MW Determination/Correction Factor/Isotonicity

Question 1

i-factor

Answer 1

(number of particles in solution) / (number of particles put into solution)

Question 2

Ideal i-factor

Answer 2

Number of ions that solute dissociates into (needs to be infinitely dilute)

Question 3

What is i-factor is solute doesn’t dissociate?

Answer 3

1

Question 4

Accurate Colligative Property Equations

Answer 4

• All the same equations from the last lecture but multiple times i
• Can back calculate to get “real” i if you know colligative properties but not hte i-value

Question 5

Freezing Point Depression

Answer 5

• Use ratio of real i to ideal i
• L = kf * i
• So delta Tf = L * m

Question 6

L

Answer 6

• Constant given on tables
• Concentration dependent
• Liso = most important to describe body fluid interactions
• allows for osmotic pressure to be controlled and freezing point depression to be measured

Question 7

Why are some solutes not osmotically active?

Answer 7

• Alternative colligative properties
• Not isotonic with bodily fluids
• Membrane permeability

Question 8

Isotonicity

Answer 8

• Parenterals, ophthalmics, nasal, oral
• Same OP as the liquid at the site
• Irritation/damage
• Solvent molecules across a membrane
• High OP can result in damage

Question 9

Pure Water

Answer 9

• Hypotonic (decreases OP): water enters cell and cause bursting and tissue swelling, <0.9% NaCl
• Hypertonic (increases OP): water leaves cell and causes crenation and function loss, > 0.9% NaCl
• Different areas of the body have different tonicity tolerances

Question 10

Sodium Chloride Equivalents

Answer 10

• Method for OP adjustment

- Tonic equivalents proportional to MW of each multiplied by the i-value of the other

Question 11

E-Value

Answer 11

• MUST know MW and i-value
• Used when preparing a product that is isotonic with a body fluid
• Multiply quantity of substance by its E value

Question 12

Isotonicity Calculation Steps

Answer 12

1. Find sodium chloride equivalents - E
2. Check for both drugs and excipients
3. Determine total contribution
   - Remember: isotonic with 0.9% NaCl
   - Watch out for mass!!!

Question 13

White-Vincent Method for OP Adjustment

Answer 13

• E values for adjustment
• Quantity of water for isotonicity
• Only calculated quantity of water is added
• Taking isotonic vehicle to qs

Question 14

Method of Sprowls

Answer 14

• White-Vincent equation used to calculate V values for drugs/excipients
• Choose 0.3 g as weight of ingredient
• Calculate V for that weight (at 0.3g - Sprowls V)

Question 15

Advantage of Sprowls

Answer 15

• Fewer steps
• Fewer ingredients to weight
• Good for reptitiveness
• Good with access to pre-prepared drug-free diluting solutions (normal saline, phosphate buffers)