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Year 1 > Pharmacology Principles > Flashcards

Pharmacology Principles Flashcards

1
Q

What are the determinants of drug deposition in the body?

A

Absorption (enteral/paraenteral)
Distribution: How it enters the blood and perfuses tissue
Metabolism: tissue enzymes catalyse the usually lipid soluble drug to a polar and less active form that is rapidly excreted.
Excretion: remove drug or metabolites from body (usually renal(

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2
Q

What PHYSIOCHEMICAL factors influence absorption of drug?

A
  • Degree ionization (influences lipid solubility dec. abs.)
  • Chemically unstable (therefore easily destroyed by HCL for example, dec. abs.)
  • Lipid to water partition coefficient
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3
Q

What factors influence the movement of drug between fluid compartments?

A
  • ionised and unionised drugs that are not bound to protein can diffuse freely
  • Only unionised drugs move READILY by diffusion
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4
Q

What does lipid to water partition coefficient mean?

A

Rate of diffusion across membrane for given concentration of drug on either side of membrane.
The higher the coeffcient the greater the rate of diffusion.

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5
Q

TRUE/FALSE

Only unionised forms readily diffuse across the lipid bilayer

A

True

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6
Q

What two factors does degree of ionization depend upon?

A

pKa of drug

Local pH

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7
Q

What is pKa

A

pH at which 50% of drug is ionised and 50% unionised

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8
Q

What is the Henderson Hasselbach equation?

A

pH=pKa + log(A-/AH)
A- = conjugate base
AH= weak acid
rearranged to pKa = pH+ log(AH/A-)

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9
Q

What does the Henderson Hasselbach equation do?

A

Calculates proportions of ionised and unionised drugs.
Can work out the pH or rearrange and work out percentage of total drugs ionized i.e. conjugate base/ total amount drug
A-/A-+AH

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10
Q

How does the local pH affect drug absorption?

A

Acidic drugs less ionized in acidic environment and basic drugs less ionized in BASIC environments.
Less ionized = more readily lipid soluble

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11
Q

What is considered a strong acid? (pKa)

A

pKa<3

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12
Q

What is considered a strong base? (pKa)

A

pKa>10

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13
Q

What factors affect GI absoprtion?

A

Motility
pH
Blood flow to stomach/intstine
Manufacture of tablet/capsule - release rate
Transporters - if present in epithelial cells can facilitate absorption

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14
Q

What is oral availability?

A

amount drug in systemic circulation/ amount drug administered

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15
Q

What is systemic availability?

A

amount of drug in systemic circulation/ amount absorbed (enteral/paraenteral

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16
Q

TRUE/FALSE

drugs administered intravenously (IV) have 99% systemic availability

A

false

HAVE 100%

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17
Q

What is first pass or presystemic metabolism?

A

When drugs absorbed orally are inactivate by enzymes in gut wall or liver before reaching circulation

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18
Q

What are the major fluid compartments in the body?

A 
PIFIT
Plasma 
Interstital fluid
Fat
Intracellular fluid
Transcellular fluid
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19
Q

What is Vd?

A

The APPARENT volume of distribution

amount of drug in tissue/plasma concentration

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20
Q

What does Vd<10L indicate?

A

Drug largely retained in vascular compartments - drugs bound to protein unable to diffuse across cap wall

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21
Q

What does 10-30L indicate?

A

Drug is largely restricted to extracellular water - drugs with low lipid solubility

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22
Q

What does Vd>30L

A

may indictae distribution through total body water
or accumulation in in certain tissue
or drug bound extensively to tissue protein

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23
Q

What is meant by MEC?

A

Minimum effective concentration: minimum dose to elicit effect

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24
Q

What is meant by MTC?

A

Maximum tolerated concentration: minimum amount that results in unwanted side effects

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25
Q

What is meant by therapeutic window?

A

Window between MEC and MTC.
Small = risky
Large = good

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26
Q

What is first order elimination?

A

Rate of elimination of drug directly related to drug concentration

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27
Q

What is t 1/2

A

T1/2 is the half life. TIme it takes for conc at any given time to fall by 50%

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28
Q

What is Cl?

A

Clearance is the volume of plasma cleared of drug in a given unit of time!

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29
Q

How can you work out rate if elimination?

A

Clearance x Plasma concentration (Cp)

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30
Q

What is steady state?

A

Rate of administration= rate of elimination (Cpss)

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31
Q

How can you work out Cpss?

A

maintenance dose rate/ clearance

32
Q

With regards to drug dosing to steady state - what is the difference between oral and IV dosage?

A

Same principle, but in oral administration the plasma volume fluctuates around an AVERAGE with each dose.
Iv is hyperbolic.

33
Q

What is a loading dose?

A

Higher dose of drug given at the start of treatment before stepping down to lower maintenance dose (to get to steady state.)

34
Q

Why is a loading dose used?

A

Decrease time taken for drugs with long half-lives to reach steady state.

35
Q

What is the relationship between loading dose and volume of distribution? ORAL

A

Oral admin: Ld=Vdx target concentration of drug in plasma

36
Q

What is the relationship between loading dose and volume of distribution? IV!!!!

A

Ld= (Vdx target concentration of drug in plasma)/ systemic availability

37
Q

What are zero order kinetics?

A

Initally eliminated at a constant rate (unaffected by concentration)

38
Q

How do most drugs leave the body?

A

Via urine, usually as highly charged or polar compounds and LESS pharmacologically active.

39
Q

Why does drug metabolism convert parent drugs to polar metabolites?

