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MPharm1 PA10308 > Pharmaceutics > Flashcards

Pharmaceutics Flashcards

1
Q

5 uses for excipients

A
  • dosing control
  • rate of absorption
  • bioavailability and stability
  • product identification
  • safety and effectiveness
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2
Q

5 types of excipients?

A
  • diluents
  • binders
  • glidants
  • dry-lubricants
  • disintegrants
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3
Q

What is a brønsted-lowry acid?

A

a proton donor

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4
Q

What is a brønsted-lowry base?

A

a proton acceptor

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5
Q

Equilibrium constant of a weak acid

A

[H3O+][A-]
Ka = ————–
[HA]

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6
Q

pKa =

A

-log Ka

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7
Q

The lower the pKa…

A

the stronger the acid

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8
Q

Equilibrium constant of weak base

A

[OH-][BH+]
Kb = ————–
[B]

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9
Q

The lower the pKb…

A

the stronger the base

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10
Q

pKa + pKb =

A

pKw

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11
Q

What are amphoteric electrolytes?

A

electrolytes which can function as acids or bases

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12
Q

What is polyprotic?

A

Capable of donating more than one proton

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13
Q

What is the henderson-hasselbalch equation?

A

pH = pKa + log([A-]/[HA])

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14
Q

([A-]/[HA]) =

A

antilog (pH-pKa)

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15
Q

What is the buffer equation for acid?

A

[salt]
pH = pKa + log ———–
[acid]

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16
Q

What is the buffer equation for base?

A

[base]
pH = pKw - pKb + log ———–
[salt]

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17
Q

What is the equation for buffer capacity?

A

β = Δ[acid/base] / ΔpH

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18
Q

What is the integrated rate equation for a 1st order reaction?

A

ln[A]t = ln[A]0 - kt

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19
Q

What is the half life equation for a first order reaction?

A

t1/2 = 0.693/k

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20
Q

What is the shelf life equation for a first order reaction?

A

t95% = 0.0513/k

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21
Q

What is the integrated rate equation for a zero order reaction?

A

[A]t = [A]0 -kt

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22
Q

What is the half life equation for a zero order reaction?

A

t1/2 = [A]0 / 2k

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23
Q

What is the shelf life equation for a zero order reaction?

A

t95% = [A]0 / 20k

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24
Q

What is the integrated rate equation for a 2nd order reaction?

A

1 1
—- = —- + kt
[A]t [A]0

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25
Q

What is the half life equation for a 2nd order reaction?

A

t1/2 = 1 / [A]0k

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26
Q

What is the shelf life equation for a first order reaction?

A

t95% = 1 / 19[A]0k

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27
Q

What is the arrhenius equation?

A

k = A exp -Ea/RT

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28
Q

What is the pre exponential factor A?

A

The fraction of molecules with sufficient energy

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29
Q

How is the arrhenius equation rearranged for graphs?

A

lnk = lnA - Ea/RT

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30
Q

What is hepatic first pass effect?

A

When a drug is goes through the portal vein to the liver and is metabolised beofre it has a chance to reach general circulation

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31
Q

What is enterohepatic recycling?

A

When a drug is excreted into bile, used to digest food and then reabsorbed into general circulation

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32
Q

3 advantages of topical application?

A
  • sustained concentration
  • reduced dosing frequency
  • bypasses liver
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33
Q

2 advantages of inhalation?

A
  • bypasses liver
  • straight to bloodstream
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34
Q

3 advantages of nasal delivery?

A
  • bypass blood brain barrier
  • straight to bloodstream
  • bypass liver
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35
Q

2 advantages of vaginal delivery?

A
  • bypasses liver
  • long term controlled release
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36
Q

3 advantages of rectal delivery?

A
  • high bioavailability
  • by-passes liver
  • advantage for those unable to take oraly
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37
Q

If the pH of the solution is higher than the drugs pKa value…

A

the drug tends to be more ionised

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38
Q

What is drug distribution?

A

The reversible transfer of drug from one site to another within the body

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39
Q

What are the stats of an average subject?

