Pharmacology Flashcards
How does Km relate to affinity?
they are inversely related
A sigmoidal Michaelis-Menten curve is indicative of what receptor characteristic?
cooperative binding
How are Km and Vmax derived from a Lineweaver-Burk plot?
- the y-intercept equals 1/Vmax
- the x-intercept equals 1/-Km
- the slope = Km/Vmax
How do competitive and non-competitive inhibitors affect the Lineweaver-Burk plot for w given ligand-receptor relationship?
- a competitive inhibitor affects Km only, so the x-intercept shifts more positive
- a noncompetitive inhibitor affects Vmax without affecting Km, so the y-intercept shifts more positive
How does a competitive inhibitor impact Km and Vmax? Potency and efficacy?
it will increase Km (lower affinity) without affecting Vmax, as such it has lowered the potency without lower the efficacy
How does a noncompetitive inhibitor impact Km and Vmax? Potency and efficacy?
it will lower Vmax without affecting Km, as such it lowers efficacy without affecting potency
How is bioavailability calculated?
F = AUC(oral)/AUC(iv)
How is Vd calculated and interpreted?
- Vd = (total amount of drug in body)/(plasma drug concentration)
- when Vd = 0.45 it has been distributed in plasma
- when Vd = 0.2 it has been distributed in ECF
- when Vd = 0.6 it has been distributed in TBW
- when Vd > 0.7 it has been distributed in tissue
How does liver disease affect Vd?
it often increases Vd because it lowers the amount of protein-bound drug, increasing the free fraction
How do we define clearance?
the volume of plasma cleared of drug per unit time
How is clearance calculated?
CL = (rate of elimination)/(plasma drug concentration) = Vd x K(el)
Give two equations for calculating K(el).
K(el) = CL/Vd = 0.7/(half life)
How long does it take for a drug to reach a new steady state?
roughly 4-5 half lives
How is a loading dose calculated?
LD = (desired plasma concentration)(Vd)/(F)
How is a maintenance dose calculated?
MD = (desired plasma concentration x CL x dosing interval)/F
How do liver and kidney disease affect the required maintenance and loading dose?
- they often decrease the maintenance dose (because CL is reduced)
- the loading dose is usually unchanged
What is a permissive drug interaction?
one in which the presence of drug A is required for the full effects of substance B
What is a tachyphylactic drug interaction? Give an example.
one in which there is an acute decrease in response to a drug after initial/repeated administration (e.g. MDMA depletes NT stores and so there is an acute decrease in response)
How does zero-order kinetics compare to first-order kinetics?
drugs that experience zero-order kinetics are cleared at a constant amount per time (independent of drug concentration) while drugs that experience first-order kinetics are cleared at a constant fraction per time (dependent of drug concentration)
What three drugs classically experience zero-order kinetics?
- ethanol
- phenytoin (at high concentrations)
- aspirin (at high concentrations)
How can you treat an overdose of a drug that is a weak acid?
you can alkalinize the urine with bicarbonate to trap the drug in urine and promote elimination of the drug
Drugs that are weak bases become trapped in what environment?
a pH more acidic than their pKa, under which circumstance they become deprotonate and trapped in their ionized form
What reactions constitute phase I and phase II drug metabolism?
- phase I: oxidation, reduction, hydrolysis
- phase II: methylation, glucuronidation, acetylation, sulfation, glutathione conjugation
What changes in phase I and II drug metabolism pathways do geriatric patients experience?
they typically lose phase I reactions first
What are the efficacy and potency of a drug?
- potency: amount of drug needed for a given effect (i.e. ability to bind the receptor), defined by EC50
- efficacy: maximal effect a drug can produce (i.e. ability to active the receptor once bound), defined by Vmax
- e.g. a HTN med that reduces BP by only 5 mmHg but at a very low dose has high potency but low efficacy
How are therapeutic index and margin of safety calculated?
- TI = LD50/ED50
- MoS = LD1/ED99
Where are most nicotinic receptors found in the PNS?
- at the ganglionic synapse of both the SNS and PNS
- at the adrenal medulla
- at the neuromuscular junction
Describe the basic anatomy of the SNS and PNS.
- the PNS has craniosacral outputs with long pre-ganglionic fibers and short post-synaptic fibers
- the SNS has thoracolumbar outputs with short pre-ganglionic fibers synapsing on long post-synaptic fibers in paravertebral chain ganglia
How are the two types of sweat glands innervated?
- eccrine (thermoregulatory) receive input from the SNS but express muscarinic receptors
- apocrine receive input from the SNS and express a1 receptors
What is the basic structure of nicotinic and muscarinic receptors?
