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ESA 2 Membranes and Receptors > Pharmacokinetics (9) > Flashcards

Pharmacokinetics (9) Flashcards

0
Q

What is the pharmacokinetic process?

A
  • Drug getting to site of action
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1
Q

What is meant by a pharmaceutical process?

A
  • Drug getting into patient
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2
Q

What is meant by the pharmacodynamic process?

A
  • Is the drug producing the desired effect.
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3
Q

What is meant by the therapeutic process?

A
  • Drug is translated into a therapeutic process
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4
Q

In the pharmaceutical process what is meant by formulation and compliance?

A
  • Formulation: tablets/liquid - rate of action depends on dissolution
  • Compliance: E.g take once a day
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5
Q

What are the advantages of using specific sites of administration?

A
  • Concentrates drug at site of action

- Less systemic absorption and less side effects

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6
Q

What is meant by the oral bioavailability of a drug?

A
  • Proportion of the drug given orally that reaches circulation unchanged
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7
Q

How is bioavailability measured?

A
  • Amount: depends on 1st pass and gut absorption

- Rate: depends on pharmaceutical factors and gut absorption

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8
Q

What does the graph of injected and oral administration of a drug look like. Plasma conc against time

A
  • Injected has immediately high initial amount and decreases linearly over time
  • Oral has a slow increase to a much lower peak then plateaus and decreases slowly
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9
Q

What is the therapeutic window?

A
  • The drug concentration between the minimum effective dose and maximum tolerated dose before it becomes toxic.
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10
Q

How can you change the drug to affect the therapeutic window?

A
  • Can’t change the therapeutic window but can change the release rate, a slower overall release will allow the drug conc to remain in the therapeutic window for longer.
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11
Q

What is meant by first pass metabolism?

A
  • Drugs that are administered orally are first exposed to the liver
  • Here they may be extensively metabolised before reaching rest of body
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12
Q

How can first pass metabolism be avoided?

A
  • Injections: IM, IV and SC
  • Rectal (drains to portal and systemic systems)
  • Sublingual (under the tongue)
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13
Q

What is volume of distribution?

A
  • The theoretical volume into which the drug is distributed if this occurred instantaneously
  • Obtained by extrapolation of plasma levels to 0 time
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14
Q

What are the two possible fates for free drugs?

A
  • Reaches target receptor

- Elimination (kidney/liver)

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15
Q

When are protein binding interactions important?

A
  • When highly bound to albumin (>90%)
  • Has small volume of distribution
  • Has low therapeutic ratio
16
Q

What is a class 1 drug?

A
  • Object drug

- Used at a dose lower than number of albumin binding sites

17
Q

What is meant by a class 2 drug?

A
  • Precipitant

- Used at doses greater than the number of binding sites and thus displacing class 1 drugs

18
Q

What is meant when binding interactions are said to be transient?

A
  • If free drug levels rise so will the elimination rate
  • Steady state is restored quickly in a few days
  • Transient = short lived
19
Q

Give an example of an object drug and its precipitant.

A
  • Warfarin: sulfonamides, aspirin, phenytoin

- Tolbutamide: sulfonamides, aspirin

20
Q

If you graphed 1st order kinetics what would it look like and why?

A
  • Linear on a log y axis against time
  • Rate of elimination is proportional to drug level
  • Constant half life
21
Q

What is the characteristic of zero order kinetics?

A
  • The rate of elimination is constant
22
Q

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

A
  • 5 half lives

- Irrespective of dose/frequency of administration

23
Q

What can be implemented if the half life of a drug is long but a rapid response is needed?

A
  • Implement a loading dose

- Often determined by volume of distribution.

24
Q

What is the most common way for drugs to act in?

A
  • 1st order

- Predictable therapeutic response from dose increase

25
Q

Which drugs undergo zero order reactions?

A
  • Alcohol & pheryroin

- Therapeutic response can suddenly escalate as elimination mechanism saturates

26
Q

What are the 2 main methods of drug elimination?

A
  • Metabolism: predominantly liver

- Excretion: predominantly renal

27
Q

How are drugs eliminated in metabolism?

A
  • Drug enters phase 1 or phase 2
  • Phase 1: drug is oxidised/reduced/hydrolysed which either activated/inactivates or doesn’t change the drug
  • Phase 2: conjugation of products normally inactivates the drug
28
Q

What are the different types of drug interactions and give some examples.

A
  • Enzyme inducer: Phenobarbitone, Rifampicin, cigarette smoke
  • Enzyme inhibitor: Cimetidine, Warfarin
  • Drug affected: Warfarin, phenytoin, OC pill, Theophylline
29
Q

How does renal elimination occur?

A
  • Via the glomerulus filtration

- Only free drugs can be filtered

30
Q

What happens at the proximal tubule?

A
  • Active secretion into the tubule
31
Q

What happens in the distal tubule?

A
  • Passive reabsorption of lipid-soluble un-ionised drug
32
Q

What happens in the collecting duct?

A
  • Ionised, lipid-insoluble drug excretion in to urine
33
Q

Passive reabsorption of a drug is dependent on what in the kidneys?

A
  • pH
34
Q

What effect does pH have on absorption in the kidney?

A
  • Only non-ionised moiety is lipid soluble and crosses membrane easily
35
Q

What are the best conditions for a weak acid/base to be absorbed in the kidneys?

A
  • Weak acids: acidic urine increases absorption

- Weak base: alkaline urine increases absorption

36
Q

What affect does being secreted by the kidneys have on a drug?

A
  • Half lives are longer
37
Q

As the half lives are longer what is needed clinically when treating?

A
  • Lower maintenance dose of drug (otherwise accumulates and becomes toxic levels)
  • Loading does and protein binding can be altered to compensate for a longer half life.

ESA 2 Membranes and Receptors (11 decks)

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