Drug Stability and Reaction Orders

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Questions and Answers

What is the overall order of a reaction if the individual orders are 2 for A and 3 for B?

5 (correct)

Which of the following statements correctly defines a zero order reaction?

The rate is independent of the concentrations of the reactants. (correct)

The rate increases as the concentration of the reactants decreases.

The rate is directly proportional to the concentration of one reactant.

The rate depends on the concentration of two reactants.

Which factor does NOT influence the stability of a drug?

Temperature

Solubility

Molecular weight (correct)

What is the purpose of determining the half-life of a drug?

To assess the time for degradation of half the drug amount. Signup and view all the answers

Which of the following describes solvolysis in the context of drug stability?

Chemical reaction facilitated by a solvent molecule. Signup and view all the answers

What designation is given to the period where 90% of the original drug concentration remains?

Shelf life Signup and view all the answers

Which of the following is an example of an external factor affecting drug stability?

Temperature Signup and view all the answers

What is the significance of the sampling plan in stability testing?

To cover the entire stability study effectively. Signup and view all the answers

What does a first order reaction indicate about the relationship between reaction rate and reactant concentration?

The rate is directly proportional to the concentration of one reactant. Signup and view all the answers

Which of the following best describes the term 'half-life' in the context of drug stability?

The time required for one-half of the material to degrade. Signup and view all the answers

What do inherent factors in drug stability refer to?

Chemical reactions within the drug molecule itself. Signup and view all the answers

What is the meaning of shelf life (t90) for a drug?

The period during which 90% of the original concentration is still effective. Signup and view all the answers

Which aspect of drug stability is NOT included as an external factor?

The inherent chemical structure of the drug. Signup and view all the answers

How is overall order of a chemical reaction defined?

The sum of the individual orders with respect to all reactants. Signup and view all the answers

What is the significance of sampling time points in stability testing?

To establish a stability profile of the drug over time. Signup and view all the answers

Which of the following best describes solvolysis related to drug stability?

The splitting of a drug molecule via a solvent molecule. Signup and view all the answers

Study Notes

Law of Mass Action

The reaction rate is proportional to the product of reactant concentrations, each raised to a power equal to the number of molecules undergoing reaction.
Rate ∝ [A]^a [B]^b
Rate = k[A]^a[B]^b
Reaction order = sum of exponents (a + b)
Order of A = a, Order of B = b
Overall order = a + b

Reaction Order Examples

Zero Order: Reaction rate is independent of reactant concentrations.
First Order: Reaction rate is directly proportional to the concentration of one reactant.

Drug Stability

Factors affecting drug stability:
- Inherent factors: Molecular changes due to energy changes & molecular breakdown (solvolysis, oxidation, photolysis, dehydration, racemization).
- External factors: pH, pKa, solubility/dissolution, excipient interactions, temperature.

Drug Stability Measures

Half-life (t_1/2): Time required for one-half of the material to degrade.
Shelf life (t₉₀): Time for 90% of the drug to remain at the original concentration (expiration dating period).
- The 10% loss criterion is generally based on negligible clinical consequences of such loss
  - This is the time period during which a drug product is expected to remain within the approved specification for use, provided it is stored under the conditions defined on the container label.

Stability Testing Considerations

Sampling time points: Testing frequency must be sufficient to establish the stability profile of the new drug substance.
Sampling plan: Sampling plan for stability testing involves planning for the number of samples to be charged to the stability chambers and sampling from the charged batch to cover the entire study.
Test parameters: Stability test protocol should define the test parameters to evaluate stability samples. Chosen tests monitor quality, purity, potency, and identity which could be expected to change upon storage.

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Description

This quiz covers the Law of Mass Action and the concepts of reaction order as well as factors influencing drug stability. Explore the different order reactions and how various internal and external factors can affect the stability of pharmaceuticals. Test your understanding of these important scientific principles.