Lecture 10 Flashcards
sterile liquid formulations (2/8)
isotonic (iso-osmotic)
solutions containing the same concentration of particle
exceptions to the rules of pH and osmolarity
certain isotonic, pH neutral infusates cause phlebitis
example - erythromycin, oxacillin, chemotherapeutic drugs
concentrations
tend to equalize over time through diffusion or osmosis
diffusion
permeable membrane
solute moves from the region of higher concentration to the region of lower concentration
osmosis
water moves from the region of higher concentration to the region of lower concentration
semipermeable membrane
isotonicity
parenteral vehicles have the ability to shrink or burst open blood and venous endothelial cells
impermeable
cell starves
nothing goes through
permeable
cell ends as an empty shell, dead again
everything goes through
semipermeable
viable cell
somethings can cross
hemolysis
cell bursts open due to increased water flow in the cell
water dilution
water will move into the more concentrated side to dilute the solution (the solute cannot move through in a semipermeable membrane)
any hypotonic vehicle could do the same
how can we measure the risk of any given preparation?
by knowing the osmolarity/osmolality of the preparation through an instrument (osmometer)
practical use of colligative properties
colligative properties examples
freezing point depression
lowering of vapor pressure
osmotic pressure
elevation of boiling point
colligative properties
properties of solutions that depend on the quantity of molecule particles (m-particles) in solution rather than the chemical nature of the dissolved materials
osmolarity/osmolality determinants
by the total concentration of solutes dissolved (aka m-particles) including the drug
NaCLl (solid) –> Na+ + Cl- (solution)
1 molecule of NaCL
2 m-particles of Na+ and Cl-
Molarity vs osmolarity
osmolarity is molarity multiplied by the number of m-particles in the solution
example - salts would be multiplied by 2 as they dissociate
osmolarity equation
number of osmoles / volume of solvent and solute
g/L
osmolality equation
number of osmoles / weight (in Kg) of only the solvent
g/kg
interchangeable of osmolarity/osmolality?
often used but only at low concentrations
very dangerous at high concentrations (example - TPN dextrose solutions)
osmolarity/osmolality
a number, a concentration value, measured by an instrument (osmometer)
osmometer
will not distinguish between NaCl and sulfuric acid (a living cell will)
tonicity
effect on living cells
iso-osmotic vs isotonic example
a solution of sulfuric acid gives the same osmolarity value as NS
the two solutions are iso-osmotic (= same concentration of m-particles)
only NS is isotonic (=compatible with living cells)
iso-osmotic/isotonic
iso-osmotic is a rectangle
isotonic is a square
all isotonic solutions are iso-osmotic but not all iso-osmotic solutions are isotonic
iso-osmotic mixed solution
recall colligative properties
isotonic mixed solution
all non-damaging solutes
normal saline and D5W
both isotonic
not always interchangeable so always check the drug monograph/package insert
compatibility with the product is a separate issue that must be checked every time
hyperosmotic solution
the presence of the drug adds to the total osmolarity
when an iso-osmotic solution is used to dissolve a large amount of drug
will shrink cells
not as bad
hypo-osmotic solution
will result in hemolysis (cell burst)
worse than hyperosmotic ones
