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Block 1 - Treatment And Prevention Of Illness > Chemistry Respiratory Disorders > Flashcards

Chemistry Respiratory Disorders Flashcards

1
Q

Hydrophobicity

A

effects the ability of the drug molecule to cross cell membranes and/or perform a suitable binding interaction

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2
Q

The partition coefficient

A

P = [Drug]Octanol / [Drug]Aqueous

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3
Q

High P =

A

High P = hydrophobic compound

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4
Q

Low P =

A

Low P = hydrophilic compound

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5
Q

Lipophilicity (log P)

A

Substituent hydrophobicity constant, π
§ Is a measure of how hydrophobic a substituent is, relative to hydrogen
§ It allows the partition coefficient, for a particular compound, to be calculated (rather than being measured experimentally)

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6
Q

positive π value

A

A positive value = more hydrophobic than hydrogen

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7
Q

negative π value

A

A negative value = less hydrophobic than hydrogen

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8
Q

The importance of pKa

A

o Drug absorption is determined by solubility, molecular weight and the degree of ionisation
o The local pH will dictate the degree of drug ionisation
o The pH at the mucosal surface is 7.39

pKa values for weak acids (HA) that exceed 10 to11 = little, if any, anionic contribution in the pH ranges used in pharmaceutical formulations and in the physiological pH ranges.
Similarly, pKa values for the conjugate acid of a weak base (BH+) that are below 2 to 3 = little, if any cationic contribution.

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9
Q

pKa graph

A

The pKa of the acid is the pH where it is exactly half dissociated

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10
Q

alcohols are..

A

weak acids

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11
Q

For a weak acid, HA

A

o At a pH above its pKa the acid exists mostly as A–

o At a pH below its pKa the acid exists mostly as HA (unionised)

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12
Q

For a weak base, B

A

o At a pH above its pKa the base exists mostly as B (unionised)
o At a pH below its pKa the base exists mostly as BH+

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13
Q

The more stable the conjugate

base,

A

The more stable the conjugate base, the stronger the acid

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14
Q

drugs to treat asthma

A

nitrogen is the most basic group

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15
Q

Drugs to treat asthma…

Muscarinic antagonists

A
  • A quaternary ammonium derivative of atropine
  • Stable in neutral and acidic solution, but rapidly hydrolysed in alkaline solutions.
  • Drug effects last for about 6h. eg atropine
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16
Q

Tiotropium

A

thiapine s membered ring is aromatic and can remove chirality at the centre

Log P = -0.86

17
Q

Drugs to prevent asthma… LABA - salmeterol

A
  • Contains a N-phenylbutoxyhexyl substituent
  • Associates slowly with β2-receptors resulting in slow onset
  • Dissociates at an even slower rate
  • Resistant to both MAO & COMT
  • Very long acting (12h), which is attributed to the highly lipophilic phenylalkyl substituent
  • The R isomer of phenylethanolamines possesses the activity
18
Q

Drugs to prevent asthma… LABA - formoterol

A
  • Contains a 3’-formylamino group & 2 chiral centres!
  • No clinical advantage of using optically pure material due to high potency and low dose required - so racemate is used
  • Much faster onset than salmeterol due to lower lipophilicity
  • Very long acting (12h) which is comparable to salmeterol
19
Q

Drugs to prevent asthma… methylxanthines - therophylline

A
  • Contains the xanthine alkaloid structure
  • Naturally occurring (found in tea)
  • Less lipophilic than caffeine
  • NH provides Brønsted acid potential and imino N provides Brønsted base potential
20
Q

what increases lipophilicity

A

more carbons

21
Q

what is a formyl group

A

formyl is a aldehyde attached to amine

22
Q

which group has a low log p

A

Fluro

23
Q

which group has a high log p

A

Chloro

24
Q

what doesnt have a pka

A

a weak base

25
Q

what effects whether it is predominantly ionised or un-ionised

A

the environment

26
Q

more resonance forms means

A

higher stability

27
Q

S and R configuration

A

S is anticlockwise and R is clockwise configuration

28
Q

Drugs to treat asthma examples

A

o β2-adrenoceptor agonists

o Muscarinic antagonists

29
Q

Drugs to prevent asthma examples

A

o Long-acting β2-adrenoceptor agonists (LABAs)
o Methylxanthines
o Glucocorticoids
o Leukotriene receptor antagonists

Block 1 - Treatment And Prevention Of Illness (32 decks)

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