USMLE Gen Pharm Flashcards
Km: Definition
Km = Substrate at 0.5*Vmax
Km reflects the affinity of the enzyme for its substrate
Vmax indicates what?
Vmax is directly proportional to the enzyme concentration.
Relationship between Km and affinity
–The lower the Km, the higher the affinity
–Smaller Km means enzyme is saturated earlier, which means that small amounts of substrate are picked up by the enzyme.
Reading an inverse curve: Y–intercept equals ?
1/Vmax
The higher the Y–intercept the lower the Vmax
Reading an inverse curve: X–intercept equals ?
(1/–Km)
The further to the right the x–intercept, the greater the Km
Reading an inverse curve: Slope equals ?
Km/Vmax
Reading an inverse curve: Effect of a competitive inhibitor
X–intercept farther to the right, meaning Km is greater, because you need more substrate to get the same effect as the competitive inhibitor is hogging the enzyme.
The y–intercept is the same, meaning Vmax hasn’t changed, because there isn’t any more enzyme.
The slope is greater, because Km has increased while Vmax has stayed the same.
Reading an inverse curve: Effect of a noncompetitive inhibitor
The x–intercept is the same, meaning Km is the same, because the affinity for the enzyme hasn’t changed, there’s just less of it.
The y intercept has increased, meaning Vmax has decreased, because enzyme has been inactivated by the noncompetitive inhibitor
The slope is greater, because Vmax has decreased while Km has stayed the same.
Competitive inhibitor: Resemble substrate
Yes
Competitive inhibitor: Overcome by increased substrate?
Yes
Competitive inhibitor: Binds active site?
Yes
Competitive inhibitor: Effect on Vmax
Unchanged. The amount of enzyme has not changed.
Competitive inhibitor: Effect on Km
Increased. A lot more substrate needs to be available to seize the active sites.
Noncompetitive inhibitor: Resemble substrate?
No
Noncompetitive inhibitor: Overcome by increased substrate?
No
Noncompetitive inhibitor: Binds active site?
No
Noncompetitive inhibitor: Effect on Vmax
Decreased. Takes the enzyme out.
Noncompetitive inhibitor: Effect on Km
Unchanged. Does not change the affinity for the enzyme.
Volume of distribution: Abbreviation
Vd
Vd: Stands for what?
Volume of distribution
Volume of distribution: definition
Vd = (amount of drug in the body)/(plasma drug concentration)
Volume of distribution: What alters it?
Liver and kidney disease
Where are drugs with a low Vd distributed?
plasma
Where are drugs with a medium Vd distributed?
extracellular space
Where are drugs with a high Vd distributed?
tissues
Clearance: definition
(rate of elimination of drug)/(plasma drug concentration)
=Vd x Ke where Ke=elimination constant
Half life: definition
The time required to change the amount of drug in the body by 1/2 during elimination (or during a constant infusion).
What percentage of steady state is a drug at after: 1 half life
50%
What percentage of steady state is a drug at after: 2 half lives
75%
What percentage of steady state is a drug at after: 3 half lives
87.50%
What percentage of steady state is a drug at after: 3.3 half lives
90%
What percentage of steady state is a drug at after: 4 half lives
94%
How many half lives does it take for a drug to reach the following percentage of steady state: 50%
1 half life
How many half lives does it take for a drug to reach the following percentage of steady state: 75%
2 half lives
How many half lives does it take for a drug to reach the following percentage of steady state: 87.5%
3 half lives
How many half lives does it take for a drug to reach the following percentage of steady state: 90%
3.3 half lives
How many half lives does it take for a drug to reach the following percentage of steady state: 94%
4 half lives
Cp stands for what?
target plasma concentration
What is the abbreviation for target plasma concentration?
Cp
In pharmacology, what is F an abbreviation for?
Bioavailability
What is the abbreviation in pharmacology for bioavailability?
F
Loading dose: Definition
Loading dose = (Cp * Vd)/F (where Cp equals the target plasma concentration, Vd equals volume of distribution, and F equals bioavailability)
Maintenance dose: Definition
Maintenance dose = (Cp * CL)/F (where Cp is the target plasma concentration and CL is clearance and F is bioavailability)
Zero–order elimination: definition
Constant elimination over time regardless of drug.
How does Cp vary with time during zero–order elimination?
Cp decreases linearly with time.
Zero–order elimination: Drug examples
–Ethanol
–Phenytoin
–Aspirin (at high concentrations)
First–order elimination: definition
Rate of elimination is proportional to drug concentration
Zero–order elimination vs First–order elimination: Comparison
Zero–order: Constant amount of drug eliminated per unit time
1st–order: Constant fraction of drug eliminated per unit time
How does Cp vary with time during first–order elimination?
Cp decreases exponentially with time.
