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Primary FRCA > Pharmacology 1 > Flashcards

Pharmacology 1 Flashcards

1
Q

Medications unsafe in porphyria?

A 
Amiodarone
Barbiturates
Etomidate
Steroids
Alcohol
Clonidine
Progestogens
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2
Q

How are organic compounds classified?

A

Aliphatic / Aromatic

Aliphatic:

  • Carbon chain with varying functional groups attached
  • Carbon atoms in longest chain numbered starting with the carbon participating in the defining functional group, then additional groups are added to the root
  • ‘R’ denotes a variable group or side chain

Aromatic:

  • Contain a benzene ring of six carbon atoms with alternate single and double bonds
  • Carbon atoms numbered from atom to which principle group is attached
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3
Q

What defines an alkene?

A

double C=C bond

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4
Q

What defines an amine?

A

-NR2 group

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5
Q

What defines an alcohol?

A

-OH group

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6
Q

What defines a halide?

A

a halogen atom bonded to a carbon

-eg. Cl, Br, I, F

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7
Q

What defines a carboxylic acid?

A

-C(=O)-OH

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8
Q

What defines a ketone?

A

C=O

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9
Q

What defines an amide?

A

C(=O)-NR2)

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10
Q

What defines an ether?

A

C-O-C

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11
Q

What defines an ester?

A

R-C(=O)-O-R

Acid and alcohol part

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12
Q

What is a phenol?

A

A benzene ring with a hydroxyl group attached

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13
Q

How are volatile anaesthetics classified chemically?

A

Halogenated hydrocarbons / Halogenated ethers

Halogenated hydrocarbons:

  • Halothane
  • Trichloroethylene
  • Chloroform

Halogenated ethers:

  • Enflurane
  • Isoflurane
  • Sevoflurane
  • Desflurane
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14
Q

What are the chemical structural components of local anaesthetic drugs?

A

Aromatic group / Intermediate chain / Amine group

The intermediate chain may be:

  • Ester (-C(=O)-O-)
  • Amide (-C(=O)-NR-)
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15
Q

What are the clinical consequences of differing intermediate chains in local anaesthetic drugs?

A

Esters are rapidly hydrolysed by plasma esterases

Amides are more slowly metabolised in the liver

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16
Q

How can local anaesthetic compounds be made more lipid soluble and protein bound?

A

-Increasing bulk of amine or aromatic parts of the compound

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17
Q

Amine - acid or base?

A

Base - free electron pair can bond to free proton forming an ammonium group

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18
Q

Phenol - acid or base?

A

Weak acid

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19
Q

How does midazolam’s structure and preparation lend itself to clinical use?

A
  • Midazolam is a weak base due to its amine group
  • Must be buffered to an acidic pH of 4 to protonate the amine group and render it soluble in water
  • When injected into the body’s pH of 7.4, the amine group is incorporated into a benzodiazepine ring (pH dependent ring closure), rendering it lipid soluble and able to cross the BBB
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20
Q

How does thiopental’s structure and preparation lend itself to clinical use?

A
  • Prepared in an alkaline solution (pH 10.5) in which it is ionised and thus water soluble
  • Following injection at pH 7.4 it transforms into a non-ionised lipid-soluble molecule
  • This is known as tautomerism
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21
Q

What are the features of ionically bonded compounds?

A
  • Transfer of electrons between atoms, forming charged ions
  • High melting and boiling points due to strong intramolecular forces
  • Water soluble
  • Conduct electricity when melted or dissolved
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22
Q

What are the features of covalently bonded compounds?

A
  • Shared electrons, with atoms held together by attraction between nuclei and shared electrons
  • Normally formed between pairs of non-metallic elements
  • Often liquids or gases with relatively low melting/boiling points
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23
Q

What are the features of co-ordinate bonding?

Give two examples

A
  • One atom donates both electrons of a lone pair
  • eg. NH3 -> NH4+ (ammonia -> ammonium)
  • eg. H2O -> H3O+ (water -> hydronium)
24
Q

What is polar bonding?

