Steve Stielberg's Pharmacology Phrenzy Flashcards
Km means what
Is the concentration of Substrate at 1/2Vmax;
it is inversely related to the affinity of the enzyme for it substrate
Pharmacokinetics
the effects of the body on the drug;
ADME: Absoprtion, Distribution, Metabolism, Excretion
Pharmacodynamics
The effects of the drug on the body; Includes concepts of receptor binding, drug efficacy, drug potency, toxicity
Pharmacokinetics: Bioavailability (F)
Fraction of administered drug that reaches systemic circulation unchanged. IV dose is F=100%, oral is usually lower
Pharmacokinetics: Volume of Distribution (Vd)
Theoretical volume occupied by the total absorbed drug amount at the plasma concentration. Apparent Vd of plasma protein-bound drugs can be altered by liver and kidney disease (decreased protein binding, increased Vd). Drugs may distribute in more than one compartment. Vd= (amount of drug in the body)/ (plasma drug concentration)
Pharmacokinetics: half life (t1/2)
The time required to change to amount of drug in the body by 1/2 during elimination (or constant infusion). Porperty of first-order elimination A drug infused at a constant rate takes (4-5) half lives to reach steady state. It takes 3.3 half lives to reach 90% of steady state level:
T1/2=(.693 X Vd)/CL
Pharmacokinetics: Clearance (CL)
The volume of plasma cleared of drug per unit time. Clearance may be impaired with defects in cardiac, hepatic, or renal function:
CL=(rate of elimination of the drug)/(Plasma drug concentration) = Vd x Ke (elimination constant)
Pharmacokinetics: Loading dose calculations
Loading dose= (Cp x Vd)/F;
Cp= target plasma concentration;
Note- in renal disease you do not change loading dose
Pharmacokinetics: Maintenance dose calculations
Maintenance dose= (Cp x CL x τ)/ (F);
τ= dosage interval, if not administered continuously;
Cp= target plasma concentration at steady state;
Note= in renal disease you adjust the maintenance dose
Zero order elimination
rate of elimination is constant regardless of Cp (i.e. constant amount of drug eliminated per unit time). Cp decreases linearly with time. Examples are Phenytoin, Ethanol, Aspirin (at high or toxic levels);
Capacity limited elimination
First order elimination
rate of elimination is directly proportional to the drug concentration (i.e. constant fraction of drug eliminated per unit time). Cp decreases exponentially over time.
Urine pH and drug elimination: Weak acids
Examples would be phenobarbital, methotrexate, aspirin. Trapped in basic environments. Treat overdose with bicarbonate. Remember that ionized species are trapped in urine and cleared quickly, neutral forms can be reabsorbed.
Urine pH and drug elimination: Weak bases
Examples: amphetamines, trapped in acidic enivronments. Treat overdose with ammonium chloride. Remember that ionized species are trapped in urine and cleared quickly, neutral forms can be reabsorbed.
Phase 1 drug metabolism
Reduction, oxidation, hydrolysis with cytochrome P-450 usually yield a slightly polar, water-soluble metabolite (often still active).
Geriatric patients often lose phase 1 first
Phase 2 drug metabolism
Conjugation (Glucuronidation, Acetylation, Sulfation) usually yields a very polar, inactive metabolite (Renally excreted). Patients who are slow acetylators have greater side effects from certain drugs because of decreased rate of metabolism
Define efficacy of a drug
Maximal effect a drug can produce. High efficacy drug classes are analgesic, antibiotics, antihistamines, and decongestants. Partial agonists have less efficacy than full agonists.
Define potency of a drug
Amount of drug needed for a given effect. Increased potency, increased affinity for receptor. Highly potent drug classes include chemotherapeutic drugs, antihypertensive drugs, and lipid lowering drugs.
Competitive Antagonist
Effect: shifts curve to right (decrease potency), no change in efficacy. Can be overcome by increase in the concentration of agonist substrate
Noncompetitive antagonist
shifts curve down (decrease efficacy). Cannot be overcome by increase agonist substrate.
Irreversible antagonist is the same idea, it just never lets go.
Partial agonist
Acts at the same site as full agonist but with lower maximal effect (decrease efficacy). Potency is an independent variable.
Therapeutic index
Measurement of drug safety:
TD50/ED50=(median toxic dose)/(median effective dose)
Safer drugs have higher TI values. LD50 (lethal dose) is used in animal studies
Nicotinic ACh receptors
ligand-gated Na/K channels; Nn (found in autonomic ganglia) and Nm (found in neuromuscular junction) subtypes.
Muscarinic ACh receptors
Are G-protein-coupled receptors that usually act through 2nd messengers, 5 subtypes: M1, M2, M3, M4, M5
What G protein does this receptor work through and what is its functions: alpha 1
q class; increases vascular smooth muscle contraction, increases pupillary dilator muscle contraction (mydriasis), increases intestinal and bladder sphincter muscle contraction. Phenylephrine and midodrine are alpha 1 agonists
What G protein does this receptor work through and what is its functions: alpha 2
i class; decreases sympathetic outflow, decreases insulin release, decreases lipolysis, increases platelet aggregation
What G protein does this receptor work through and what is its functions: beta 1
s class; increases hear rate, increases contractility, increases renin release, increases lipolysis
What G protein does this receptor work through and what is its functions: beta 2
s class; Vasodilation, bronchodilation, increases hear rate, increases contractility, increases lipolysis, increase insulin release, decrease uterine tone (tocolysis), ciliary muscle relaxation, increase aqueous humor production.