Urine: Which species get trapped in urine?
Ionized species
In what kind of environment is the following trapped?: Weak acids
Basic environments
In what kind of environment is the following trapped?: Weak bases
Acidic environments
In what kind of environment is the following digested?: Weak acids
Acidic environments (below pKa)
In what kind of environment is the following digested?: Weak bases
Basic environments (above pKa)
How do you treat an overdose of the following?: Weak acids
Bicarbonate
How do you treat an overdose of the following?: Weak bases
Ammonium chloride
Phase I metabolism: Processes
Cytochrome P450
–reduction
–oxidation
–hydrolysis
Phase II metabolism: Processes
Conjugation
–acetylation
–glucuronidation
–sulfation
Phase I metabolism: Metabolites
–slightly polar
–water–soluble
–often still active
Phase II metabolism: Metabolites
–very polar
–renally excreted
–inactive
What phase of metabolism do geriatric patients lose first?
Phase I
Effect on dose/effect curve of: competitive antagonist
Shifts curve to the right, decreasing potency and increasing EC50.
Effect on dose/effect curve of: noncompetitive antagonist
Shifts curve downward, decreasing efficacy
What is EC50?
Dose causing 50% of maximal effect
What is Kd?
Concentration of drug required to bind 50% of receptor sites
How many half lives does it take for a drug to reach the following percentage of steady state: 97%
5 half lives
What percentage of steady state is a drug at after: 5 half lives
97%
Effect on dose/effect curve: Spare receptors
The drug binding and drug effect are independent of each other with effect to the left of binding.
This means that EC50 is lower than Kd, so very little drug needs to bind to get 50% of the effect.
Effect on dose/effect curve: Partial agonist
–Lower maximal efficacy
–Potency independent (amount of dose to get to maximum effect)
Therapeutic Index: Definition
ERROR!
Where are nicotinic receptors found?
Preganglionic synapses before:
–Cardiac and smooth muscle (Parasympathetic and Sympathetic)
–Gland cells (Parasympathetic and Sympathetic)
–Nerve terminals (Parasympathetic and Sympathetic)
–Renal vascular smooth muscle (Sympathetic)
Neuromuscular junctions for skeletal muscle
What is the neurotransmitter at Nictoinic receptors?
Acetylcholine
What is the neurotransmitter at Muscarinic receptors?
Acetylcholine
Where are muscarinic receptors found?
Parasympathetic end plates:
–Cardiac and smooth muscle
–Gland cells
–Nerve terminals
Sympathetic end plate:
–Sweat glands
Where are D1 receptors found?
Sympathetic:
Renal vascular smooth muscle
What type of G–protein is associated with the following receptor type?: alpha–1
Gq
What type of G–protein is associated with the following receptor type?: alpha–2
Gi
What type of G–protein is associated with the following receptor type?: beta–1
Gs
What type of G–protein is associated with the following receptor type?: beta–2
Gs
What type of G–protein is associated with the following receptor type?: M1
Gq
What type of G–protein is associated with the following receptor type?: M2
Gi
What type of G–protein is associated with the following receptor type?: M3
Gq
What type of G–protein is associated with the following receptor type?: D1
Gs
What type of G–protein is associated with the following receptor type?: D2
Gi
What type of G–protein is associated with the following receptor type?: H1
Gq
What type of G–protein is associated with the following receptor type?: H2
Gs
What type of G–protein is associated with the following receptor type?: V1
Gq
What type of G–protein is associated with the following receptor type?: V2
Gs
What types of receptors are associated with the following G–proteins: q
–alpha–1 –M1 –M3 –H1 –V1
What types of receptors are associated with the following G–proteins: i
–alpha–2
–M2
–D2
What types of receptors are associated with the following G–proteins: s
–beta–1 –beta–2 –D1 –H2 –V2
What are the major functions of the following receptor type: alpha–1
Increase vascular smooth muscle contraction
What are the major functions of the following receptor type: alpha–2
–Decrease sympathetic outflow
–Decrease insulin release
What are the major functions of the following receptor type: beta–1
–Increase heart rate –Increase contractility –Increase renin release –Increase lipolysis –Increase aqueous humor formation
What are the major functions of the following receptor type: beta–2
–Vasodilation
–Bronchodilation
–Increased glucagon release
What are the major functions of the following receptor type: M1
CNS
What are the major functions of the following receptor type: M2
Decrease heart rate
What are the major functions of the following receptor type: M3
Increase exocrine gland secretions
What are the major functions of the following receptor type: D1
Relax renal vascular smooth muscle
What are the major functions of the following receptor type: D2
Modulate transmitter release (especially in brain)
What are the major functions of the following receptor type: H1
–Increase nasal/bronchial mucus production
–Contraction of bronchioles
–Pruritus
–Pain
What are the major functions of the following receptor type: H2
Increased gastric acid secretion
What are the major functions of the following receptor type: V1
Increased vascular smooth muscle contraction
What are the major functions of the following receptor type: V2
–Increased water permeability and reabsorption in the collecting tubules of the kidney
Gq protein pathway
–Receptor stimulated
–Gq protein stimulates Phospholipase C
–Phospholipase C catalyzes the conversion of Lipids to PIP2
–PIP2 splits into IP3 and DAG
IP3 stimulates an increase in Calcium concentration
DAG activates Protein Kinase C
Gs protein pathway
–Receptor stimulated –Gs protein stimulates Adenylylcyclase –Adenylylcyclase catalyzes conversion of ATP to cAMP –cAMP activates Protein Kinase A
Gi protein pathway
–Receptor stimulated
–Gi protein inhibits Adenylylcyclase
–Decreases conversion of ATP to cAMP
–Decreased activation of Protein kinase A
Cholinergic pathway (presynaptic events to receptor)
- Choline transported into presynaptic bulb
- Acetyl–Coa joints with Choline–ChAT to form acetylcholine, and the two are taken up by a vesicle.
