Pharmacology Flashcards
Difference b/t elimination half-time and elimination half-life.
Half-time: PLASMA CONCENTRATION of drug
Half-life: TOTAL AMOUNT of drug
Formula for VD
Amount of drug injected/plasma concentration
VD = Q/Cp t=0
What is pharmacokinetics?
What the BODY does to the DRUG
Do MR have a large VD in adults or neonates?
Neonates d/t their expanded ECF
Why do neonates need more Sux on a mg/kg basis?
- Larger VD
- Immature NMJ - inadequate # of nicotinic receptors OR nicotinic receptors not as response to Ach
* Dosing is the same for NDMR - less drug required to block small # of channels
Smaller VD means…
Shorter half-life of elimination
Ex: Alfentanil
Zero Order Kinetics
Constant AMOUNT of drug is eliminated per unit time 2 mg per min *I have ZERO tolerance for APA! ALCOHOL PHENYTOIN ASA
First Order Kinetics
Constant FRACTION of drug is eliminated per unit time
Natural log (ln)
One Compartment: looks just like zero
Two Compartment: fast curvilinear decline then linear
What organs are found in the central compartment?
Liver* Kidneys* Lungs* Heart Brain VRG
What is the alpha phase? Beta phase?
In reference to First Order Kinetics, two compartment model
alpha = distribution phase
beta = elimination phase
Drugs will be eliminated rapidly if…
Clearances are high
VD are small
T1/2 = Vd/Cl
How many half-lives are required to eliminate at least 98% of a drug?
6
Phase 1 Reactions
Oxidation Reduction Methylation Hydrolysis Cytochrome P450 system
Phase 2 Reactions
Glucuronidation
Glutathione conjugation
Sulfation
Acetylation
Dose-Response Curves
Increased potency…shift to the left or right?
Shift to the LEFT
Left-shift = less drug required (increased receptor affinity)
Dose-Response Curves
What does the slope of the line indicate?
# of receptors that must be occupied before a drug effect occurs Steep slope = majority of receptors must be bound (Ex: MR, inhaled anesthetics)
Dose-Response Curves
What does the plateau indicate?
Efficacy or the ability of a drug to produce a given clinical effect
Higher plateau = greater efficacy
Dose-Response Curves
What kind of shift would be observed in the presence of a competitive antagonist?
Shift to the RIGHT
NO change in efficacy (plateau)
NO change in slope
Dose-Response Curves
What kind of shift would be observed in the presence of a non-competitive antagonist?
Shift to the RIGHT and DOWN
Decrease in slope!
Maximal effect cannot be achieved (noncompetitive block cannot be reversed by excess agonist)
What is LD50/ED50?
Therapeutic index
*The larger the therapeutic index of a drug the greater margin of safety!
PCN shows a cross-sensitivity with…
Cephalosporins
Increased or decreased MAC in cocaine abuser?
Increased MAC
Weak Acids
Barbiturates (Thiopental) Ibuprofen Propofol POSITIVE IONS – Na, Mg, Ca *The higher the pKa of a weak acid, the greater the amount of drug in non-ionized form at physiologic pH.
Weak Bases
LA Benzos Ketamine Opioids Ephedrine Phenylephrine NEGATIVE – Cl, SO4
What’s wrong with mixing a weak acid with a low pH solution?
Formation of a precipitate
Explain trapping of LA in fetal circulation.
pH of the fetus is lower than mom
Non-ionized form of LA crosses the placental barrier
Equilibrium reestablished
More LA is now in the ionized form (weak base into acidic baby)
Ionized LA is trapped in baby
The ______ the fetal pH, the greater the amount of local anesthetic in the ionized form remains trapped in the fetus.
Lower
*Maternal alkalosis and fetal acidosis will most facilitate trapping
What is the range of pKas for LA?
7.6-9.1
Why doesn’t local anesthetic work well in an acidotic foot?
LA is a weak base
If put in an acidotic environment, remains in ionized form
What LA will precipitate with bicarb?
