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ICPP > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

What are the enteral drug administration methods?

A

Oral
Sub-lingual
Rectal

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2
Q

What are the parenteral drug administration methods?

A 
Intravenous
Inhalation
Transdermal
Subcutaneous
Intramuscular
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3
Q

What are the different ways drugs can be absorbed in the gut?

A

Passive diffusion
Facilitated diffusion
Active transport
Endocytosis/Exocytosis

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4
Q

What types of molecules get transported passively by each transport type?

A

Passive diffusion: lipophilic molecules, non-ionised hydrophillic molecules
Facilitated diffusion: ionised molecules through SLC’s

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5
Q

What are the two types of SLC’s?

A

OAT: Organic Anionic Transporter
OCT: Organic Cationic Transporter

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6
Q

What types of molecules get transported actively by each transport type?

A

Active transport: molecules that resemble endogenous molecules for binding to specific carrier proteins
Endocytosis/Exocytosis: large molecules (requires Intracellular signalling)

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7
Q

What are some of the factors affecting absorption in the gut?

A

pH (pKa of drug ~ pH of target site as non-ionised form passes easiest)
Blood flow (High blood flow, keeps conc. gradient high)
Surface Area
Time to absorption surface, time at absorption surface (drug will start to be degraded)
Solubility of the drug
First-pass metabolism
Expression of P-glycoprotein

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8
Q

What is the P-glycoprotein?

A

Protein found on cell membranes that pump drugs out of the cells
Therefore in High expression, there is low drug absorption

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9
Q

What is first-pass metabolism?

A

The metabolism of a drug that occurs in the gut wall, hepatic portal vein and (mainly) liver, which lowers the bioavailability of a drug

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10
Q

What is the bioavailability of a drug and why do IV drugs have 100% bioavailability?

A

Percentage of a drug reaching circulation

IV drugs have no physical or metabolic barriers

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11
Q

What is oral bioavailability equal to?

A

Oral bioavailability (F) = total amount of drug (giving orally) reaching circulation / total IV drug given

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12
Q

What is bioequivalence?

A

Comparison of 2 drugs with:
Similar bioavailability
Similar time to reach peak Cp

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13
Q

How are drugs distributed from the blood to the target?

A 
Bulk flow (arteries —> capillaries)
Diffusion (capillaries —> interstitial fluid —> cells)
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14
Q

What are some of the barriers to diffusion?

A 
Capillary permeability
pH
Blood flow 
Distribution of transporters
Non-target binding
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15
Q

What is non-target binding?

A

When drugs bind to proteins outside their targets (plasma proteins or tissue proteins)
These proteins can act as reservoirs of a drug

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16
Q

What are some examples of plasma proteins that bind to drugs and what is their normal function?

A

Albumin (Globulins) - maintain oncotic pressure

17
Q 
What is:
Ab
Cp
Vd
and what is the equation that links them all?
A

Ab: Amount of a drug in the body
Cp: Plasma concentration of a drug
Vd: Volume of distribution of a drug
Ab = Cp * Vd

18
Q

If a drug has increased penetration into tissues, how does the Ab, Vd, Cp change?

A

Ab: constant
Vd: increases
Cp: decreases
(Half life also increases)

19
Q

If the Vd > 5 what does that say about the drug?

A

Vd > 5 means the drug is not just in the blood

Vd < 5 means the drug is most likely contained within the blood

20
Q

What are the two stages of getting a drug into the body?

A

Absorption

Distribution

21
Q

What are the two stages of getting a drug out of a body?

A

Metabolism

Excretion

22
Q

In hepatic metabolism what are phase I enzymes and what are phase II enzymes?

A

Phase I: Cytochrome-P450

Phase II: Transferases

23
Q

Describe Phase I metabolism

A

Oxidative reactions to increase the charge on molecules (cannot pass membrane)
Some sufficiently polarised molecules will leave via kidneys
Some drugs are only activated by CYP450

24
Q

Describe phase II metabolism

A

Add charged species to molecules (increasing the ionic charge and molecular weight)
Molecules with a molecular weight < 300 leave in the urine via the kidneys
Molecules with a molecular weight > 300 become bile in the (liver then) gallbladder

25
Q

Describe how CYP450 inducers work

A

Increase the rate of transcription and translation of specific CYP450 enzymes
Increased number of these enzymes increases the rate of metabolism, increasing the Cp of specific drug

26
Q

Describe how CYP450 inhibitors work

A

Inhibition of the enzymes (competitive and non-competitive)

Decreases the number of available enzymes, decreasing the rate of metabolism and increasing the Cp of specific drug

27
Q

Explain how CYP450 enzymes can metabolism such a wide variety of drugs

A

Many different genes coding many different CYP450 isoforms
Each isoform can metabolise many different drugs
(Some overlap between enzymes)
Polymorphism: genetic variability between same enzymes

28
Q

What are the 3 stages of renal excretion?

A

Glomerular filtration
Proximal tubular secretion
Distal tubular reabsorption

29
Q

Explain what happens at glomerular filtration

A

Unbound drugs move into the glomerulus (bowmans capsule) from renal arterioles

30
Q

Explain what happens at proximal tubular secretion

A

Ionised drugs are carried into the kidney tubules via SLC’s
Peritubular capillaries reabsorb water from the renal tubules
Increasing the concentration of solutes in the renal tubules

31
Q

Explain what happens at distal tubular reabsorption

A

Increased concentration of solutes in the nephron lumen
This causes the secretion of lipophilic molecules - those that haven’t undergo phase I or II metabolism and therefore those the body wants to keep - into the peritubular capillaries

32
Q

Define clearance and state which factors it depends upon

A

Rate of elimination of a drug from the body (volume of plasma completely cleared of a drug per unit time)

Hepatic clearance (Metabolism) + Renal clearance (Excretion)

33
Q

Define half life and state it’s equation

A

Amount of time for the concentration of a drug to decrease to half of its original bioavailability
T = (0.693 * Vd) / Cl

ICPP (8 decks)

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