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Membranes And Receptors > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

Where does the majority of drug metabolism occur?

A

Liver

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2
Q

Where does drug excretion occur?

A

Kidneys

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3
Q

What is the pharmaceutical process and what does it depend on?

A

If the drug is getting into the patient

Depends on: formulation and compliance

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4
Q

Rate of action depends on …

A

Dissolution

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5
Q

What is topical administration?

A

Giving the drug directly to the target (eg. Inhaled steroids for asthma)

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6
Q

What are the advantages of topical administration?

A

Less systemic absorption

Less off-target (side) effects

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7
Q

Define oral bioavailability

A

The proportion of drug given orally (or any route except IV) that reaches circulation unchanged

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8
Q

What is the formula for bioavailability?

A

(AUC oral / AUC injected) x100

AUC = area under curve where x=time, y=plasma conc of drug

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9
Q

What is the formula for therapeutic ratio?

A

LD50 / ED50

Maximum tolerated dose / minimum effective dose

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10
Q

Does warfarin have a narrow or wide therapeutic window, and what does this mean?

A

Narrow

Easy to produce unwanted effects

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11
Q

Define toxic concentration

A

The concentration that starts to produce unwanted, adverse effects

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12
Q

Which drugs are less likely to reach toxic conc, fast or slow release?

A

Slow release

With fast release drugs the conc rises very rapidly

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13
Q

Describe first pass metabolism

A

Drugs administered orally are exposed to the liver first and may be extensively metabolised. This means much less drug is received by the systemic circulation.

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14
Q

Name alternative routes that avoid first pass metabolism

A

Parenteral (IV, IM, SC)
Rectal
Sublingual

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15
Q

Define volume of drug distribution

A

The theoretical value into which drug is distributed if this occurred instantaneously

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16
Q

How do we obtain the value for volume of distribution?

A

Extrapolation of the plasma drug concentrations on a graph back to time zero

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17
Q

Protein binding interactions are important when the object drug:

A

Is highly bound to albumin
Has a small volume of distribution
Has a low therapeutic ratio

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18
Q

What is another name for the object drug?

A

Class I drug

19
Q

What is another name for the precipitant drug?

A

Class II drug

20
Q

Describe a class I drug alone

A

Dose lower than number of albumin binding sites
Most drug molecules bound to albumin
Free drug concentration low
Little effect

21
Q

Describe a class II drug alone

A

Doses greater than the number of binding sites
Most albumin sites contain a drug molecule but the free drug concentration is still significant
More effective alone than class I is alone

22
Q

Describe class I and class II drugs together

A 
Displacement of class I from binding sites
Free concentration of class I drug increased
Class I drug effect increased than if it were alone
23
Q

Define 1st order kinetics

A

The rate of elimination is proportional to drug concentration in the body

24
Q

Define zero order kinetics

A

Rate of elimination is constant, no matter the drug concentration in the body

25
Q

How do you spot 1st order kinetics on a graph?

A

x = time
y = plasma conc (linear or log)
Linear scale - graph is curved
Log scale - graph is straight line

26
Q

How do you spot zero order kinetics on a graph?

A

x = time
y = plasma conc in linear scale
Graph will be a straight line

27
Q

At lose doses, drug concentration has ……kinetics

A

1st order

28
Q

At high doses, drug metabolism has ……. kinetics

A

Zero order

As maximum rate of elimination is reached

29
Q

On repeated drug administration, how long does it take to reach a steady state?

A

5 half lives

30
Q

Define bolus

A

The administration of a distinct amount of drug in order to raise its concentration in blood to an effective level

31
Q

Which kinetics have a more predictable therapeutic response and why?

A

1st order kinetics
(Double dose = double action)
The therapeutic response of zero order kinetics can suddenly escalate as elimination mechanisms saturate

32
Q

What occurs during phase I of drug metabolism?

A

Oxidation, reduction and/or hydrolysis

Drug usually inactivated

33
Q

What occurs during phase II of drug metabolism?

A

Conjugation products formed
Conjugated to make them more soluble
Drugs usually completed inactivated by the end of this phase

34
Q

What type of enzymes work at phase II?

A

Mixed function oxidases

35
Q

Name 3 properties of mixed function oxidases

A

Affinity for lipid soluble drugs
Low substrate specificity
Inducible and inhibitable

36
Q

Drug interactions matter most clinically when:

A

Drug has a low therapeutic ratio
Drug is being send at the minimum effective concentration
Drug metabolism follows zero order kinetics

37
Q

What are the effects of drug metabolism enzyme inducers and give an example?

A

Increase rate of drug metabolism
Drug is less effective

Rifampicin is an enzyme inducer of the oral contraceptive pill

38
Q

What are the effects of drug metabolism enzyme inhibitors and give an example?

A

Inhibits drug metabolism
Drug concentration can be excessive, may be toxic

Cimetidine is an enzyme inhibitor of warfarin

39
Q

If the drug is a weak acid, what conditions will increase and decrease reabsorption in the kidneys?

A

Acid urine = increases reabsorption of drug (drug is less likely to dissociate into its ions)
Alkali urine = decreases reabsorption

40
Q

If the drug is a weak base, what conditions increase and decrease reabsorption of the drug in the kidneys?

A

Acid urine = decreases reabsorption

Alkali urine = increases reabsorption

41
Q

How do we speed up aspirin elimination if someone has an overdose?

A

Aspirin is a weak acid therefore we must infuse the patient with bicarbonate (alkali) to speed up elimination

42
Q

What are the pH ranges for acidic and alkali urine?

A

Acid - pH

43
Q

Describe the effects of renal disease on drug excretion

A

Drugs will have a longer half life due to less excretion from kidneys
Patient needs a lower maintenance dose of drug
Takes a longer time to reach the steady state

Membranes And Receptors (14 decks)

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