A partial agonist produces the biological response but cannot produce 100% of the biological response even at very high doses.
• Therapeutic Index
Therapeutic index is a measure of drug safety. A drug with a higher therapeutic index is safer than one with a lower therapeutic index.
Therapeutic index is a measure of drug safety. A drug with a higher therapeutic index is safer than one with a lower therapeutic index.
• Antagonist
Antagonists block or reverse the effect of agonists. They have no effect of their own.
Antagonists block or reverse the effect of agonists. They have no effect of their own.
Competitive antagonists make the agonist look less potent by shifting the dose response curve to the right.
A noncompetitive antagonist reduces the maximal response that an agonist can produce.
Inverse agonists have opposite effects from those of full agonists. They are not the same as antagonists, which block the effects of both agonists and inverse agonists.
• First Pass Effect
The liver is a metabolic machine and often inactivates drugs on their way from the GI tract to the body. This is called the first-pass effect.
The liver is a metabolic machine and often inactivates drugs on their way from the GI tract to the body. This is called the first-pass effect.
For a weak acid, when the pH is less than the pK, the protonated form (nonionized) predominates. When the pH is greater than the pK, the unprotonated (ionized) form predominates.
For a weak base, when the pH is less than the pK, the ionized form (protonated) predominates. When the pH is greater than the pK, the unprotonated (nonionized) form predominates.
In the stomach (pH 2.0), weak acids are uncharged and will be absorbed into the blood- stream, whereas weak bases are charged and will remain in the GI tract.
Bioavailability is the amount of drug that is absorbed after administration by route X compared with the amount of drug that is absorbed after intravenous (IV) administra- tion. X is any route of drug administration other than IV.
Clearance is a term that indicates the rate at which a drug is cleared from the body. It is defined as the volume of plasma from which all drug is removed in a given time. Thus, the units for clearance are given in volume per unit time.
Total body clearance is the sum of the clearances from the various organs involved in drug metabolism and elimination.
Volume of distribution (VD) is a calculation of the apparent volume in which a drug is dissolved.
Most drugs disappear from plasma by processes that are concentration-dependent, which results in first-order kinetics. With first-order elimination, a constant percentage of the drug is lost per unit time. An elimination rate constant can be described.
The half-life (t1/2) is the period of time required for the concentration of a drug to decrease by one half.
Drugs that saturate routes of elimination disappear from plasma in a non–concentration dependent manner, which is zero-order kinetics.