Bupivacaine
Which ester LA is a weak acid?
Benzocaine
pKa 3.5 - almost completely ionized at physiologic pH - ideally suited for topical anesthesia
The lower the pKa of the LA, the greater the proportion of LA in the ______ form at pH = 7.4 and the ______ the onset of the conduction block.
Non-ionized
Faster
*Exception: Chloroprocaine (pka 9.1, 0% protein bound)
Lipid solubility indicates…
Protein-binding indicates…
pKa determines…
Potency - highly lipid soluble = very potent (and usually prolonged DOA)
DOA - highly protein bound = prolonged DOA
Speed of onset - lower pKa = faster onset
The loss of LA from the injection site is primarily by _______. The rate of absorption of LA from an injection site is influenced by what 2 things?
Vascular absorption
- Presence of a vasoconstrictor
- Blood flow
High blood flow to an area does what to DOA and toxicity of a LA?
DOA is reduced
Toxicity is increased
Which results in higher blood concentrations after injection: epidural or subarachnoid?
Epidural
Rank tissues from HIGHEST to LOWEST blood flow.
- IV - HIGH blood flow
- Tracheal
- Intercostal
- Caudal
- Paracervical
- Epidural
- Brachial Plexus
- Subarachnoid, Sciatic, Femoral
- Subcutaneous - LOW blood flow
* In Time, I Can Please Everyone But Susie and Sally!
How do LA work?
Block Na channels
Non-ionized form diffuses into the nerve axon
Ionized form binds to receptors on the Na channel when the channel is in the inactivated state
How many nodes of Ranvier must be blocked to stop nerve conduction for myelinated axons?
2-3 nodes
Conduction block is frequency dependent, which means what?
The greater the frequency of action potentials, the fast the nerve is blocked by LA
Where are voltage-gated Na channels found?
ONLY in the nerve’s axon
Differential Block after Spinal
Sympathetic 2-6 dermatomes Sensory 2 dermatomes Motor
Metabolism fo Esters vs. Amides
Esters: plasma pseudocholinesterase
Amides: liver
What is the max dose for bupivacaine?
3 mg/kg (175 mg)
What is the max dose for lidocaine with and without Epi?
With Epi - 7 mg/kg (500 mg)
Without Epi - 4.5 mg/kg (300 mg)
What is the treatment of LA toxicity?
Lipid emulsion
20% Intralipid
2 mL/kg
0.5 mL/kg/min
Order of Toxic Manifestations of LA
Circumoral and tongue numbness Lightheadedness and tinnitus Visual disturbances Muscular twitching Unconsciousness Convulsions Coma Respiratory arrest Cardiovascular collapse
What is the therapeutic plasma concentration of lidocaine?
2-4 mcg/mL
At 3 mcg/mL - circumoral and tongue numbness
Concerns with Ester LAs
Prolonged action in a patient with atypical pseudocholinesterase
Prolonged action if patient is on acetylcholinease inhibitors (edrophonium, physostigmine, echothiophate)
PABA is a metabolic end-production of ester or amide metabolism?
Ester
*This metabolite may mediate the hypersensitivity rxns
Which LA is a vasoconstrictor and is naturally-occurring?
Cocaine
Administration of what 4 LA may induce the development of methemoglobinemia?
- Prilocaine - metabolite = O-toluidine (oxidizing agent)
- EMLA cream
- Benzocaine
- Cetacaine
(Met-Hgb has iron in the ferric state Fe3+)
What is the treatment for Methemoglobinemia?
Methylene Blue 1-2 mg/kg
Ester LA are derivates of what?
Benzoic acid
Which contributes more to the hypotension after spinal and epidural anesthesia: decrease in preload 2ndary to venodilation OR decrease in SVR?
Decrease in preload 2ndary to venodilation
Max doses of ester LAs. All are 200 mg EXCEPT…
Procaine - 1000 mg
Chloroprocaine - 800 mg
What ester LA is the most toxic?
Tetracaine - hydrolyzed by plasma cholinesterase much more slowly
What ester LA is the least potent?
