Stability in Pharmaceutics
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Stability in Pharmaceutics

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Questions and Answers

Which of the following substances would likely form a eutectic mixture?

  • Ammonia
  • Camphor (correct)
  • Sodium Chloride
  • Carbon Dioxide

    • What effect occurs when a drug is added to a poorly soluble solvent?

  • Precipitation (correct)
  • Decomposition
  • Absorption enhancement
  • Increased solubility

    • What is the definition of stability according to USP?

  • The extent to which a product can undergo chemical changes without any impact.
  • The maximum concentration at which a drug remains effective.
  • The ability of a product to retain its properties throughout its period of storage and use. (correct)
  • The extent to which a product's composition changes during its shelf life.

    • Which temperature indicates a polymorphic form of Cocoa Butter that should not be exceeded?

    <p>340°C</p> Signup and view all the answers

    Which of the following is a responsibility of pharmacists regarding product stability?

    <p>Observe products for signs of instability.</p> Signup and view all the answers

    In chemical kinetics, the rate of reaction can be described as proportional to what?

    <p>Product of molar concentrations of reactants</p> Signup and view all the answers

    What is the rate equation in a generalized chemical reaction aA + bB = Products?

    <p>Rate = -1/a d(A)/dt</p> Signup and view all the answers

    What happens to chlorpromazine base if its concentration exceeds its water solubility when the pH is raised?

    <p>It precipitates out of the solution.</p> Signup and view all the answers

    Which statement about digoxin's solubility is accurate?

    <p>Digoxin has a water solubility of 0.08 mg/ml.</p> Signup and view all the answers

    Why is refrigeration recommended for certain drug solutions?

    <p>To increase chemical stability and retard microbial growth.</p> Signup and view all the answers

    What are common factors that affect the rates of reaction in chemical kinetics?

    <p>Concentration, Temperature, Light, and Catalysts</p> Signup and view all the answers

    What characteristic defines efflorescent powders?

    <p>They release water of hydration under certain conditions.</p> Signup and view all the answers

    What distinguishes deliquescent powders from hygroscopic ones?

    <p>They dissolve in the moisture they absorb to form a solution.</p> Signup and view all the answers

    Why is it important to heat Cocoa Butter slowly and not exceed 340°C?

    <p>To prevent solidification into an undesirable polymorph</p> Signup and view all the answers

    Which of the following drugs should not be refrigerated due to precipitation effects?

    <p>Fluorouracil</p> Signup and view all the answers

    Which of the following accurately defines hygroscopic drugs?

    <p>They absorb moisture from the air.</p> Signup and view all the answers

    What is the formula for calculating the zero order rate constant?

    <p>k0 = k x [aspirin in solution]</p> Signup and view all the answers

    What keeps the concentration of a drug in a zero order suspension relatively constant?

    <p>Release from suspended particles</p> Signup and view all the answers

    In a first order reaction, how is the rate of change of concentration expressed?

    <p>-d[A]/dt = k[A]</p> Signup and view all the answers

    For a liquid aspirin preparation containing 6.5 g in 100 ml, what is the maximum concentration left after it has decomposed to 90% of its original concentration?

    <p>0.65 g</p> Signup and view all the answers

    What is the calculated shelf life of the aspirin suspension at 250C?

    <p>5.0 days</p> Signup and view all the answers

    Which of the following is true regarding the integration of a first order reaction?

    <p>ln c - ln c0 = kt</p> Signup and view all the answers

    What unit is used for the zero order rate constant in this context?

    <p>grams per 100 ml per hour</p> Signup and view all the answers

    What does the equation C = C0 - kt represent in the context of drug concentration?

    <p>Linear decay of drug concentration over time</p> Signup and view all the answers

    What is the overall order of the reaction between ethyl acetate and sodium hydroxide?

    <p>Second order</p> Signup and view all the answers

    What does the rate constant k represent in a reaction?

    <p>The proportionality constant in the rate equation</p> Signup and view all the answers

    In the context of pseudo first order reactions, which statement is true?

    <p>The reaction rate is dependent only on one reactant's concentration</p> Signup and view all the answers

    What is the unit of the rate constant k for a second order reaction?

    <p>liter sec-1 mole-1</p> Signup and view all the answers

    How does the concentration change in zero order reactions?

    <p>It decreases linearly over time.</p> Signup and view all the answers

    What is the half-life in the context of zero order reactions?

    <p>It is the time for half of the reactant to be consumed.</p> Signup and view all the answers

    Which of the following statements accurately describes the integration of zero order reaction rate equations?