A

A bond where the electrons are attracted more strongly to one atom than the other, somewhere between ionic and covalent bonding.

Results in one atom having a slight positive charge and the other a negative charge.

The polarity of the molecule is governed by the electronegativity of the atoms involved in the bond

25
Q

How does the molecular difference between isoflurane and desflurane explain differences in metabolism?

A

The only difference between isoflurane and desflurane is the C-F in desflurane that replaces a C-Cl in isoflurane.

The C-F bond is more polarised than the C-Cl bond and is therefore harder to break and metabolism is decreased compared to isoflurane

26
Q

What types of intermolecular forces exist?

A
  1. Van der Waal’s forces
    - Weak
    - Due to transient momentary dipolar interactions between molecules or atoms
  2. Dipole-dipole interactions
    - Moderate strength
    - Permanent dipole-dipole interactions between polar molecules
  3. Hydrogen bonding
    - Strongest intermolecular force
    - Produced by the strong dipole produced by hydrogen bonding to a strongly electronegative atom, which interacts with another dipolar molecule
27
Q

How do anaesthetic agents affect intermolecular interactions?

A
  • Disruption of van der Waal’s forces and H-bonding within lipid membranes, including neurotransmitter-receptor bonding
  • Formation of H-bonds between hydrogen atoms of volatile anaesthetic agents and aromatic rings, for example
28
Q

What is the relevance of molecular bonding to drug-receptor interactions?

A

Drugs must bind to their receptors and remain there for long enough to exert an effect. The bond must:

  • Form rapidly
  • Be strong enough
  • Exhibit attraction from a sufficient distance to bring the molecules together

For these reasons the bonds are usually ionic in nature, but to maintain stability of the complex, secondary forces are required (eg. vdWs, H-bonding)

29
Q

How does the ACh-AChR interaction exemplify the importance of molecular forces in drug-receptor interactions?

A

+vely charged ammonium ion forms an initial ionic bond with the -vely charged receptor site

vdWs forces between methyl groups on the ACh and AChR confer stability

H-bonding between the C=O esteratic group and hydrogen on the receptor increases stability and specificity of the interaction.

30
Q

How may a covalent bond be broken?

A

Homolytic or heterolytic fission

Homolytic fission:

  • Each element takes one electron to form a free radical
  • Requires UV light or high temperatures

Heterolytic fission:
-One element takes both electrons and two oppositely charged ions are formed

31
Q

What characteristics of organic molecules confer water solubility?

A

Ability to disrupt water-water hydrogen bonding

This can be achieved through ionisation and polar functional groups

Size of molecule is an impediment to solubility, such that a large molecule with a single functional group is unlikely to be soluble, whereas a smaller one may be

32
Q

How may a molecule dissociate in solution?

A

Complete dissociation - ‘strong electrolyte’

Partial dissociation - ‘weak electrolyte’

33
Q

Which functional groups are important in allowing weak electrolyte function to organic molecules?

A

Carboxyl (-COOH)

Amine (-NH2)

Phenols can become proton donors and ketone groups proton acceptors outside of physiological pH

34
Q

To what degree does difference between pKa and ambient pH affect ionisation?

A

Once ambient pH is >2 pH units away from pKa, the equilibrium is shifted 99% to the favoured side

35
Q

State the Henderson-Hasselbalch equation

A

pH = pKa + log([proton acceptor] / [proton donor])

For blood gases, ususally:

pH = 6.1 + log ([HCO3-] / [H2CO3])

36
Q

What is the pKa of the phosphate buffer system?

Why is this relevant?

A

6.8

This is closer to intracellular pH than the pKa of the bicarb system is to plasma pH. This makes it a relatively efficient intracellular buffer

37
Q

What are the main buffers in the renal system?

A

Bicarb
Ammonia
Phosphate

38
Q

What is the pKa of morphine?

Acid or base?

A

7.9

Weak base

39
Q

What is the pKa of fentanyl?

Acid or base?

A

8.4

Weak base

40
Q

What is the pKa of aspirin?

Acid or base?

