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Part 3 – PM3B > (PM3B) Pharmacokinetics > Flashcards

(PM3B) Pharmacokinetics Flashcards

1
Q

What is the therapeutic window of a drug?

A

The drug level in blood

Between toxicity & poor therapeutic activity

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2
Q

What is Cmax?

A

Maximum concentration of a drug in the blood

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3
Q

What is Cmin?

A

Minimum concentration of a drug in the blood

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4
Q

Define bioavailability.

A

The fraction of an administered dose that reaches the bloodstream

F - symbol in an equation

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5
Q

How is bioavailability determined?

A

(1) Blood sample taken from patient
(2) Blood cells are centrifuged out
(3) HPLC used to measure drug conc. in plasma

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6
Q

What is HPLC?

A

High performance liquid chromatography

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7
Q

What does a graph of drug plasma concentration over time indicate?

A

Absorption

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8
Q

How is absorption of a drug known?

A

Cp (plasma concentration) vs t (time)

Area under the curve

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9
Q

How can the absorption of IV and oral routes of a drug be compared?

A

Cp (plasma concentration) vs t (time)

Calculate and compare area under curve

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10
Q

What is the symbol representing bioavailability?

A

F

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11
Q

How is bioavailability of a route of administration calculated?

A

F(route) = AUC(route) / AUC(IV)

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12
Q

What does AUC refer to?

A

Area under curve

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13
Q

What does F refer to?

A

Bioavailability

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14
Q

What are the commonly used models for distribution?

A

(1) One compartment model

(2) Two compartment model

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15
Q

What is the one compartment model?

A

Model for distribution of a drug

Assumption that a drug is distributed in the body in a single homogenous department

Assumes perfusion to heart/ liver/ lungs from blood

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16
Q

What is the two compartment model?

A

Model for distribution of a drug

Central & peripheral compartments

Central: Blood/ heart/ lungs/ liver

Peripheral: Fat/ muscle/ skin

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17
Q

What does Vd refer to?

A

Volume of distribution

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18
Q

What is volume of distribution shortened to?

A

Vd

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19
Q

What is Vd?

A

Plasma drug concentrations related to total amount of drug present in the body

‘Apparent’ volume of distribution

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20
Q

How is blood plasma concentration calculated?

A

Cp = (Mass of drug in body) / Vd

Cp = (SxFxD) / Vd

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21
Q

How is Vd calculated?

A

Vd = (Mass of drug in body) / Cp

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22
Q

In a calculation, what is the mass of the drug in body for an IV injection?

A

Mass of the drug in the body = 1

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23
Q

How many litres of blood are there in the body?

A

Approx. 5L

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24
Q

What can be inferred from a volume of distribution (Vd) of greater than 5L? Why?

A

Drug has been distributed into tissues/ systems OTHER than the blood

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25
Q

How is IV loading dose calculated?

A

(Desired Cp) x Apparent volume of distribution

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26
Q

How is rate calculated?

A

Change in amount over time

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27
Q

What does K refer to?

A

Rate constant

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28
Q

What does n refer to, with regards to rate of reaction?

A

Order of the process

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29
Q

What is a zero order reaction?

A

When n=0

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30
Q

When is the rate of change constant?

A

When X^n = 1, because n=0

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31
Q

Is the rate constant negative or positive? Can that change?

A

Positive

Always positive

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32
Q

Is dX/dt negative or positive when X is diminishing?

A

Must be negative

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33
Q

(1) When is the rate constant accompanied by a minus symbol?

(2) Give an example.

A

(1) When X is diminishing

(2) When a drug is being eliminated from the body

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34
Q

(1) What can {Xt = X(0) - K(0)t} be written as?

(2) What does it mean?

A

(1) C(pt) = C(p0) - K(0)t
(2) For a zero order elimination, Cp at time t equals Cp at time 0, minus the zero order elimination rate constant multiplied by the time taken

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35
Q

What is the equation {Xt = X(0) - K(0)t} in the same format as?

A

y = mx + c

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36
Q

(1) If a Cp vs t graph is a straight line, what can be assumed?
(2) What information can be taken from this?

A

(1) Elimination is zero order

(2) Rate constant and Cp can be found at time zero

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37
Q

What does X represent?

