Pharmacology: Zero-Order Kinetics in Suspensions
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Questions and Answers

What is the order of reaction if a plot of 1/(a – x)2 against t produces a straight line with all reactants at the same initial concentration?

  • Second order
  • Zero order
  • Third order (correct)
  • First order

    • What is the relation between half-life and initial concentration in a zero order reaction?

  • Half-life is independent of initial concentration
  • Half-life is proportional to the square root of initial concentration
  • Half-life is proportional to initial concentration (correct)
  • Half-life is inversely proportional to initial concentration

    • What is the effect of a 10K rise in temperature on the rate constant?

  • It does not affect the rate constant
  • It increases the rate constant by 2 or 3 folds (correct)
  • It decreases the rate constant by half
  • It decreases the rate constant by 10 times

    • What is the unit of R in the Arrhenius equation?

    <p>Calorie/degree.Mole</p> Signup and view all the answers

    What is the equation that governs the general effect of temperature on reaction kinetics?

    <p>K = Ae^(-Ea/RT)</p> Signup and view all the answers

    What is the effect of light on the rate of reaction?

    <p>It increases the rate of reaction</p> Signup and view all the answers

    What is the method called when a reaction is carried out at different temperatures?

    <p>Temperature variation method</p> Signup and view all the answers

    What is the relation between half-life and initial concentration in a second order reaction?

    <p>Half-life is inversely proportional to initial concentration</p> Signup and view all the answers

    What is the main objective of Accelerated Stability Studies?

    <p>To determine the expiration date of a drug</p> Signup and view all the answers

    How is the rate constant evaluated in Accelerated Stability Studies?

    <p>By plotting the stability data at multiple temperatures</p> Signup and view all the answers

    What is the purpose of plotting the logarithm of k against reciprocal absolute temperature?

    <p>To determine the activation energy Ea</p> Signup and view all the answers

    What is the typical range of activation energy Ea values?

    <p>50-96 KJmol-1</p> Signup and view all the answers

    What is the ultimate goal of Accelerated Stability Studies?

    <p>To predict the shelf-life of a drug</p> Signup and view all the answers

    What is the advantage of using Accelerated Stability Studies?

    <p>It predicts the shelf-life of a drug under storage conditions</p> Signup and view all the answers

    What is the equation that relates the logarithm of rate constants at two different temperatures?

    <p>Log K1 - Log K2 = Ea / 2.303R(T1 - T2)</p> Signup and view all the answers

    What is the effect of increasing the polarity of the solvent on the reaction rate?

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

    What is the relationship between the specific rate constant and ionic strength?

    <p>The specific rate constant is directly proportional to the ionic strength</p> Signup and view all the answers

    What is the dielectric constant related to in a solvent?

    <p>Ability to separate reactants</p> Signup and view all the answers

    What is the unit of activation energy?

    <p>Joules per mole</p> Signup and view all the answers

    What is the effect of increasing the temperature on the rate constant?

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

    What is the equation that relates the logarithm of rate constants at infinite ionic strength?

    <p>Log K = Log Ko + 1.02ZAZBõ</p> Signup and view all the answers

    What is the effect of a reaction involving a neutral molecule on the ionic strength?

    <p>The rate constant is independent of the ionic strength</p> Signup and view all the answers

    What is the characteristic of zero-order kinetics?

    <p>Concentration of the reactant remains constant</p> Signup and view all the answers

    What is the shelf-life of a drug product?

    <p>The time period during which a drug product is expected to remain within the approved specification</p> Signup and view all the answers

    What is the order of reaction in the equation Rate = k[A]a[B]b, where a + b = 1?

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

    What happens to the suspended particles in a suspension as the drug decomposes in solution?

    <p>More drug is released from them</p> Signup and view all the answers

    What is the expiration date of a drug product?

    <p>The date before which the product is expected to remain within the approved shelf-life specification</p> Signup and view all the answers

    What is the characteristic of a first-order reaction?

    <p>The rate of reaction is proportional to the concentration of the reactant</p> Signup and view all the answers

    What is the time required for 10% of the material to disappear?

    <p>Shelf-life</p> Signup and view all the answers

    What happens to the system after all the suspended particles have been converted into drug in solution?

