Pharmaceutics - NAPLEX

1. What is the definition of isotonicity for a pharmaceutical solution relative to blood/tears?

   Same osmotic pressure as blood/tears; no net water movement. Ensures osmotic equilibrium with physiological fluids, preventing cellular dehydration or swelling upon administration.

2. What is the Henderson–Hasselbalch equation for an acidic drug (HA) relating pH, pKa, and ratio?

   $\text{pH}=\text{p}K_a+\log\left(\frac{[A^-]}{[HA]}\right)$. Describes the relationship between pH and the ionization state of a weak acid, where the log ratio of conjugate base to acid shifts the equilibrium.

3. What is the equation for calculating required HLB of a blend using weight fractions?

   $\text{HLB}_{mix}=f_1\text{HLB}_1+f_2\text{HLB}_2$. Provides a weighted average to achieve the optimal HLB for stabilizing a specific emulsion by blending surfactants.

4. What is the formula for percent ionized of a weak acid at a given pH and pKa?

   $\%\text{ionized}=\frac{100}{1+10^{(\text{p}K_a-\text{pH})}}$. Derived from the Henderson-Hasselbalch equation, quantifies the proportion of ionized weak acid molecules based on the pH-pKa difference.

5. Identify the primary purpose of a buffer system in an oral liquid formulation.

   Maintain pH to optimize stability, solubility, and patient acceptability. Resists pH changes from external factors, ensuring consistent drug properties and tolerability in the formulation.

6. What is the definition of HLB in surfactant selection for emulsions?

   Hydrophilic–lipophilic balance; higher HLB indicates more hydrophilic surfactant. Quantifies surfactant polarity to match emulsion type, with higher values favoring oil-in-water systems for better stability.

7. What is the USP definition of a sterile product in pharmaceutics?

   Free of viable microorganisms (bacteria, fungi, and spores). Ensures absence of living microbes to prevent infection, critical for parenteral and ophthalmic preparations.

8. State the equation for absolute bioavailability using AUC and dose for extravascular vs IV dosing.

   $F=\frac{\text{AUC}_{po}}{\text{AUC}_{iv}}\times\frac{\text{Dose}_{iv}}{\text{Dose}_{po}}$. Compares the systemic exposure from oral dosing to intravenous, adjusted for dose differences, to determine absorption efficiency.

9. What is the formula for percent ionized of a weak base at a given pH and pKa?

   $\%\text{ionized}=\frac{100}{1+10^{(\text{pH}-\text{p}K_a)}}$. Derived from the Henderson-Hasselbalch equation, quantifies the proportion of ionized weak base molecules based on the pH-pKa difference.

10. Which emulsion type is typically formed when the emulsifier is more oil soluble (lower HLB)?

    Water-in-oil (W/O). Lower HLB surfactants preferentially stabilize water droplets in oily continuous phase due to greater oil affinity.

11. Which emulsion type is typically formed when the emulsifier is more water soluble (higher HLB)?

    Oil-in-water (O/W). Higher HLB surfactants preferentially stabilize oil droplets in aqueous continuous phase due to greater water affinity.

12. What is the definition of an emulsion in pharmaceutics (phases and stabilization)?

    Two immiscible liquids with one dispersed in the other, stabilized by emulsifier. Enables delivery of immiscible phases by reducing interfacial tension and preventing coalescence through emulsifier stabilization.

13. Which particle-size change increases dissolution rate according to Noyes–Whitney (all else equal)?

    Decreasing particle size (increases surface area $A$). Smaller particles provide greater surface area for solvent interaction, accelerating the dissolution process per the Noyes-Whitney equation.

14. What is the definition of a preservative in a multidose aqueous dosage form?

    Agent added to inhibit microbial growth during storage and use. Prevents contamination and spoilage in products susceptible to repeated exposure, extending shelf life and safety.

15. What is the definition of a suspension in pharmaceutics regarding phases and particle solubility?

    Insoluble solid particles dispersed in a liquid vehicle. Provides a heterogeneous system for poorly soluble drugs, allowing uniform dosing upon shaking for even particle distribution.

16. What is the key difference between flocculated and deflocculated suspensions regarding sediment behavior?

    Flocculated: fast settling, easy resuspension; deflocculated: slow, caking risk. Flocculation forms loose aggregates that settle quickly but redisperse easily, while deflocculation leads to compact sediments prone to hardening.

17. Which relationship between pH and pKa makes a weak acid mostly unionized (more membrane permeable)?

    $\text{pH}<\text{p}K_a$. At lower pH, the environment favors the protonated, unionized form of the weak acid, enhancing lipid solubility and membrane permeation.

18. What is the Henderson–Hasselbalch equation for a basic drug (B) relating pH, pKa, and ratio?

    $\text{pH}=\text{p}K_a+\log\left(\frac{[B]}{[BH^+]}\right)$. Describes the relationship between pH and the ionization state of a weak base, where the log ratio of base to conjugate acid shifts the equilibrium.

19. What is the definition of bioavailability ($F$) in terms of the fraction of dose reaching systemic circulation?

    Fraction of administered dose reaching systemic circulation unchanged. Quantifies the extent of drug absorption into the bloodstream without alteration, critical for assessing oral versus intravenous efficacy.

20. Which relationship between pH and pKa makes a weak base mostly unionized (more membrane permeable)?

    $\text{pH}>\text{p}K_a$. At higher pH, the environment favors the deprotonated, unionized form of the weak base, enhancing lipid solubility and membrane permeation.

21. What is the definition of pKa in pharmaceutics regarding ionization at a specific pH?

    pH where ionized and unionized forms are equal ($50\%$ each). Represents the equilibrium point where half the molecules are protonated and half deprotonated, indicating equal concentrations of ionized and unionized forms.

22. What is the Noyes–Whitney equation expressing dissolution rate as a function of surface area and gradient?

    $\frac{dC}{dt}=\frac{DA}{h}(C_s-C)$. Models the rate of drug dissolution as proportional to the diffusion coefficient, surface area, and concentration gradient across the boundary layer.

23. What is the meaning of a drug being a prodrug in pharmaceutics?

    Inactive/less active form converted in vivo to active drug. Allows for improved pharmacokinetics, such as enhanced solubility or targeted activation, by metabolic conversion to the therapeutic moiety.

24. What is the relationship between osmolarity and osmolality (units) in pharmaceutics?

    Osmolarity: Osm/L; osmolality: Osm/kg (water). Osmolarity measures solute concentration per liter of solution, while osmolality measures per kilogram of solvent, accounting for temperature-independent properties.

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