A

Total amount of drug present in the body

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38
Q

If X is raised to the power of 1, what does this mean in terms of rate of reaction?

(2) What does this mean for the rate of reaction?

A

(1) First Order reaction

(2) Rate of reaction is not constant, because X is always changing

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39
Q

What does K(0) represent?

A

Zero order elimination rate

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40
Q

What does K(1) represent?

A

First order elimination rate

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41
Q

How is the drug concentration of the plasma at time (t) calculated?

A

Cp(t) = Cp(0)exp^{-K(1)t}

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42
Q

In an equation, what does ‘exp’ represent?

A

The exponential

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43
Q

(1) What does Cp(t) = Cp(0)exp^{-K(1)t} look like in logarithmic form?
(2) What is this equation used for?

A

(1)
lnCp(t) = lnCp(0) - K(1)t

(2) Calculating the drug concentration of the plasma at a time (t)

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44
Q

What assumption is made when a drug is injected IV, regarding a Cp vs t plot?

A

That 100% of the drug is present at t = 0

i.e. volume in body = volume injected

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45
Q

What format can the Cp vs t equations be rearranged to, to be used to calculate values given on the plot?

A

y = mx + c

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46
Q

What does it mean if a ln(Cp) vs t plot is a straight line?

A

Reaction (elimination) is first order

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47
Q

What does it mean if a Cp vs t plot is a straight line?

A

Reaction (elimination) is zero order

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48
Q

What assumption is made for Cp vs t plots of elimination rates?

A

Based on ONE compartment model

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49
Q

What order of elimination do most drugs undergo?

A

First order elimination

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50
Q

How are drugs eliminated from the body?

A

(1) Metabolism

(2) Excretion

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51
Q

What does KE represent?

A

Rate of elimination

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52
Q

What is the short-hand for rate of elimination?

A

KE

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53
Q

Is the rate of a zero order elimination dependent on Cp?

A

No, it is a constant.

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54
Q

When does zero order elimination most commonly occur?

A

When elimination pathways for a drug are saturated

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55
Q

Is the rate of a first order elimination dependent on Cp?

A

Yes. Proportional

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56
Q

What does a ln(Cp) vs t plot look like, using a TWO compartment model?

A

(1) 1st phase: Distribution and elimination
- ln(Cp) drops rapidly

(2) 2nd phase: Elimination ONLY
- ln(Cp) decreases at a slower rate

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57
Q

What occurs during the first phase of the curve of a ln(Cp) vs t plot?

A
  • Drug is being distributed from central compartment to peripheral
  • Drug is being eliminated from the central compartment
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58
Q

What occurs during the second phase of the curve of a ln(Cp) vs t plot?

A
  • Central and peripheral compartments are at drug conc. equilibrium
  • Drug is being eliminated from central compartment
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59
Q

What does ‘biliary’ mean?

A

Referring to bile or the bile duct

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60
Q

What are the main types of excretion?

A

(1) Kidneys -> Urine - primary route

(2) Biliary -> Faeces

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61
Q

What does ‘clearance’ refer to?

A
  • Irreversible removal of a drug from systemic circulation by metabolism or excretion
  • The volume of blood from which the drug is completely removed per unit of time
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62
Q

Where does clearance occur?

A

When blood flows through an organ of elimination

(1) Liver - metabolism
(2) Kidneys - excretion

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63
Q

Which organ is primarily associated with metabolism?

A

Liver

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64
Q

Which organ is primarily associated with excretion?

A

Kidney

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65
Q

How is the total clearance calculated?

A

CL(total) = CL(renal) - CL(non-renal)

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66
Q

Where does most non-renal clearance occur?

A

Metabolism in the liver

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67
Q

What is renal clearance?

A

Irreversible removal of a drug from the systemic circulation via excretion in the kidney

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68
Q

What is hepatic clearance?

A

Irreversible removal of a drug from the systemic circulation via metabolism in the liver

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69
Q

What are the units of clearance?

A

mL/ minute
OR
L/ hour

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70
Q

What equation is used to calculate first order clearance of a drug?

A

CL(s) = K(E)V(d)

Subscript (s) denotes systemic

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71
Q

Is drug clearance considered constant (first order)? Give a reason for your answer.

A

Yes.