A

70kg
5L of blood (3L plasma)
cardiac output 5.5L/min

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40
Q

What is paracellular movement?

A

movement influenced by the tightness of intercellular junctions

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41
Q

What is transcellular movement?

A
  • passage by simple diffusion
    or
  • facilitative methods like transporters
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42
Q

Which 4 factors affect passive diffusion?

A
  • smaller MW diffuses faster
  • lipid-water partion coefficient
  • plasma binding
  • membrane thickness
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43
Q

Why do some drugs rely on transporters?

A

They have poor passive permeability

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44
Q

Which 3 membranes are the most particular to cross?

A
  • blood-brain barrier
  • renal tubules
  • hepatocyte
45
Q

Membrane transport for charged drugs is

A

Slower

46
Q

Bound fraction?
Fbound =

A

[drug]bound / [drug]total

47
Q

Unbound/free fraction?
Ffree

A

[drug]free / [drug]total

48
Q

Unbound/free concentration?

A

Ctotal x Fu

49
Q

Amount of drug in the body (A) =

A

V . Cp

50
Q

Volume of distribution in terms of amount in body wrt free fractions (V) =

A

Vp + Vt x ( fu/fu,tissue)

51
Q

What is the partion coefficient when plasma-tissue equilibrium has been achieved?

A

P = Ct/Cp

52
Q

Volume of distribution in terms of amount in body wrt the partition coefficient (V) =

A

Vp + ΣVt x P

53
Q

Percentage of drug present in plasma

A

%plasma = (Vp/V) x 100

54
Q

Percentage of drug present in tissue

A

%tissue = (V-Vp/V) x 100

55
Q

What are the two parts of permeability rate-limited distribution?

A
  • membrane permeability changes modify distribution
  • distribution kinetics dependent on drug properties
56
Q

What is perfusion rate-limited distribution?

A
  • occurs when tissues don’t affect distribution
  • access to tissues limited by blood flow
  • changes in blood flow modify distribution
57
Q

What is the rate of dug uptake in tissues

A

= Q(Ca - Cv)

58
Q

What is the tissue distribution rate constant (Kt)?

A

(Q/Vt)
= ——–
P

59
Q

What is perfusion rate?

A

Q/Vt

60
Q

The larger the Kt…

A

The faster the distribution

61
Q

Drug distribution is faster when?

A
  • tissues have low perfusion
  • tissues have low affinity for the drug
62
Q

What is elimination?

A

The irreversible loss of drug by excretion or metabolism

63
Q

What are the two definitions of clearance?

A
  1. The factor relating elimination rate with the drug conc in plasma
  2. Volume of fluid cleared of drug per unit of time
64
Q

Rate of elimination =

A

Cl x Cdrug

65
Q

Rate in = Rate out

A

dose/time = Cl x Css

66
Q

How does the liver metabolise drugs?

A

Lipophilic chemicals metabolised into hydrophilic then excreted in urine or bile

67
Q

What is the michaelis-menten equation?

A

Vmax x C
elim rate = ———
Km + C

68
Q

What are Vmax and Km in the michaelis-menton?

A

Vmax - max elimination rate
Km - michaelis constant / conc at which rate equals 1/2 Vmax

69
Q

What is the extraction ratio (E)?

A

C entering - C leaving
Eh = ———
C entering

70
Q

What is hepatic clearance (Clh)?

A

= Qh x Eh

same for renal clearance

71
Q

What is the maximum hepatic clearance rate?

A

90 L/h aka hepatic blood flow

72
Q

What can be an issue of high hepatic clearance?

A

high loss of drug to hepatic first pass effect

73
Q

What is the maximum renal clearance rate?

A

72L/h aka renal blood flow

74
Q

Which three processes contribute to renal excretion?

A
  • glomerular filtration
  • active tubular secretion
  • passive and active reabsorbtion
75
Q

How much water in the kidney is reabsorbed?

A

99%

76
Q

How does passive reabsorbtion work?

