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Pharmacology > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

What is pharmacology ?

A

The study of how chemical substances interact with living systems

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2
Q

What is a drug?

A

A potentially toxic substance that alters a physiological process

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3
Q

What is pharmacokinetics ?

A

Time course of the drug concentration in the body, i.e. what the body does to the drug.

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4
Q

What is pharmacodynamics?

A

This is the study of the relationship between drug concentration to pharmacologic effects, i.e. what the drug does to the body

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5
Q

What is meant by the term bioavailability?

A

The fraction of drug absorbed into systemic circulation. I.e. the amount of drug that makes it into the blood stream

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6
Q

What are the different routes that we can administer a drug? 9

A
  1. Parenteral (administered or occurring elsewhere in the body other than the mouth or alimentary canal) IV 2. Parenteral IM 3. Parenteral SC 4. Transdermal 5. Topical 6. Oral 7. Sublingual 8. Buccal 9. Inhaled
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7
Q

What methods of drug administration cause the most immediate effects?

A
  1. IV 2. Inhalation (oral or nasal) 3. Sublingual
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8
Q

How long can orally administered drugs take to provide relief?

A

It can take up to 30 minutes.

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9
Q

Meals can retard the absorption of certain drugs.

A

Drugs interact

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10
Q

Liquids or powders dissolved in water will act more quickly than tablets of capsules

A

K

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11
Q

What is first pass metabolism?

A

1st pass metabolism refers to the elimination (of a drug) that occurs when it is first absorbed by the small intestine and passes through the liver via the portal system.

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12
Q

Explain how a drug is eliminated by first pass metabolism.

A

When a drug is administered orally, it must pass through the digestive tract before it enters systemic circulation. En route, the drug will pass through the hepatic portal vein and enter then liver. The liver will metabolise some of the drug. Whats left of the drug will then enter systemic circulation

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13
Q

When a drug is administered orally, what factors play a role? 3

A
  1. Gut metabolism 2. Food 3. Liver metabolism and blood flow
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14
Q

How does parenteral IV differ from oral administration in terms of bioavailability?

A

When a drug is administered through parenteral IV it is delivered directly into the systemic circulation. Therefore, 100% of the drug is present. Whereas, when the drug is taken orally, it can interact with food, the gut and liver. This results is metabolism and elimination of the drug prior to reaching systemic circulation. Therefore, the bioavailability will be less than 100%

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15
Q

What are the 4 pharmacokinetic practices?

A
  1. Absorption: how is the drug absorbed2
  2. Distribution: how is the medicine spread throughout the body
  3. Metabolism/Biotransformation: is the drug converted into other chemicals in the body
    1. Excretion: how is the drug eliminated from the body
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16
Q

In order for a drug to produce a therapeutic effect, what must first occur?

A

For a drug to produce a therapeutic effect, it must be absorbed into the blood stream and distributed into circulation.

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17
Q

Once the drug is in circulation, how does it cross the plasma membrane?

A

There are four ways in which the drug can cross the plasma membrane, namely: 1. Passive diffusion 2. Facilitated passive diffusion 3. Active transport 4. Pinocytosis

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18
Q

What is passive diffusion?

A

Passive diffusion is the movement of water, water soluble molecules and small lipids from an area of high concentration to an area of low concentration. This process is: 1. The most common and most important mechanism of drug absorption. 2. No energy is required 3. Not saturable 4. Non-selective 5. A non ionized drug is lipid soluble and will diffuse easily

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19
Q

What is facilitated passive diffusion?

A

Facilitated passive diffusion is similar to passive diffusion but is mediated by carrier proteins. Transport against the concentration can’t occur. Energy is not required.

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20
Q

What is pinocytosis ?

A

Pinocytosis is the physical engulfment of a substance by the cell. It has a small role in drug transport. Fat soluble vitamins such as vitamin KADE are absorbed this way.

21
Q

What is active transport?

A

Active transport is the movement of a substance against a concentration gradient with the use of energy. This process is: 1. Relatively unusual 2. Selective, e.g. iodide, amino acids, sugars, vitamins 3. Competition for transport can occur 4. Drugs resembling natural substrates can be transported 5. Requires energy 6. Can occur against the concentration gradient.

22
Q

What is pKA?

A
  1. pKa is a method used to indicate the strength of an acid 2. A lower pKa, indicates that acid is stronger. The lower the value the more dissociation will occur. 3. Remember we want to keep drugs in their uncharged form for absorption, so weaker acids are required.
23
Q

Explain the role the environment plays on a drugs absorption.

A

For a drug to be absorbed across the the cell membrane, we require it to be in its uncharged form. Therefore, a weak acid requires a acidic environment which will keep the drug in its non-ionized form facilitating easy movement across the lipid-bilayer. These acidic conditions are found in the stomach. Conversely, a weak base requires a strongly basic environment. Conditions like this are present in the small intestine

24
Q

What does distribution of the drug depend on? 6

A

Distribution depends on: 1. Physiochemical properties of the drug 2. Tissue permeability; lipid solubility 3. Cardiac output and blood flow 4. Perfusion rate of the tissue 5. Transmembrane pH 6. Binding of plasma and tissue proteins

25
Q

True or false a bound drug has an effect?