Both K(E) and Vd are constants

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72
Q

In an equation, what does t(1/2) refer to?

A

Elimination half-life

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73
Q

What is elimination half-life {t(1/2)}?

A

Time taken for Cp to drop to Cp/2

e.g. 50mg/mL -> 25mg/mL

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74
Q

How is elimination half-life {t(1/2)} calculated?

A

t(1/2) = 0.693 / K(E)

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75
Q

What is the significance of 0.693 in an equation, relating to elimination?

A

It is the numerator for the equation used to calculate elimination half-life

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76
Q

What is the main reason a drug may be formulated as a salt or hydrate?

A

To increase solubility

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77
Q

What is the salt factor referred to as in short-hand?

A

S

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78
Q

What is the salt-factor?

A

The fraction of the administered dose that is the active pharmaceutical ingredient

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79
Q

How is the salt factor (S) calculated?

A

(Mr of API) / (Total Mr of drug)

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80
Q

How can blood plasma concentration be calculated?

A

Cp = (Total mass of drug in body) / Vd

Cp = (SxFxD) / Vd

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81
Q

What does ‘steady state’ refer to?

A

When the amount of drug administered in a given time is equal to amount of drug eliminated in the same given time

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82
Q

What is the steady state plasma concentration?

A

CpSS

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83
Q

How long does it take for a drug to reach steady state?

A

Depends on t(1/2), elimination half-life

When the amount of drug being absorbed = amount of drug being eliminated

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84
Q

(1) What is CpSS?

(2) How can it be calculated?

A

(1) Steady state plasma concentration

2
CpSS = (SxFxD) / (Clearance x dosing interval)

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85
Q

Define dosing interval.

A

The frequency of intermittent drug administration, based on elimination half-life {t(1/2)}

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86
Q

How does the time to steady state compare to the half-life?

A

Time to steady state is approximately equal to 5 half-lives

87
Q

Does a higher dose affect the time taken to reach steady state?

A

No

88
Q

What is steady state, with regard to a continuous IV infusion?

A

Rate of infusion is equal to rate of elimination

89
Q

In an equation, what does ‘R’ refer to?

A

Rate of elimination

90
Q

What is R / CL equal to?

A

CpSS (Blood plasma steady state)

91
Q

How can time to steady state be decreased?

A

Administer a loading dose

92
Q

What is the purpose of a loading dose?

A

To decrease time taken to achieve a steady state

93
Q

What is the purpose of achieving a steady state quickly?

A

To achieve appropriate therapeutic effect faster

94
Q

What is gentamicin?

A

Powerful antibiotic

Considered as last-resort

95
Q

What is the oral bioavailability of gentamicin?

A

Approximately 0

96
Q

(1) How is gentamicin administered?

(2) What dose is given?

A

(1) IV

(2) 5-10mg/ L

97
Q

When is gentamicin indicated?

A

For serious bacterial infections

98
Q

Define ototoxic.

A

Having a toxic effect on ear/ ear nerve supply

99
Q

Define nephrotoxic.

A

Having a toxic effect on kidney - damaging or destructive

100
Q

What are the adverse effects of an overdose of gentamicin?

A

(1) Ototoxicity - damaging ear/ ear nerve supply

(2) Nephrotoxic - damaging to kidney

101
Q

What significance does 5 times the half-life have?

A

Time taken to reach steady state for a drug

102
Q

What effect does increased dosing have on the peaks and troughs of plasma drug concentration?

A

Increases difference between peaks and troughs

Does NOT increase time taken to reach steady state

103
Q

If a drugs half-life is 6.5hrs, how long can we assume it takes the drug the reach steady state in the blood plasma?

A

6.5 x 5 = 32.5hrs

104
Q

What does TDM refer to?

A

Therapeutic drug monitoring

105
Q

What is therapeutic drug monitoring written as in short-hand?

A

TDM

106
Q

What is therapeutic drug monitoring (TDM)?

A

Optimising patient individual therapy using:

(1) Drug levels
(2) Pharmacokinetics
(3) Pharmacodynamics

107
Q

What is TD50?

A

Median toxic dose

108
Q

What is ED50?

A

Median effective dose

109
Q

When is TDM used?