A

Prevents them from being reabsorbed by kidneys (non-polar lipid soluble), facilitates excretion.

40
Q

What are some UNUSUAL pathways for metabolized drugs?

A

Go from inactive to ACTIVE to satisfy purpose (codeine to morphine)

No change in activity

Metabolite may have a DIFFERENT spectrum of action

41
Q

What is the USUAL pathway for drug metabolism? PHASE 1

A

CATABOLIC PROCESS

Drugs become polar due to addition of chemically reactive group. This is done via oxidation, reduction or hydrolysis.

42
Q

What is the USUAL pathway for drug metabolism? PHASE 2

A

ANABOLIC PROCESS

Addition of endogenous compound to increase polarity and prime for excretion.

43
Q

What is the cytochrome P450 family of monooxygenases (CYP)?

A

Enzymes that mediate a lot of phase 1 oxidation reactions of drugs

44
Q

What are the products of the c. monooxygenase pd450 (CYP) cycle?

A

Two products:
H20
hydroxyl product (hydroxylated parent drug)

45
Q

What are some common Phase 2 reactions?

A

Addition of more stuff to chemically reactive group on drug (following phase 1)
i.e. adding stuff to hydroxyl group

46
Q

What is glucuronidation?

A

Phase 2 reaction involving transfer of GLUCURONIC ACID to electron rich atoms of the substrate

47
Q

TRUE/FALSE

Many endogenous substances are subject to glucuronidation (e.g. bilirubin, adrenal corticosteroids)

A

True

48
Q

Which part of the systemic circulation does the glomerular capsule associate with?

A

The interlobular artery/arteriole

49
Q

Which part of the systemic circulation does the TUBULE associate with?

A

The peritubular capillary network

50
Q

Under what conditions does glomerular filtration occur?

A
  • drugs with a MW less than 20 000 (most)
  • drugs NOT bound to large plasma proteins
  • drug charge is unimportant
51
Q

TRUE/FALSE
if a drug binds appreciably plasma protein, its concentration in the glomerular filtrate will be MORE than total plasma concentration

A

FALSE it will be less as proteins cannot pass into glomerulus

52
Q

TRUE/FALSE
Up to 80% of renal plasma flow filtered through the glomerulus, but remaining 20% delivered to the peritubular capillaries

A

FALSE

most plasma will flow through the peritubular capillaries

53
Q

Epithelial cells of the —– contain —–, independent, transporter systems that —— secrete drugs into the lumen of the nephron

A

proximal tubule, two, actively

54
Q

Which transporter system in the proximal tubule secretes ACIDIC drugs?

A

OAT

Organic anion transporter

55
Q

Which transporter system in the proximal tubule secretes BASIC drugs?

A

OCT

Organic cation transporter

56
Q

TRUE/FALSE

Proximal tubular secretion of drugs is a SATURABLE process

A

True

each carrier has Tm transport maximum for particular drug

57
Q

TRUE/FALSE

Proximal tubular secretion CANNOT secrete drugs that are highly protein bound

A

False, it can :D

58
Q

What is the effect of proximal tubular secretion (of drugs) on the concentration of FREE DRUGS?

A

Free drug concentration reduced because:

  • secretion establishes a NEW equilbrium between bound and unbound drug
  • causes drugs to dissociate from proteins
59
Q

Factors that increase reabsorption in the kidney

A

High lipid solubility
Increased production of urine (diuresis)
Unpolar drugs - highly polar drugs excreted without reabsorption

60
Q

What is the effect of urinary pH on reabsorption in the kidneys?

A

Alkaline pH increases excretion of ACIDS
Acidic pH increases excretion of BASES
(opposite makes more polar!)

61
Q

?What is depolarization

A

Membrane potential becomes LESS negative

62
Q

What is hyperpolarization?

A

Membrane potential becomes MORE negative

63
Q

TRUE/FALSE

Na+ flows inwardly

A

True,

electrochemical gradient more Na+ on outside

64
Q

Why does K+ generate an outward current?

A

Lower conc outside cell - electrochemica gradient

65
Q

K+ channel opening?

A

effluc K+ and hyperpolarization

66
Q

Na+ channel opening ?

A

influx

Na+ depolarization

67
Q

TRUE/FALSE

Action potentials are all-or-none

A

True, generated when threshold is reached

68
Q

Activation of K+ channels is due to which type of feedback?

A

Negative. Self limiting, outward movement causes repolarization which turns off stimulus for ppening

69
Q

Activation of Na+ channels is due to which type of feedback?

A

Positive, some open then more open. Self-reinforcing.

70
Q

Phases of Na+ channel inactivation?

A

Maintained depolarization enter inactive state. This is a refractory period!
Needs repolarization to CLOSE.
Depolarization causes it to OPEN.

71
Q

TRUE/FALSE

Absolute refractory period is when Na+ channel is CLOSED following repolarization

A

FALSE, this describes relative refractory period

72
Q

TRUE/FALSE

Relative refractory period describes the inactivation of Na+ channels during maintained depolarization

A

FALSE, this describes absolute refractory period. No stimuli can open this at this time.

73
Q

Features of un-myelinated axons?

A

Passive spread of current
“leaky” axon
Current does not spread far from site of origin as some of the current goes outside the cell.

74
Q

How to increase passive current spread?

A

Increase membrane resistance (rm) this is done by adding insulating material such as myelin and oligodenrocytes

75
Q

What is the node of Ranvier?

A

Gaps between areas of axon wrapped in myelin sheath. AP jumps from one NoR to another.

Year 1 (15 decks)

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