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intro to pharmacology > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

How is drug delivered? (2)

A

Through absorption and distribution

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2
Q

What does pharmacokinetics allow? (2)

A

Control and estimate concentration of drug at target site

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3
Q

How is drug eliminated? (2)

A

Metabolism
Excretion

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4
Q

What does ADME allow (absorption, distribution, metabolism and excretion)? (2)

A

Determine the concentration of the drug at the target site which effects the Onset, Intensity & Duration of the drug’s action

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5
Q

What is absorption? (1)

A

The movement of drug from the site of administration to the systemic circulation

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6
Q

Which type of route of administration results in 100% bioavailability? (1)

A

Intra venous (I.V.) infusion

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7
Q

What are enteral routes of drug administration and give examples (4)

A

Via the GI tract
Oral
Sublingual
Rectal

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8
Q

What are parenteral routes of drug administration and give examples (8)

A

Not via GI tract
I.V.
subcutaneous
intra muscular (I.M.)
inhalation
intranasal
topical
transdermal

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9
Q

Why is oral drug administration the most common route? (4)

A

good for self-dosing
Cost-effective to make
Easy to dose.
Onset is rapid (10-20 min) but the drug must dissolve first

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10
Q

What is dissolution? (1)

A

The ability of the drug to dissolve in the fluid at the site of drug absorption

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11
Q

How can dissolution rate be increased? (1)

A

Increasing surface area

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12
Q

Where are most durgs absorbed and why? (2)

A

Via the small intestine, so large quantities can be absorbed due to large surface area and good blood supply

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13
Q

Why is oral drug administration the most complicated route for a drug? (4)

A

Survive gastric acid.
Survive digestive enzymes.
Co-exist with, or need to avoid, food.
Cope with gut bacteria – metabolism and metabolites.

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14
Q

How does absorption occur? (3)

A

Mainly via transcellular passive diffusion – drugs must be lipophilic to diffuse over two plasma membranes

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15
Q

What is the pH of most orally-active drugs? (1)

A

Weak acids of weak bases

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16
Q

Which form of orally-active drugs will be absorbed? (1)

A

Unionised

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17
Q

What can pH of gut fluids affect? (2)

A

Drug solubility and ionisation

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18
Q

What is P-glycoprotein? (2)

A

An ATP-powered drug-efflux pump which removes a wide range of substrates from the cell interior back into the gut lumen.

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19
Q

What is the first pass effect? (2)

A

Venus drainage from most of the GI tract enters the hepatic portal vein and hence goes to the liver and then and enters into inferior vena cava.

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20
Q

What is sublingual drug administration? (3)

A

Drug preparation placed under tongue and sucked
Absorption is rapid and via transcellular diffusion – drugs must be lipophilic
Quantity is limited due to small surface area

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21
Q

Why is absorption rapid in sublingual drug administration? (2)

A

Good blood supply under tongue, which drains into jugular vein and then into heart, hence no 1st pass effect

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22
Q

What is rectal drug administration? (3)

A

Drug preparation is placed into the rectum via the anus
Absorption via transcellular diffusion – drugs must be lipophilic

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23
Q

Why is rectal drug administration useful? (2)

A

Useful when oral route is compromised e.g. due to vomiting or gastric acid sensitivity
Useful if drug can damage the stomach lining. e.g. non-steroidal anti-inflammatory (NSAID) drugs

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24
Q

What is intramuscular and subcutaneous administration? (3)

A

The drug is placed into the connective tissue matrix and absorbed into local vessels.

Blood vessels and lymphatic vessels have low impedance (fenestrations) which allows for paracellular diffusion

Hence, hydrophilic drugs (e.g. gentamicin via i.m.) and large drugs (e.g. insulin via s.c.) can be absorbed.

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25
Q

What are the advantages of intramuscular and subcutaneous administration? (4)

A

No 1st pass effect
Control of onset
An aqueous formulation for fast onset
A microcrystal formulation for sustained onset
A suspension of non-aqueous drug for slow and sustained release … creates a “Depot”, a dopamine receptor blocker used to treat schizophrenia (see notes).