Procaine
What ester LA is the least toxic?
2-Chloroprocaine
Which amide LA is least toxic?
Prilocaine
What are the 3 least potent amides?
- Lidocaine
- Mepivacaine
- Prilocaine
Which amide LA is most cardiotoxic?
Bupivacaine
*Binds to gated Na channels with great intensity
What are the advantages of Ropivacaine over Bupivacaine?
Less cardiotoxic
Less motor blockade
Hypersensitivity reactions are more common with esters or amides.
Esters
B/c of PABA
What are the 3 most cardiotoxic LA?
- Bupivacaine
- Etidocaine
- Ropivacaine
* BB, digitalis, and CCB may decrease the threshold for cardiotoxicity
In general, lipid solubility/potency is increased by increasing the total # of _____ atoms in the molecule.
Carbon
Epinephrine does not prolong the DOA for what 3 LA?
- Bupivacaine
- Ropivacaine
- Etidocaine
Oil:Gas Partition Coefficients
Halothane 224 Isoflurane 91 Sevoflurane 47 Desflurane 19 N2O 1.4
All volatile agents decrease BP, but which agent the least?
Sevoflurane
All volatile agents decrease SVR, but which agents the least?
Halothane
Sevoflurane
Which volatile agent decreases CO the most?
Halothane
Which volatile agent decreases CO the least?
Isoflurane
Which volatile agent increase HR?
Isoflurane
Which volatile agent causes sensitization to catecholamines?
Halothane
The solubility of a gas in a liquid _______ as temp increases.
Decreases
More inhalational agent will dissolve in blood if the patient is hypothermic
*Le Chatelier’s law explains this
What does the blood:gas partition coefficient tell us?
Speed of onset and offset
*Ostwald solubility coefficient
Brain uptake is directly or inversely related to CO?
Inversely
Blood:Gas Partition Coefficients
Halothane 2.5 Isoflurane 1.46 Sevoflurane 0.65 Desflurane 0.42 N2O 0.46
The more soluble the agent, the greater the blood:gas partition coefficient, the _____ the uptake.
Slower
*Slow uptakes - small Fa/Fi ratios - low uptake curve
Halothane - B:G 2.5, very soluble, slowest uptake
List the order of volatile agents as they are seen on the uptake curve graph. Start with the agent that represents the top curve.
Write in the % equilibrated at 30 min.
N2O - 99% Desflurane - 91% Sevoflurane - 85% Isoflurane - 73% Enflurane - 65% Halothane - 58%
Nitrous oxide equilibrates with all tissues within about…
2.5 hrs
Which is less soluble in blood…N2 or N2O?
N2 is 34x less soluble in blood than N2O
*When N2O is turned on, distensible gas spaces expand and nondistensible gas spaces increase in pressure - this is due to Fick’s law of diffusion
Explain the concentration effect.
N20 is turned on N2O is super soluble More N2O leaves the alveoli Alveoli shrink in size Alveolar concentration of N2O remains high More rapid uptake aka overpressuring *Fick's law of diffusion
Explain the second gas effect.
Same as concentration effect
Now the concentrations of both N2O and another gas remain elevated
Increases the rate of diffusion
*Fick’s law of diffusion
Explain the dilutional effect when N2O is turned off.
The reverse of the concentration effect occurs
Alveoli expand and gases such as CO2 and O2 are diluted - diffusional hypoxia
*Fick’s law of diffusion
Name something about the chemical formula for each volatile agent.
Halothane - only one with Br, (alkane)
Isoflurane - 5 F, Cl (methyl ethyl ether)
Desflurane - 6 F, completely halognated w/ F
Sevoflurane - 7 F, (isoprop)
What is the name of the C-O-C functional group?
Ether bond
*ALL of the volatile agents are ethers EXCEPT Halothane (alkane derivative)
Which 3 volatile agents are methyl ethyl ethers?
