipid soluble and need to be transported into and out of cells with something other than lipid diffusion
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so if we have taken too much salicylates (acidis) how can we get them out
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make pee alkaline (basic)by giving bicarb
??? not totalyl sure how this works |
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is dose standard
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nope, the Dose is the amt of drug needed to have the desired effect
**dose is individualized based on maturation of organ fx, age of pt, Organ pathology (liver or kidney) |
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wht is abs
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its the way drugs gets into teh blody fluids (blood) that will move it around
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what things affect absorption
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1. Solubility
2. Dissolution 3. Conc 4. Blood Flow 5. surface that is absorptin it 6. pH 7. Contact time |
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what is... and how does it affect absorption
solibility? dissolution? Concentration? |
Solubility: drugs in aq soln are abs better than drugs in oily or solids
Dissolution: things in tablets need to dissolve first, this can vary in pts and so absorption can vary among pts 3. higher conc are absorbed easier |
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how does blood flow affect abs
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increased BF increased BF
**massage or heat will increase BF **mm get more BF than CT adn so abs is higher in mm |
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how does epi affect drug abs
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epi constricts so blood flow decreases and absorption is decreased
**shick, cold compress, disease will all slow absorption |
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what does absorbing surface have to do with rate of absorption
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increased surface, increased abs
*things like the lungs and liver and intectines are large and abs faster |
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how does pH affect absorption
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pH determines if things are ionized or not. the non ionized form absorbs
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where is a great example of drug abs increasing bc of duration
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sm intestine
**in the small intestine drugs stay around for a long time adn tehre is a lrage surface area so lots of abs occurs here |
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is abs of an oral drug 100%
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almost never
**the amt of drug at the site of activation is called bioavailibility |
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what is bioavailibility
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the amt of ACTIVE drug available at the site of action
**remember not 100% of a drug taken orally is absorbed |
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in what type of administration is there 100% bioavailability
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for IV drugs
**the bioavailibility/abs of a drug given oral or rectal is not 100% |
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how is bioavailability calculated?
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AUC oral/rectal
_______________ AUC iv |
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the bioavailability of a drug is the amt of ACTIVE drug at the site of action: it is the summary result of
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1. decomposition/inactivation of the drugs in the intestine
2. degree of absorption 3. metabolism in the gut or liver 4. Transport of the drug by p glycoproteins back into the lumen of hte gut |
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what is teh first pass effect
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initial metabolism of a drug while passing through the gut/liver
**morphine is orally abs at almost 100% BUT it is metabolized by the liver so its bioavailability is only like 33% High extraction ratio/high first pass effect |
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is all of what is absorbed bioavailable
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NOPE!
first pass effect: the drug may be metabolized as it initially passes through the gut and liver |
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what are some examples of drugs with high first pass rates and what does it mean
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high first pass rate (high extraction ratio) means that a lot of the drug is metabolized after absorption. abs and bioavailability dont match
Ex morphine lidocaine meperidine propranolol labetalol verapamil INH Imipramine |
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what are some drugs with a lot extraction ratio (low first pass(
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not lots of the drug is metabilized in teh GI adn liver. absorption and bioavailability are pretty simliar
digitoxin phenytoin theophylline tolbutamide chlorpropamide diazepam linezolid |
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so drugs like morphine, lidocaine, verapamil, and propanolol have a high first pass rate, what are the clinical implications of this
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lots of variation of [plasma] in patients
due to variation in hepatic function/hepatic blood flow **eliminate these effects by giving drug IV, IM, sublingual, rectal, topical, transderma, inhaled etc |
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what are the 3 main modes of drug administration
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1. Enteric: by mouth. safe, economical, convenient,
2. Paraenteric: IV, IM, Subcut, 3. Topical: skin, eyes, nose, throat, vagina |
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tell me about PO drugs
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by mouth
enteric **safe **convenient **cheap |
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what are some disadvantages about PO meds
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emesis
destruction of drug by enzymes or pH poor absorption pt compliance metabolism by intestical flora liver metabolism food gastric emptying **cant take them if you barf, they can irritate the intestinal mucosa and cause vomiting |
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pH, normal flora, the liver, and enzyme actitity are all things that can affect which type of drug administration
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oral
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how does gastric emptying time affect PO drugs
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delayed gastric emptying will inhibit absorption
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why take drugs on empty stomach
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so they dont bind to food and hace decreased absorbance
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what are slow relase drugs, what are some pros and cons
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slow uniform abs of drug
**good bc it can maintain a steady plasma conc, decreased administration and increase pt compliance, **UNFORTUNATLY: abs is erratic/irregular with these |
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are slow relase drugs the way to go?