A

False. A bound protein has no effect.

26
Q

What are the 3 things that drug binding depends on?

A

The amount of bound drug depends on: 1. Free drug concentration 2. The protein concentration 3. Affinity for binding sites.

27
Q

List and explain 3plasma proteins that bind drugs.

A
  1. Albumin: binds many acidic and a few basic drugs 2. Beta-globulin and an alpha1 acid glycoprotein have also been found to be in certain basic drugs .
28
Q

List 5 things that have an fact on plasma protein binding :

A
  1. Renal failure 2. Inflammation 3. Fasting 4. Malnutrition 5. Competition from other drugs can also affect the percentage of drugs bound
29
Q

What will allow the drugs to have a broader distribution?

A

Drugs with a high lipid solubility can easily penetrate fat stores and cross membrane barriers. This allows the drug to have a broader distribution.

30
Q

What drugs are more easily eliminated from the body?

A

Water soluble or charged drugs are more easily eliminated from the body. Whereas fat soluble drugs can be stored in the body, providing longer lasting effects.

31
Q

Which two barriers prevent free distribution of drugs?

A
  1. The blood brain barrier 2. Placenta
32
Q

What is metabolism of drugs?

A

Drug metabolism is the chemical conversion of medication inside the body into metabolites.

33
Q

What is the purpose of drug metabolism?

A

Drug metabolism is a clearing process that breaks down substances into their water soluble or charge form which is required for easy excretion.

34
Q

What is the primary site of drug metabolism?

A

The primary site of drug metabolism is the liver. However, this process may also occur in the kidneys, GI tract and the lungs.

35
Q

Metabolism is the chemical conversion of drugs into metabolites. Explain what metabolized drugs may be?

A

Metabolised drugs maybe: 1. Inactive 2. Less active 3. More active 4. More toxic 5. Similar activity to a parent compound

36
Q

What is phase 1 drug metabolism?

A

Phase 1 drug metabolism is the metabolic modification of the drug. This includes: 1. Oxidation 2. Reduction 3. Hydrolysis Phase 1 drug metabolism is made possible by the cytochrome P-450 enzymes.

37
Q

What is phase II drug metabolism?

A

Phase II drug metabolism is the synthesis or conjugation phase. Adding a polar group to facilitate drug elimination.

38
Q

Cytochrome p 450 enzymes are involved in phase 1 drug metabolism. What substances induce cytochrome p 450 enzyme activity? 5

A
  1. Ethanol (alcohol) 2. Phenobarbitone (epileptic drug) 3. Rifampacin (anti-bacterial drug used to treat TB, leprosy and Legionnaires disease). 4. Phenytoin (anti-seizure medication) 5. Smoking (nicotine) The presence of any of these substances results in activation of tea cytochrome p 450 enzymes. This results in an increased conversion of drugs into their water-soluble or charged states. Therefore, any increased activation of these enzymes will result in increased elimination of a drug.
39
Q

Cytochrome p 450 enzymes are involved in phase 1 drug metabolism. What substances inhibit cytochrome p 450 enzyme activity? 5

A
  1. Cimetidine (proton pump inhibitor) 2. Erythromycin (anti-bacterial used for resp tract infections, chlamydia, syphilis and pelvic inflammatory disease) 3. Grapefruit juice (furancoumarins in the juice block enzyme activity). 4. Ketoconazole (anti-fungal medication) 5. Quinidine (anti-arrhythmic medication)
40
Q

List the different routes of drug elimination. 7

A

Drugs can be eliminated in the following ways: 1. Urine 2. Lungs 3. Sweat 4. Milk 5. Saliva 6. Faeces 7. Bile

41
Q

Is drug elimination dependent on route of administration?

A

No, drug elimination is independent of route of administration. I.e. drugs are eliminated the same regardless of how they get into the body.

42
Q

Name the 3 processes involved in renal elimination.

A
  1. Active tubular secretion 2. Glomerular filtration 3. Tubular reabsorbtion
43
Q

Describe the process of active tubular secretion.

A

Active tubular secretion: - occurs in the proximal convoluted tubule - weak acids such as probencid, penicillins and salicylic acid -weak bases such as amphetamine, quinine and imipramine

44
Q

Describe the process of glomerular filtration. 3

A
  1. Molecules smaller than 20 kDa pass into filtrate.
  2. Drug must be free and not protein bound.
  3. Drugs with high lipid solubility are reabsorbed passively and are therefore, slowly excreted.
45
Q

Describe the process of tubular reabsorption.

A

Tubular reabsorption can be : 1. Active or passive 2. Reabsorption id governed by the pH of the tubular fluid and the pKa of the drug. 3. Acids are best eliminated in alkaline urine 4. Bases are best eliminated in acidic urine

46
Q

What is tubular reabsorption governed by?

A

Tubular reabsorption is governed by the pH of the tubular fluid and the pKa of the drug.

47
Q

How is an acidic drug best eliminated?

A

Acidic drugs are best eliminated in basic urine.

48
Q

How are basic drugs best eliminated?

A

Basic drugs are best eliminated in acid urine.

Pharmacology (13 decks)

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