- The vesicle joins with the cell membrane and ACh is exocytosed
- ACh is released into the synapse
- Acetylcholine joints with the Cholinoceptor or is degraded by AChE into Choline + Acetate
Hemicholinum: Action and mechanism
Inhibits cholinergic transmission
Mechanism: Inhibits transfer of choline into presynaptic bulb
Vesamicol: Action and mechanism
Inhibits cholinergic transmission
Mechanism: Inhibits uptake of ACh into a vesicle in the presynaptic bulb
Ca2+: Action on presynaptic vesicles
Stimulates exocytosis of neurotransmitters from presynaptic bulb
Botulinum: Action and mechanism
Inhibits cholinergic transmission
Mechanism: Inhibits exocytosis of neurotransmitters from presynaptic bulb
Noradrenergic pathway (presynaptic events to receptor)
- Tyrosine is transferred into the presynaptic bulb
- Tyrosine is converted into DOPA
- DOPA is converted to Dopamine
- Dopamine is converted to Norepinephrine and transferred into a vesicle
- Norepinephrine is exocytosed from the presynaptic terminal
- 3 possibilities happen
a. Norepinephrine binds to a beta adrenoreceptor.
b. Norepinephrine is reuptaken by the releasing neuron
c. Norepinephrine binds to an alpha–2 receptor on the releasing neuron
d. It diffuses away/is metabolized.
Metyrosine: Action and mechanism
Action: Inhibits noradrenergic transmission
Mechanism: Inhibits step where tyrosine is converted into DOPA
Reserpine: Action and mechanism
Action: Inhibits noradrenergic transmission
Mechanism: Prevents sequestration of norepinephrine into vesicles
Guanethidine: Action and mechanism
Action: Inhibits noradrenergic transmission
Mechanism: Inhibits exocytosis of Norepinephrine from presynaptic bulb
Amphetamine: Action and mechanism
Action: Stimulates noradrenergic transmission
Mechanism: Stimulates exocytosis of norepinephrine from presynaptic bulb
Tricyclic antidepressant: Mechanism
Decreases reuptake of norepinephrine from synaptic cleft into releasing neuron
Cocaine: Mechanism
Decreases reuptake of norepinephrine from synaptic cleft into releasing neuron
Angiotensin II: Effect on noradrenergic pre–synaptic neurons
Enhances release of NE
Cholinomimetics: Direct agonists
Bethanechol, Carbachol, Pilocarpine, Methacholine
Cholinomimetics: Indirect agonists
Neostigmine (AChE inhibitor), Pyridostigmine, Edrophonium, Physostigmine, Echothiophate
Use of: Bethanechol
Postoperative and neurogenic ileus and urinary retention
Use of: Carbachol
–Glaucoma
–pupillary contraction
–release of intraocular pressure
Use of: Pilocarpine
Potent stimulator of:
–Sweat
–Tears
–Saliva
Use of: Methacholine
Challenge test for diagnosis of asthma
Use of: Neostigmine
AChE inhibitor
–Postoperative/neurogenic ileus/urinary retetnion
–Myasthenia Gravis
–Reversal of neuromuscular junction blockade (postoperative)
–No CNS penetration
Use of: Pyridostigmine
–Myasthenia Gravis (increases strength)
–does penetrate CNS
Use of: Edrophonium
Diagnosis of myasthenia gravis (extremely short acting)
Use of: Physostigmine
–Glaucoma (crosses blood–brain barrier into CNS)
–Atropine overdose
Use of: Ecthiophate
–Glaucoma
Mechanism of indirect cholinomimetics
Increase endogenous ACh
Synonym for indirect cholinomimetics
Anticholinesterases
Synonym for anticholinesterases
indirect cholinomimetics
Bethanechol: mechanism
–Activates bowel and bladder smooth muscle
–Resistant to AChE
Carbachol: mechanism
–Contracts ciliary muscle of eye (open angle)
–Contracts Pupillary sphincter (narrow angle)
–Resistant to AChE
Methacholine: mechanism
Stimulates muscarinic receptors in airway when inhaled
Symptoms of cholinesterase inhibitor poisoning