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noep they often have erratic absorption
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what are some common paraenteral administrations of drug
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1. IV: direct, bypass absorption, easier to dose. dont use oily drugs here
2. IM: good abs here, can interefere with dx tests 3. Subcutaneous: slower abs, hyularaniase helps abs. used for solid pellets 5. Intrathecal/ Intraarterial: used to get high doses in specific organs 7. Intraosseous: 8. Intraperitoneal: not really used 9. Inhalation |
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whats the good and bad of IV
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good
-direct/fast -bypass absorption barriers -good for large volums/irritating drug -easy titration bad -dont use for oily/suspension -risk w/high [drug] after administration |
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the good and bad of IM
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paraenteric
good -aq soln fast abs -fat soln slow abs/resevoir (give high blood level of drug for week) bad -dont use if drug causes pain/tissue damage -can interefere with dx tests (creatine phosphokinase) |
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what is the good and bad of subcu drugs
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good
- used to implant solid pellets (norplant) -slower abs -if a large volume use hyularinase to help it abs (break CT) bad -dont use for large volumes/irritating things |
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whats the good and bad of intraperitoneal drugs
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pretty much bad, not used bc of risk of infection
-large surface area for abs but passes portal vein (liver metabolism- first pass effects seen) |
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what are the good and bad of intrathecal and intraarterial drug admin
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good
-large dose to a certain organ |
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what sthe good and bad of inhaled drugs
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used for gaseous anesthetics and aerosols
good -increased abs bc of large surface area of lungs and lots of BF -drug can target the airway itself (asthma) bad -local adn systemic allergies -entry of toxins |
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where are topical meds used
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skin
eyes nose throat vagina **these lead to systemic absorption adn local absorption |
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tell me about skin abs
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-drugs must be lipid soluble
-more abs in dermis (increased abs in wounds, abraised skin) -increased abs with increased surface area -increased abs with increased blood flow (BF) (inflammation, heat pack) |
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tell me about transdermal abs of drug
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-used for systemic
-special formulations the enhance skin abs Nitoglycerine Nicotine Scopolamine- motion sickness Clonidine- BP |
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how can the eye be used to abs drugs
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topical drug for local effects
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tell me about sublingual drugs
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self administered drugs that are screwed by first pass
**high blood flow in mucosa, abs into systemic veins, NOT the portal vein, slower abs bc of small surface area |
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if a drug is screwed by the first pass effect how can it be administered instead
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any paraenteral, sublingual
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why do rectal drug?
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-if you barf
-if your unconscious -it wont pass the liver :) BUT abs is often irregular/incomplete and can irritate the rectal mucosa |
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do rectal drugs experience the first pass effect
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nope, dont enter portal circulation, enter systemic circulation
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what is the formula for Volume of Distribution
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Vd= Total amt of drug in body
----------------------------------- Conc in plasma Vd= Div ---- c0 Div= IV dose C0= Plasma conc at time 0 |
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how can the dose give IV and the plasma conc of drug at time 0 be sued to find the volume of distribution
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Vd= total drug in body (Iv dose)
----------------------------------------------- [plasma][ ([plasma] at time 0 |
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what is the total amt of drug in body/conc of drug in plasma at time zero
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volume of distribution (Vd)
Vd= Div/C0 |
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200 mg of Drug A is administered IV. the plasma conc of Drug A at time 0 was 5 mg/L
wht is the volume of distribution |
Vd= Div/C0
Vd = 200/5 Vd=40L |
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Vd is measured in what units?
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Liters
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waht is teh standard amt of body fluid in the following compartments
Plasma Extracellular Total Body water |
Plasma 3 L
Extracellular 12 L Total Body Water 41 L **assuming a 70kg person |
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what compartment typicall has the following volumes
3 12 41 |
plasma
extracellular total body water *assuming a 70kg person |
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does Vd of a drug represent its actual distribution in body fluid?
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nope
**Vd is conceptual |
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what does a high Vd mean?
what about low? |
High Vd: wide distrubution/binding in periphery
Low: most drug is in plasma: drugs with ihgh plasma protein binding have low Vd |
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drugs with a HIGH plasma protein binding have a _____ Vd
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LOW
Vd= total drug in body/plasma conc |
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what are some drugs with a high Vd, what does this mean
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atropine
chloroquine fluoxetine digoxin labetalol **large Vd when the drug distributes or binds lot in the peripheral tissues (low Vd means lots of drug in the plasma) |
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what factors affect volume of distribution
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age
body weight organ pathology disease |
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what can decrease plasma levels of drug and prolong the half life?