M1 receptor: what does it work through, major functions
q subtype of g protein class; CNS, enteric nervous system
M2 receptor: what does it work through, major functions
i subtype of the g protein class; decreases heart rate and contractility of atria
M3 receptor: what does it work through, major functions
q subtype of g protein; Increases exocrine gland secretions (lacrimal, salivary, gastric), increases gut peristalsis, increases bladder contraction, bronchoconstriction, increases pupillary sphincter muscle contraction (miosis), ciliary muscle contraction (accommodation)
D1 dopamine receptor: what does it work through, what does it do
s subtype of g protein; relaxes renal vascular smooth muscle
D2 dopamine receptor: what does it work through, what does it do
i subtype of g protein; modulates transmitter release, especially in the brain
Histamine H1 receptor: what does it work through, what does it do
q subtype of g protein; increase nasal and bronchial mucus production, increases vascular permeability, contraction of bronchioles, pruritus, and pain
Histamine H2 receptor: what does it work through, what does it do
S subtype of g protein: increased gastric acid secretion
Vasopressin V1 receptor: what does it work through, what does it do
q subtype of g protein; increases vascular muscle contraction
Vasopressin V2 receptor; what does it work through, what does it do
S subtype of g protein; increases H2O permeability and reabsorption in the collecting tubules of the kidney (V2 is found in the 2 kidneys)
What is the downstream effect of a Gq receptor being stimulated (and what are the types of Gq receptors)
(h1, alpha1, V1, M1, M3); Gq activates Phospholipase C which cleaves PIP2 into DAG and IP3. DAG activates protein kinase C while IP3 increases Ca in the cell and you get smooth muscle contraction
What is the downstream effect of a Gs receptor being stimulated (what are the types of Gs receptors)
Beta1, Beta2, D1, H2, V2; Activates Adenylyl cyclase which turns ATP into cAMP. cAMP goes into protein kinase A which increase Ca inside heart cells and inactivates myosin light chain kinase in smooth muscle
What is the downstream effect of a Gi receptor being stimulated (and what are the types of Gi receptors)
M2, alpha 2, D2; Gi blocks the activation of Adenylyl cyclase (the same molecule that Gs stimulates)
Betanechol
Cholinomimetic agent; direct agonist; Activates bowel and bladder smooth muscle; resistant to AChE. Postoperative ileus, neurogenic ileus, and urinary retention
Carbachol
Cholinomimetic agent; direct agonist; Glaucoma, pupillary constriction, and relief of intraocular; Carbon copy of acetylcholine
Pilocarpine
Cholinomimetic agent; direct agonist; Contracts ciliary muscle of eye (open-angle glaucoma), pupillary sphincter (closed-angle); resistant to AChE. “you cry, drool and sweat on your PILOw.
Methacholine
Cholinomimetic agent; direct agonist; Stimulates muscarinic receptors in airway when inhaled. Challenge test for diagnosis of asthma
Neostigmine
Indirect agonist (anticholinesterase); Increases endogenous ACh Neo CNS= No CNS penetration; Postoperative and neurogenic ileus and urinary retention, myasthenia gravis, reversal of neuromuscular junction blockade (postoperative)
Pyridostigmine
Indirect agonist (anticholinesterase); Increases endogenous ACh; increases endogenous ACh; increases strength. long acting myasthenia gravis treatment, does not penetrate CNS
Physostigmine
Indirect agonist (anticholinesterase); Anticholinergic toxicity (crosses BBB); increases endogenous ACh; fixes atropine overdose
Donepezil
Indirect agonist (anticholinesterase); Used in alzheimer dieases; Increase endogenous ACh
Rivastigmine
Indirect agonist (anticholinesterase); Used in alzheimer dieases; Increase endogenous ACh
Galantamine
Indirect agonist (anticholinesterase); Used in alzheimer dieases; Increase endogenous ACh
Edrophonium
Indirect agonist (anticholinesterase); old way of diagnosing myasthenia gravis (extremely short acting); now we look for anti-AChR Ab
With all cholinomimetic agents the side effects are
Exacerbation of COPD, asthma, and peptic ulcers in susceptible patients
Cholinesterease inhibitor poisoning
often due to organophosphate, such as parathion, that irreversibly inhibit AChE. Causes DUMBBELSS: Diarrhea, Miosis, Bronchospasm, Bradycardia, Excitation of skeletal muscle and cns. Lacrimation, Sweating, and Salivation.
