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ICPP > Pharmacodynamics > Flashcards

Pharmacodynamics Flashcards

1
Q

What is the pharmaceutical process?

A

Is drug getting into patient?

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2
Q

What is the pharmacokinetic process?

A

Is drug getting to site of action?

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3
Q

What is the pharmacodynamic process?

A

Is drug producing desired effect?

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4
Q

What is the therapeutic process?

A

Is this translated to a therapeutic effect?

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5
Q

What does rate of drug action depend on?

A

Rate of action depends on dissolution e.g soluble aspirin used to treat MI rather than tablet

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6
Q

What are some drug delivery methods?

A
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7
Q

What is Oral Bioavailability of a drug?

A

Proportion of drug given orally (or any other route except iv) that reaches circulation unchanged..

Measured by:

– Amount (depends on 1st pass metabolism and gut absorption)

– Rate (depends on pharmaceutical factors, gut absorption

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8
Q

Give an equation for working out oral bioavailabity from a graph

A
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9
Q

What is therapeutic ratio?

A
  • Defined as LD50/ED50
  • Maximum tolerated dose / minimum effective dose
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10
Q

What is the difference between a fast and slow release prep?

A
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11
Q

What is the difference between oral and intravenous administration?

A
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12
Q

How can first pass metabolism be avoided?

A

–Parenteral (iv,im,sc)
– Rectal (note drainage to both portal and systemic systems)

– Sublingual (e.g. use of glyceryl trinitrate in angina)

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13
Q

What is volume of distribution determined by?

A

– Theoretical volume into which drug is distributed if this occurred instantaneously

– Obtained by extrapolation of plasma levels to zero time

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14
Q

Why is free drug concentration important?

A

Free drug determines its action at receptor

Displacement of drugs from binding sites causes Protein Binding Drug Interactions

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15
Q

When are protein binding interactions important?

A

Protein Binding interactions are important when object drug:

– Is highly bound to albumin (>90%)

– Has a small volume of distribution

– Has a low therapeutic ratio

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16
Q

What is the difference between a class 1 drug and class 2 drug? (with respect to protein binding)

A
  • Class I drug (object drug) is used at dose lower than number of albumin binding sites
  • Class II drug (precipitant) drug is used at doses greater than number of binding sites, and thus displaces the Class I drug
17
Q

Describe the nature of drug binding to proteins

A
  • Binding interactions are transient
  • Although free drug levels rise (i.e. greater effects at receptors), Elimination rate will also rise (since this depends on Free drug levels). Steady state is restored quickly in a few days.
18
Q

Give two examples of object drugs and their precipitant drugs

A
  • Warfarin (used for AF, TIA). Precipitant Drugs are Sulfonamides, Aspirin, Phenytoin.
  • Tolbutamide (used for NIDDM). Precipitant drugs are sulfonamides, Aspirin.
19
Q

Describe drug elimination

A

Metabolism – predominantly liver

Excretion – predominantly renal

20
Q

Describe the difference between first and zero order kinetics

A

1st order kinetics:

Rate of elimination is proportional to drug level. Constant fraction of drug eliminated in unit time. Half life can be defined.

Zero Order kinetics:
Rate of elimination is a constant.

21
Q

How are first order drug kinetics shown on a graph?

A
22
Q

How are zero order drug kinetics shown on a graph?

A
23
Q

Describe the relationship between dosage and kinetics

A
24
Q

How is steady state achieved in repeated drug administration?

A

During repeated drug administration, a new steady state is achieved in 5 half lives. This is irrespective of dose or frequency of administration.

E.G. Digoxin Half life- 36h. If maintenance dose used, will take 5 x 36 h (180 h) to steady state.

25
Q

What are loading doses?

A

If the half life is long and a rapid effect is desired, use a loading dose.

This is often determined by the volume of distribution.

26
Q

Why is the kinetics of a drug relevant?

A
27
Q

Describe how the liver functions to metabolise drugs

A

Mixed function oxidases (liver microsomal enzyme) consists of cytochrome P450 reductase

Main CYP isoenzymes 1A2, 2C9, 2C19, 2D6, 3A4

– Low substrate specificity
– Affinity for lipid soluble drugs

28
Q

When are drug interactions in metabolism likely to matter clinically?

A
  • Drugs with low therapeutic ratio
  • Drug is being used at minimum effective concentration (e.g. OC pill)
  • Drug metabolism follows zero order kinetics
29
Q

Give some examples of drug interactions clinically

A
30
Q

Describe the process of renal excretion of drugs

A
  • Only the free fraction of drug is filtered
  • Drugs can be actively secreted by the tubules (e.g. penicillin secreted by proximal tubule)
31
Q

How is pH linked to reabsorption?

A

Passive reabsorption of drug is dependent on pH.

  • pK of drug is pH at which half of it is ionised, half is non-ionised
  • Only the non-ionised moiety is lipid soluble and crosses membranes easily
32
Q

Describe the renal excretion of weak acids

A
33
Q

Describe the renal excretion of weak bases

A
34
Q

Describe the renal clearance of aspirin, and how it is affected by pH

A
35
Q

What are factors to consider in prescribing for renal disease?

A
  • If drug is excreted by kidneys, half lives of drug are longer. Lower maintenance dose of the drug.
  • longer half lives also means longer time to reach a steady state (remember it takes 5 half lives to reach equilibrium).
  • Loading dose can be altered.
  • Protein binding can be altered

ICPP (10 decks)

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