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storing drugs
stored in fat tissues bone plasma binding protein transcellular resevoirs |
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a drug with a high plasma protein binding ability experiences what in terms of Vd? what about plasma conc and half life
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decreased Vd, increased plasma conc and longer half life
Vd= total drug amt/[drug in plasma] **the plasma conc included bound AND free |
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where are some common resevoirs for drug to be stored
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1. Fat: hard to anestetize fat ppl
2. Tissues: sk mm is sig 3. Bone: dont use tetracycline in kids 4. Plasma Protein binding: lowers Vd, increase plasma conc, increase t 1/2 5. Transcellular resevoirs |
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where are 5 places drugs wont go
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1. CSF
2. Ocular fluid 3. Endolymph 4. Fetal Fluid 5. Pleural fluid |
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what kinds of things can alter drug conc if that drug binds plasma proteins
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1. decreased albumin --> increased free drug!!
2. drug::protein interaction --> toxic 3. Administration of otehr things can compete for binding to plasma protein |
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can babies get drugs in utero
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yep, the placenta isnt a great barrier
**teratogens, most harmful in first trimester due to organogenesis |
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can babies get drugs from mom milk
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you bet!
can eve get drugs from cow milk if the cow has meds - passive diffusion of lipid soluble drugs and basic drugs |
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whats this called?
a drug initially is distributed to places with high BF like the brain, then it goes to the fat and is released from fat slowely. what drugs do this |
redistribution of of drugs
**common in thiobarbituates |
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what is first order drug elimination
what is zero order drug elimination |
first: constant PROPROTION of drug is eliminated per unit time. elimination depends on initial conc (100 --> 50 --> 25 ---> 12.5 etc)
zero: constant amt is eliminated in a unit time (100--> 90 --> 80 --> 70 etc) elimination is saturated |
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what is the rate limiting factor in a 1st order and 0 order elimination
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1st: initial conc (constant proportion is eliminated)
0: biological system (constant amt). independent of initial conc |
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what do the graphs of 1 and 0 order eliminations look like
Linear scale Log scale |
First: (depend on initial conc, prroportional elimination)
Linear: curve Semi Log: Straight Zero: (constant amount elimination) Linear: straight Log: curve **first order reactions are straight on a log scale, 0 order reactions are straight on a linear scale |
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clearance relates what variables
Systemic clearance is the sum of what |
Cl= proportionality constant that related rate of drug elimination and plasma conc
Systemic clearance is the sum of: renal, hepatic, and lung clearance |
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plasma conc of a drug and its rate of elimination are related by what parameter
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clearance
CL = Vd x Kel (Kel is elimination constant) CL= Vd x (0.693/t1/2) |
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what are 2 clearance equations
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CL = Vd x Kel
CL = Vd x (0.693/t1/2) *clearance is the ability of the body to remove a drug *clearance is a proprotionality constant that relates rate of drug elimination and plasma conc of that drug |
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what is teh elimination order of most drugs?
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most are 1st order, elimination depends on the initial conc
BUT there are some drugs like EtOH that have saturable elimination systems and are 0 order, elimination is constant |
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how are Kel Cl and Vd releated?
how is t1/2 related to Kel |
Kel = Cl/Vd
Kel is an elimination constant t1/2 = 0.693/Kel t1/2 = 0(.7 x Vd)/CL |
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what is t 1/2
what are the assumptions |
its the time required to decrease the drug by 50%
Assumes: body is single compartment drug distributes equally drug is in equilibrium |
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First Order Kinetics is an ______ process, there is a ______ fraction eliminated in a given time
Zero order kinetics is an _______ process, there is a _________ fraction eliminated in a given time |
First order: exponential process, constant FRACTION eliminated
Zero: non exponential process, constant AMOUNT eliminated |
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how many half lives does it take to see a steady state condition/concentration after repetetive dosing
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5
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how is the steady state concentration related to the: dose, clearance nad t1/2
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Css is directly proportional to dose adn t 1/2
Css is inversely proportional to the clearance |
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what factors affect the time to reach the steady state condition (after multiple doses of drug is given)
**note, steady state CONDITION, not concentration |
it takes 5 half lives to reach Css
Css is reached faster with increased dose and t 1/2 and decreased clearance |
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is clearance constant for most drugs
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yes
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ok so the steady state [CONC] happens when the steady state conditions is achieved in the course of repetitive administration. when else can we have a steady state concentration
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loading dose that is maintained with maintanience doses given
**steady state happens when elimination equals dosing (Dose= Cl c Css) ultimate repetetive administration is infusion |
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why is 5 t 1/2 such a popular number
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1. its the time needed to get steady state plasma levels of drug
2. takes this long to eliminate most of the drug after the last dose of drug **true for 1 order drugs |
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is the time that it takes to reach a steady state related to the soze of the dose
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nope
5 t1/2 to reach steady state plasma level of drug **true for 1st order drugs |
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what happens to the steady state con when you decrease the dosing interval of a drug?
