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Step 1 > Pharmacology > Flashcards

Pharmacology Flashcards

0
Q

Enzyme kinetics- what is the Km? How is it associated with affinity?

A

Km: the substrate concentration at which the reaction progresses at 1/2 the maximal velocity
Km is inversely related to enzyme affinity–> the lower the Km, the higher the affinity

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1
Q

What do enzymatic reactions that exhibit a sigmoid curve indicate?

A

cooperative kinetics (eg. hemoglobin)

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2
Q

How is Vmax related to enzyme concentration?

A

Vmax is directly proportional to enzyme concentration

-the higher the enzyme concentration, the higher the Vmax

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3
Q

What is the equation for the lineweaver-burk plot?

A

1/V = (Km/Vmax)(1/[S]) + 1/Vmax or Y=mx + b

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4
Q

Lineweaver-burk plot: x-intercept?

A

x-intercept = -1/Km

-the smaller the x-intercept, the higher the Km= the lower the affinity

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5
Q

lineweaver burk plot: y-intercept?

A

y-intercept = 1/Vmax

-the higher the y-intercept, the lower the Vmax

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6
Q

Competitive inhibitors (irreversible)

A

:compete for active site and stay bound, decreases efficacy

  • Vmax: decreased
  • Km: unchanged
  • lineweaver burk plot: y-intercept increases, x-intercept stays the same
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8
Q

Competitive inhibitors (reversible) actions

A

:compete for active site, causes a decrease in potency

  • Vmax: unchanged (can be achieved with increased substrate)
  • Km: increase
  • lineweaver burk plot: y-intercept stays the same, x-intercept decreases
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8
Q

Pharmacokinetics

A 
What the body does to the drug; 
Absorption 
Distribution 
Metabolism 
Elimination
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9
Q

Noncompetitive inhibitor actions

A

: bind to allosteric site, decreases efficacy

  • Vmax: decreases
  • Km: unchanged
  • lineweaver burk plot: y-intercept increases, x-intercept unchanged
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10
Q

Pharmacodynamics

A

What the drug does to the body

-receptor binding, drug efficacy, potency, toxicity

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11
Q

Bioavailability

A

:F; the fraction of administered drug that reaches systemic circulation unchanged
-IV dose, F=100%

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12
Q

What route of drug administration has the highest absorption?

A

Inhalation

Recall: IV administration does not require absorption

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13
Q

Volume of distribution

A

:Vd; theoretical volume occupied by the total absorbed drug

  • tells where the drug is distributed
  • Vd= low; mostly in the blood, large/charge or plasma protein bound
  • V=medium; in ECF, small hydrophilic
  • Vd= high; mostly in tissues, small lipophilic or bound to tissue protein
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14
Q

Half-life

A

:the time it takes to lower the plasma concentration of a drug by 50%

1/2 life = 0.7 x Vd/CL

-characteristic of first order elimination

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15
Q

How long does it take to reach steady state?

A

4-5 half lives

16
Q

What factors determine the time to steady state?

A

the half life ONLY
- frequency of dosage and dosage are independent factors, but increasing the dose, increases the plasma concentration achieved at steady state

17
Q

Clearance (CL) of a drug

A

: the volume of plasma cleared of drug per unit time; may be effected by defects in cardiac, renal or hepatic function

CL= rate of elimination of drug/plasma drug concentration

CL= Vd x Ke, where Ke= the rate of elimination constant

18
Q

Loading dose

A

:puts serum concentration of drug at target concentration within one dose

LD= Ctarget x Vd/F

19
Q

Maintenance dose

A

MD= Ctarget x CL x T/F

where T is the time interval between doses
- In renal or hepatic disease, maintenance dose should decrease b/c of effect on CL

20
Q

Zero-order elimination

A

:constant amount of drug eliminated per unit time; plasma concentration decreased linearly with time

PEA: Phenytoin, EtOH, Aspirin

21
Q

First order elimination

A

:constant fraction of drug eliminated per unit time; plasma concentration decreases exponentially with time

22
Q

What form of a drug is easily cleared in the urine?

A

the ionized form

23
Q

What kind of environment aids in renal clearance of weak acids?

A

basic environment b/c weak acids are ionized in a basic environment

24
Q

What kind of environment aids in renal clearance of weak bases?

A

an acidic environment because bases are ionized in acidic environments

25
Q

Weak acid drugs

A

Aspirin, penicillin, cephalosporins, loop and thiazide diuretics, phenobarbital, methotrexate
“Please Don’t Make ACid”

26
Q

Weak base drugs

A

morphine, local anesthetics, amphetamines, PCP

“Local Patrons Always Move”

27
Q

How do you treat overdose with a weak acid?

A

bicarbonate

28
Q

How do you treat overdose with a weak base?

A

ammonium chloride (NH4Cl)

29
Q

Phase I metabolism

A

Reduction, oxidation, hydrolysis with cytochrome P450

  • yields slightly polar, often still active metabolites
  • geriatric patients lose phase I first
30
Q

Phase II metabolism

A

“Attach something” or conjugation
glucorondidation, acetylation, sulfation
-yields very polar, inactive metabolite
-patients who are slow acetylators have greater side effects from certain drugs b/c have decreased rate of metabolism –> drug induced SLE

31
Q

Therapeutic index

A

TI= TD50/ED50 “TITE”
- safer drugs have higher therapeutic indices

TD50: dose that 50% of the population experienced toxicity
ED50: dose that in 50% of the population was effective
LD50: TD for animal studies

32
Q

Drugs with low therapeutic indices?

A

digoxin, lithium, theophylline, warfarin

- low TI means that its takes very little drug over optimal dosing to produce toxicity

33
Q

Inducers of cytochrome P450 - Chronic alcoholic Mona Steals Phen-Phen and Never Refuses Greasy Carbs

A 
Chronic EtOH 
Modafinil 
St. John's Wort 
Phenytoin 
Phenobarbitol 
Nevirapine 
Rifampin 
Griseofulvin 
Carbamezepine
34
Q

Inhbitors of cytochrome P450- Acute Gentleman Cipped Iced Grapefruit Juice Quickly And Kept Munching on Soft Cinnamon Rolls

A 
Acute EtOH
Gemfibrozil 
Ciprofloxacin 
Isoniazid 
Grapefruit juice 
Quinidine 
Amiodarone 
Ketaconazole 
Macrolides- Erythro 
Sulfonamides 
Cimetidine 
Ritonavir
35
Q

Substrates for cytochrome P450 interactions - Always Always Always Think When Starting Others

A 
Anti-epileptics 
Antidepressants 
Antipsychotics 
Anesthetics 
Theophylline 
Warfarin 
Statins 
OCPs

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