Pharmaceutical Stability Kinetics: Reaction Orders and Shelf-Life Estimation

Shelf-Life Estimation (t90)

Time within which product contains at least 90% of the labeled amount of active ingredient(s).

Accelerated stability studies

Studies determined via high temperature and high humidity.

Responsibility of the Pharmacist

Dispense oldest stock first and observe expiration dates.

Proper storage conditions

Store products under conditions stated in USP monographs and/or labeling.

Instability observation

Observe products for evidence of instability.

Repackaging responsibility

Properly treat/label products that are repackaged, diluted, or mixed with other products.

Dispensing requirements

Dispensing in proper container with proper closure.

Patient education

Informing/educating patients concerning proper storage and use of products, including the disposition of outdated or excessively aged prescriptions.

Expiration date considerations

Expiration date given at room temperature: What is the expiration extension if refrigerated?

Temperature effects on expiration

Expiration date for refrigerated temperature given: How long if left at room temperature?

Heating effects on expiration

Expiration date for room temperature given and it is desired to heat (autoclave): What is the % decomposition?

Kinetics

The study of the rate of chemical change and the way this rate is influenced by conditions of concentration of reactants, products, and other chemical species that may be present and by factors such as solvent, pressure, and temperature.

Reaction Kinetics

Kinetic data includes reaction order and reaction rate.

Reaction Order

The order of reaction refers to the way in which concentration of drug or reactants influences the rate of chemical reaction or process.

Rate of reaction

The rate of a chemical reaction is the velocity with which the reaction occurs.

Rate expression

If the amount of drug A is decreasing with respect to time, then rate of this reaction can be expressed as - dA/dt.

Concentration function

The rate of decrease in the concentration C of reactant A to form product B can be described as a function of time.

Blood Alcohol Content (BAC)

The concentration of alcohol in blood, usually measured as mass per volume.

First-Order degradation

[drug] decreases exponentially with time; rate of degradation is proportional to [drug]; plot of log [drug] or ln[drug] vs. time is linear; t 1/2 is constant regardless of [drug].

Zero-Order degradation

[drug] decreases linearly with time; rate of degradation is constant; rate of elimination is independent of [drug]; plot [drug] vs. time is linear; no true t 1/2.

Rate equations

Rate = k C; C = Co e-kt; Rate = k; C = Co - kt.