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Introduction to Metabolism and Pharmacology > Basic Principles > Flashcards

Basic Principles Flashcards

1
Q

What is Pharmacology ?

A

The study of drugs. It can also be defined as in which the function of living systems is affected by chemical agents

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2
Q

What is Pharmacology divided into and explain them ?

A
  1. Pharmacokinetics - What the body does to the drug

2. Pharmacodynamics - What the drug does to the body

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3
Q

Explain further what pharmacokinetics is ?

A
  1. The study of the bodily absorption, distribution, metabolism, and excretion of drugs
  2. The characteristic interactions of a drug and the body in terms of its absorption, distribution, metabolism, and excretion
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4
Q

What does Pharmacokinetics describe?

A

How the concentration of a dosed drug and its metabolites in body fluids and tissues changes with time

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5
Q

What can Pharmacokinetics also sometimes be described as ?

A

What the body does to a drug, refers to the movement of drug into, through, and out of the body - the time course of its absorption , bioavailability, distribution, metabolism and excretion

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6
Q

Why is pharmacokinetics important ?

A

Allows us to understand the best way to administrate it, how often it should be administered, how much should be administered to achieve an effective concentration, drug interactions, and if a treatment is unsuccessful with a specific drug why that might be and what we can do to rectify that

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7
Q

What does the pharmacokinetics of a drug determine?

A

The onset, duration, and intensity of its effect

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8
Q

What happens to the drug once it enters the body?

A

A - absorption: the transfer of the drug from the site of administration into the blood stream (systemic circulation)
D - distribution: the transfer of the drug from the systemic circulation into the different organs of the body
M - metabolism: the process by which the drug molecule is chemically modified in the body
E - excretion: the removal of the drug, and/or its metabolites, from the body

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9
Q

What does metabolism and excretion together account for ?

A

They account for drug elimination

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10
Q

What are some different drug forms ?

A
  1. Oral liquids - solutions, suspensions and emulsions
  2. Tablets & Capsules
  3. Injections & infusions
  4. Creams & ointments
  5. Patches
  6. Inhalers
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11
Q

What is an excipient in a drug ?

A

Substances that are included in a pharmaceutical dosage form not for their direct therapeutic action, but to aid the manufacturing process, to protect, support or enhance stability, or for bioavailability or patient acceptability

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12
Q

What are some examples of excipients ?

A
  1. Diluents/fillers (bulking agents) e.g. lactose, water
  2. Surfactants e.g. polysorbates
  3. Lubricants e.g. Magnesium stearate
  4. Disintegrants e.g. starch
  5. Viscosity enhancing agents e.g. cellulose derivatives
  6. Flavours, colours, perfumes
  7. Sweetening agents
  8. Preservatives
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13
Q

What are some Examples of Excipient Substances in a generic Paracetamol Caplet?

A
  1. Povidone - suspending agents
  2. Maize starch - bulking agent
  3. Methylcellulose - bulking agent
  4. Talc - diluent
  5. Calcium Stearate - bulking agent
  6. Methyl-hydroxy-propyl-cellulose - binder
  7. Polyethylene Glycol - enteric coating
  8. Purified water
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14
Q

What is the bioavailability (F) of the drug ?

A

The fraction of the drug being administered that reaches (i.e. being absorbed into) the systemic circulation

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15
Q

What has a bioavailability of 1 (100%) ?

A

Drugs that administered intravenously (IV) - i.e. all of the drugs are administered into the blood stream directly

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16
Q

As most drugs are administered orally, and therefore, need to be absorbed through ? and how does it cross it ?

A

Needs to be absorbed through the cell membrane. Most orally administered drugs are absorbed though simple diffusion through the large surface area of the microvilli

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17
Q

What are some factors influencing transport across cell membranes and explain them ?

A
  1. Chemical size - smaller chemicals pass across the cell membrane more easily
  2. Solubility - lipid or fat-soluble (hydrophobic) substances pass across freely because of phospholipid arrangement. Water-soluble (hydrophilic) substances have great difficulty entering the cell
  3. Charge - uncharged and non-polar molecules enter cells more readily than charged ions (e.g. electrolytes such as Na+ and K+) and polar molecules (e.g. glucose)
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18
Q

What are some different routes of drug administration?

A
  1. Enteral - Oral, Sublingual, Buccal and Rectal
  2. Parenteral - Intradermal, Subcutaneous, Intramuscular, Intravenous, Intra-arterial, Intra-articular, Intrathecal
  3. Topical - Eyes, Ears, Nose, Lungs, Vagina, Urethra, Transdermal and Colon
19
Q

For each route of administration explain how it affects the drug absorption ?