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26
Q

What are the disadvantages of intramuscular and subcutaneous administration? (2)

A

Invasive and may require supervised care.
Can be costly (compared with oral drugs).

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27
Q

What are the advantages of inhalation administration? (2)

A

The lungs have a large surface area (100 m2).
The lung parenchyma is very permeable and has low metabolism

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28
Q

What is intranasal administration? (3)

A

The nasal mucosa enables direct absorption into the systemic circulation via the jugular vein – rapid onset & no 1st pass effect.
Enables peptides to be absorbed
It may be a route which can be used to enable drugs to cross the blood brain barrier

29
Q

What is topical administration? (3)

A

Includes drug delivery to the eye, vagina and skin.
Local effects – application is direct to site. Ideally, there is no effect elsewhere – targeted action

30
Q

What is transdermal administration? (2)

A

“Patches” – a depot of drug targeted for systemic absorption.
Must be lipid soluble.

31
Q

What is distribution? (2)

A

The (reversible) movement of drug from the systemic circulation to the cells and interstitium of tissues

32
Q

What kind of diffusion do capillaries allow and why? (2)

A

Paracellular passive diffusion
Because they are highly porous

33
Q

The penetration of drugs into cells by diffusion depends on what three things? (3)

A

Molecular size
Lipid solubility
Degree of ionisation

34
Q

Which drugs can cross the cell membrane and what kind of targets can they access? (2)

A

Lipophilic drugs can cross cell membrane
Access intracellular drug targets

35
Q

Which drugs cannot cross the cell membrane and what kind of targets can they access? (2)

A

Hydrophilic and large drugs cannot cross the plasma membrane
Can only access exposed drug targets (extracellular and membrane proteins)

36
Q

How are drugs distributed? (2)

A

Drugs are distributed around the body by blood
Drugs are diluted in total blood volume within a few minutes of absorption

37
Q

Drugs being distributed in the blood efficiently depends on what? (2)

A

Blood flow (perfusion) to certain tissues is faster than to others
Blood-tissue boundaries vary in different tissues

38
Q

Distribution of lipophilic drugs (4)

A

Cross all blood-tissue boundaries
Extensive distribution
Distribution depends only on the perfusion rate in that tissue
Onset of action quicker in liver/ kidney/ lungs/ heart/ brain, compared with skin/ fat/ bone

39
Q

Distribution of hydrophilic and large molecular weight drugs (2)

A

More limited distribution
Distribution limited by the permeability of the blood-tissue boundary

40
Q

What is redistribution? (1)

A

The transfer of a drug from the brain back into blood and then into peripheral organs

41
Q

Describe the blood-brain barrier and how it affects drug distribution (3)

A

The brain have tight junctions and do not allow paracellular diffusion
Drugs must be lipid soluble and take the transcellular route to diffuse quickly into the brain
The blood-brain barrier may limit treatment of CNS diseases with hydrophilic drugs

42
Q

How can some hydrophilic drugs penetrate the blood-brain barrier (1)

A

By carrier-mediated transport

43
Q

Describe the placenta barrier and how it affects drug distribution (3)

A

The placental membranes behave like a lipid membrane, so hydrophilic drugs traverse the placenta much more slowly than lipid soluble unionized drugs
The placental membrane acts as a “metabolic barrier”
P-glycoprotein pumps molecules back into the mother’s blood

44
Q

How do many drugs bind to plasma proteins (4)

A

Many drugs bind reversibly
Bound drugs do not exit the blood system.
Only the unbound fraction of drug is available for diffusion into tissues.
Can be responsible for drug-drug interactions

45
Q

What is biotransformation/metabolism? (1)

A

Chemical modification of drugs and other foreign compounds

46
Q

Where is the main site of metabolism and what do most drugs require before they can be excreted (2)

A

Liver
Most drugs require biotransformation before they can be excreted

47
Q

What is the purpose of biotransformation? (2)

A

The purpose of biotransformation is to convert the drug into a more excretable form
Usually the metabolites are less pharmacologically active and less toxic but not always

48
Q

What are phase 1 reactions? (4)

