Pharm Exam 2 Flashcards
Chelator
“A compound that fosters the formation of a chemical ring by binding the metal that’s in this ring with two or more metallic ions (Tetracycline)
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Phase 1 reactions
Oxidative reactions
Phase 2 reactions
Conjugation reactions
Tetracycline Effect
Tetracycline is chelated by by Ca++. This inhibits the absorbtion of Tetracycline which reduces it antibacterial effect. More importantly it reduces availability of Ca++ which is needed by the fetus.
Example of chelation therapy
It is used in lead poisoning to quickly remove lead from the body
How do drugs Indirectly Reduce Absorbtion
Altering gastric pH. Altering Gastric Motility. P- Glycoprotein
What is P-Glycoprotein
A member of the Superfamily of eflux transporters which can pump the drug back into the GI tract to keep it from being absorbed.
Displacement
When one drug replaces another from a binding site which increases the free drug available. This plays a minimal role in drug interactions. Unbound drug only can cross the plasma membrane
What happens when the drug binds to CYP450?
Makes the drug more polar and more reactive which facilitates excretion or biotransformation.
CYP450 accounts for what % of drug oxidation
80%
CYP450 is not substrate specific because?
One or more drugs can be metabolized by the CYP isoforms. Oxygen of the complex is a powerful oxidizing agent that can react with numerous substrates
Conjugation and hydrolysis enzymes are located where
In the cytosol and the ER of hepatocytes
Conjugation occurs in what 2 ways
Directly with the drug or with reactive intermediaries generated during phase 1
What happens during phase 2 reactions?
A polar group is added which increases H2O solubility and facilitates excretion.
Polar groups; glucuronide, glutathione, acetate, sulfate
Phase 2 reactions are subject to what
Polymorphisms such as aceytlation. 40-50% of the population exhibit slow aceytlation and this have a slow metabolism.
Once satration occurs in drug elimination what happens?
The clearance rate fails to increase with concentration
How are drugs excreted form the liver into bile?
By an ATP family of transporters
What happens to drugs that undergo enterohepatic circulation?
They are reabsorbed by the SI and then into the portal and systemic circulation.
What is the role of bacteria in enterohepatic circulation?
Hydrolysis of Glucuronides.
What happens if abx kill of the bacteria in the gut?
It interferes with enterohepatic circulation.
The ability of one drug to inhibit the excretion of another depends on?
Filtration, Tubular Secretion, Reabsorbtion and Urine pH.
An example of a drug interaction with renal filtration.
If drug A inhibits the Albumin binding of drug B it increases the free abount of drug B which can then be eliminated by filtration.
An example of a drug interaction with tubular secretion.
If drug A limits the secretion of drug B than the amount of B in the body increases. Example Cimetidine decreases the secretion of Metformin which leads to an increased serum level of Metformin.
An example of a drug interaction with renal reabsorbtion.
A drug can decrease the kidney’s ability to reabsorb. Example a diuretic can cause more Na to be excreted than is desireable. The body will then stimulate the reabsorbtion of Na. The body can inadvertently reabsob other monovalent ions such as Li which can be toxic.
An example of a drug interaction with changes in urine pH.
Changes in either gatric pH or urine pH can cause changes in the absorbtion or secretion of drugs. Example is in alkaline urine renal excretion and clearance may be reduced compared to the same drug in an acidic unine pH.
What are synergistic effects and give an example.
Additive effects. Example is Gynco and Warfarin taken at the same time increase the risk of hemorrhage
What can cause drug interactions other than prescriptions drugs.
OTC, Illicit drugs, foods and alcohol
Example of a food causing a drug interaction.
Warfarin and green leafy vegetables which contain Vitamin K.
Acute ingestion of ETOH does what to drug metabolism?
Inhibits the CYP450 system