Block 1 Drug metabolism/elimination/clinical pharmacokinetics Flashcards
Describe what pharmacodynamics studies
Drug concentration & it’s effect
Describe Pharmacokinetics
Drug concentration & time
Describe the purpose of phase 1 reactions
Aka microsomal metabolism:
Turns lipophilic into a polar/hydrophilic metabolite via c-P450 (liver) via one of the following reactions:
- Oxidation*
- Reduction
- Hydrolysis
Describe the purpose of phase 2 reactions
Involves conjugating a drug into a polar metabolite (inactive) via one of these reactions:
- Glucuronidation*
- Acetylation
- Sulfation
- Methylation
Drug make up:
Describe the properties of lipophilic drugs
- Usually non-polar they can cross lipid membranes via passive diffusion (BBB, placenta etc)
- Mostly excreted via liver
Drug make up:
Describe the properties of hydrophilic drugs
- Usually Polar they need facilitated diffusion to pass lipid membranes
- Mostly excreted via liver
Drug make up:
Describe the properties of Amphiphilic drugs
have both lipo/hydro-philic properties
How does Vd change for the elderly?
- In hydrophilic drugs
Hydrophilic drugs = The elderly tend to have less total body water therefor they tend to have lower Vd
How does Vd change for the elderly?
- In acidic drugs
Acidic drugs = The elderly have less albumin therefor drugs can’t bind or stay in plasma (high Vd)
How does Vd change for the elderly?
- In lipophilic drugs
The elderly tend to have more body fat therefor Higher Vd
Drug metabolism:
Describe what zero order kinetics are
- When the metabolism/elimination rate stays constant (independent of plasma concentration of the drug at steady state)
- It’s capacity limited meaning the drug can become over saturated (toxicity)
Types of conjugation:
What are the drugs metabolized via phase II Acetylation?
Sulfonamide
Hydralazine
INH
Procainamide & Penicillamine
Dapsone
“SHIPD”
Gastric patients have an increased _____ phase metabolism
Phase II metabolism
Drug half-life:
Describe what the:
1. rate of elimination
2. Drug examples
- The rate of elimination is constant meaning it can become over saturated
- “It takes zero PHEN-TAS-E”
- Phenytoin
- Aspirin
- Ethanol
Describe the features of 1st order kinetics
The rate of metabolism is directly proportional to the drug’s plasma concentration (meaning it’s dependent on the elimination)
What’s the equation for Vd?
Vd =
Q (conc of drug in body)
/
C (conc of drug in plasma)
Intravascular drugs have _____ Vd
Low Vd because they are large + charged molecules with a high binding affinity to plasma proteins
ECM drugs have a _____ Vd
Medium Vd because they are small but hydrophilic
Tissue/fat drugs have a ____ Vd
High Vd because they are small + lipophilic & have a higher binding affinity for tissue proteins
What is the equation for the half life of a drug (t1/2)
t1/2 = (0.7 * Vd) / CL in first order eliminations
How many half lives does it take a drug to reach steady state when infused at a constant rate?
4-5 t1/2’s
Describe what steady state is
When the rate of a drugs elimination is equal to its rate of administration
What’s the key equation for CL?
CL = 0.7 * (Vd / t1/2)
OR
CL = Dosage rate / Plasma concentration
What’s the equation for the loading dose (also what is the loading dose)?
Loading dose = CP * Vd / F (bioavail)
Loading dose is the amount of drug needed to cause an initial therapeutic effect (typically administered in ER situations to stabilize
In renal & liver disease (hypoalbuminemia) how are loading & maintenance doses effected?
Loading dose is unaffected
&
Maintenace dose decreases
What is the equation for Maintenace dose?
Maintenance dose = CP * CL * t (dosage int) / F
Lipophilic drugs are metabolized via one of two phases:
Phase 1 is primarily CYP450 dependent & involves which reactions and produces what kind of metabolites?
Reactions:
Hydroxylation
Oxidation
Reduction
Metabolites:
slightly polar
Lipophilic drugs are metabolized via one of two phases:
Phase 2 involves which reactions and produces what kind of metabolites?
Reactions:
Methylation
Acetylation
Glucuronidation
Sulfation
Metabolites:
Very polar (except acetylation)
In phase 2 metabolism, all reactions products are very polar except for acetylation. Which drugs are metabolized in this phase via acetylation?
Sulfonamides
Hydralazine
INH
Procainamide
Dapsone
“SHIPD”
Efficacy describes the what?
The max effect a drug can cause (aka the Vmax)
Potency describes the what?
The amount of drug that is needed to cause an effect (EC50)
What type of receptor binding is this, describe it
Competitive antagonist:
Decreased potency
unchanged efficacy
Can be overcome with lots of agonists
Diazepam + Flumazenil on GABA receptors = decreased potency describes flumazenil as what type of binding receptor?
competitive antagonist
What type of receptor binding is this, describe it
Decreased Efficacy
Unchanged potency
It can’t be overcome by more agonists
Norepi + phenoxybenzamine on alpha receptors = decreased efficacy describes phenoxybenzamine as what type of binding receptor?