A
  1. For Enteral is it inefficient- only part of the drug is absorbed
    Some routes subject to first pass metabolism
    Destruction by gastric acid and digestive juice
  2. For Parenteral, IV administration gives a 100% bioavailability (F=1)
    First pass metabolism avoided
    Bypass GIT
    Fast onset of action
  3. For topical absorption depends on lipid solubility - only lipid soluble drugs can penetrate intact skin
20
Q

Explain Oral administration?

A
  1. Most common method of drug administration - easy and non-invasive
  2. Subject to the same digestive processes as the food we eat
  3. Most absorption occurs in the small intestine due to its large surface area
  4. Usually by passive diffusion, therefore affected by ionisation state (pKa of the drug)
21
Q

Explain Sublingual and rectal administration ?

A
  1. Avoids first-pass metabolism (absorbed into vena cava, not portal vein)
  2. Sublingual (applied under the tongue)
    Glyceryl trinitrate - relieves angina
    Buprenorphine (treating drug addiction)
  3. Rectal (suppositories)
    Antiemetic drugs (prevent vomiting; oral administration may not be possible)
    Diazepam (anxiolytic and anti-epileptic) administration to small children
22
Q

How can Bioavailability (F) vary ? state some and their bioavailabily

A

It can vary among different formulations and dosage forms of a drug
Digoxin elixir - F=0.8
Soft gelatin capsules - F=1
Tablets - F= 0.7

23
Q

What do different compartments of the body have?

A

They have different pH

e.g. stomach pH = 1.3, blood pH = 7.4

24
Q

When will a drug have different ionisation states ?

A

Different body compartments

25
Q

What can only the uncharged form do ?

A

Cross membranes and move between compartments

26
Q

What can uncharged forms lead to ?

A

Ion trapping - concentration of the drug in certain compartments

27
Q

An acidic drug will be concentrated in ?

A

A compartment with high pH

28
Q

A basic drug will be concentrated in ?

A

A compartment with low pH

29
Q

What is Area under the curve (AUC) used for ?

A

To calculate bioavailability

30
Q

What is AUC a measure of ?

A

It’s a measure of total drug exposure in plasma

31
Q

Explain Bioavailability (F), Volume of Distribution (Vd) and Clearance (CL) ?

A

Bioavailability (F) - fraction (or percentage) of unchanged drug reaching the systemic circulation after administration
Volume of Distribution (Vd) - the “apparent” volume from which the drug is distributed
Clearance (CL) - volume of blood or plasma from which the drug is being removed over time (e.g. per hour or per day)

32
Q

How do you measure the volume of distribution (Vd)? explain the different results you could get ?

A
  1. Administer a known dose of a drug (by IV injection)
  2. Measure the plasma concentration (Cp)
    Confined to plasma = high concentration
    Distributed throughout the body - low concentration
33
Q

What is the apparent volume of distribution (Vd) ?

A

This is the hypothetical volume into which the drug (Q) would be distributed in order to obtain the measured plasma concentration (Cp) and account for the total amount of drug administered

34
Q

Why calculate the half-life ?

A

It can indicate:

  • how much of the drug will be effective at a given time interval after dosing
  • when the effects of a drug can be expected to wear off
  • how often a drug should be given in order to maintain a reasonably stable level of effect
35
Q

Explain the Blood Brain Barrier (BBB) ?

A

A special ‘barrier’ that prevents distribution of drug to area where their effects may be dangerous (e.g. cerebrospinal fluid, CSF)

36
Q

What limits passage of molecules ?

A

Tight junctions between the endothelial cells which line the blood vessels supplying the brain

37
Q

What needs to happen in order for a drug to penetrate the brain ?

A

It must either traverse the endothelial cell, which requires high lipid solubility, or it must be transported by a specific transported system (e.g. amino acid uptake system)

38
Q

Therefore drug penetration into the brain is ?

A

Selective, this has given rise to the concept of the blood-brain barrier

39
Q

How is the Intrathecal injection administered ?

A

Intrathecal injection administers a drug directly into CSF, useful for impermeable drugs

40
Q

What are some similar barriers ?

A

Placental barrier, blood-occular barrier

41
Q

Explain 1st generation antihistamine ?

A

Sedating because it can cross BBB

Alimemazine, chlorphenamine, diphenhydramine, promethazine

42
Q

Explain 2nd and 3rd generations ?

A

Non-sedating because it cannot cross BBB

Acrivastine, cetirizine, desloratadine, loratadine

43
Q

What does Pharmacokinetics deal with?

A

It deals with dose - concentration relationship. Also, relates how the dose delivered affects the concentration within the body

44
Q

What does Pharmacodynamics control ?

A

It controls the concentration - effect relationship. Also, determines how the effect varies with concentration achieved

Introduction to Metabolism and Pharmacology (16 decks)

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