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Medsci 204 > ADME > Flashcards

ADME Flashcards

1
Q

How does one typically get a drug past all of the barriers within the body?

A

LARGE drug dosage

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2
Q

What is albumin?

A

Plasma protein

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3
Q

What is the organ associated with the metabolism of drugs?

A

Liver

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4
Q

What is the organ associated with the excretion of drugs?

A

Kidneys

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5
Q

4 mechanisms of transport across a membrane.

A

Passive diffusion, facilitated diffusion, active transport and endocytosis.

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6
Q

What type of drug is usually taken up via endocytosis?

A

Those with a high molecular weight (>1000)

Including cytokines, GF’s, hormones, etc.

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7
Q

What is the most important mechanism of transport?

A

Passive Diffusion

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8
Q

Can active transport become saturated?

A

Yes.

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9
Q

Name two sites where filtration occurs.

A

Blood capillaries and glomerular capillaries.

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10
Q

The area under the concentration-time curve indicates what?

A

Drug exposure.

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11
Q

Describe how a drug tablet is absorbed into the body.

A
  1. Disintegration
  2. Dissolution (dissolved)
  3. Absorption
  4. Metabolism (and remainder distributed to body tissue - bioavailability).
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12
Q

Factors influencing oral bioavailability of drugs.

A 
Acidic gastric juices
Hydrolytic gut enzymes
Gut microorganisms
Food
Gut wall enzymes
Liver enzymes before reaching blood
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13
Q

In absorption, what is the rate limiting step?

A

Emptying of the stomach to the intestines

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14
Q

When taken with milk, the bioavailability of a drug ___ .

A

Decreases.

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15
Q

True or False. Brain capillaries have pores.

A

False. Blood brain barrier (additional layer of glial cells). Only lipid soluble drugs diffuse across BBB.

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16
Q

How many litres of ICF, ECF and plasma is there?

A

ICF: 28L
ECF: 11L
Plasma: 3L

Therefore total body water = 42L

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17
Q

Perfused organs (muscle, skin and fat) receive what blood flow rate?

A

A SLOW blood flow rate

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18
Q

Esterases in the plasma are important for which stage of ADME?

A

Metabolism

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19
Q

A metabolising enzyme helps to make a drug more water soluble, which in turn means what?

A 
Less likely to enter cells
Inc. excretion favoured
Usually terminates drug action
BUT
it can promote activity (prodrug)
There could be no change in activity
It could produce toxic metabolites
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20
Q

What is phase 1 of metabolism?

A

addition or uncovering of reactive group
(oxidation, reduction, hydrolysis)
oxidation is most important (CYP450)

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21
Q

What is phase 2 of metabolism?

A

Conjugation of endogenous molecule (with large charge) with drug. This makes the molecule more POLAR.

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22
Q

Where are CYP450’s located?

A

Smooth ER

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23
Q

What 3 things do CYP’s require?

A

oxygen, NADPH and cytochrome 450 reductase

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24
Q

What happens during the metabolism of phenytoin?

A

Highly lipophilic -> PHASE 1 -> Slightly soluble -> PHASE 2 -> Very soluble

25
Q

What is the common endogenous conjugate protein during drug metabolism?

A

Glucuronate

26
Q

When >600 daltons, molecules are excreted how?

A

Faecal excretion

27
Q

Neonates (new borns) have a reduced capacity to metabolise what?

A

Theophyline

28
Q

When is enzyme synthesis initiated during the induction of metabolism?

A

within 24 hours, increasing over 3-5 days at plateau

29
Q

BBQ meat can induce the metabolism of what drug?

A

Phenacetin (pain relief)

30
Q

How long does the onset of inhibition of drug metabolism last?

A

Rapid (1 day)

31
Q

What type of inhibitor is grapefruit juice?

A

Reversible inhibitor

32
Q

Why can heavy metals inhibit drug metabolism?

A

Forms complex with CYP450 (located on smooth endoplasmic reticulum)

33
Q

What percentage of blood is filtered at the glomerulus of the kidney during excretion?

A

10%, at about 130ml/min

34
Q

What are the 3 stages of kidney excretion of a drug?

A
  1. Glomerular filtration
  2. Active secretion of free and protein-bound drugs
  3. Reabsorption by passive diffusion
35
Q

How do you calculate exposure?

A

Area under time-concn curve (mg.h/L)

36
Q

What are the 4 parameters of pharmacokinetics?

A

Bioavailability, volume of distribution, CL and plasma half life

37
Q

How do you calculate volume of drug distrib?

A

Amount of drug in body divided by plasma drug conectrations

38
Q

Loading Dose (LD) = ?

A

LD - V x target concn

39
Q

What parameter is associated with drug elimination (but not total elimination)?

40
Q

What is clearance?

A
  • ratio
  • = dose / AUC
  • elimination rate = CL x concn
41
Q

What does half life depend on?

A

Volume and clearance. Larger the volume, larger the half life

42
Q

How to calculate half life?

A

= 0.7 V/CL

43
Q

4 half lives is equal to how much elimination?

A

> 90% drug elimination

44
Q

What is accumulation?

A

A drug accumulates in body till input rate = elimination rate. Steady state occurs when accumulation is complete and concentrations have plateaued.

45
Q

What is the use of a loading dose?

A

Targets concentration/steady state faster!

46
Q

What is the effect of smoking on theophyline?

A

It lowers plasma concentration of the drug.

47
Q

What happens when you take grapefruit juice with Felodipine?

A

The grapefruit juice inhibits the enzyme that breaks down Felodipine so you overdose on the drug. Results in an increase in the bioavailability of Felodipine.

48
Q

What are 4 main factors that influence renal drug excretion?

A

Gender
Age
Pregnancy
Disease

49
Q

What are 3 things that can alter renal excretion of drugs?

A

Competitive inhibition of tubular secretion
pH
Urinary flow rate

50
Q

How does competitive inhibition effect renal excretion of drugs?

A

Some drugs may have a higher affinity for active transport than the ‘normal’ target drug, so the 1/2 life of the ‘normal’ drug increases, taking longer to excrete.

51
Q

How does pH influence renal excretion?

A

If ionisation occurs, substrates are not actively absorbed and so there is more excretion.

52
Q

How does urinary flow rate effect renal excretion?

A

If you are to drink more water, urinary flow rate increases, diluting the drug along the tubule, therefore a decrease in conc gradient for passive readsorption of the drug and enhanced excretion.

53
Q

How does pH effect the excretion of methamphetamine?

A

Ionisation reducing the pH (acidic) increases the excretion (e.g. treat with ammonium chloride).

Ionisation increasing the pH (basic) decreases the excretion (e.g. treat with baking soda). –> Prolongs the effect.

54
Q

What is the first-pass effect?

A

Loss of the drug occurring before the drug reaches the systemic circulation.

55
Q

How do you calculate the volume of distribution (V)?

A

V = (amount of drug in body) / (plasma drug conc)

56
Q

What 3 factors determine V?

A

Body mass
Tissue binding
Drug binding to plasma elements

57
Q

What is maintenance dose rate (MD)?

A

Dose rate to achieve and maintain a target concentration.

58
Q

How do you calculate MD?

A

MD(mg/h) = CL(L/h) x target conc(mg/l)

Medsci 204 (18 decks)

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