DUMBBELS SAC
–Diarrhea –Urination –Miosis –Bronchospasm –Bradycardia –Excitation of skeletal muscle and CNS –Lacrimation –Sweating –Salivation –Abdominal Cramping
Antidote to cholinesterase inhibitor poisoning
–Atropine (muscarinic antagonist) +
–Pralidoxime (chemical antagonist used to regenerate active cholinesterase)
Cholinesterase inhibitors
–Parathion
–Other organophosphates
Cholinoreceptor blockers
–Atropine (homatropine, tropicamide) –Benztropine –Scopolamine –Ipratropium –Methscoplamine (oxybutin, glycopyrrolate)
Cholinoreceptor blockers used to produce: mydriasis and cycloplegia
Atropine, homatropine, tropicamide
Cholinoreceptor blockers used for: Parkinson’s disease
Benztropine
Cholinoreceptor blockers used for: Motion sickness
Scopolamine
Cholinoreceptor blockers used for: Obstructive pulmonary disease
Ipratropium
Cholinoreceptor blockers used for: Genitourinary problems
–Methscopolamine
–Oxybutin
–Glycopyrrolate
Application of: Atropine
Produce mydriasis and cycloplegia
Application of: Homatropine
Produce mydriasis and cycloplegia
Application of: Tropicamide
Produce mydriasis and cycloplegia
Application of: Benztropine
Parkinson’s Disease
Application of: Scopolamine
Motion sickness
Application of: Ipratropium
Obstructive pulmonary diseases
Application of: Methscopolamine
–Reduce urgency in mild cystitis
–Reduce bladder spasms
Application of: Oxybutin
–Reduce urgency in mild cystitis
–Reduce bladder spasms
Application of: Glycopyrrolate
–Reduce urgency in mild cystitis
–Reduce bladder spasms
Glaucoma drugs: Categories
–alpha–agonists –beta–blockers –diuretics –cholinomimetics –prostaglandins
Glaucoma drugs – alpha agonists:
Epinephrine
Brimonidine
Which glaucoma drug should not be used in closed–angle glaucoma?
Epinephrine
Epinephrine: Mechanisms and side effects
–M: ––Increased outflow of aqueous humor –E: ––Mydriasis ––Stinging ––Do not use in closed angle glaucoma
Brimonidine: Mechanisms and side effects
M: Decreased aqueous humor synthesis
E: No pupillary or vision changes
Glaucoma drugs – beta blockers:
Timolol
Betaxolol
Carteolol
Glaucoma drugs – beta blockers: Mechanism and side effects
M: Decreased aqueous humor secretion
E: No pupillary or vision changes
Glaucoma drugs – diuretics: Drugs
Acetazolamide
Glaucoma drugs – diuretics: mechanisms and side effects
M: Decreased aqueous humor secretion due to decreased bicarbonate (via inhibition of carbonic anhydrase)
E: No pupillary or vision changes
Glaucoma drugs – Cholinomimetics: Drugs
Direct: Pilocarpine, Carbechol
Indirect: Physostigmine, Ecthiopate
Glaucoma drugs – Cholinomimetics: Mechanism and Side effects
M:
–Increase outflow of aqueous humor
–Contract ciliary muscle and open trabecular meshwork
–Use pilocarpine in emergencies
–Very effective at opening canal of Schlemm
E:
–Miosis
–Cyclospasm
Glaucoma drugs – Prostaglandins: Drugs
Latanoprost (PGF–2alpha)
Glaucoma drugs – Prostaglandins: Mechanism and Effects
M: Increase outflow of aqueous humor
E: Darkens color of iris (browning)
Atropine: General effects mnemonic
Blocks BUMBLED ASS
B: Bradycardia U: Urination M: Miosis B: Bronchospasm L: Lacrimation E: Excitation of skeletal muscle and CNS D: Diarrhea A: Abdominal cramping S: Sweating S: Salivation
Atropine: Side effects
–Hot as a hare (Increased body temperature; hyperthermia in infants)
–Dry as a bone (Dry mouth and dry skin; Urinary retention in men with prostatic hypertrophy; Constipation)
–Red as a beet (Flushed skin)
–Blind as a bat (Cycloplegia, Acute angle–closure glaucoma in elderly)
–Mad as a hatter (disorientation)