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Pharmacokinetics > Drug Distribution > Flashcards

Drug Distribution Flashcards

1
Q

How do drugs cross the epithelium / endothelium?

A
  • Paracellular

- Transcellular ( Diffusion / Active Transport / Pinocytosis )

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2
Q

What are the two substances which aid with active transport?

A 
Solute Carriers  (Organic Anion / Cation Transporters) 
ATP - Binding Cassettes (P - Glycoprotein)
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3
Q

Which barrier is more permeable to allow substances to be metabolised?

A

Liver Endothelium

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4
Q

Which barrier is more permeable to allow substances to be eliminated?

A

Renal Endothelium in the Glomerulus

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5
Q

What state would lipid insoluble substances be in?

A

Ionised State

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6
Q

What state would lipid soluble substances be in?

A

Unionised State

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7
Q

What is pKa?

A

Hydrogen Ion Concentration at which:
50% of the drug is ionised
50% of the drug is unionised

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8
Q

What is protein binding?

A

Drugs can bind to plasma proteins.

Is a reversible reaction therefore can be bound and unbound.

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9
Q

What is the purpose of plasma proteins?

A

Major transporters of endogenous lipids and steroid hormones.

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10
Q

Why is protein binding important?

A

Some proteins are TOO LARGE to pass through most endothelia and epithelia and only free drugs can bind o their site of action.

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11
Q

What happens to bound proteins?

A

They remain in the blood and are unable to exert their pharmacological effect.
CAN NOT be metabolised or excreted.

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12
Q

Which drugs can reach an equilibrium across different compartments?

A

Unbound drugs can reach an equilibrium across different compartments.

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13
Q

Which drugs can’t reach an equilibrium across different compartments?

A

Bound drugs can’t reach an equilibrium across different compartments.

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14
Q

Which drugs act as a reservoir?

A

Bound Proteins.

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15
Q

What effect does protein binding have on a drug’s half - life?

A

Heavily protein bound drugs have a LONGER half - life.

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16
Q

What factors affect protein binding?

A
  • Affinity of drug to protein binding sites.
  • Drug Concentration.
  • Plasma Protein Concentration.
17
Q

What is the most important plasma protein for drug binding?

A

Albumin

18
Q

Why is albumin the most important plasma protein?

A

Negatively charged
High affinity for acidic drugs BUT has a low capacity.
Low affinity for basic drugs BUT has a high capacity.

19
Q

At higher dosages, some drugs begin to show an upward curve.
Why is this?

A

Plasma proteins become saturated.

20
Q

Where are highly lipophilic drugs more likely to bind?

A

Extensively to fat stores.

21
Q

Where does tissue binding occur a lot?

A
  • Fat
  • Bone
  • Muscle
22
Q

How does drug distribution occur in overweight patients?

A

They have a greater ratio of lipid levels to other body tissue.
Drug which are HIGHLY LIPID BOUND will be distribute more freely in overweight patients.

23
Q

How does osteoporosis occur?

A

Increased resorption and thus bones begin to thin.

INCREASES RISK OF FRACTURES.

24
Q

What is the purpose of bisphosphonates?

A

Binds to calcium in bones and inhibits resorption.

25
Q

Name the 2 main bisphosphonates.

A

Alendronic Acid = Tablet taken : ONCE A WEEK

Zoledronic Acid = Injection : ONCE A YEAR

26
Q

What is the equation for volume of distribution?

A

VD = total amount of drug in body / plasma concentration of drug

27
Q

What is the definition of VD?

A

Apparent volume in to which a drug disperses in order to produce the observed plasma concentration.

28
Q

What is the extent of distribution of a drug throughout the body?

A
  • Plasma
  • Interstitial Fluid
  • Intracellular Fluid
  • Fat
29
Q

What happens if the drug remain in the plasma?

A

Volume of distribution is low.

Drug dosage is LOW.

30
Q

What happens if the drug disperses to other fluids / tissues?

A

Volume of distribution is high.

Drug Dosage is HIGH.

31
Q

How does protein binding affect VD?

A

Bound drugs CAN’T leave the circulatory system.
HIGHER proportion remains in the plasma.
Total plasma concentration is HIGHER.
VD is LOWER.

32
Q

What drug factors affect VD?

A

Plasma Protein Binding
Tissue Binding
Physiochemical Properties
(Size / Charge / pKA / lipid and water solubility)

33
Q

What patient factors affect the VD?

A 
Age
Sex
Body Muscle / Fat Proportion 
Level of Hydration 
Water Distribution
34
Q

What implication does VD have on the dosage?

A

Impacts on the loading dosage of a drug.

Pharmacokinetics (18 decks)

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