A

3.5

Weak acid

41
Q

What is the pKa of ibuprofen?

Acid or base?

A

4.9

Weak acid

42
Q

What is the pKa of paracetamol?

Acid or base?

A

9.4

Weak acid

43
Q

What factors govern speed of crossing BBB?

A

Lipid solubility
pKa
Protein binding

44
Q

What is the pKa of propofol?

Acid or base?

A

11

Weak acid

45
Q

What is the pKa of etomidate?

Acid or base?

A

4.2

Weak base

46
Q

What is an isomer?

A

A compound with the same molecular formula (number of each atom) but different arrangement of molecules

47
Q

How are isomers classified?

A

Structural isomers / Stereoisomers

Structural isomers:

  • Same numbers of atoms but different chemical structure
  • May differ hugely in pharmacological properties
  • eg. isoflurane, enflurane
  • Includes tautomers (dynamic structural isomers) - molecules which change structure according to ambient conditions and may vary in functional groups and pharmacodynamics (eg. thiopental)

Stereoisomers:

  • Same molecular formula AND chemical structure
  • Different spatial configurations
  • May be geometric or optical

Geometric isomers:

  • Occur in compounds with an alkene C=C group
  • Comprise cis- and trans- isomers depending on where they are in relation to the double bond

Optical isomers:

  • Occur when 4 different groups are attached to a single atom, which becomes a ‘chiral centre’
  • Comprise ‘enantiomers’ which are mirror images of one another
  • Enantiomers rotate plane polarised light in opposite directions - dextrorotatory / levorotatory enantiomers
48
Q

Why is the changes midazolam undergoes following IV injection NOT an example of true isomerisation?

A

Closure of the benzodiazepine ring at physiological pH involves elimination of a molecule of H2O, thus the chemical formula changes

49
Q

What is a racemic mixture?

A

An equal mixture of dextro- and levo- enantiomers which has no effect on polarised light

50
Q

What is the R / S naming system?

A

Another naming system for enantiomers based on the configuration of the groups attached to the chiral centre

Groups are ranked according to their atomic number. The lowest atomic number becomes the uppermost in the molecular model and if the lower atoms follow their order in a clockwise or anticlockwise order when viewed from below they are named R- or S- accordingly.

R- clockwise (latin: rectus = right)
S- anticlockwise (latin: sinister = left)

There is no correlation between d/l and r/s compounds

51
Q

What is a diastereoisomer?

A

A compound with more than one chiral centre

This produces multiple isomers which are not all mirror images of each other

52
Q

Which anaesthetic drugs form diastereoisomers?

A

Methohexital
Atracurium
Tramadol

53
Q

Why is optical isomerism important in pharmacology?

A

Enantiomers may have differing:

  • Potency
  • Intrinsic activity
  • Clinical responses
54
Q

Give two examples of enantiomeric drugs?

A

Ketamine:

  • S (+) enantiomer is useful agent
  • R (-) enantiomer causes agitation, pain and emergence reactions

Bupivacaine:

  • S (-) enantiomer causes prolonged LA effect
  • R (+) enantiomer causes convulsant and cardiotoxic side effects
55
Q

How is isomerism relevant to muscle relaxants?

A

Aminosteroids:
-Vec and Roc have many chiral centres but are synthesised as single isomers

Isoquinolones:

  • Atracurium and Miv have 4 chiral centres, thus 16 possible stereoisomers
  • Atracurium is produced as a mixture of 10 isomers each with different characteristics
  • Cisatracurium differs in that it is 3x more potent than atracurium, has minimal autonomic effects and histamine release and reduced laudanosine levels
56
Q

How is isomerism relevant to LAs?

A
  • Bupivacaine, prilocaine, mepivacaine and ropivacaine all exist as pairs of optical isomers
  • S-enantiomers are most useful due to increased local vasoconstriction, reduced cardiotoxicity and reduced motor blockade
  • Ropivacaine and bupivacaine are produced as single S-enantiomers
57
Q

Which is more useful - S-etomidate or R-etomidate?

A

R-etomidate

Primary FRCA (34 decks)

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