A
  • Drugs with a narrow therapeutic range
  • Drugs with a low therapeutic index
  • Drugs where dose and effect are not strongly correlated
  • Drugs with wide variance in patient clearance
110
Q

What is LD50?

A

Median lethal dose

111
Q

What should Cp be in practice?

A

Steady state

Takes about 5 times the half-life to reach this point

112
Q

Do analytical methods distinguish between bound and unbound drug in blood plasma concentration? If so, which method(s)?

A

No.

Analytical methods give total Cp levels

Give no distinction

113
Q

What is important when considering implementation of a second drug which interacts with the protein-binding of a strongly protein-bound first drug?

A

Increase in free (as opposed to protein-bound) will be PROPORTIONATELY significant

Likely to cause the patient a problem

114
Q

What is important when considering implementation of a second drug which interacts with the protein-binding of a strongly protein-bound first drug?

A

Increase in free (as opposed to protein-bound) will be PROPORTIONATELY insignificant

Not likely to cause the patient a problem

115
Q

What could cause a disproportionate rise/ increase in the blood plasma level of a highly protein-bound drug?

A

Saturation of protein binding sites

116
Q

How are Vd and Clearance values determined?

A

From an average of the population

117
Q

How do Vd and Clearance values differ for specific drugs in TDM?

A

(1) Begin with average population values

(2) Adjust for individual patients

118
Q

How are Vd and Clearance values adjusted to be more specific for the patient?

A

(1) Patient CpSS (steady state) is measured
(2) Compare with expected average population values
(3) Adjust KE (rate of elimination) to better match drug clearance in individual patient
(4) Use patient-specific Clearance values for future dosing calculations

119
Q

If the individual/ specific Clearance or Vd values vary significantly from the average values from the population, why could this be?

A
  • Concurrent drug therapy (interaction)
  • Compliance
  • Medication error
  • Malabsorption
  • Incorrect assay results

Specific patient may be genuinely different from average population data

120
Q

How can specific/ individual patient clearance be estimated PRIOR to waiting for steady state blood plasma concentration being achieved?

A

Blood sample taken

Measure of creatinine clearance

121
Q

How is creatinine produced?

A

Creatinine is a breakdown product of creatine phosphate in muscles

122
Q

Where is creatine phosphate broken down?

A

In muscles

123
Q

What does creatine phosphate produce when broken down?

A

Creatinine

124
Q

At what rate is creatinine produced?

A

Constant rate

125
Q

Does creatinine protein-bind?

A

No

126
Q

Is creatinine reabsorbed in the kidneys?

A

No, almost entirely not

127
Q

What is creatinine clearance a useful measure of?

A

(1) Kidney function
(2) Predicted patient-specific drug clearance
(3) Approximation of actual glomerular filtration rate

128
Q

How can actual glomerular filtration rate be approximated?

A

Measurement of creatinine clearance

mg/mL

129
Q

What is C(urine)?

A

Creatinine concentration in the urine

130
Q

What is V(urine)?

A

Volume of urine collected in mL/min

131
Q

What is C(plasma)?

A

Creatinine concentration in the plasma

mg/mL

132
Q

What are the units for creatinine clearance?

A

mL/minute

Clearance has units of volume per time

133
Q

What equation is used to measure creatinine clearance definitively?

A

CLcr = {C(urine) x V(urine)} / C(plasma)

134
Q

What equation is used to measure creatinine clearance approximately?

A

Cockcroft-Gault equation

CLcr(est) = {(140-age) x Weight x Constant} / C(s)

135
Q

In an equation, what does C(s) represent?

A

Serum creatinine

136
Q

What is the constant used, for men, to calculate estimated creatinine clearance?

A

1.23

137
Q

What is the constant used, for women, to calculate estimated creatinine clearance?

A

1.04

138
Q

What is the significance of 1.23, regarding elimination?

A

Creatinine clearance

Constant (numerator) for MEN

139
Q

What is the significance of 1.04, regarding elimination?

A

Creatinine clearance

Constant (numerator) for WOMEN

140
Q

What is the Cockcroft-Gault equation?

A

CLcr(est) = {(140-age) x Weight x Constant} / C(s)

141
Q

What is the Cockcroft-Gault equation used for?

A

Estimation of creatinine clearance for an individual

142
Q

What happens to serum creatinine concentration as GFR decreases?

