pharm calc

• solvent passes through a semi-permeable membrane from a dilute solution into a more concentrated one
• concentrations become equalized

• undissociated
• solution contains only molecules
• osmotic pressure varies with the concentration of the solute

total number of particles=osmotic pressure

• dissociated
• solution contains ions

osmotic pressure varies with both the concentration of the solute and its degree of dissociation

2 solutions that have the same osmotic pressure

• solution having the same osmotic pressure as a specific body fluid
• (equal tone)
• not being isotonic is painful for the patient (stinging or burns)

solutions of lower osmotic pressure than that of the body fluid

solutions of higher osmotic pressure than that of a body fluid

• opthalmic (eye)
• nasal (nose)
• parenteral (injection)
• enema (rectal)

• isotonic solutions are better tolerated by the patient
• homeostasis with the bodys intracellular fluids

• comarison of freezing points are used for determining tonicity
• preezing point of both blood serum and lacrimal fluid are the same -.52 degrees C
• lacrimal=eye fluid
• (standard to compare to)

• one gram molecular weight of any non electrolyte
• dissolve in 1000g of H2O (1000mL)
• freezing point of the solution is about -1.86 degrees C below the freezing point of pure water

can calculate the weight of any non electrolyte that should be dissolved in each 1000 g of water if the solution is to be isotonic with body fluids

• osmotic pressure depends more on the number than on kind of particles
• substances have a tonic effect that increases with the degree of dissociation

greater the dissociation, the smaller the quantity required to produce any given osmotic pressure

• molecules divided by molecules start with before dissociation
• the multiplier to use with isotonic equation

1

1.8

2.6

3.4

4.2

calculate the amount (in grams) of NaCl represented by the ingredients in the prescription. Multiply the amount (in grams) of each substance by its NaCl equivalent

calculate the amount (in grams) of NaCl alone that would be contained in an isotonic solution of the volume specified in the prescription

subtract the amount of NaCl represented by the ingredients in the prescription fom step 1 from the amount of NaCl alone that would be represented in the specific volume of an isotonic solution from step 2. THe answer is in grams

If an agent other than NaCa such as boric acid, dextrose or potassium nitrate is to be used to make a solution isotonic, divide the amoint og NaCl in step 3 by the NaCl equivalent of the other substance