exam 1 lecture 1 Flashcards
Types of liquid dosage forms
Solution: homogenous molecular dispersion (nothing suspended - see through)
Emulsion: oil in water, water in oil (liquid drops suspending)
Suspension: solid in water or oil (solid suspended)
Advantages of solutions
Homogenous – no problems of content uniformity
Easy to manufacture
Good bioavailability –> already dissolved molecular level
Disadvantage: more reactive/ less stable
components of solution dosage form
API
solvent: water, vegetable oil
co-solvent: ethanol, glycerin, propylene glycol
buffering agent: maintain pH
preservative: maintain stablility
antioxiadant/chelating agent
flavor: sucrose/sorbitol
buffer principle
a solution of a weak acid and a salt of its conjugate base
weak acid removes base: HA+ + OH- –> H2O + A-
salt removes added acid: A- + H3O+ –> HA + H2O
buffer equations
henderson hassalback
pH = pKa + log (A-/HA)
b = 2.3C * ((Ka[H3O+])/(Ka + [H3O+])^2))
selection of pH
select pKa close to pH bc minimize buffering capacity and allows for most stability
if cannot match pH of solution to pH of body fluid
minimize irritation with parenteral, opthalmic, or nasal dosage forms
adjust pH to be the same as pH of body fluid (7.4)
antimicrobial preservatives
purpose: protect patient from pathogens + maintain potency and stability
MOA:
preservative absorb to bacterial membrane and disrupt the membrane. membrane is lipophilic and has net negative surface charge
absorption due to lipid solubility +electrostatic interactions
bacterial content allowed in dosage forms
ampules: must be sterile, single dose, no perservative
multiple dose vials: must be sterile, up to 10 doses, need preservative.
opthalmic solutions: must be sterile, need preservatives in multiple dose container
oral liquids: not sterile, but no pathogens
oral solids: less likely to have bacteria bc no water
ideal preservatives
effective in low concentrations against wide variety of organisms
soluble in formulation
nontoxic
stable
pharmaceutical preservatives
alcohols, acids, esters, quaternary ammonia compounds
factors affecting preservative action
pH: unionized species of weak acids are effective as a preservative
complex formation: only uncomplexed (free) preservative is active
absorption by solids: only unabsorbed preservative is active
chemical stability: consider shelf-life
alcohols
ethanol: limited to oral products bc overtime conc. drops
benzyl alcohol: not orally used, water soluble, stable over wide pH range
chlorobutanol: not orally used
acids
only active in unionized form (lipid soluble)
benzioc acid (pka - 4.2) –> oral products
sorbic acid (pka 4.8) –> oral products, molds + yeast
esters
widely used orally
hydrolyzed rapidly at pH above 7
most lipophilic: propyl + butyl paraben
less lipophilic: methyl + ethyl paraben
low solubility = problem
can cause skin sensitization
