CHEM 455 EXAM 3 Flashcards
Drug resistance
formerly effective drug dose is no longer effective
drug synergism
synergism arises when the therapeutic effect of two or more drugs used in combination is greater than the sum of the effect of the drugs individually
5 types of drug synergism
- Inhibition of a Drug-Destroying Enzyme
- Sequential Blocking Inhibition
- Inhibition of Targets in Different Pathways
- Efflux Pump Inhibitors
- Use of Multiple Drugs for the Same Target
why is resistance a problem
it causes drugs to be inhibited and ineffective which can be costly and deadly
why is drug synergism important
important in order to both combat drug resistance and to improve effectiveness of drugs
what are the 8 mechanisms of drug resistance
- Altered target enzyme or receptor
- overproduction of the target enzyme or receptor
- overproduction of the substrate or ligand for the target protein
- increased drug destroying mechanisms
- decreased drug (prodrug) activating mechanism
- activation of new pathways circumventing the drug effect
- reversal of drug action
- altered drug distribution to the site of action-modified cell membrane
- altered drug distribution to the site of action-efflux pumps
Altered Target Enzyme or Receptor
mutation of AA residue→ drug binds poorly, but substrate binding is unchanged
Overproduction of the Target Enzyme or Receptor
- induction of extra copies of the same gene encoding the target protein
- taking a larger dose may help until is reaches toxic levels
Overproduction of the Substrate or Ligand for the Target Protein
-overproduction of the substrate for a target enzyme would competitively block the ability of the drug to bind at the active site
Increased Drug-Destroying Mechanisms
-resistance by induction of genes→ produce new enzymes, increase quantities of existing enzymes, or produce other substances to degrade or sequester the drug
Decreased Drug (Prodrug)-Activating Mechanism
Prodrug- compound that is converted to the active substance after its administration
Activation of New Pathways Circumventing the Drug Effect
-if the drug inhibits an enzyme that blocks production of a metabolite, the organism could induce a new metabolic pathway that produces the same metabolite
Reversal of Drug Action
-drug acts in the opposite way that it is supposed to
Altered Drug Distribution to the Site of Action- Modified Cell Membrane
- organism excludes the drug from the site of action by preventing cellular uptake of the drug
- adjust net charge of plasma membrane
Altered Drug Distribution to the Site of Action- Efflux Pumps
- Efflux pumps- transmembrane proteins that act as transporters to carry drugs out of the cell before they elicit their therapeutic effect
- multidrug resistance pumps- broad specificity transporters that efflux a wide range of drugs against microorganisms and tumor cells
what are the factors that affect metabolism
increased lipophilicity increases metabolism
species, strain, sex, age, hormones, pregnancy, liver diseases, other drugs you’re taking
what are the two primary routes of metabolism for drugs and how do they differ
- via mouth: it is absorbed through small intestine/stomach-> blood stream -> liver
drugs metabolized by liver enzymes are presystemic or first pass effect - avoid liver
-sublingual, rectal, IV, IM, subcutaneous injections, pulmonary absorption, topical application
how is drug metabolism studied
mass spectrometry, radioactive labels, HPLC/NMR
Principal steps in drug metabolism studies
- Sample preparation– extractions, ion exchange—sometimes omitted and urine injected directly into HPLC
- Separations – HPLC, gas chromatography (GC), and capillary electrophoresis (CE)
- Identification – mass spectrometry (MS), NMR: link to separation with LC-MS, GC-MS, or CE-MS; good for
why are prodrugs used
aqueous solubility, absorption and distribution, site specificity, instability, prolonged release, toxicity, poor patient acceptability, formulation problems, delivery of nucleoside drugs
what is carrier prodrug
a compound that contains an active drug linked to a carrier group that is removed enzymatically
types of carrier prodrug
bipartite: comprised of a carrier attached to a drug
tripartite: carrier connected to a linker that is connected to a drug
mutual (codrug): two usually synergistic drugs that are attached to each other
bioprecursor prodrug
a compound that metabolized by molecular modification into a new compound, which is a drug or is metabolized further to a drug- or just simple cleavage of a group from the product