Kaplan High Yield Pharm Flashcards
What is Vmax?
Vmax is the maximum velocity for a given amount of enzyme
-Proportional to enzyme concentration
What is the Michaelis constant (Km)?
Km is the substrate concentration required to reach half Vmax
Km = 1/affinity
What does a high Km mean?
A high Km means low affinity (opposite for low Km)
What is the equation for the intersection of the Y-axis on a Lineweaver-Burk plot?
Intersection of the Y-axis = 1/Vmax
What is the equation for the intersection of the X-axis on a Lineweaver-Burk plot?
Intersection of the X-axis = -1/Km
What are the characteristics of a competitive inhibitor?
- Resemble substrate, bind at active site
- Increasing substrate concentration can overcome inhibition
- Decrease potency
What is the effect on Vmax and Km by a competitive inhibitor?
No effect on Vmax
Increases Km
What are the characteristics of non-competitive inhibitors?
- Bind to allosteric site, not near active site
- Cannot be overcome with increased substrate concentration
- Decrease efficacy
What is the effect on Vmax and Km by a non-competitive inhibitor?
Decreases Vmax
No effect on Km
Do the Lineweaver-Burk plots of competitive or non-competitive inhibitors cross with the Lineweaver-Burk plot with no inhibitor?
The Lineweaver-Burk plot of a competitive inhibitor crosses the Lineweaver-Burk plot with no inhibitor
What is the equation for volume of distribution (Vd)?
Vd = total amount of drug in body/conc. of drug in plasma
A low Vd (4-8 L) means the drug is mostly contained in?
Blood
A medium Vd (12-14L) means the drug is mostly contained in?
Extracellular fluid
A high Vd (> total body water) means the drug is?
Distributed in all tissues, non-fluid compartments (fat)
What is the effect of hepatic disease on the Vd of plasma protein bound drugs?
Decreased synthesis of plasma proteins -> Drugs diffuse into body tissues, effectively increasing the drug’s Vd
What is the effect of renal disease on the Vd of plasma protein bound drugs?
Plasma proteins (and bound drugs) are excreted in the urine
What is the equation for drug clearance?
Drug clearance = Rate of drug elim./plasma drug conc.
Vd x Ke
When is renal clearance equal to GFR?
When there is no reabsorption, secretion, or plasma protein binding
What 2 substances are used to estimate the GFR?
Inulin and creatinine
What is the equation for the clearance of protein bound drugs (not cleared)?
Clearance = free fraction x GFR
What is the half life equation?
T1/2 = (.7 x Vd)/clearance
How many half lives does it take to reach steady state with continuous infusion?
Steady state is reached in 4-5 half lives with continuous infusion
What is a loading dose?
- Large initial dose given to fill up Vd
- Can increase plasma concentration in less than 4-5 half lives
What is the equation for loading dose?
LD = (Vd x Cp)/F
Cp=blood plasma conc.
F=bioavailability
What is a maintenance dose?
- A dose given to maintain constant blood plasma levels
- Lowered if hepatic/renal function is impaired
What is the equation for maintenance dose?
MD = (Cl x Cp)/F
Cl = clearance
What is bioavailability (F)?
- Fraction of administered drug that reaches systemic circulation
- Some drugs fail to be absorbed, or are metabolized before reaching circulation
What is the bioavailability of an IV infusion?
F = 1 for IV infusion
What is zero order elimination?
Constant amount of drug eliminated with time
Example: 100 mg -> 90 mg -> 80 mg…10 mg being eliminated per hr
What are substances that exhibit zero order elimination?
Phenytoin, aspirin, ethanol
What is first order elimination?
- Constant fraction of drug eliminated with time
- Most drugs follow first order kinetics
- Example: 100 mg -> 50 mg -> 25 mg…elimination of half concentration per hour
Explain the renal excretion of ionized and non-ionized substances
- Both ionized forms and non-ionized forms are filtered
- Only non-ionized forms are actively secreted or reabsorbed
- Ionized forms of drug are trapped in the filtrate
What are some examples of drugs that are weak acids?
Barbiturates, methotrexate, aspirin
How would you increase the elimination of a weak acid to save a patient from an overdose?
Give them base (HCO3-) -> alkalinize the urine (opposite for a weak base -> give NH4Cl)
What is an example of a drug that is a weak base?
Amphetamines
What is biotransformation?
Conversion of lipid soluble drugs into water soluble metabolites in the liver -> increases renal excretion
-Two forms of drug metabolism-phase 1 and 2
What is phase 1 drug metabolism?
Oxidation, reduction, and hydrolysis of drugs by cytochrome P450 enzymes
- Located in the smooth endoplasmic reticulum of the liver
- Require O2 and NADP
Name the drugs that are cytochrome P450 inducers (9)
-What is the acronym?
QRBPSGGCC
- Quinidine
- Barbiturates
- Phenytoin
- St. John’s Wort
- Rifampin
- Griseofulvin
- Glucocorticoids
- Carbamazepine
- Chronic alcohol use
Name the drugs that are cytochrome P450 inhibitors (10)
-What is the acronym?
HIS COCK MR G
- HIV protease inhibitors
- Isoniazid (INH)
- Sulfonamides
- Cimetidine
- Omeprazole
- Chloramphenicol
- Ketoconazole
- Macrolides
- Ritonavir
- Grapefruit juice
What are the non-cytochrome P450 enzyme phase 1 metabolism mechanisms?