- Enflurane
- Isoflurane
- Desflurane - completely halogenated
(*Sevo is a methyl isopropyl ether)
Volatile agents halogenated exclusively with fluorine are less soluble in blood. Which 2 volatile agents have only fluorine as the halogen substitutions?
- Desflurane
2. Sevoflurane
List 4 contraindications to the use of N2O.
- Closed pneumo
- Tympanoplasty (middle ear surgery)
- Pneumocephalus
- VAE
Other Concerns with N2O.
Increases PVR and PAP
Increases CBF and ICP
Risk of PONV
There is approx. ___ reduction in MAC for every 1% of nitrous oxide delivery.
1%
By what mechanism does Isoflurane cause hypothermia?
Depresses the temp regulating centers of the hypothalamus
How do volatile anesthetics alter the ventilatory responses to CO2? To hypoxemia?
Dose-dependent decreases in response to CO2
0.1 MAC completely blocks the ventilatory response to hypoxemia
Which 2 volatile agents least depress the baroreceptor reflex?
- Isoflurane
- Desflurane
HR tends to increase reflexly with the decrease in BP
Water is added as a preservative to which volatile anesthetic agent?
Sevoflurane
An inhalational agent has a large blood:gas partition coefficient, what does this mean?
Highly blood soluble
Uptake by the blood will be fast
Speed of onset and the rise in Fa/Fi is slow
Meyer-Overton Theory
Anesthesia occurs when a sufficient # of anesthetic molecules dissolves in the lipid bilayer of neuronal membranes
The membranes expand - keep channels closed
Inhaled anesthetics work on what receptors?
GABA
For most volatile agents, the highest MAC values are for what age group?
Infants 1-6 mo
Sevoflurane is the exception - highest in the neonate 0-30 days
Which electrolyte abnormality will cause MAC to increase? To decrease?
Increased MAC - hypernatremia
Decreased MAC - hypercalcemia, hyponatremia
Vapor Pressures
Halothane - 244 Isoflurane - 240 Enflurane - 172 Sevoflurane - 157 Desflurane - 669
How are volatile anesthetics metabolized?
Liver
Cytochrome P-450
Oxidative processes
What % of each of the volatile agents are metabolized?
Halothane - 20% Sevoflurane 3-5% Enflurane - 2% Isoflurane - 0.2% Desflurane - 0.02%
What 2 things does halogenation do?
- Decreases flammability
2. Decreases toxicity
What are the acceptable levels of inhaled agents in the OR?
N2O + volatile agent - 25 ppm + 0.5 ppm
Volatile agent - 2 ppm
Where and how is N2O metabolized?
Metabolized into N2 in the intestine by anaerobic bacteria
Reductive processes
What are 2 adverse effects of Etomidate?
- Directly depresses cortisol output from the adrenal cortex
- Depresses the immune system
How are the IV anesthetics primarily terminated after bolus injection?
Redistribution
Do benzos have muscle relaxant actions? Are they protein bound?
Yes
They are extensively protein bound
What is the antagonist of benzos?
Flumazenil 0.2 mg IV
Series of small doses up to a total of 5 mg
Nonspecific antagonists: physostigmine, aminophylline
Name 2 induction agents that are associated with excitatory phenomena.
- Methohexital
2. Etomidate
Ketamine is related chemically to which drug of abuse?
Phencyclidine
What receptors does Ketamine work on?
Antagonistic at NMDA Non-NMDA glutamate receptors Nicotinic receptors Muscarinic receptors Opioid receptors - kappa Sigma receptors (dysphoria)
Which non-opioid anesthetic produces bronchodilation?
Ketamine
What is the chemical name for Etomidate?
Imidazole derivative
What is in Etomidate that causes pain on injection?
Additive - propylene glycol
What 3 drugs are most likely to cause venous thrombosis and phlebitis after IV administration?
- Diazepam
- Lorazepam
- Etomidate
* All dissolved in propylene glycol
Which produces are greater decrease in BP? Thiopental or propofol?
Propofol
What is another name for propofol?