A

When the water is reabsorbed, it creates a higher Cdrug in the urine which can then diffuse back into the plasma, reduces renal elimination

77
Q

What is tubular renal secretion?

A

substances can be transported into tubules if not filtered

78
Q

What is glomerular filtration?

A

Waste products are squeezed out of the blood into the bowmans capsule. Most is reabsorbed in tubules but wastes makes urine

79
Q

How do you work out renal clearance?

A

Clfiltration + Clsecretion - Clreabsorption

80
Q

Why is Clcreatinine used as a standard?

A

It is unbound in plasma and only eliminated by glomerular filtration

81
Q

How can you work out renal clearance with Clcr

A

funbound x Clcr

82
Q

The renal clearance of a drug filtered and secreted…

A

will exceed rate of filtration

83
Q

The renal clearance of a drug filtered and reabsorbed…

A

will be less than rate of filtration

84
Q

When urine is more acidic…

A

weakly basic drugs more ionised, less reabsorbed, more renal clearance

85
Q

When urine is more alkaline…

A

weakly acidic drugs more ionised, less reabsorbed, so more renal clearance

86
Q

What is the one-compartment model?

A

drug is assumed to instantaneously distribute into homogenous fluid, only accounts for drug elimination

87
Q

What is k in the one compartment model equations?

A

the elimination rate constant, can also be considered the fractional rate of drug removal, eg 0.14h-1means 14% of drug per hour

88
Q

How are A, V and C related in one compartment model equations

A

A = amount in body
V = volume of distribution
C = concentration
A / V = C

89
Q

How can we estimate k from one compartment model equations?

A

plot ln of equation against time, the gradient of slope is -k

90
Q

How do you explain if the one compartment model is a good fit?

A

plot lnC v time and it should be a straight line

91
Q

How do you work out loading dose?

A

V x desired Co x body weight

92
Q

How can you estimate V with IV bolus data?

A

V = dose/Co

93
Q

Which equation links volume of distribution, clearance and k?

A

Cl = V x k

94
Q

How do you change the lnC equation to account for half life?

A

lnCo /2 = lnCo - k x t1/2

95
Q

C =
wrt to t1/2 and n

A

Co(1/2)n
n = number of half lives elapsed

96
Q

AUCo for IV =

A

Co / k
and
D / (k x V)
and
D / Cl

97
Q

How do you estimate AUC?

A

trapezoidal rule

98
Q

What is the trapezoidal area equation?

A

(B+b) x h /2

99
Q

What is absolute bioavailability?

A

the ratio of AUC obtained with extravascular formation and AUCiv of the same dose, e.g.
AUC syrup / Dosesyrup
Fabsolute = ———————————-
AUCiv / Doseiv

100
Q

What are three advantages of IV infusion?

A
  • drug plasma levels easily controlled by adjusting infusion rate
  • constant drug plasma levels can be achieved
  • less problems of irritation/toxicity
101
Q

What are three disadvantages of IV infusion?

A
  • continous monitoring
  • solubility and stability of drugs
  • fluid restricted patients
102
Q

What are the three assumptions of the one compartment model for IV infusion?

A
  • elimination is first order
  • drug input is zero order
  • linear kinetics
103
Q

How can we calculate concentration for an IV bolus followed by IV infusion?

A

Just add together
C = Co x e-kt + Css (1-e-kt)

104
Q

How can you find B graphically?

A

plot the elimination phase lnC over time and extrapolate to the y axis, you have lnB

105
Q

AUCo for extravascular?

A

F x D / Cl

106
Q

What is bioavailability?

A

The rate and extent to which the active ingredient is absorbed and becomes available at the site of drug action

107
Q

What is relative bioavailability?

A

AUCcapsules / Dose capsules
Frelative = ———————
AUCsyrup / Dose syrup

108
Q

What must be remebered when dealing with extravascular doses?

A

F!

109
Q

What is Css mean for extravascular doses?

A

F x D
Css = ———–
Cl x tau

MPharm1 PA10308 (2 decks)

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