A

Increases

Less creatinine is being cleared

143
Q

What drug categories is TDM used for?

A

(1) Antiepileptics
(2) Aminoglycoside antibiotics
(3) Cardiac drugs - e.g. digoxin, lidocaine
(4) Others - theophylline, lithium, methotrexate

144
Q

What are anti-epileptics used for?

A

Treating/ prophylaxis of seizures

145
Q

What are example(s) of the ‘old-style’ anti-epileptic drugs?

A
  • Phenytoin
  • Carbamazepin
  • Sodium valproate/ valproic acid
146
Q

What are example(s) of the ‘new-style’ anti-epileptic drugs?

A

Gabapentin

147
Q

What is phenytoin?

A

An old-style anti-epileptic drug

148
Q

(1) What is the therapeutic range of phenytoin?

(2) What happens if there is an overdose?

A

(1) 10-20mg/L

2
- Blurred vision
- Drowsiness

149
Q

How significantly is phenytoin metabolised?

A

Heavily metabolised

150
Q

Is phenytoin protein bound?

A

Yes. Highly protein bound

151
Q

What is Vmax?

A

Reaction rate when binding site is fully saturated

Maximum rate of reaction

152
Q

In an equation, what does V refer to?

A

Rate of reaction

153
Q

In an equation, what does K(m) stand for?

A

Michaelis-Menten constant

154
Q

How is the daily dose of a drug, such as phenytoin, calculated?

A

Daily dose = (Vmax x CpSS) / (Km + CpSS)

155
Q

How is Vmax for a drug derived?

A

Calculated from population data

Population average for that specific drug

156
Q

How is Km for a drug derived?

A

Calculated from population data

Population average for that specific drug

157
Q

What is Km?

A

The substrate concentration when the rate of reaction is 1/2 of Vmax

158
Q

What is the equation used to calculate steady state blood plasma (CpSS), with regard to daily dose?

A

CpSS = (Daily dose x Km) / (Vmax - Daily dose)

159
Q

What is lithium indicated for?

A
  • Acute mania

- Prophylaxis of manic depression

160
Q

Describe the therapeutic window of lithium.

A

Narrow

0.4-1.2mmol/L

161
Q

What is the effective dose for lithium?

A

Varies significantly from patient to patient

162
Q

What are the effects of toxicity/ overdose of lithium?

A
  • Blurred vision
  • Drowsiness
  • Confusion
  • Palpitations
163
Q

Define teratogen.

A

A factor which causes malformation of an embryo

164
Q

Does lithium require therapeutic drug monitoring (TDM)?

A

Yes.

Because the therapeutic dose varies SIGNIFICANTLY in patients

165
Q

Describe metabolism of lithium.

A

Not metabolised

166
Q

Describe the excretion of lithium, relating to rate clearance.

A

First order elimination

Clearance approximates to 25% of creatinine clearance

167
Q

How does the clearance of lithium compare to the clearance of creatinine?

A

Approximates to 25% of creatinine clearance

168
Q

What can decrease the elimination of lithium?

A
  • Decreased renal function
  • Diuretics
  • most NSAIDs
169
Q

What can increase the elimination of lithium?

A
  • Aminophylline

- OTC antacids

170
Q

What is aminophylline?

A

A compound of theophylline

A bronchodilator

171
Q

What formulations are available for lithium?

A

(1) Oral solids:
- e.g. lithium carbonate

(2) Oral liquids:
- e.g. lithium citrate

172
Q

What is the therapeutic range of lithium, in mmol per litre?

A

0.4-1.2mmol/L

173
Q

How much does 1mmol of lithium weigh?

A

Mr of lithium = 7

Therefore, 1mol = 7g, so 1 mmol = 7mg

174
Q

What is the therapeutic range of lithium, in mg per litre?

A

2.8-8.4 mg/L

175
Q

What is the salt factor for lithium carbonate?

Lithium carbonate = Li2CO3

A

0.19

176
Q

Describe the therapeutic range of theophylline.

A

Narrow therapeutic range

5-15 mg/L

177
Q

When is toxicity reached in theophylline?

A

> 20 mg/L

178
Q

What are the symptoms of theophylline toxicity?