2,6-diisopropylphenol
In addition to metabolism in the liver, propofol undergoes an extrahepatic route of elimination. Identify this route.
Lungs
In what 2 ways does Clonidine produce its effects?
- Stimulates alpha-2 receptors of inhibitory neurons in the vasomotor center of the medulla oblongata (decreasing sympathetic outflow)
- Stimulates alpha-2 receptors in the surface membrane of the presynaptic nerve terminal (decreasing release of NE)
Why is it not safe to abruptly withdraw Clonidine?
Rebound HTN 8-36 hours after last dose
Tx: Clonidine, hydralazine
*BB only in the presence of alpha-adrenergic blockade to avoid unopposed alpha-vasoconstricting actions
*TCA potentiate the pressor effects of NE
What is your anesthetic concern for the patient on chronic clonidine therapy?
Perioperative hypothermia
Alters central thermoregulatory control
How much does pretreatment of patients with clonidine decrease MAC?
50%
Name 3 direct acting vasodilators.
- Hydralazine - arterial > venous
- Nitroprusside - arterial + venous
- Nitroglycerine - venodialtor
List the 4 contraindications for using nitroprusside.
- Liver disease
- Kidney disease
- Hypothyroidism
- Vit B-12 def
Cyanide Toxicity and Nitroprusside
How?
S/S?
Tx?
Ferrous iron of nitroprusside reacts with sulfhydryl groups in RBCs and releases cyanide
S/S: metabolic acidosis (*base deficit), cardiac arrhythmias, increased venous oxygen content (unable to utilize oxygen), tachyphylaxis
Tx: sodium thiosulfate 150 mg/kg IV over 15 min, if no improvement - sodium nitrate 5 mg/kg IV or Vit B12
When the nitroprusside infusion is started, you observe that PaO2 decreases. Why did this happen?
Presumed to inhibit HPV
Shunt increases
Increased V/Q mismatch
Decreased PaO2
The therapeutic benefit of nitroglycerine in the treatment of MI is attributable to what action?
Venodilator
Decreases preload, SV, CO, BP
Reduction in myocardial work
Reduced myocardial O2 consumption
What syndrome occurs in 10-20% of patients treated chronically (> 6 mo) with hydralazine?
Systemic lupus erythematosus-like syndrome
Slow acetylators
Hydralazine, nitroglycerine, and sodium nitroprusside all may cause angina. How?
Hydralazine - reflex increase in HR and CO
Nitroglycerine - if DBP falls excessively
Sodium nitroprusside - coronary steal
Antidysrhythmic Classes
Class I - Block Na channels - membrane stabilizers
Class II - Beta blockers - decrease phase 4 depolarization
Class III - Block K channels - prolong repolarization (amiodarone)
Class IV - CCB
Identify 4 drugs for cardiac dysrhythmias d/t digoxin toxicity.
- Lidocaine
- Procainamide
- Phenytoin
- Propranolol
*Enhance dig toxicity: HYPOkalemia, HYPERcalcemia, HYPOmag
What 4 drugs should you avoid with digitalis?
- Quinidine
- Sux
- Beta agonists
- Calcium
What is your concern with giving phenytoin to the hyperglycemic patient?
Phenytoin partially inhibits insulin release
Explain how digitalis works.
Inhibits the Na-K pump Sodium accumulates in the cell Na-Ca exchange system is inhibited Ca accumulates in the cell Contractility increases
Which CCB causes a reflex increase in HR?
Nifedipine
Which CCB is used for coronary artery vasospasm? Cerebral artery vasospasm?
Coronary - nifedipine, diltiazem
Cerebral - nimodipine
Chemotherapeutic Agents
Doxorubicin - Heart (2-32%) - ECHO
Bleomycin - Lungs (10-25%) - PFTs - restrictive
Cisplatin - Kidney
Cyclophosphamide, streptozocin, methotrexate - Liver
Melatonin enhances the activity of what drug class?
Benzos
All immunosuppressive regimens carry what 3 major risks?
- Infection
- Malignancy
- Vascular disease