    <p>The system changes to a first-order reaction</p> Signup and view all the answers

    What is the minimum time period covered by data for a long-term study at 25°C ± 2°C/60% RH ± 5% RH?

    <p>12 months</p> Signup and view all the answers

    At what temperature and relative humidity is an intermediate study typically conducted?

    <p>30°C ± 2°C/65% RH ± 5% RH</p> Signup and view all the answers

    What is the minimum time period covered by data for an accelerated study at 40°C ± 2°C/75% RH ± 5% RH?

    <p>6 months</p> Signup and view all the answers

    At what temperature is a long-term study typically conducted for active pharmaceutical ingredients intended for storage in a refrigerator?

    <p>5°C ± 3°C</p> Signup and view all the answers

    What is the minimum time period covered by data for a long-term study at -20°C ± 5°C?

    <p>12 months</p> Signup and view all the answers

    What is the key application of reaction kinetics mentioned in the text?

    <p>Transport processes of drugs in the body</p> Signup and view all the answers

    What is the rate of breakdown of Benzocaine at 30°C?

    <p>1.6 x 10^-7 sec^-1</p> Signup and view all the answers

    What is the criterion for a drug to be considered ineffective?

    <p>After 70% decomposition</p> Signup and view all the answers

    Study Notes

    Zero-Order Kinetics

    • The velocity of fading is constant and independent of the concentration of the color used.
    • Suspensions are a case of zero-order kinetics, where the concentration in solution depends on the drug's solubility.
    • The concentration remains constant as the drug decomposes in solution, and more drug is released from the suspended particles.

    Shelf-Life

    • Shelf-life is the time required for 10% of the material to disappear, or the time at which a material has decreased to 90% of its original concentration.
    • It is the time period during which a drug product is expected to remain within the approved specification for use, provided that it is stored under the conditions defined on the container label.

    First-Order Reactions

    • The rate of a reaction is proportional to the 1st power of concentration of a reactant and may be expressed mathematically as Rate = k[A]a[B]b.
    • The order of reaction is a + b = 1.
    • The rate of reaction is dependent on only one of the reactants.

    Half-Life Method

    • In a zero-order reaction, the half-life is proportional to the initial concentration, a.
    • The half-life of a 1st order reaction is independent of a.
    • ti/2 for a second-order reaction, in which a=b, is proportional to 1/a.
    • In a third-order reaction, in which a=b=c, it is proportional to 1/a2.

    Factors Affecting the Rate of Reactions

    • Temperature: an increase in temperature increases the rate of reaction.
    • A 10K rise in temperature increases the rate constant 2 or 3 folds.
    • The general effect of temperature is governed by Arrhenius Equation (1889).

    Arrhenius Equation

    • K = Ae-Ea/RT, where K is the specific reaction rate, Ea is the activation energy, A is the frequency factor, R is the gas constant, and T is the absolute temperature.
    • The equation can be modified to LogK = LogA - Ea/2.303RT.

    Solvents

    • Three properties of solvents that can influence the reaction rate:
      • Polarity: a more polar solvent can favour the reaction.
      • Ionic strength: the specific rate constant is directly proportional to the ionic strength.
      • Dielectric constant: the ability of the solvent to separate the reactant and product.

    Accelerated Stability Studies

    • A method to predict chemical stability of a formulation during pre-formulation studies.
    • The study involves determining the order of reaction from the plotting of stability data at several elevated temperatures.

    WHO Stability Information

    • Study conditions and minimum time periods covered by data at submission to regulatory bodies:
      • Long-term: 25°C ± 2°C/60% RH ± 5% RH, 12 months.
      • Intermediate: 30°C ± 2°C/65% RH ± 5% RH, 6 months.
      • Accelerated: 40°C ± 2°C/75% RH ± 5% RH, 6 months.

    Application of Reaction Kinetics

    • Transport process of drug in the body, including absorption, distribution, and elimination.
    • Pharmaceutical sciences, such as physical pharmacy and pharmaceutical sciences.

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    Description

    This quiz covers zero-order kinetics in suspensions, including the concept of constant velocity of fading and apparent zero-order kinetics.

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