    <p>The integration results in a linear relationship when concentration is plotted against time.</p> Signup and view all the answers

    If a reaction is first order with respect to ethyl acetate and sodium hydroxide, what will happen if the concentration of sodium hydroxide is significantly increased?

    <p>The reaction appears to be first order with respect to ethyl acetate only.</p> Signup and view all the answers

    What is the formula for calculating the half-life of a first order reaction?

    <p>t1/2 = 0.693/k</p> Signup and view all the answers

    In the context of a first order reaction, what does 'k' represent?

    <p>The rate constant</p> Signup and view all the answers

    For a substance in a first order reaction that starts with an initial concentration of 500 units/ml and is measured at 300 units/ml after 40 days, what is the rate constant 'k'?

    <p>0.0128 day-1</p> Signup and view all the answers

    If the half-life of a first order reaction is determined to be 54.3 days, what will be the concentration of the drug after one half-life if the initial concentration was 500 units/ml?

    <p>250 units/ml</p> Signup and view all the answers

    What type of reactions typically involve bimolecular reactions where two reactants combine?

    <p>Second order reactions</p> Signup and view all the answers

    For second order reactions, what does the integration for calculating 'k' include?

    <p>2.303 log(b/a-x)</p> Signup and view all the answers

    In a second order reaction with equal initial concentrations of A and B, how is the half-life expressed?

    <p>t1/2 = 1/ak</p> Signup and view all the answers

    What method can be used to determine the order of a reaction based on concentration versus time?

    <p>Logarithmic transformation</p> Signup and view all the answers

    Study Notes

    Stability in Pharmaceutics

    • Definition of stability: A product retains its properties within specified limits throughout its storage and use period.
    • Pharmacist's responsibilities:
      • Adhering to expiration dates and rotating stock
      • Observing products for signs of instability
      • Proper handling of extemporaneously prepared drugs
      • Using recommended containers and closures
      • Educating patients about storage and use

    Examples of Instability

    • Chlorpromazine: An increase in pH of an aqueous solution can convert the soluble hydrochloride salt to the insoluble base.
    • Temperature effects: Solubility of most drugs decreases with lower temperature. Refrigeration may retard degradation, but can cause precipitation.
    • Efflorescent powders: Powders containing water of hydration can release moisture during trituration or low humidity.
    • Hygroscopic and Deliquescent powders: These powders absorb moisture from the air. Deliquescent powders absorb enough moisture to dissolve and form a solution.
    • Eutectic mixtures: Two or more substances that liquefy when mixed at room temperature.
    • Solvent effects: Adding a solvent in which the drug is poorly soluble to a solution can cause precipitation.
    • Polymorphic conversions: Drugs can exist in various crystalline structures, impacting their properties.

    Chemical Kinetics

    • Rate of reaction: The speed at which a reaction occurs, often expressed as the change in concentration over time.
    • Law of Mass Action: The rate of a reaction is proportional to the product of the molar concentrations of the reactants raised to their respective powers.
    • Rate constant (k): A proportionality constant that quantifies the rate of a reaction.
    • Order of reaction: The sum of the powers to which the concentrations of reactants are raised in the rate equation.
    • Pseudo first-order reaction: A reaction that appears first order because the concentration of one reactant is in vast excess and changes negligibly.

    Types of Reactions

    • Zero-order reactions: The rate of reaction is independent of the concentration of the reactant(s).
      • Example: Loss of color of a drug. Half-life: t1/2 = 0.5A0/k0
      • Apparent zero-order: Suspensions, where the drug in solution stays relatively constant as more is released from the suspended particles.
    • First-order reactions: The rate of reaction is directly proportional to the concentration of the reactant.
      • Example: Decomposition of a drug. Half-life: t1/2 = 0.693/k
    • Second-order reactions: The rate of reaction is proportional to the square of the concentration of the reactant.
      • Example: Bimolecular reactions.

    Determination of Reaction Order

    • Substitution method: Test data in equations for different orders to determine the best fit.
    • Graphic method: Plot concentration vs time for different orders (zero-order: straight line, first-order: logarithmic).
    • Half-life method: Calculate half-lives at different concentrations and use the relationship between half-life and order.

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    Related Documents

    Drug Stability Lecture Notes PDF

    Description

    This quiz explores the concept of stability in pharmaceutics, defining its significance in maintaining product properties during storage and use. It covers the responsibilities of pharmacists regarding expiration dates, signs of instability, and proper handling of drugs. Additionally, examples of various instabilities are reviewed to understand their implications on pharmaceutical products.

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