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Pharmacology & Toxicology > L5-Pharmacokinetics (Part 1) > Flashcards

L5-Pharmacokinetics (Part 1) Flashcards

1
Q

What is pharmacokinetics?

A

Pharmacokinetics is the study of what the body does with a drug or toxin, including how it is absorbed, distributed, metabolized, and excreted.

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2
Q

How do drugs move across cell membranes?

A
  1. Diffusion through the lipid bilayer.
  2. Diffusion through aqueous pores formed by aquaporins.
  3. Via transmembrane carrier proteins.
  4. By pinocytosis.
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3
Q

Which passage routes are important for drug movement?

A

Lipid-mediated and carrier-mediated transport are the most important in relation to pharmacokinetics, while diffusion through aquaporins is not considered significant for most drugs.

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4
Q

Where is Pinocytosis used?

A

For the transport of some macromolecules like insulin but not for small molecules like drugs.

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5
Q

What is Pinocytosis?

A

Process by which the cell takes in the fluids along with dissolved small molecules.

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6
Q

What is the role of lipid solubility in drug transport?

A

Lipid solubility is a key determinant of a drug’s pharmacokinetics.

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7
Q

Lipid solubility influences…

A
  • Rate of absorption from the gut.
  • Penetration into tissues (such as the brain).
  • Extent of renal elimination.
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8
Q

How does the ionization state of a drug affect its ability to cross lipid membranes?

A

Only the uncharged form of a drug can cross lipid membranes. For weak acids and bases, the ionization state depends on the pH of the environment.

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9
Q

A weak acid (AH ↔ A- + H+)

A

can cross when in the protonated (uncharged) form

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10
Q

A weak base (BH+ ↔ B + H+)

A

can cross when in the unprotonated (uncharged) form

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11
Q

PKa equilibrium constant

A

The pH where 50% of the drug is ionized (charged)

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12
Q

pH partition

A
  • pH partitioning occurs when drugs accumulate in parts of the body where the pH favors their ionized or unionized state.
  • Weak acids tend to accumulate in compartments of relatively high pH (alkaline), whereas weak bases do the reverse.
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13
Q

How does acidifying urinary affect drug excretion?

A
  • Acidifying the urine increases the excretion of weak bases and decreases the excretion of weak acids.
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14
Q

How does alkalinizing urinary affect drug excretion?

A
  • Alkalinizing the urine has the opposite effect, increasing the excretion of weak acids and decreasing that of weak bases.
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15
Q

How does the increase in plasma pH affect drug distribution?

A

Increasing plasma pH can cause weakly acidic drugs to move from the central nervous system (CNS) to the plasma, reducing neurotoxicity.

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16
Q

. How does the decrease plasma pH affect drug distribution?

A

Lowering plasma pH can cause weakly acidic drugs to become concentrated in the CNS, increasing neurotoxicity.

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17
Q

How do carrier-mediated transport systems work?

A
  • Carrier-mediated transport involves a transmembrane protein that binds one or more molecules or ions, changes conformation, and releases them on the other side of the membrane.
  • It shows saturation kinetics because of the limited number of transport proteins.
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18
Q

In which parts of the body is carrier-mediated transport important?

A
  • Renal tubules
  • Biliary tract
  • Blood-brain barrier
  • Gastrointestinal tract
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19
Q

Where can P-glycoprotein be found in the body?

A
  • Renal tubules
  • Micro vessels in brain
  • Gastrointestinal tract
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20
Q

What’s the role of P-glycoprotein?

A
  • Absorption of drugs
  • Distribution of drugs
  • Elimination of drugs
21
Q

What’s the drug transporter responsible for multidrug resistance in cancer cells?

A

P-glycoprotein

22
Q

What’s the physiological role of P-glycoprotein?

A

Elimination of environmental toxins.

23
Q

. How do plasma proteins affect drug activity?

A
  • Drugs bound to plasma proteins are pharmacologically inactive. Only the free (unbound) fraction of a drug is active.
  • The extent of protein binding depends on the concentration of the free drug, its affinity for the binding sites, and the concentration of the plasma proteins.
24
Q

Most important protein in plasma that binds many acidic drugs…

A

Albumin

25
Q

Binding depends on…

A
  • concentration of free drug
  • affinity for the binding sites
  • concentration of protein
26
Q

How does plasma protein binding affect drug elimination?

A

Extensive plasma protein binding slows down the elimination of a drug, as it reduces the amount of free drug available for metabolism and excretion.

27
Q

How do lipid-soluble drugs accumulate in the body?

A

Lipid-soluble drugs can accumulate in body fat when given chronically. Environmental contaminants like insecticides, which are poorly metabolized, also accumulate in body fat.

28
Q

Example for a lipid-soluble drug:

A

Benzodiazepines

29
Q

How does environmental contaminants work when ingested regularly?

A

Xenobiotics (insecticides) will accumulate slowly but progressively in body fat.

30
Q

What is Chloroquine used for?

A
  • Antimalarial drug
  • Additional in treating rheumatoid arthritis
31
Q

Chloroquine has high affinity for…

A

Melanin

32
Q

Chloroquine can cause…

A

Retinopathy due to the retina that are rich in melanin granules uptake the drug.

33
Q

What is the blood-brain barrier?

A

The blood-brain barrier is formed by tightly packed endothelial cells in the brain’s capillaries.

34
Q

How does blood-brain barrier affect drug distribution?

A

This structure prevents drugs with low lipid solubility from passing into the brain, limiting the effectiveness of certain antibiotics and cancer drugs.

35
Q

What is drug absorption?

A

Drug absorption is the passage of a drug from its site of administration into the plasma. It is important for all routes of administration except intravenous injection.

36
Q

How does drug ionization affect oral absorption?

A

Strong acids and bases are poorly absorbed from the intestine because they are fully ionized and cannot easily cross lipid membranes.

37
Q

What is an example of a drug that is poorly absorbed due to ionization?

A

Curare, a strong base used as an arrow poison, is poorly absorbed through the intestine because it is fully ionized.

38
Q

In which case does drug not enter plasma before its site of action?

A

Inhalation of bronchodilator aerosol to treat asthma.

39
Q

What factors influence gastrointestinal drug absorption?

A
  • Gastrointestinal motility.
  • Splanchnic blood flow (higher blood flow leads to greater absorption).
  • Particle size and formulation (e.g., slow-release capsules).
  • Physicochemical factors, such as ion binding impairing absorption.
40
Q

What are examples of non-oral drug administration routes?

A
  • Cutaneous administration
  • Nasal sprays.
  • Eye drops
  • Inhalation
41
Q

Cutaneous administration

A
  • Nicotine
  • Estrogen patches
42
Q

Eye drops

A

Glaucoma medications

43
Q

Inhalation

A

Bronchodilators

44
Q

How is drug distribution measured?

A

Drug distribution is measured by the volume of distribution (Vd), which is the volume of fluid required to dissolve a dose of drug at the same concentration as detected in the blood plasma.

45
Q

How is the volume of distribution (Vd) calculated?

A

Vd = Dose / [Drug]plasma

46
Q

If 400 mg of a drug is administered and the plasma concentration is 0.01 mg/L, the Vd is calculated as:

A

Vd = Dose / [Drug]plasma
Vd = 400 mg / 0.01 mg/L = 40,000 L

47
Q

What are examples of drugs with different volumes of distribution?

A
  • Insulin
  • Morphine
48
Q

Insulin has low Vd…

A

because it is retained highly in plasma.

49
Q

Morphine has high Vd…

A

because accumulates in fat tissue.

Pharmacology & Toxicology (10 decks)

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