General Principles Flashcards
What is pharmacokinetics vs. pharmacodynamics?
Pharmacokinetics - what the body does to the drug
Pharmacodynamics - what the drug does to the body
What form(s) of a drug contribute to the concentration gradient?
Only the free, unionized form
Why is intramuscular injection usually more effective than subcutaneous?
Faster absorption because intramuscular is more vascular
What is the pKa?
pH at which 50% of drug is ionized and 50% is not ionized
Which form of the drug can cross membranes?
Non-ionized (uncharged) form - lipid soluble
Which form of the drug is better renally excreted?
Ionized (charged) form - water soluble
Name 4 common weak acid drugs.
Aspirin, penicillins, cephalosporins, loop/thiazide diuretics
Name 4 common weak base drugs.
Morphine, local anesthetics, amphetamines, PCP
Compare weak acid vs. base and their charged forms.
From acidic to basic environments:
Weak acid HA A- and H+
Weak base BH+ B and H+
In other words, a weak acid is in its charged form in a BASIC environment vs. a weak base is in its charged form in an ACIDIC environment
Which forms of a drug are filtered?
Kidney only filters unbound drug but it will filter BOTH the ionized and unionized forms.
Ionized forms are trapped in the filtrate while the unionized form can be involved in secretion/reabsorption.
What are 3 things you can give to try and acidify the urine (i.e. to get rid of a weak base drug)?
- NH4Cl
- Vitamin C
- Cranberry juice
What are 2 things you can give to alkalinize the urine (i.e. to get rid of a weak acid drug)?
- NaHCO3
2. Acetazolamide
What is the bioavailability of an IV administered drug?
100% - does not involve absorption
How can we define bioavailability in terms of oral vs. IV administration.
f = oral/IV since IV is 100% bioavailability (gold standard)
What is the first pass effect?
Hepatic metabolism when drugs are taken orally - absorbed into the portal circulation
If a drug crosses blood brain barrier it will also likely cross what other barrier?
Placenta
What are 3 characteristics of drugs that would tend to be safe to give to pregnant women?
- Large
- Protein-bound
- Water soluble
What does high vs. low Vd tell you?
High Vd = drug sequestered in tissues
Low Vd = drug is highly bound to plasma proteins
Because Vd = dose / plasma concentration
What are approximate Vd values for plasma, blood, ECF, total body water?
Plasma - 3 L
Blood - 5 L
ECF - 12 to 14 L
Total body water - 40 to 42 L
What are 5 classic CYP450 inducers?
Phenobarbital Phenytoin Carbamazepine Rifampin Chronic alcohol
What are 6 classic CYP450 inhibitors?
Cimetidine Macrolides (esp. erythromycine) Ketoconazole "avirs" Acute alcohol Grapefruit juice
What is a high yield clinical correlation of grapefruit juice inhibiting metabolism of a certain class of drugs?
Statins - e.g. if a patient tries to change their diet and starts drinking grapefruit juice
What are the main reactions in Phase I vs. Phase II metabolism?
Phase I - Redox, hydrolysis (think CYP450)
Phase II - Conjugation via transferases (think adding things onto the drug)
Why do babies get gray baby syndrome from chloramphenicol?
Reduced activity of Phase II metabolism (glucuronidation) - decreased activity of glucuronosyl transferase