Antidote is atropine (competitive inhibitor) with prazlidoxime (regenerates AChE if given early)
what organ does it work in and its application: Atropine, homatropine, tropicamide
eye, produce mydriasis and cycloplegia (paralysis of ciliary muscle); muscarinic antagonist
what organ does it work in and its application: Benztropine
CNS; Parkinson (PARK my BENZ); muscarinic antagonist
what organ does it work in and its application: Scopolamine
CNS; Motion sickness; muscarinic antagonist
what organ does it work in and its application: Ipratropium, tiotropium
Respiratory; COPD, asthma; muscarinic antagonist
what organ does it work in and its application: Oxybutynin, darifenacin, solifenacin
Genitourinary; reduce urgency in mild cystitis and reduced bladder spasms. Other agents are tolterodine, fesoterodine, trospium (used for urinary incontinence); contraindicated in closed angel glaucoma and elderly; muscarinic antagonist
what organ does it work in and its application: Glycopyrrolate
muscarinic antagonist; gastrointestinal and respiratory; Parenteral: preoperative use to reduce airway secretions; Oral: drooling, peptic ulcer
Atropines effect on the: eyes
increase pupal dilation, cycloplegia
Atropines effect on the: airway
Decreases secretions
Atropines effect on the: Stomach
decreases stomach acid
Atropines effect on the: Gut
decreases motility
Atropines effect on the: Bladder
decreased urgency in cystitis
Atropines side effects
Increased body temperature (can’t sweat); rapid pulse, dry mouth, flushed skin; cycloplegia; constipated; disorientation; blind as a bat, mad as a hatter, red a beet, hot as a stone, dry as a bone
Can cause acute angle glaucoma in elderly due to mydriasis, urinary retention in men with prostatic hyperplasia, and hyperthermia in infants
What is this drugs effect on alpha, beta receptors and what is it used for: Epinephrine
beta > alpha; anaphylaxis, open angle glaucoma, asthma, hypotension; alpha effects predominate at high doses
What is this drugs effect on alpha, beta receptors and what is it used for: norepinephrine
alpha 1> alpha 2> Beta 1; Hypotension (but decreased renal perfusion)
What is this drugs effect on alpha, beta, and dopamine receptors and what is it used for: Dopamine
D1=D2 > Beta > alpha; Unstable bradycardia, heart failure, shock; inotropic and chronotropic alpha effects predominate at high doses.
What is this drugs effect on alpha, beta receptors and what is it used for: Dobutamine
Beta1 > Beta2, alpha; heart failure (inotropic > chronotropic), cardiac stress test
What is this drugs effect on alpha, beta receptors and what is it used for: Isoproterenol
Beta1=Beta2; Electrophysiologic evaluation of tachyarrhythmias. Can worsen ischemia
What is this drugs effect on alpha, beta receptors and what is it used for: Phenylephrine
alpha 1 > alpha 2; Hypotension (vasoconstrictor), ocular procedures (mydriatic), rhinitis (decongestant)
What is this drugs effect on alpha, beta receptors and what is it used for: Albuterol, salmeterol, terbutaline
Beta 2> Beta 1; Albuterol for acute asthma; salmeterol for long-term asthma or COPD control; terbutaline to reduce premature uterine contractions
What is this drugs effect on alpha, beta receptors and what is it used for: Amphetamine
indirect sympathomimetics; indirect general agonist, reuptake inhibitor, also releases stored catecholamines; Used for Narcolepsy, obesity, attention deficit disorder
What is this drugs effect on alpha, beta receptors and what is it used for: Ephedrine
Indirect general agonist, releases stored catecholamines; Nasal decongestion, urinary incontinence, hypotension
What is this drugs effect on alpha, beta receptors and what is it used for: Cocaine
Indirect general agonist, reuptake inhibitor; Causes vasoconstriction and local anesthesia; never give beta blockers if cocaineintoxication is suspected (can lead to unopposed alpha 1 activation and extreme hypertension)
Norepinephrine vs isoproterenol
NE causes increase in systolic and diastolic pressures as a result of alpha1 mediated vasoconstriction leading to an increase in mean arterial pressure causing bradycardia. However, isoproterenol (no longer commonly used) has little alpha effect but causes beta 2 mediated vasodilation, resulting in decrease mean arterial pressure and increase heart rate through beta 1 and reflex activity.
Clonidine
alpha 2 agonist so it decreases sympathetic output; used for HTN urgency; does not decrease renal blood flow; ADHD, severe pain, and off label ethanol and opioid withdrawl;
Toxicity: CNS depression, bradycardia, hypotension, respiratory depression, and small pupil size
alpha methyldopa
alpha 2 agonist so it decreases sympathetic output; used for pregnancy HTN; toxicity direct coombs test will be positive for hemolytic anemia; SLE like syndrome
Pheoxybenzamine
irreversible non selective alpha blocker; used for pheochromocytoma (used preoperatively) to prevent catecholamine (HTN) crisis;
Toxicity are orthostatic hypotenstion; reflex tachycardia
Phentolamine
Reversible non selective alpha blocker; Give to patients on MAO inhibitors who eat tyramine-containing foods;
What are the alpha 1 selective alpha blockers
Prazosin, terazosin, doxazosin, tamsulosin (-osin); used to treat urinary symptoms of BPH; PTSD (prazosin); hypertension (except tamsulosin); Toxicity is 1st dose orthostatic hypotension, dizziness, and headache