- nicotinic are ligand-gated Na/K channels
- muscarinic are GPCRs
a1, a2, and B receptors are linked to what second messenger cascades?
- a1: Gq
- a2: Gi
- B: Gs
M1, M2, and M3 receptors are linked to what second messenger cascades?
- M1: Gq
- M2: Gi
- M3: Gq
D1 and D2 receptors are linked to what second messenger cascades?
- D1: Gs
- D2: Gi
H1 and H2 receptors are linked to what second messenger cascades?
H1: q
H2: s
V1 and V2 receptors are linked to what second messenger cascades?
V1: Gq
V2: Gs
Describe the Gq signal cascade.
- Gq activates PLC, which then cleaves PIP2, forming IP3 and DAG
- DAG activates PKC
- IP3 serves to increase intracellular calcium
a1 receptors are tied to which second messenger system and mediate what effects?
- tied to Gq
- promote vascular smooth muscle contraction (increase TPR) , contraction of the pupillary dilator muscle (mydriasis), and contraction of intestinal as well as bladder sphincter muscles to inhibit evacuation
a2 receptors are tied to which second messenger system and mediate what effects?
- tied to Gi
- expressed on the presynaptic terminal and mediate auto-inhibition to reduce the release of NT
B1 receptors are tied to which second messenger system and mediate what effects?
- tied to Gs
- mediate an increase in HR, inotropy, renin release, and lipolysis
B2 receptors are tied to which second messenger system and mediate what effects?
- tied to Gs
- stimulation vasodilation in the lungs and skeletal muscle, bronchodilation, lipolysis, insulin release, uterine relaxation, bladder relaxation, ciliary muscle relaxation, and aqueous humor production
Describe the ANS innervation of the eye.
- a receptors are expressed by the pupillary dilator muscle and mediate mydriasis
- B receptors are expressed by the secretory epithelium and activation promotes production of aqueous humor
- muscarinic receptors are expressed by the ciliary muscle and pupillary sphincter muscle; activation promotes accommodation of the lens for near vision, drainage of aqueous humor through the canal of Schlemm, and constriction of the pupil (miosis)
M1 receptors are tied to which second messenger system and mediate what effects?
- tied to Gq
- function in the CNS and enteric nervous system
M2 receptors are tied to which second messenger system and mediate what effects?
- tied to Gi
- decreases heart rate and contractility of the atria
How does activation of B1 receptors affect ion currents in the heart?
- increases funny sodium current
- increases L-type calcium current
- increases potassium current
- no effect on sodium current (QRS complex unchanged)
How does activation of muscarinic receptors affect ion currents in the heart?
- decreases funny sodium current
- decreases L-type calcium current
M3 receptors are tied to which second messenger system and mediate what effects?
- tied to Gq
- promote glandular secretions, gut peristalsis, bladder contraction, bronchoconstriction, mitosis, and lens accommodation
H1 and H2 histamine receptors mediate what effects?
- H1 mediates mucus production, urticaria, pruritis, pain, bronchoconstriction, and an increase in vascular permeability
- H2 is primarily responsible for increasing gastric acid secretion
Describe monoamine biosynthesis.
- tyrosine is converted to DOPA by tyrosine hydroxylase
- DOPA is converted to DA by DOPA decarboxylase
- DA is packaged into vesicles by VMAT
- in the vesicle, DA is converted to NE by DA-B-hydroxylase
How are monoamines cleared from the synaptic cleft?
reuptake
How is acetylcholine cleared from the synaptic cleft?
AChE
Describe acetylcholine biosynthesis.
- acetyl-CoA from the mitochondria is combined with choline recycled from the synaptic cleft in a reaction catalyzed by ChAT
- acetylcholine is then packaged into vesicles by VAT
- in the synaptic cleft, it is degraded by AChE and choline is recycled
What is tyramine?
- an indirect sympathomimetic
- enters presynaptic vesicles and displaces monoamines, which subsequently diffuse freely into the synaptic cleft, stimulating post-synaptic receptors
What is hemicholinium?
an indirect ACh antagonist that inhibits reuptake of choline by the presynaptic terminal, thereby reducing it’s release
What is vesamicol?
an indirect ACh antagonist that inhibits VAT, so ACh stays in the intracellular space where it is degraded rather than released
How does botulinum toxin affect autonomics?
it inhibits the release of ACh
What is metyrosine?
an indirect sympatholytic drug that inhibits tyrosine hydroxylase and monoamine synthesis
What is reserpine?
an indirect sympatholytic drug that inhibits VMAT and packaging of monoamines
What is bethanechol? What are it’s uses?
