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45 Cards in this Set
- Front
- Back
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creaming
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reversible separation of a layer of emulsified particles
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cracking or irreversible phase separation
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never acceptable
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phase inversion /emulsion type reversal
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involves the reversion of an emulsion from o/w to w/o form or vice versa
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extensive chemical degradation
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cause substantial loss of active ing from dosage form
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chemical degradation
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produce toxic prdt
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instability of drug prdt
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dec bioavailabity => dec therapeutic effecacy
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rate of rxn or degradation rate
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velocity at w/c rxn occurs
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rate of rxn depends upon
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reactant conc
temp pH presence of solvents or additives |
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order of rxn
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way in w/c the conc of drug or reactant in a chemical rxn affects the rate
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zero order rxn
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rate is independent of the conc of reactants
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ist order rxn
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-rate depends on the 1st power of the conc of a single reactant
-drug conc dec exponentially w/ time |
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half life
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time required for the conc of drug to dec by 1/2
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t 1/2
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0.693/K1
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factors that affect rxn rate
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temperature
presence of solvent chg in pH presence of additives |
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inc temp
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inc rxn rate
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activation energy (ea)
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amt of energy required to put the molecules in an activated state (to react)
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water miscible solvents
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PEG
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low MW alcohols
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stabilize the drug
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H+ catalysis
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predominates at dec pH
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OH- catalysis
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operates at inc pH
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to determine effect of pH on degradation kinetics
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measure decomposition at several H conc
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ph of optimum stability
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determined by plotting the log of the rate constant as fxn of ph
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buffer salts
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added to maintain formulation @ optimum pH
affect rate of degradation => salt in inc ionic stregth |
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inc salt conc
polyelectrolytes (citrate, phosphate) |
substantially affect the magnitude of pka => chg rate constant
promote drug degradation thru gen acid or bases catalysis |
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surfactants
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may accelerate or decelerate drug degradation
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acceleration of degradation
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caused by micellar catalysis
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complexing agts
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aromatic esters => inc half life in presence of caffeines
benzocaine procaine tetracaine |
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modes of pharmaceutical degradation
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hydrolysis
oxidation photolysis |
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most common degradation
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hydrolysis
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most common catalysts of hydrolytic degradation in soln
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H+
OH- |
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esters
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undergo hydrolytic rxn=> drug instability
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oxidation
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mediated thru rxn w/ atmospheric oxygen under ambient conditions (auto-oxidation)
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medicinal compds
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at room tem undergo - auto-oxidation
affected by oxygen dissolved insolvent shld be pkgd in inert atmosphere (NTG) to exclude air fr containers |
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oxidation rxn
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free radical mechanism chain rxn
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antioxidants
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react w/ free radicals by providing electrons and easily available H atoms -> prevent propagation of chain rxns
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commonly used antioxidants
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ascorbic acid
butylated hydroxyanisole (BHA) butylated hydroxytoluene (BHT) propyl gallate sod bisulfite sod sulfite tocopherols |
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photolysis
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degradation of drug molecules by normal sunlight or room light
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undergo rxn
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acquire suff energy
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amber glass bottle ror opaque container
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acts as barrier to this light thereby preventing or retarding photolysis
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shelf life
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calculated by rate of decomposition
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water
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most commonly used vehicle for drug soln
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USP recognized types of water
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purified
wat for inj sterilize wat for inj bacteriostatic wat for inj sterile wat for inhalation sterile wat for irrigation |
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oral drug soln
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syrups
elixirs |
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galenicals formulation
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aromatic water
tinctures fluidextracts spirits |
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sucrose conc
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control of microbial growth
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