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How the body handles drugs by drug absorbption, distribution, metabolism, and excretion.
Which is absorbed better ionized or non-ionized?
Non-ionized is absorbed better.
Once absorbed what are the two main options/categories for drugs?
Active and inactive.
What are the ways a drug can be inactive?
- 1) Attached to plasma protein for storage
- 2) Stored in fat
- 3) Stored in bone
What are the 4 processes that a drug goes through?
Absorbtion, Deistribution, Metabolism, Excretion
What factors influence drug absorbtion?
Drug chemistry (i.e. solubility) route of administration, and coating of drug.
What are the routes of administration?
- Oral- Variable, slower absorbtion
- IM- rapid absorbtion (if aqueous), slower if lipid
- IV- fastest absorbtion
- Subcutaneous- same as IM
- Inhalation- rapid absorbtion
- Percutaneous or transdermal- incomplete or erratic absorbton
- Rectal- erratic absorbtion
- Sublingual- eliminates 1st pass effect
- Topical- incomplete erratic absorbtion
What type of solubility is required for a drug to be absorbed?
It must be soluble in water (and to a certain extent lipid).
Drugs that are protected from dissolving in stomach, coated with wax that only disloves in alkaline environment (in sm. intestine)
What is special about a time release capsule?
Part of drug disolves in stomach and part of drug disolves in sm. intestine.
What is the difference between drugs absorbed in the stomach and drugs absorbed in the small intestine?
Drugs absorbed in the stomach are made non-ionized by adding acid (ex. asprin). Drugs absorbed in the small intestine are made non-ionized by adding a base (ex. anphetamines)
Explain drug-drug interaction and drug activity.
If a drug (A) is alone 50% may bind to plasma protein and 50% will be active. If drug B is added to the mix, and B has a greater ability to bind to plasma protein, the B will bind to the plasma protein and less of A will bind to the plasma protien so more of A will be active.
What are two organs that specialize in acting as a barrier?
Blood-brain barrier and placental barrier
Explain the 1st pass effect.
Some drugs that are absorbed in the GI tract are metabolized in the liver before having an effect as an active drug, so a large first dose must be given or a build up of the drug over multiple doses must be done before a drug can be effective.
What do Hepatocygtes do?
Hepatocytes contain microsomal enzymes that metabolize drugs in the liver.
What are microsomal enzymes?
Enzymes that convert an active drug to a toxic metabolite.
What are the 6 metobolic fates of a drug?
- 1) Ative --> Metabolized --> inactive
- 2) Active --> Metabolized --> Less active
- 3) Inactive --> Metabolized --> Active --> (6) less or inactive drug
- 4) Less active drug --> Metabolized --> more active drug --> (6) less or inactive drug
- 5) Ecretion with no metabolization
What are some factors that affect hepatic drug metabolism?
Age, nurttional status, genetic makeup, liver disease, hormones
What is inhibition?
Inhibiting the liver enzymes in some way sot that the break down of the drug occurs slower; it increases the level of the active drug in the body.
What is stimulation?
Simulating the liver enxymes and increases its ability to metabolize other drugs; it decreases the level of the drug in the body.
What are the 2 major processes of elimination?
Glomerular flitration and tubular secretion.
Filtration moves drugs from blood to urine; protein-bound drugs are not filtered
Active; tubular "pumps" for organic acids and bases move drugs from blood to urine
Passive; lipid-soluble and nonionized drugs move back into the blood, polar and ionized drugs remain in the urine
How do you decrease drug reabsorbtion?
Make the environment in the rine tract more acidic/basic to ionize the drug (ionized drugs will not be reabsorbed)
What level is looked at to determine the therapeutic and toxic responses?
The plasma drug level
Minimus effective concentraton (MEC)
The plasma drug level below which therapeutic effects will not occur; the lowest level a drug is therapeuticly effective
The plasma drug level at which toxic effects begin
Between the Minimum effective concentration (MEC) and the toxic concentration
Onset of action
The time needed for the drug concentration to reach the minimum level
Time to peak effect
The time required for the maximum effect to occur after administration
Duration of action
The time during which blood levels are above the minimum effective concentration
The time needed for the plasma concentration of a drug to fall to 50% of its previous concentration; the faster the rate of metabolism, excretion, or both, the shorter the half-life
When the amout of drug eliminated between doses quals the dose administered, average drug levels will remain constant and plateau will have been reached.