- a choline ester and muscarinic agonist resistant to AChE
- used to activate the bowel and bladder in those with post-op ileum, neurogenic ileum, or urinary retention
What is carbachol?
a choline ester and muscarinic agonist
What is pilocarpine? What are it’s primary uses?
- a muscarinic alkaloid that is a potent stimulator of sweat, tears, and saliva
- used to treat glaucoma and xerostomia (Sjogren syndrome)
What is donepezil? What are it’s uses?
it inhibits AChE and is an indirect cholinomimetic used in the treatment of Alzheimer’s
What is galantamine? What are it’s uses?
it inhibits AChE and is an indirect cholinomimetic used in the treatment of Alzheimer’s
What is tacrine?
it inhibits AChE and is an indirect cholinomimetic
What is edrophoium? What are it’s uses?
it is an AChE inhibitor with a very short half life, primarily used to diagnose myasthenia gravis
What is neostigmine?
it is an AChE inhibitor without any CNS activity
What is physostigmine and what are it’s uses?
- it is an AChE inhibitor
- crosses the BBB
- used to treat anticholinergic toxicity (atropine poisoning)
What is pyridostigmine and what are it’s uses?
- it is an AChE inhibitor
- does not penetrate the BBB
- used to treat myasthenia gravis
Cholinomimetics are likely to exacerbate what three conditions?
COPD, asthma, and peptic ulcers
Organophosphate Poisoning
- organophosphates are AChE inhibitors that experience an “aging” effect and are essentially irreversible inhibitors
- presents with diarrhea, urination, mitosis, bronchospasm, bradycardia, excitation of skeletal muscle, lacrimation, eccrine sweating, and salivation
- primary risk is that it creates a depolarizing blockade at the NMJ of the diaphragm and leads to respiratory failure
- treat with atropine and pralidoxime
What is pralidoxime?
- a partial AChE inhibitor with very strong affinity
- used to treat organophosphate poisoning if caught early enough
What is atropine?
a tertiary amine (crosses BBB) muscarinic antagonist
What is homatropine?
a tertiary amine (crosses BBB) muscarinic antagonist
What is tropicamide?
a tertiary amine (crosses BBB) muscarinic antagonist
What is benzotropine? What is it’s primary clinical use?
- a tertiary amine (crosses BBB) muscarinic antagonist
- used to treat Parkinson disease (“park my benz”) and acute dystonia
What is glycopyrrolate? What are it’s primary clinical uses?
- a tertiary amine (crosses BBB) muscarinic antagonist
- used parenterally to reduce airway secretions preoperatively and orally to prevent drooling and peptic ulcers
What is hyoscyamine and what is it’s primary clinical use?
- a muscarinic antagonist
- used as an antispasmodic to treat IBS
What is dicyclomine and what is it’s primary clinical use?
- a tertiary amine muscarinic antagonist
- used as an antispasmodic to treat IBS
What is ipratropium and what is it’s primary clinical use?
- a quaternary amine muscarinic antagonist
- used to treat COPD and asthma
What is tiotropium and what is it’s primary clinical use?
- a quaternary amine muscarinic antagonist
- used to treat COPD and asthma
What is oxybutynin?
a tertiary amine muscarinic antagonist
What is solifenacin?
a tertiary amine muscarinic antagonist
What is tolterodine? What is it’s primary clinical use?
- a tertiary amine muscarinic antagonist with specificity for M3 receptors in the GU system
- used to reduce bladder spasms and urge incontinence
What is scopolamine? What is it’s primary clinical use?
a tertiary amine muscarinic antagonist used to treat motion sickness
Describe the effects of atropine poisoning.
“hot as a hare, dry as a bone, red as a beet, blind as a bat, and mad as a hatter”
- reduces sweating so temp rises and skin is dry and flush
- cycloplegia and acute angle-closure glaucoma
- constipation and urinary retention
- disorientation
What is jimson weed?
a herb/plant that causes mydriasis (known as “gardener’s pupil”) because it contains an alkaloid that is a muscarinic antagonist
What is albuterol?
an inhaled B2 agonist used to treat asthma
What is salmeterol?
a long-acting oral B2 agonist used to control asthma
What is formoterol?
a long-acting oral B2 agonist used to control asthma
What is terbutaline?
a B2 agonist
What is dobutamine?
a selective B1 agonist
Dopamine will activate what adrenergic receptors?
it has a greater affinity for B1 receptors than a1, but at high doses will activate both
What is the selectivity of epinephrine?
it activates all adrenergic receptors
What is the selectivity of norepinephrine?
it activates a1, a2, and B1
What is the selectivity of isoproterenol?
B1 and B2