- Hydrolysis (addition of H2O to drugs to assist metabolism, esterase/amidase)
- Monoamine oxidase
- Alcohol metabolism
What are the endogenous amines metabolized by MAO?
Dopamine, NE, and serotonin
What is the exogenous amine metabolized by MAO?
Tyramine
What is phase 2 metabolism?
Conjugation of functional groups to a drug via transferase enzymes
- Converts polar molecules to inactive molecules -> increase renal excretion
- Mechanisms of metabolism include - acetylation, glucuronidation, sulfation, methylation, and glutathione conjugation
What is potency?
- Measure of how much drug is required to give desired effect
- Typically expressed as EC50 - concentration that gives 50% of max response
What is efficacy?
Maximal effect that a drug can produce
See graphs on slides 17 and 18
…
What is a full agonist?
With receptor saturation, drug can reach full efficacy
What is a partial agonist?
Acts at the same site as agonist, but lower EFFICACY
-Can have higher or lower potency than agonist
What are physiologic antagonists?
Substrate that produces opposite effect of an agonist, but acts through different receptor/pathway
What is therapeutic index?
- Measure of drug safety
- Higher therapeutic index indicates safer drug
What is the equation for therapeutic index?
TI = LD50/ED50
-See graph on slide 20
Draw out the diagram on slide 22
…
What is a nicotinic Ach receptor (nAchr) and what are the different types?
Ligand gated Na/K channels
- Nn-autonomic
- Nm-somatic muscular (neuromuscular junction)
The cAMP system for GPCRs includes receptors for?
- Catecholamines beta1, beta2 (Gs), and alpha2 (Gi)
- Ach M2 (Gi)
- Glucagon (Gs)
The PIP2 system for GPCRs includes receptors for?
ALL are Gq
- Catecholamines alpha1
- Ach M1-M3
- Angiotensin II
- Vasopressin
Study the rest of slide 24 and 25
…
What are 3 examples of drugs that act at the cholinergic nerve terminal?
- Hemicholinium
- Botulinum toxin
- Vesamicol
What is the MOA of hemicholinium?
Inhibits choline uptake into nerve terminal -> decreases Ach production
What is the MOA of botulinum toxin?
Inhibits the release of Ach containing vesicles from the nerve terminal
What is the MOA of vesamicol?
Stops the conversion of acetyl CoA to Ach by inhibiting choline acetyl transferase
What are some examples of drugs that act at the adrenergic nerve terminal?
- Metyrosine
- Reserpine
- Cocaine, TCAs, and amphetamines
- Guanethidine
What is the MOA of metyrosine?
Inhibits the conversion of tyrosine to Dopa by inhibiting tyrosine hydroxylase
What is the MOA of reserpine?
Blocks the uptake of NE into vesicles
What is the dual action MOA for amphetamines?
- Directly block the reuptake of NE
- Increase the release of NE into the synapse
What is the MOA of cocaine and TCAs?
Directly block the reuptake of NE
What is the MOA of guanethidine?
Blocks the release of NE into the synapse
What are examples of cholinomimetics (parasympathomimetics)?
- Bethanechol
- Carbachol
- Pilocarpine
- Methacholine
What is bethanechol?
- Muscarinic agonist
- Longer acting than Ach (resistant to acetylcholinesterase)
- Tx of ileus and urinary retention (Bowels and bladder)
What is carbachol?
- Muscarinic/nicotinic agonist
- Also resistant to acetylcholinesterase
- Applied to eye to cause contraction of ciliary muscle, relief to open angle glaucoma, also constricts pupil
What is pilocarpine?
- Muscarinic agonist
- Stimulates tears, sweat, saliva
- Constricts pupil and ciliary muscle
- Also used for acute glaucoma
What is methacholine?
- Muscarinic agonist
- Causes bronchoconstriction when inhaled
- Used for asthma challenge test
What are examples of anticholinesterases (indirect cholinomimetics)?
- Neostigmine
- Pyridostigmine
- Edrophonium
- Physostigmine
- Echothiophate
What is neostigmine?
- Quaternary amine-acts on peripheral nervous system (no entry into CNS)
- Tx of ileus, urinary retention, and myasthenia gravis
- Post-operative reversal of neuromuscular junction blockade
What is pyridostigmine?
- Quaternary amine-acts on peripheral nervous system (no entry into CNS)
- Treatment of myasthenia gravis
What is edrophonium?
- Very short acting (10-20 mins)
- Diagnosis of myasthenia gravis
What is physostigmine?
- Tertiary amine (can enter CNS)
- Tx of glaucoma, antidote for atropine toxicity
Echothiophate is used for the tx of?
Glaucoma
What are the symptoms for cholinesterase inhibitor poisoning (high systemic Ach)? What is the acronym?
DUMBBELSS
- Diarrhea
- Urination
- Miosis
- Bronchoconstriction
- Bradycardia
- Excitation (skeletal muscle and CNS)
- Lacrimation
- Salivation
- Sweating
What is the treatment for cholinesterase inhibitor poisoning (high systemic Ach)?
- Atropine (muscarinic antagonist)
- Pralidoxime (2PAM) (regenerates cholinesterase)