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increased
**when the dosing is stretched out the steady state conc is decreased **true for 1st order drugs |
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what are some clinical implications of 0 order drugs?
*reach saturable levels and have a constant amt of drug excreted over time |
1. dont reach steady state levels
2. drugs given in doses higher than their excretion rate will build up in tha plasma and be toxic |
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what order drugs reach steady state conditions when given repete doses
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first order
**0 order drugs dont do steady states |
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whats a maintenance dose
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the amt of drug needed to maintain steady state plasma levels
**its equal to the amt of drug eliminated from teh body since the last dose **given at selected intervals |
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if you loose 8 g of a drug over 6 hours and then replace it by giving 8 g 6 hours later what is this
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maintence dose
**it bring a drug to a steady state level |
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when is accumulation of drug equal to elimination of drug
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at steady state
dosing rate=Elimination = CL x TC/F CL- clearance TC- Desired target Conc F- bioavailability (1 if IV admin) |
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CL x TC / F=
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elimination rate= dosing rate
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what is the formula for maintence dose
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(CL x TC / F) x F(r)
CL- clearnace TC- desired target conc r- dosing interval F- bioavailability |
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what is the maintience dose?
body eliminates 0.1 mg of drug A in 24 hrs. What is maintence dose |
(CL X TC/ F) x dosing interval(r)
**recall CLxTC/F is the dosing rate maintaince is 0.1 mg, its the amt that was eliminated |
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what is the maintience dose
TC- 10 mg/L CL- 2.8L/h/70kg IV admin |
1st find dosing rate
Dosing Rate= CL X TC/F (F-1 bc IV) 10 x 2.8/70 = 28 mg/70Kg 2nd find Maintenance dose (CLxTC/F) x dosing interval 28 x 12 hrs= 350 mg |
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dosing rate x dosing interval equals what
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maintenance dose
**Dosing Rate: CLxTC/F **dosing interval is time |
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loading dose is dependent on what variables?
maintence dose is dependent on what variables? |
Vd TC (volume and target conc)
CL TC (clearance and target conc) |
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when is a loading dose used
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for IMMEDIATE theraputic conc
LD = Vd x TC **the loading dose can be followed by the proper maintence dose (dose rate x dose interval) |
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what is given for the immediate theraputic response? whats it followed with
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loading dose initial immediate conc
then followed by maintenance dose LD = Vd x TC MD = CLxTC/F x dose interval |
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what is...
1. Time for onset 2. Time to Peak effect 3. Duration of Action |
1. time for onset: latency period, the time btwn the first dose and the first measureable response
2. time to peak effect: time needed to reach max effect/conc at site of action 3. Duration of Action: time from first measuranle effect to the time when effect is no longer measured |
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what is it...
1. latency btwn given a dose of meds and seeing the effect 2. Time needed to reach max effect/conc at the site of drug action 3. time from first measureable action ro time when effect is no longer measured |
1. Time for onset
2. Time to peak effect 3. Duration of Action |
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whats TDM
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theraputic drug monitoring
**monitor plasma levels to make sure drug is doing what you want it to. used when drug has narrow theraputic range or pt has lots of disease |
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what are brand name drugs
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they have their name protected forever and the cmpg protected for 20 years, this gives the company time to recover the cost of developing it
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whats the deal with generic drugs
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same active ingredient but different formulation of the binders and things
**simliar dissolution **simmiliar AUC **FDA approved **CHeap!!! **they need to wait 20 years til the brand name is dont with its protection to make theri money |
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Vd=
t1/2= Cl= LD= IR= |
Vd= Dose/Co
t1/2= 0.7 x Vd/Cl Cl = 0.7 x Vd/t1/2 LD= Vd x TC IR= CL x TC |
