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Pharmacokinetics (Elimination (Half-life (Plasma half-life (time taken for…

- - - - constant percentage of drug lost per unit time
        
        an elimination constant can be described
        
        drug elimination from plasma is dose dependent
        
        the higher the plasma drug concentration, the higher the rate of elimination and the faster the drug is eliminated from the plasma
        
        Most drugs follow first order kinetics: exponential disappearance of drug from plasma
        
        constant percentage of drug is eliminated in any given time period
        
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  - - - elimination from plasma is described by a straight line when plotted on a logarithmic scale y-axis, consistent with exponential drug decay of plasma concentration.
        
        Exponential decay is described by first-order kinetics where the rate of elimination of drug from plasma is proportional to the concentration of drug in the plasma.
  - - - initial exponential distribution phase
        
        first order kinetics
        
        linear plasma elimination phase
        
        Failure to account for the distribution phase in some drugs can lead to errors in calculation and estimation fo plasma drug concentration
  - - - constant amount of drug lost per unit time
        
        rate of elimination is independent of drug concentration because the elimination route is readily saturated = saturation kinetics
        
        ex- alcohol
        
        Alcohol dehydrogenase )elimination enzyme for alcohol) reaches a maximum catalytic rate at very low alcohol concentrations
        
        for most levels of consumed alcohol, the elimination rate cannot increase beyond saturation and so a constant amount of alcohol is lost per hour
        
        allowing the creation of charts that say exactly how much alcohol should be in your system x number of hours after drinking y number of beers
        
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        elimination pathways for some drugs are easily saturated at low levels of drug
        
        once saturated the rate of elimination cannot increase, stays at constant value
        
        an amount rather than a percentage of the remaining drug is then lost
  - - - time taken for plasma drug concentrations to fall exactly half of their original levels
        
        from whatever time point after administration you calculate half-life it will be the same
        
        half-life is a unique constant for any individual drug
    - - time taken for the pharmacological effect of the drug to decay
        
        Reversible receptor
        
        may be the same as plasma half-life because as soon as drug leaves the receptor, receptor stimulation ceases and so does the drug effect
        
        most drugs have similar pharmacologic and plasma half-lives in terms of time
        
        rate of elimination is proportional to plasma drug concentration following first order kinetics
        
        Differences in peak starting concentration have no effect on drug elimination half-life
        
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        Irreversible receptor
        
        increase pharmacologic half-life compared to plasma half-life as the drug would maintain effect even if completely cleared from plasma circulation
        
        ex- DNA damaging drugs that intercalate with DNA or otherwise damage DNA
        
        drug effects would and does persist long after the drug has been eliminated
- - - - relative measure of drug absorption which describes the amount of drug that is absorbed after administration by route X (often oral administration) compared to amount absorbed after intravenous (IV) administration.
        
        assumes IV administration provides 100% of available drug dose into circulation
        
        functionally related drugs should have comparable bioavailability
  - - - Therapeutic equivalence
        
        Drugs classified as therapeutically equivalent can be substituted with the full expectation that the substituted product will produce the same clinical effect and safety profile as the prescribed product
        
        = they are bioequivalent and they also have the same active ingredients, dosage form, route of administration and strength.
  - - - drug swing between dosing interval = td
        
        dose administered = amount eliminated in time td
        
        Second dose administered before initial dose has been entirely eliminate
        
        cumulative: peak plasma concentration will be higher than the original peak plasma concentration
        
        drugs are administered recurrently over a period of time at equal time intervals
        
        time period between doses is called a dosing interval
        
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  - - - may be calculated by multiplying the target dose by the volume of distribution
        
        after loading dose, drug is administered at the required maintenance dose,
        
        IV infusion
        
        repeated dose administration
        
        plasma drug reaches and remains at the required maintenance dose
- - - - two compartments
        
        first compartment
        
        where the drug first localizes, ex- liver, heart, lungs, brain
        
        second compartment
        
        gradual dispersion throughout the entire body