Non-competitive antagonist
What type of receptor binding is this, describe it
Decreased efficacy
Unchanged potency
It acts on the same site as the full agonist
Morphine + buprenorphine at mew opiod receptors = decreased efficacy & independent potency depending on the drugs
Partial agonist
Effects of drugs:
When the effect of A & B together is equal to their individual effects
Additive effect
Aspirin + acetaminophen administered together is an example of what type of drug effect?
Additive effect
Effects of drugs:
When drug A is needed to get the full effect of Drug B
Permissive effect
Drug effect:
When the effect of drug A & drug B together is greater than their individual effects
Synergistic effect
Clopidogrel increases the effect of aspirin administered together, describes what kind of drug effect?
Synergistic effect
When the effects of drugs A & B together are grater but drug B doesn’t actually have a therapeutic effect, this describes what type of drug effect?
Potentiation effect
Carbidopa only blocks the enzyme that metabolizes levodopa but this increases levodopa’s effect, this describes what type of drug effect?
potentiation effect
When the effect of drugs A & B together is LESS than their individual effects, describes which type of drug effect?
Antagonistic effect
Ethanol is used as an antidote to decrease the effect of methanol toxicity, describes what type of drug effect?
Antagonistic effect
Repeated use of a drug causes it to have less of an effect (sensitization), describes what kind of drug effect?
Tachyphylactic effect
Describe what redistribution means for drugs
this describes the fast acting & terminating effects of very lipid soluble drugs on the BBB & Heart
Thiopentone sodium & Propofol are examples of drugs that undergo ________
Redistribution
Describe zero order kinetics
drug elimination is capacity limited meaning it can become over saturated (the graph won’t be linear)
Zero order drugs include (4)
Phenytoin
Ethyl alcohol
Theophylline
Aspirin
List the CYP450 Inducers
St. Johns wort
Phenytoin
Phenobarbitone
Modafinil
Nevirapine
Rifampin
Griseofulvin
Carbamazepine
Chronic alcohol
St. Johns wort
Phenytoin
Phenobarbitone
Modafinil
Nevirapine
Rifampin
Griseofulvin
Carbamazepine
Chronic alcohol
Are all examples of CYP450
Inducers
St. Johns wort
Phenytoin
Phenobarbitone
are examples of
CYP450 Inducers
Modafinil
Nevirapine
Rifampin
Are examples of
CYP450 Inducers
Griseofulvin
Carbamazepine
Chronic alcohol
Are examples of
Cyp450 Inducers
List the CYP450 Inhibitors
Sodium Valproate
Isoniazid (INH)
Cimetidine
Ketoconazole
Fluconazole
Acute Alcohol
Chloramphenicol
Erythromycin
Sulfonamides
Ciprofloxacin
Omeprazole
Amiodarone
Ritonavir
Grapefruit juice
Sodium Valproate
Isoniazid (INH)
Cimetidine
Ketoconazole
Fluconazole
Acute Alcohol
Chloramphenicol
Erythromycin
Sulfonamides
Ciprofloxacin
Omeprazole
Amiodarone
Ritonavir
Grapefruit juice
Are all examples of
CYP450 Inhibitors
SICK FACES COme when I AM Really drinking GF juice
Sodium Valproate
Isoniazid (INH)
Cimetidine
Are examples of
CYP450 Inhibitors
Ketoconazole
Fluconazole
Acute Alcohol
Are examples of
CYP450 Inhibitors
Chloramphenicol
Erythromycin
Sulfonamides
Are examples of
CYP450 Inhibitors
Ciprofloxacin
Omeprazole
Amiodarone
Are examples of
CYP450 Inhibitors
Ritonavir
Grapefruit juice
Are examples of
CYP450 Inhibitors
List the substrates of CYP450
Theophylline
OCP’s
Anti-Epileptics
Warfarin
Theophylline
OCP’s
Anti-Epileptics
Warfarin
Describes what
CYP450
Theophylline
OCP’s
Describes what
CYP450 substrate
Anti-Epileptics
Warfarin
Describes what
CYP450 Substrates
Describe the actions of an agonist
they bind & mimics a substance in our body (i.e morphine)
Affinity & Efficacy = 1
Describe an antagonist
a drug that blocks receptors of a substance preventing its effect. i.e Naxolone
Describe an inverse agonist
When a drug binds a receptor but produces the opposite effect that the endogenous substance was supposed to (vasocontraction instead of vasodilation)
flumazenil binds to the same receptors as benzodiazepines (drugs that reduce anxiety) but instead of calming the brain, it produces an opposite effect and increases anxiety levels
This describes a ______
Inverse agonist
Describe a partial agonist
When a drug is only partly as effective as a full agonist. But it acts as a competitive antagonist when there is a full agonist around
Affinity = 1
Efficacy < 1
buprenorphine, which is used to treat opioid addiction. It has both agonist and antagonist properties and binds to opioid receptors in the brain, producing some opioid-like effects but not as strongly as full agonists like heroin
This describes ______
Partial agonist that can act as a competitive inhibitor to heroin