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Flashcards in Pharmacology Deck (42):
1

Define...

1) Pharmacokinetics

2) Pharmacodynamics

3) Therapeutics 

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The ______ __ __________

 

affects the speed of the drug's action

 

 

 

Route of administration

3

 

 

The _____ given affects the concentration delivered to the tissues

 

 

Dose

4

 

 

Name the four processes in pharmacokinetics

 

 

 

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What is the term for drugs delivered by 

1) the digestive tract

2) by injection into the cardiovascular system, the skin or other body cavities

3) application onto the skin or mucous membranes

1) Enteral 

2) Parenteral 

3) Topical

6

 

Name the physical factors affecting drug absorption 

 

Name the chemical factors affecting drug absorption

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What are the main factors modulating drug absorption in the GIT?

  • Total surface area of small intestine
  • Contact time
  • Presence of food
  • Blood flow

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Describe First Past Metabolism 

  • Substances absorbed across the intestinal wall enter blood vessels known as the hepatic portal system, carries blood directly to the liver.
  • Orally administered drugs also enter this hepatic portal vein and are transported to the liver where they undergo pre-systemic metabolism.
  • The drug is metabolised in the liver before reaching the circulation.

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What is drug distribution?

The process by which drugs are transported, after they have been absorbed or administered directly into the bloodstream, until they find the site in the body on which to act.

10

 

1) What are most circulating drugs bound to?

2) What does this mean about them pharmacologically?

3)  What does the drug-protein complex acts as?

4) Which drugs are pharmacologically active?

 

1) Proteins

2) They are inactive

3) A drug reservoir, releasing drug as plasma concentrations of free drug falls.

4) Only free, unbound drugs

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The Volume of Distribution

1) What is this?

2) How is it calculated?

3) When a drug is administered, and its concentration is measured in the plasma, the figure obtained usually does not correlate with the amount given, why?

1) A theoretical measurement of the extent to which drugs partition between the vascular & non-vascular compartments. Recorded as Vd

2) Calculated by drug dose/concentration of drug in drug plasma

3) This is due to the fact that many drugs move from the blood into tissues

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Special Compartments

Describe...

1) the blood brain barrier 

2) the blood-placenta barrier

3) the blood-testicular barrier

 

1) This is very effective and prevents many drugs accessing the brain

2) This is not very effective and permits access of most drugs. Almost all of the drugs in the mother's blood will cross into the unborn baby's circulation

3) This exists between the blood and the male reproductive tissue. Little is known about the adverse effects that may occur when drugs cross this barrier.

13

Metabolism 

1) Describe this process

2) What is the main organ involved?

3) How does it link to bioavailability? 

1) The process through which a drug is converted to a water soluble form to enable it to be excreted easily from the body. Requires enzyme activity

2) Liver

3)Metabolism has an effect on the amount of intact drug that reaches the bloodstream to work in the body (bioavailability)

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Metabolism has two phases...

1) Describe Phase I

 

2) Describe Phase II

1) involves oxidation, reduction or hydrolysis of the drug to make it more water-soluble. (CYP 450 one of the main enzyme family involved or other enzymes)

2) involves conjugation reactions in which the drug is chemically combined with a more water-soluble substance. The result is a very water-soluble compound that can easily be excreted by the kidneys.

15

 

What is enterohepatic cycling?

 

How can it be used therapeutically?

The conjugated drug produced during phase II of metabolism is reabsorbed from the gut lumen and re-enters the hepatic portal vein.

Can be used therapeutically to maintain systemic levels of drugs taken at low doses (e.g. oral contraceptives maintain plasma concentrations via enterohepatic cycling)

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Drug Excretion

Describe drug excretion and the main methods of excretion

Excretion is the process by which drugs are removed from the body (the last step in pharmacokinetics) 

Excreted in:

  • Body fluids– sweat, tears, milk, bile and urine.
  • Expired gases
  • Solid matter–hair, faeces
  • The kidney excretes the majority of drugs.

17

 

What is the half-life of a drug?

Length of time required for the concentration of drug to decrease by half.

A measure of how long the drug is active in the body

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18

Concentration

  1. What is the principle behind therapeutic dosing?
  2. What is the overall aim?

  1. Minimal effective concentration is the principle behind therapeutic dosing
  2. to keep within the margin of safety

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19

Steady state concentration

  1. What is this?
  2. What will affect how long it takes to achieve a steady state?

  1. Maintaining therapeutic effect at a steady level.

  2. Half-life of a drug 

20

PHARMACODYNAMICS

 

Describe this term

 

Drugs are small organic molecules that can change existing biochemical or physiological processes in the body.

To exert these changes the drug needs to interact with specific molecules and chemicals found within the body.

21

What conditions must be met in order for a drug to act?

  1. Must gain entry to the body (enter the organism)
  2. Must exert some chemical influence on one or more cell constituents (bind to a target)
  3. Should be specific
  4. Should have a specific half-life

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Condition 1: it must gain entry to the body...

What affects the drugs ability to enter an organism?

the chemical nature of the drug

  • Molecular weight
  • Water & lipid solubility – Ionisation
  • PH

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Condition 2: it must exert some chemical influence on one or more cell constituents (bind to a target)

1) What is the normal function of receptors?

