Chapter 7 Important Notes — D.Pharm 1st Year Pharmaceutics: 117 flashcards
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1. What is the primary focus of Chapter 7 in D.Pharm 1st Year Pharmaceutics?
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Chapter 7 typically covers pharmaceutical calculations, including systems of weights and measures, percentage solutions, dilution and concentration, alligation, and isotonic solutions.
2. Define the **metric system** of weights and measures.
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A decimal system based on the meter, liter, and gram, with units scaled by powers of 10.
3. What is the **avoirdupois system**?
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A system of weights used in the United States for commercial and pharmaceutical purposes, where 1 pound = 16 ounces and 1 ounce = 437.5 grains.
4. Convert 1 kilogram to grams.
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$1 \text{ kg} = 1000 \text{ g}$
5. Convert 1 liter to milliliters.
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$1 \text{ L} = 1000 \text{ mL}$
6. What is a **percentage solution**?
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A solution in which the concentration is expressed as a percentage, typically weight/volume (w/v), volume/volume (v/v), or weight/weight (w/w).
7. Define **weight/volume (w/v) percentage**.
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The number of grams of solute in 100 mL of solution. For example, a 5% w/v solution contains 5 g of solute in 100 mL of solution.
8. Define **volume/volume (v/v) percentage**.
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The number of milliliters of solute in 100 mL of solution. For example, a 10% v/v solution contains 10 mL of solute in 100 mL of solution.
9. Define **weight/weight (w/w) percentage**.
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The number of grams of solute in 100 g of solution. For example, a 20% w/w solution contains 20 g of solute in 100 g of solution.
10. How do you calculate the amount of solute needed to prepare a percentage solution?
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Use the formula: $\text{Amount of solute} = \frac{\text{Percentage} \times \text{Volume or Weight of solution}}{100}$
11. What is **dilution** in pharmaceutical calculations?
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The process of reducing the concentration of a solution by adding more solvent.
12. State the **dilution equation**.
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$C_1 V_1 = C_2 V_2$, where $C$ is concentration and $V$ is volume.
13. What is **alligation**?
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A method used to solve problems involving the mixing of two or more solutions of different concentrations to obtain a desired concentration.
14. Explain the **alligation alternate** method.
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A diagrammatic method where the desired concentration is placed in the center, higher and lower concentrations on the sides, and differences are calculated diagonally to find the proportions needed.
15. What is an **isotonic solution**?
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A solution that has the same osmotic pressure as body fluids (e.g., blood, tears), causing no net movement of water across cell membranes.
16. Why are isotonic solutions important in pharmacy?
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They prevent cell damage (hemolysis or crenation) when administered, ensuring comfort and safety, especially for parenteral and ophthalmic preparations.
17. What is the **sodium chloride equivalent (E value)**?
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The amount of sodium chloride that is equivalent to 1 gram of a drug in terms of osmotic effect.
18. How do you calculate the amount of adjusting substance needed to make a solution isotonic using the **sodium chloride equivalent method**?
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Use the formula: $\text{Amount of adjusting substance} = \frac{0.9 - (E \times \text{weight of drug})}{\text{weight of solution}} \times 100$ for a given volume, or more precisely: $\text{NaCl needed} = 0.9\% \times \text{volume} - (E \times \text{weight of drug})$.
19. What is the **freezing point depression method** for isotonicity?
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A method where the freezing point of a solution is measured; a solution isotonic with body fluids has a freezing point of -0.52°C.
20. Convert 1 grain to milligrams.
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$1 \text{ grain} = 64.8 \text{ mg}$ (approximately 65 mg).
21. Convert 1 ounce (avoirdupois) to grams.
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$1 \text{ ounce} = 28.35 \text{ g}$
22. Convert 1 pound to grams.
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$1 \text{ pound} = 453.6 \text{ g}$
23. What is the **ratio strength** expression?
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A concentration expressed as a ratio, such as 1:1000, meaning 1 part solute in 1000 parts solution.
24. How do you convert a ratio strength to a percentage?
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Divide 100 by the ratio denominator. For example, 1:1000 = $\frac{100}{1000}\% = 0.1\%$.
25. What is the **proof spirit**?
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A standard for alcohol content in the US and UK; in the US, 100 proof = 50% v/v ethanol; in the UK, 100 proof = 57.1% v/v ethanol.
26. Define **milliequivalent (mEq)**.
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One thousandth of an equivalent weight, used to express the concentration of electrolytes in solution.
