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Pharmaceutical Calculations > Buffers > Flashcards

Buffers Flashcards

1
Q

Buffers are used in which state of matters?

A

Only liquids

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2
Q

Some pharmaceutical solutions that buffers can act on

A

Lotion
Oral solutions
Injections
Eye drops
Topical solutions

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3
Q

What are the topical solutions

A

Solutions that patients cannot swallow, e.g: mouth wash

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4
Q

Buffers are examples of:

A

Excipients

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5
Q

Vehicles are examples of excepients, what are vehicles?

A

Solvents

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6
Q

The pH scale

A

0-3 Strong acid
4-6 Weak acid
7 Neutral
8-10 Weak base
11-14 Strong base

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7
Q

The pH of the drug solutions is

A

From 6 to 8

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8
Q

What is the formula of the pH

A

pH= -log[H+]

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9
Q

What is the pH of the following body fluids
Blood plasma
Saliva
Sweat/urine
Tears
Gastric juice
Intestinal juice/ pancreatic juice
Interstitial fluid
Intracellular fluid/ Cerebrospinal fluid/ Skin

A

Blood plasma - Neutral (7.4)
Saliva - Slightly acidic due to the bacteria
Sweat/urine - Slightly acidic
Tears - Neutral
Gastric juice - Strongly acidic
Intestinal juice/ pancreatic juice/ interstitial fluid - neutral - slightly basic
Intracellular fluid/ Cerebrospinal fluid/ Skin - Neutral
(The skin may sometimes be slightly acidic, due to the presence of sweat)

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10
Q

What happens if 1 mL of 0.1 M HCl is added to 100 mL of pure water?

A

The pH will drop from 7 to 3

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11
Q

What happens if 1 mL of 0.1 M HCl is added to 100 mL of water containing a buffer ?

A

The pH will drop from 7 to 6.91

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12
Q

Define Buffers

A

Solutions that resist the change in the pH, when a small amount of base or acid is added

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13
Q

What do the buffers contain?

A

Buffers consist of a mixture of a weak acid and one of its salts, or a weak base and one of its salts

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14
Q

Example of weak acid/its salt used in buffers

A

• Acetate buffer is made of:
-Acetic acid and sodium acetate
• Citrate buffer is made of:
-Citric acid and sodium citrate
• Phosphate buffer is made of:
-Phosphoric acid and sodium phospate

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15
Q

The pH of phosphate buffers

A

7.4, it is used in blood and it is found in the body

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16
Q

What happens if a strong acid such as HCl is added to the acetate buffer solution?

A

CH3COO-Na+ + H+Cl- = CH3COOH + NaCl

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17
Q

What happens if a strong base such as NaOH is added to the acetate buffer solution?

A

CH3COO-H+ + Na+OH- = H2O + CH3COONa

18
Q

What is the buffer capacity?

A

The resistance to change in pH is known as buffer action or buffer capacity

19
Q

The effect of the strength of the buffer on resisting the change in the pH

A

A concentrated buffer can neutralize more added acid or base than a dilute buffer

20
Q

What could be the pH of the eye drops?

A

7

21
Q

What do you think the pH of the IV injection should be?

A

7.4

22
Q

What do you think the pH of the IV injection should be?

A

7.4

23
Q

The pH of the buffer solution depends on:

A

The drug
The site of application

24
Q

The suffixes
-ate
-ine
-ose

A

-ate —> salt
-ine —> weak base
-ose —> sugars

25
Q

The range of the pH in the blood

A

6.9/ 7.0/ 7.2 —-> 7.6/ 7.8

26
Q

What happens if 1 mL of HCl is added to 1000 mL of human blood?

A

The pH will drop from 7.4 to 7.3
Due to the presence of buffers in the body

27
Q

The buffer system in the body can be divided into two parts:

A

Intracellular fluid
Extracellular fluid

28
Q

The intracellular fluid buffers include

A

Phosphate buffer system
Protein buffer system (including haemoglobin(RBCs) buffer and amino acid buffer (all proteins))

29
Q

The extracellular fluid buffer include

A

Protein buffer system (including amino acids (all proteins) and plasma protein buffers)
Carbonic acid - bicarbonate buffer system (CO2 when dissolved in H2O)

30
Q

Which of the following dosage forms needs adjustment of pH?
1. Tablets
2. Injections
3. Eye drops
4. All of the above
5. 2 & 3

A
  1. 2 & 3
    Tablets are not included, as buffers only work in liquids
31
Q

Why do we need to adjust the pH of pharmaceutical solutions.?

A
  1. To prevent tissue irritation
  2. To improve drug water solubility
  3. To enhance drug chemical stability
  4. To enhance drug biological activity
  5. To protect the solution from pH changes brought about by:
    5.1 The carbon dioxide of the air
    5.2 The alkalinity of glass bottles
32
Q

prevent tissue irritation

A

• Low and high pH pharmaceutical solutions can be hazardous to different tissues.
• For example, eyes and mucous membranes are prone to damage by low or high pH solutions.
• Skin can be harmed by very high or very low pH.
• Low pH can be dangerous due to acidity.
• High pH can be caustic and can cause tissue
damage.

33
Q

Products that cause irritation if the pH was not optimum

A

• Ophthalmic solutions (eye drops),
• Parenteral products (injections),
• Fluids to be applied to abraded surfaces
(Irrigation solutions).
• Mouth wash - It should be slightly basic to neutralize the acidity of the saliva
• Contact solutions

34
Q

To improve the drug water solubility

A

Many drugs are poorly water-soluble, and their solubility in water can be improved by changing the pH of the pharmaceutical solution by using buffers.

35
Q

enhance drug chemical stability

A

Morphine injections are not decomposed during sterilization when heated for 60 minutes at l00 oC if the pH of the injection is less than 5.5, but are decomposed under these conditions if the pH is neutral or alkaline.

36
Q

To protect the pharmaceutical solution until the expiration date (shelf life)

A

from pH changes brought about by the carbon dioxide of the air dissolving and forming carbonic acid and/or the alkalinity of glass bottles.

37
Q

enhance the anti-microbial activity of preservatives (enhance the activity of certain excepients)

A

For example, sodium benzoate is used as preservative and is effective in a concentration of 4% at pH 7.0, 0.1% at pH 4 and 0.03% at pH 2.3.

38
Q

Formuls for the pKa of the base

A

pKa of the base = pKw - pKb
pKw = 14

39
Q

Why are buffers mostly made of weak acid and their salts, rather than weak bases and their salts?

A

because of the volatility and instability of the bases and the dependence of their pH on pKw, which is affected by temperature changes.

40
Q

Which buffer system gives the best buffer capacity?

A

The buffer system giving the best buffer capacity will be that containing an acid/base with a pKa closest to the desired pH of the solution. (Equal concentration of acid and salt)

41
Q

Some factors influencing the pH of buffered solutions

A
  1. The addition of neutral salts such as NaCl due to change in ionic strength.
  2. Dilution with water may cause a small increase or decrease in pH due to changes in activity of the buffer or because water itself can act as a weak acid or base.
  3. Temperature. The pH of acetate buffer was found
    to increase with temperature while the pH of borate buffer decreased with temperature.
  4. Basic buffers change more markedly with temperature compared to acidic buffers.
42
Q

What is the dilution value?

A

Dilution value is defined as the change in pH on diluting the buffered solution to one-half of its original strength.

Pharmaceutical Calculations (17 decks)

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