A

Modify the drug by oxidation, reduction or hydrolysis
Phase I metabolism leads to the formation of more polar, less lipid soluble metabolites. These are more easily excreted than the parent drug; hence metabolism helps prevent accumulation of lipophilic “junk” within the body
Either introduces or uncovers a reactive chemical group (i.e. -OH or -NH2) and this facilitates phase II metabolism

49
Q

What are oxidation reactions in metabolism? (2)

A

The liver is the main organ involved in oxidative metabolism
Catalysed by cytochrome P450 (CYP)

50
Q

What are reduction reactions in metabolism? (2)

A

This type of reaction often occurs for drugs that contain either a nitro (-NO2) or azo (-N=N-) group in their structure
Catalysed by the CYPs

51
Q

What are hydrolysis reactions in metabolism ? (2)

A

The addition of water to split the drug molecule across the ester or amide bond
The enzymes that catalyse hydrolysis are usually referred to as esterases and these are found in the liver, plasma and gastro-intestinal flora

52
Q

What are phase 2 reactions? (2)

A

The addition of a new chemical group to either the parent drug or phase I metabolite. This process is often called conjugation

The resulting conjugates are more polar and are less lipid soluble than the parent compound; hence they are more easily excreted from the bodyi

53
Q

Where does conjugation mainly take place? (1)

A

Liver

54
Q

What is Glucuronidation (2)

A

Most frequent phase II conjugation
occur for compounds that contain OH (alcohols, phenols), carboxylic acid (-COOH) and amine (-NH2) groups
Glucuronides are hydrophilic and are readily excreted by organic anion transporters in the kidney (into urine) and liver (into bile)

55
Q

What is enzyme induction? (5)

A

This process leads to increased activity of some or most of the enzymes involved in biotransformation

The enzymes most commonly induced include the hepatic CYP P450s and UGTs.

Induction of these enzymes is a reversible adaptive response triggered by increased exposure to foreign compounds such as drugs

Induction involves the binding of drug or foreign compound to either cytosolic or nuclear receptors (sensor) and the interaction of the sensor with specific regions of DNA (response elements) that switch on the transcription of genes for enzymes such as the CYPs and UGTs

Increased transcription of such genes results in enhanced levels of enzyme and to increased rates of metabolism.

56
Q

What is enzyme inhibition? (1)

A

Drugs can inhibit each others metabolism and give rise to drug-drug interactions

57
Q

What are the factors that affect metabolism? (3)

A

Age
Disease
Genetics

58
Q

How does the affect metabolism? (3)

A

Infants have immature livers and hence inefficient metabolism of drugs
Elderly or ill patients may have impaired liver function.
Hence, in these cases dosage must be adjusted to account for slow metabolism

59
Q

How does genetics affect metabolism? (2)

A

Rates of drug metabolism vary considerably in the population and this due to environmental (e.g. diet), physiological (e.g. age) and genetic factors
It has become clear that genetically determined differences in the activity of some drug metabolising enzymes have important clinical consequences

60
Q

How does disease affect metabolism? (1)

A

Diseases affecting the liver can also impair drug metabolism

61
Q

What is excretion? (1)

A

The removal of drugs and their metabolites from the body

62
Q

What are the routes of excretion? (7)

A

Bile / faeces
Lungs
Saliva
Sweat
Tears
Milk

But the main route for excretion is in urine via the kidney.

63
Q

What is renal excretion? (1)

A

Renal excretion = (filtration + secretion) - reabsorption

64
Q

What are kinetics? (2)

A

The study of the rate of a process and the factors affecting on it

65
Q

What is pharmacokinetics? (2)

A

The science of the kinetics of ADME, considering both experimental and theoretical approaches.

66
Q

What is experimental pharmacokinetics? (3)

A

Biologic sampling techniques
Analytical methods for detecting drugs / metabolites
Data collection and handling

67
Q

What is theoretical pharmacokinetics? (2)

A

Development of pharmacokinetic models that facilitate prediction of drug disposition after drug administration

68
Q

What is the volume of distribution (Vd)? (1)

A

Div / Cplasma

69
Q
A

intro to pharmacology (5 decks)

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