27. How do you calculate milliequivalents?
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$\text{mEq} = \frac{\text{weight (mg)} \times \text{valence}}{\text{atomic or molecular weight}}$
28. What is the **body surface area (BSA)** method used for?
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Calculating pediatric doses based on the child's surface area relative to an average adult.
29. State the **Young's rule** for pediatric dosing.
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$\text{Child dose} = \frac{\text{Age (years)}}{\text{Age} + 12} \times \text{Adult dose}$
30. State **Clark's rule** for pediatric dosing.
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$\text{Child dose} = \frac{\text{Weight (lb)}}{150} \times \text{Adult dose}$
31. What is the **Dilling's formula**?
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$\text{Child dose} = \frac{\text{Age (years)}}{20} \times \text{Adult dose}$
32. What is a **stock solution**?
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A concentrated solution that is diluted to create a working solution of desired concentration.
33. How do you prepare a working solution from a stock solution?
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Use the dilution equation $C_1 V_1 = C_2 V_2$ to calculate the volume of stock solution needed, then add solvent to reach the final volume.
34. What is **percentage error** in pharmaceutical calculations?
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The difference between the measured value and the true value, expressed as a percentage of the true value.
35. Calculate the percentage error if a 100 mg dose is actually 95 mg.
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$\text{Percentage error} = \frac{|100 - 95|}{100} \times 100\% = 5\%$
36. What is the **alligation medial** method?
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A method to calculate the final concentration when two or more solutions of known concentrations are mixed.
37. How do you calculate the final concentration using alligation medial?
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Calculate the total amount of drug from each solution, sum them, then divide by the total volume.
38. What is the **displacement value**?
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The number of parts by weight of a drug that displaces one part by weight of the base (e.g., cocoa butter) in suppository preparation.
39. Why is displacement value important in suppository preparation?
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It ensures the correct amount of base is used to prepare suppositories with accurate drug dosage.
40. What is the **alcohol dilution** calculation?
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Determining the volume of water needed to dilute a given volume of alcohol to a desired concentration using $C_1 V_1 = C_2 V_2$.
41. Convert 1 teaspoon to milliliters.
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$1 \text{ teaspoon} = 5 \text{ mL}$
42. Convert 1 tablespoon to milliliters.
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$1 \text{ tablespoon} = 15 \text{ mL}$
43. Convert 1 fluid ounce to milliliters.
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$1 \text{ fluid ounce} = 29.57 \text{ mL}$ (approximately 30 mL).
44. What is the **apothecary system**?
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An older system of weights and measures used in pharmacy, with units like grains, scruples, drams, and ounces.
45. Convert 1 dram to grams.
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$1 \text{ dram} = 3.888 \text{ g}$ (approximately 4 g).
46. What is the **minimum measurable quantity** in a prescription balance?
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The smallest weight that can be accurately weighed on a balance, often related to its sensitivity requirement.
47. What is **sensitivity requirement (SR)** of a balance?
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The minimum weight that will cause a discernible change in the balance's equilibrium point.
48. What is the **least weighable quantity**?
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The smallest amount that can be weighed accurately on a given balance, typically 20 mg for a Class II prescription balance.
49. How do you calculate the **percentage of error** in weighing?
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$\text{Percentage error} = \frac{\text{Sensitivity requirement}}{\text{Quantity weighed}} \times 100\%$
50. What is the **isotonicity** of a 0.9% w/v sodium chloride solution?
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It is isotonic with body fluids, meaning it has the same osmotic pressure as blood and tears.
51. What is **hemolysis**?
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The rupture or destruction of red blood cells, which can occur if a hypotonic solution is administered.
52. What is **crenation**?
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The shrinkage of red blood cells due to water loss, which can occur if a hypertonic solution is administered.
53. What is the **freezing point** of blood?
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$-0.52^\circ\text{C}$
54. How do you calculate the amount of sodium chloride needed to make a solution isotonic using the **cryoscopic method**?
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Use the formula: $\text{Amount of NaCl} = \frac{0.52 - \text{freezing point depression of drug}}{0.58} \times \text{volume}$, where 0.58 is the freezing point depression of 1% NaCl.
55. What is the **White-Vincent method** for isotonicity?
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A method to calculate the volume of water needed to make a solution isotonic by adding water to the drug until the freezing point is -0.52°C, then adding an isotonic buffer solution to the final volume.
