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E-lfh FRCA Primary: Pharmacology - Pharmacodynamics > Ionization > Flashcards

Ionization Flashcards

1
Q

The pH of a 2.5% solution of sodium thiopental is 11. What is the single best explanation of why this is necessary?

A. Thiopental is a weak acid
B. Sodium thiopental can only form at this pH
C. The pH is high enough to prevent precipitation of thiopentoic acid
D. Isomerism of thiopental to the thiol form occurs at this pH
E. Thiopental is highly lipid-soluble except at high pH

A

C. Thiopental acid has a pKa of 7.6 in water but the unionized form is insoluble, and so would precipitate out at a pH near 7.6. At pH 11 the ratio of ionized to unionized form is about 5000:1 so acid precipitation does not occur.

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2
Q

The following drug is a weak acid (true or false):

Aspirin

A

True

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3
Q

The following drug is a weak acid (true or false):

Etomidate

A

False. Weak base

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4
Q

The following drug is a weak acid (true or false):

Fentanyl

A

False. All opioids are weak bases

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5
Q

The following drug is a weak acid (true or false):

Propofol

A

True

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6
Q

The following drug is a weak acid (true or false):

Thiopental

A

True

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7
Q

Morphine has a pKa of 7.9. Regarding the ionization of morphine (true or false):

At pH 7.4 the ratio of the ionized to the unionized form of morphine is approximately 30:1

A

False. The ratio is approximately 3:1.

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8
Q

Morphine has a pKa of 7.9. Regarding the ionization of morphine (true or false):

At physiological pH morphine is more ionized than fentanyl

A

False. Fentanyl has a pKa of 8.4 so is more ionized than morphine at pH 7.4.

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9
Q

Morphine has a pKa of 7.9. Regarding the ionization of morphine (true or false):

Morphine has a tertiary amine group

A

True

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10
Q

Morphine has a pKa of 7.9. Regarding the ionization of morphine (true or false):

Morphine is a weak base that is 50% ionized at pH 7.9

A

True

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11
Q

Morphine has a pKa of 7.9. Regarding the ionization of morphine (true or false):

In a patient who is severely acidaemic, more morphine exists in the unionized form than is found in a normal person

A

False. If plasma pH drops below normal, as is seen in acidaemia, then a greater proportion of morphine exists in the ionized form.

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12
Q

Regarding the buffer system (true or false):

H2CO3 ⇔ HCO3- + H+

This is the only buffer system present in red blood cells

A

False. Haemoglobin is present in red blood cells and can also act as a buffer.

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13
Q

Regarding the buffer system (true or false):

H2CO3 ⇔ HCO3- + H+

Carbonic acid is the weak acid and bicarbonate the conjugate base

A

True

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14
Q

Regarding the buffer system (true or false):

H2CO3 ⇔ HCO3- + H+

The pKa of this system is less than 0.5 pH units from normal plasma pH

A

False. The pKa of this system is around 6.4 compared with a normal plasma pH of 7.4.

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15
Q

Regarding the buffer system (true or false):

H2CO3 ⇔ HCO3- + H+

This is the most abundant extracellular buffer system

A

True

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16
Q

Regarding the buffer system (true or false):

H2CO3 ⇔ HCO3- + H+

Carbonic anhydrase in the plasma is essential for this system to operate

A

False. Carbonic anhydrase is present in the red blood cell not the plasma.

17
Q

Which of the following drugs are weak acids?

A. Remifentanil
B. Naproxen
C. Meperidine
D. Diclofenac
E. Meloxicam

A

A. False. Opioids are weak bases.

B. True. NSAIDs are all weak acids.

C. False. Opioids are weak bases.

D. True.

E. True.

18
Q

This drug is 50% or more ionized at physiological pH (true or false):

Paracetamol

A

False. Paracetamol is a weak acid with a pKa of 9.4, so is not ionized at pH 7.4.

19
Q

This drug is 50% or more ionized at physiological pH (true or false):

Etomidate

A

False. Etomidate is a weak base with a pKa of 4.2, so is not ionized at pH 7.4.

20
Q

This drug is 50% or more ionized at physiological pH (true or false):

Remifentanil

A

False. Remifentanil is a weak base with a pKa of 7.1.

21
Q

This drug is 50% or more ionized at physiological pH (true or false):

Ibuprofen

A

True

22
Q

This drug is 50% or more ionized at physiological pH (true or false):

Ketamine

A

True

E-lfh FRCA Primary: Pharmacology - Pharmacodynamics (2 decks)

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