Session 1 - Pharmacokinetics Flashcards

1
Q

What does ADME stand for?

A

Absorption
Distribution
Metabolism
Elimination

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2
Q

What are two potential routes drugs can be administered?

A

Oral and parenteral

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3
Q

What is oral administration?

A

Enter via GI tract, sublingual or rectal

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4
Q

What is parenteral admin?

A

Any route that doesn’t involve GI tract

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5
Q

What are two overarching factors which effect peak plasma concentration of a drug?

A

Rate of uptake of a drug and first pass metabolism

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6
Q

Give four factors which can effect systemic entry of a drug

A

Gastrointenstinal motility, splanchnic blood flow, molecular size, pH levels

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7
Q

What is first pass metabolism?

A

Any metabolism drug undergoes before reaching systemic circulation. This occurs via liver, gut lumen or gut wall.

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8
Q

How can the gut lumen effect drugs?

A

Gastric acid or proteolytic enzymes

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9
Q

How can gut wall effect drugs?

A

Glycoprotein efflux pumps drugs out of intenstinal enterocyte back into the lumen

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10
Q

What is bioavailability?

A

The amount of drug which reaches the systemic circulation in an unchanged form relative to that if administered via IV.

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11
Q

How is bioavailability calculated?

A

Amount of drug reaching systemic circulation/total amount of drug adminstered

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12
Q

What is the difference between oral bioavailability and bioavailability?

A

Oral bioavailability is normally synonymous with bioavailability, yet specifically refers to when drug is administered orally. It can be calculated by AUCoral / AUCintravenous.

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13
Q

Why is bioavailabiity different between patients?

A

Affected by intestinal motility, food, age and first pass metabolism

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14
Q

What are the main factors which determine drug distribution? (ability to “dissolve” in the body)

A

Lipophilicity/hydrophilicity

Protein binding

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15
Q

What is an object drug?

A

Amount of drug administered lower than the binding site numbers (warfarin)

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16
Q

What is a prepicitant drug?

A

Number of molecules administered higher than the number of binding sites (aspirin/phenytoin)

17
Q

When can changes to protein binding happen physiologically?

A

From factors such as hypoalbuminaemia, pregnancy, renal failure, or displacement by other drugs

18
Q

When will physiological changes in protein binding be important?

A
  • High protein binding
  • Low Vd
  • Drug has a narrow therapeutic ratio
19
Q

What is volume of distribution?

A

Vd (l/kg) = total amount of drug in the body/plasma conc of drug (at time =0)

20
Q

What does a larger Vd mean?

A

The more drug distributes throughout the body

21
Q

What facotr is Vd proportional to?

A

The half life of the drugs

22
Q

What main factors in Vd affected by?

A

Protien binding

23
Q

What causes acute changes in Vd?

A

Sepsis (increased vascular permeability), concurrent drugs (binding site taken up, lower Vd), hypoalbuminaemia

24
Q

What is the family of enzymes necessary for phase 1 reactions?

A

CYP450

25
Q

Give a few drugs which induce CYPs

A

Phenytoin, Carbamazapine, Barbiturates, Rifampicin, Alcohol, and Sulphonylureas (PCBRAS)

26
Q

Give a few drugs which inhibit CYPs

A

Omeprazole, Disulfiram, Erythromycin, Valproic acid, Isoniazid, Cimetidine, Ethanol (acute) and Sulphonamides (O-DEVICES)

27
Q

What three factors determine the rate of renal excretion of drugs?

A

GFR, passive tubular reabsorption and active tubular secretion

28
Q

What is clearance?

A

a measure of both hepatic clearance and renal clearance; any reduction in GFR will reduce renal clearance so increase a drugs t1/2.

29
Q

What are needed to excrete drugs into nephron lumen?

A

Organic Anion and Cation Transporters (OAT and OCT) act as renal transporters (via active transporter.
defined as the rate of elimination of a drug from the body

30
Q

What three factors affect clearance?

A

HRH
Heart
Renal
Hepative

31
Q

How does heart affect clearance?

A

Cardiovascular system factors affect blood flow to the main organs of elimination

32
Q

How can you determine half life?

A

By using Vd and clearance levels

t1/2 = 0.693 x Vd/ Clearance

33
Q

Define half life

A

‘the amount of time over which the concentration a drug in plasma decreases to once half of the concentration value it had when measured

34
Q

What are 1st order kinetics?

A

rate of elimination is proportional to drug level. Constant fraction of drug eliminated in unit time and a half life can be defined.

35
Q

What are 0 order kinetics?

A

rate of elimination is constant and no half life can be defined. Drug monitoring is essential.

36
Q

How can drugs administration be tailored to maintain a steady state?

A

During repeated drug administration, a new steady state (Steady State Concentration in Plasma (CpSS)) can be achieved allowing levels to stay within a therapeutic window

37
Q

How do you calculate CpSS?

A

CpSS = dose rate / clearance.

38
Q

What is a loading dose?

A

When a clinician wants to achieve a CpSS within the therapeutic window quickly (i.e. without waiting for 4-5 half lives), a loading dose (DoseL) can be used

39
Q

How is loading dose calculated?

A

Loading Dose (DoseL) = Vd x CpSS