A
  • Arrhythmias

- Seizures

179
Q

Describe the inter-patient variability of theophylline?

A

Significant inter-patient variability

180
Q

What was theophylline previously indicated for?

A

COPD

181
Q

Why is theophylline no longer widely used for treatment of COPD?

A

There are now longer-acting inhaled agonists available

182
Q

What is the most common formulation of theophylline?

A

Sustained-release

183
Q

Describe the rate of elimination of theophylline?

A

First order elimination

184
Q

What causes the significant variation in clearance of theophylline?

A

(1) Age
(2) Liver cirrhosis - decreases clearance/ elimination
(3) Cystic fibrosis - increases clearance/ elimination
(4) Co-medication

185
Q

Describe the effect of liver cirrhosis on clearance/ elimination of theophylline.

A

Decreases clearance/ elimination

Due to reduced hepatic clearance - metabolism

Decreased by 40%

186
Q

Describe the effect of cystic fibrosis on clearance/ elimination of theophylline.

A

Increases clearance/ elimination

187
Q

Describe the effect of phenytoin on clearance/ elimination of theophylline.

A

Increases clearance/ elimination

Increased by 75%

188
Q

Describe the effect of oral contraceptives on theophylline clearance/ elimination.

A

Decreases clearance/ elimination

Decreased by 30%

189
Q

Describe the effect of acute pulmonary oedema on clearance/ elimination.

A

Decreased by 50%

190
Q

Describe the effect of congestive heart failure on clearance/ elimination.

A

Decreased by 40%

191
Q

Define congestive heart failure.

A

Fluid build up in the heart

Creates inefficiency of heart pumping

192
Q

Describe the effect of liver cirrhosis on clearance/ elimination.

A

Decreased by 40%

193
Q

Describe the effect of mild smoking on clearance/ elimination.

A

Increased by 50%

194
Q

Describe the effect of heavy smoking on clearance/ elimination.

A

Increased by 100%

195
Q

How do the effects of heavy smoking and mild smoking on clearance/ elimination compare?

A

Mild - Increase by 50%

Heavy - Increase by 100%

196
Q

Define cystic fibrosis.

A

Condition where the lungs become filled with thick, sticky mucous

197
Q

Describe the effect of propranolol on clearance/ elimination.

A

Decreased by 30%

198
Q

Describe the effect of oral contraceptives on clearance/ elimination.

A

Decreased by 30%

199
Q

Describe the effect of cimetidine on clearance/ elimination.

A

Decreased by 40%

200
Q

What is cimetidine?

A

H2 receptor antagonist

Reduces stomach acid production

201
Q

Describe the effect of carbamazepine on clearance/ elimination.

A

Increased by 50%

202
Q

Describe the effect of phenytoin on clearance/ elimination.

A

Increased by 50%

203
Q

Describe the effect of rifampicin on clearance/ elimination.

A

Increased by 50%

204
Q

Why are biologics/ biomacromolecules not suitable for oral administration?

A

Broken down by proteases in the GIT

205
Q

How are biologics/ biomacromolecules administered?

A

(1) IV - most common
(2) SC - leads to lymphatic system
(3) IM

206
Q

How are biologics/ biomacromolecules distributed in the body?

A

Vascular space -> Lymphatic system

via interstitial tissue space

207
Q

How does the volume of distribution (Vd) vary in biologics/ biomacromolecules?

A

8-20L

208
Q

Define catabolism.

A

Metabolic pathway which breaks down molecule into smaller sub-components

209
Q

Describe the elimination of biologics/ biomacromolecules.

A

Too large to be filtered by the kidneys

Usually reabsorbed in the kidney

Mostly eliminated via intracellular catabolism

210
Q

(1) What are biologics/ biomacromolecules broken down into?

(2) How are they broken down?

A

(1) Constituent amino acids

(2) Intracellular catabolism

211
Q

Describe the t(1/2) of a biologic/ biomacromolecule.

A

Typically very long half-life

Measured in days

212
Q

What effect does the long half-life of biologics/ biomacromolecules have on dosing?

A

Long dosing intervals

213
Q

What does ‘MAB’ refer to?

A

Monoclonal antibody

214
Q

How is a monoclonal antibody abbreviated?

A

MAb

Part 3 – PM3B (32 decks)

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