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Phase 2a - ICS > Pharmacokinetics in practice and pharmacogenomics > Flashcards

Pharmacokinetics in practice and pharmacogenomics Flashcards

1
Q

First order kinetics

A

Rate of elimination is proportional to the plasma drug concentration (does not become saturated).

A constant % of the plasma drug is eliminated over a unit of time.

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2
Q

Zero order kinetics

A

Rate of elimination is NOT proportional to the plasma drug concentration (metabolism processes become saturated).

A constant amount of plasma drug is eliminated over a unit of time.

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3
Q

Cmax

A

Maximum plasma concentration

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4
Q

Tmax

A

time taken to reach cmax

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5
Q

Clearance (CL)

A

removal of drug by all eliminating organs

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6
Q

Slower absorption

A

Increased tmax

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7
Q

MR formulation caused less complete absorption from GI tract

A

reduced Cmax

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8
Q

Modified release formulations usually require…

A

Less frequent dosing

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9
Q

In IV drugs bioavailability is 100%

A

Therefore absorption and tmax are NOT relevant

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10
Q

t1/2

A

Time taken for plasma drug concentration to fall 50%

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11
Q

Half life t1/2 depends on

A

Clearance and volume distribution .

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12
Q

A drug with large Vd

A

Cleared more slowly

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13
Q

A drug with small Vd

A

Cleared rapidly

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14
Q

t1/2 is NOT dependent on

A

Dose or formulation

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15
Q

A drug will be 97% cleared from the body after

A

5 half lives

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16
Q

Gentamicin

A

Small molecule, hydrophilic, small distribution - t1/2= 2-3 hours

17
Q

Digoxin

A

Small molecule, lipophilic, t1/2= 30-40 hours.

18
Q

If a drug has short 1/2 life it needs

A

More frequent dosing

19
Q

If there is an organ dysfunction

A

t1/2 may be increased

20
Q

How is t1/2 relevant in clinical practice?

A

ADR and management of toxicity (how long it takes for the symptoms to revolve)

21
Q

Short t1/2 increases the risk of what?

A

Discontinuation/withdrawal symptoms - weaning dose on cessation.

22
Q

STAT doses are useful in

A

Treating acute conditions.
Effect wears off after a few minutes/hours.

*Most drugs require repeated dosing for a more prolonged therapeutic effect.

23
Q

Steady state

A

Rate of drug input is equal to rate of drug elimination.

24
Q

Css

A

Drug plasma concentration at steady state

25
Q

Time to Css

A

5x t1/2 (after initiation and dose increase)

26
Q

Continuous IV infusion

A

Infusion rate can be titrated up and down to achieve desired therapeutic effect:
- critical care patients
- abx
- unfractionated heparin
- GA

27
Q

Does a dose reduction affect Css in continuous infusion?

A

No - t1/2 remains the same

28
Q

A 50% dose reduction in continuous IV leads to

A

50% reduction in Css

29
Q

A reduced clearance rate…

A
  • Increases t1/2
  • Time to Css increases (5x t1/2)
  • Css increases

***Dose reduction is required

30
Q

Repeat IV dosing

A

Peaks and troughs in plasma concentration causing oscillation around the mean.

Time to Css does not change.

31
Q

What can be done to reduce time to steady state?

A

A loading dose can be administered.

Digoxin
Vancomycin
Teicoplanin
Amiodarone
Heparin

32
Q

Why is steady state important?

A

Aims for Css which is between
maximum safe concentration MSC
and
minimum effection concentration MEC.

Between the two is the therapeutic window.

33
Q

Zero order kinetics

A

Drugs are metabolised by an amount (e.g in mg) in a unit of time

Metabolism is dependent on mechanisms that become saturated

Elimination is irrespective of plasma concentration

Small increases in dose may cause large increases in plasma concentration

There caution needed when adjusting doses

Ethanol and pehnytoin.

34
Q

Drugs with narrow therapeutic window

A

Drugs with a narrow window between MEC and MSC

Can have first order or zero order kinetics

Monitor drug plasma levels to ensure efficacy and avoid toxicity (therapeutic drug monitoring - TDM)

Levels are taken pre-dose (trough)/post dose (peak) or occasionally both

Levels may be affected by: organ dysfunction, albumin levels, disease states, drug interactions, patient compliance

35
Q

What are examples of narrow therapeutic window drugs?

A

Vancomycin, gentamicin, pehnytoin, digoxin, theophylline, lithium

36
Q

Pharmacogenomics

A

‘The use of genetic and genomic information to tailor pharmaceutical treatment to an individual.’

37
Q

Why is pharmacogenomics useful to prescribe drugs?

A

Patient’s genome is used to identify most appropriate treatment and dose.

38
Q

Genomic variations can results in differences in drug

A

Pharmacodynamics: variations in drug receptor (efficacy variations and increased ADR)

Pharmacokinetics: variations in drug metabolism.

39
Q

Example of application of pharmacogenomics?

A

Abacavir - variant HLA-B
Tested - swapped if needed

Phase 2a - ICS (43 decks)

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