2) What happens when a chemical binds to a receptor?

1) to bind to endogenous molecules such as hormones, neurotransmitters and growth factors

2) the cell's activity is altered. Receptors will respond to a drug or will block (inhibit) drug

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Condition 2: it must exert some chemical influence on one or more cell constituents (bind to a target)

 

List as many drug targets as you can

  • Protein macromolecules (44% all human drug targets)
  • Enzymes (29% of all human target proteins)
  • Transporter proteins
  • Carriers
  • Pumps
  • Ion channels
  • Nucleic acids – targets DNA/RNA inhibits synthesis (anti cancer drugs)

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Targets of drug action

Describe how ION CHANNELS can be a target of drug action?

 

 

Voltage gated ion channels open in response to change in voltage of cell membrane – cardiac calcium channel blockers e.g. verapramil blocks this channel

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Targets of drug action

Describe how CARRIER CHANNELS can be a target of drug action?

Proteins that transport ions/messenger molecules though the cell membranes

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Targets of drug action: Enzymes

Describe how enzymes can be used as a drug target

Enzymes bind with a substrate to produce a product

Enzyme acts as LOCK and Substrate acts as KEY

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What is an agonist?

Give an example

What does it's potency depend upon?

Molecule that binds to receptor & produces a response

e.g. adrenaline binds to receptors in heart & increases heart rate

Affinity (Tendency to bind to receptors) and Efficacy (Ability to cause response when bound)

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What is an antagonist?

Give an example

What are partial agonists?

Molecule that binds to receptor & prevents agonist binding to receptor

Drug blocks receptor – Antagonist eg. Atropine

Partial Agonists – weaker effect, do not have 100% fit with receptor but enough to create some response and effect

30

Define the following:

1) Affinity

2) Specificity 

3) Efficacy

4) Potency

1) receptors bind selectively and tightly to chemicals (or drugs) they recognise

 2) the drug is designed to bind with a particular receptor - The ability of the drug to produce an action at specific site

3) the ability of a drug to produce an effect at a receptor.

4) The amount of drug required to produce a desired effect

 

31

 

Name some factors that influence drug effects

  • Routes of administration
  • Age
  • Weight
  • Gender
  • Ethnicity/genetics
  • Nutritional status
  • Medical conditions
  • Medicine product
  • Psychological factors

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What is drug tolerance?

A patient adapts to a drug over a period of time so that higher and higher doses are needed to produce the same initial effect.

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Why does drug tolerance occur?

  • A structural change in receptors
  • Loss of receptors, body doesn’t replace
  • Exhaustion of mediators
  • Increased metabolic degradation due to enzyme induction (e.g. prolonged exposure to a drug can increase liver metabolism – alcohol)
  • Physiological adaptation (e.g.the body’s natural homeostasis working against the drug)

34

Adverse Drug Reactions (ADR) and Adverse Drug Interactions (ADI)

Very common, costly, and on the rise. Why?

Greater no. of drugs taken = more at risk

(polypharmcy)

35

What is an adverse drug reaction?

An unwanted or harmful reaction experienced following the administration of a drug combination or combination of drugs under normal conditions of use, which is suspected to be related to the drug

36

How can drug interactions occur in Pharmacokinetics?

 

 

and in Pharmacodynamics?

 

Can occur in any part of ADME

 

Additive effects of drugs with similar effects, Competing effects of drugs with opposite actions

37

What are the two types of ADR?

Type A Augmented

Type B Bizzare

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  1. Describe a Type A ADR
  2. What can they be caused by?
  3. What does it mean that they are normally 'dose dependent'?
  4. What actions should be taken if this has occurred? 

  1. Results from an exaggeration of drugs normal pharmacological actions when given at the usual therapeutic dose.
  2. Can be caused by incorrect dose, decreased elimination of drug or undue sensitivity of organs.
  3. the larger dose the larger the reaction.
  4. inform prescriber, stop drug/reduce drug, choose an alternative, Monitor Patient and record ADR in pt. notes.

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  1. Describe a Type B ADR
  2. Give an example
  3. What are the causes?
  4. What action needs to be taken?

  1. A reaction that is not expected from the normal pharmacological action of the drug, it is unrelated to the dose, unpredictable, has a high mortality rate
  2. anaphylaxis with penicillin.
  3. Genetic factors, Host factors, Environmental factors, Allergic reactions

  4. Needs prompt detection and rapid action

    Drug should be withheld & prescriber informed.

    Alternative drug chosen

    Monitor, report and act on any changes to patients condition to prevent serious complications.

    Record in patients notes - future prescribers need to be aware.

    Educate patient

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What are Adverse drug Interactions?

Alteration of the drugs effects on the body by the prior or concurrent administration of

  • another drug (drug –drug interaction) or
  • by food (drug – food interaction)

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When are dangerous drug interactions likely to occur?

  • Seriously ill patients
  • Elderly patients – sensitive to small changes in blood concentration of certain drugs.
  • When there is only a small difference between the toxic and therapeutic dose of the drug.

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