56. What is the **Sprowls method** for isotonicity?
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A method that uses the sodium chloride equivalent (E value) to calculate the amount of adjusting substance needed to make a solution isotonic.
57. What is a **buffer solution**?
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A solution that resists changes in pH upon addition of small amounts of acid or base.
58. Why are buffers important in pharmaceutical preparations?
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They maintain the pH of a formulation to ensure stability, solubility, and comfort, especially for ophthalmic and parenteral products.
59. What is the **Henderson-Hasselbalch equation**?
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$\text{pH} = \text{p}K_a + \log\left(\frac{[\text{A}^-]}{[\text{HA}]}\right)$
60. What is the **tonicity** of a solution?
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The effective osmotic pressure of a solution relative to body fluids, which can be isotonic, hypotonic, or hypertonic.
61. What is the **osmotic pressure**?
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The pressure required to prevent the flow of solvent across a semipermeable membrane due to differences in solute concentration.
62. What is **osmolarity**?
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The concentration of osmotically active particles in a solution, expressed as osmoles per liter (Osm/L).
63. What is **osmolality**?
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The concentration of osmotically active particles per kilogram of solvent (Osm/kg).
64. What is the **normal osmolarity** of blood?
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Approximately 300 mOsm/L (or 0.3 Osm/L).
65. How do you calculate the **osmolarity** of a solution?
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$\text{Osmolarity} = \text{Molarity} \times \text{number of particles per molecule (i)}$
66. What is the **van't Hoff factor (i)**?
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The number of particles a solute dissociates into in solution. For non-electrolytes, i = 1; for electrolytes, i > 1.
67. Calculate the osmolarity of a 0.9% w/v NaCl solution. (Molecular weight of NaCl = 58.5 g/mol)
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$0.9\% \text{ w/v} = 9 \text{ g/L}$. Molarity = $\frac{9}{58.5} = 0.154 \text{ M}$. Since NaCl dissociates into 2 ions, osmolarity = $0.154 \times 2 = 0.308 \text{ Osm/L} = 308 \text{ mOsm/L}$.
68. What is the **alligation alternate** formula?
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The differences between the desired concentration and the two given concentrations are calculated diagonally to determine the parts of each solution to mix.
69. How do you solve an alligation problem?
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1. Write the higher and lower concentrations on the left. 2. Write the desired concentration in the center. 3. Subtract diagonally. 4. The differences give the parts of each solution.
70. What is the **percentage strength** of a solution?
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The amount of solute in 100 parts of solution, expressed as a percentage.
71. What is the **ratio strength** of a solution?
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A concentration expressed as a ratio of solute to solution, e.g., 1:1000.
72. Convert a 1:5000 solution to a percentage.
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$\frac{100}{5000}\% = 0.02\%$
73. What is the **milligram percent**?
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The number of milligrams of solute in 100 mL of solution, often used for very dilute solutions.
74. Convert 5 mg% to a percentage.
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$5 \text{ mg}\% = 5 \text{ mg per 100 mL} = 0.005\% \text{ w/v}$
75. What is the **parts per million (ppm)** expression?
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The number of parts of solute per million parts of solution, often used for very dilute solutions.
76. Convert 1 ppm to a percentage.
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$1 \text{ ppm} = 0.0001\%$
77. What is the **dilution factor**?
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The ratio of the final volume to the initial volume of a solution.
78. How do you calculate the **dilution factor**?
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$\text{Dilution factor} = \frac{\text{Final volume}}{\text{Initial volume}} = \frac{C_1}{C_2}$
79. What is a **serial dilution**?
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A stepwise dilution of a substance in solution, often used to create a range of concentrations.
80. What is the **alligation medial** formula?
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The final concentration is the weighted average of the concentrations of the mixed solutions.
81. How do you calculate the **final concentration** when mixing two solutions?
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$C_{\text{final}} = \frac{C_1 V_1 + C_2 V_2}{V_1 + V_2}$
82. What is the **displacement value** used for?
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To calculate the amount of base needed when preparing suppositories containing a drug.
83. How do you calculate the **amount of base** needed using displacement value?
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$\text{Amount of base} = \text{Total weight of suppositories} - (\text{Weight of drug} \times \text{Displacement value})$
84. What is the **alcohol dilution** formula?
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$C_1 V_1 = C_2 V_2$
85. What is the **proof spirit** in the US?
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100 proof = 50% v/v ethanol.
86. What is the **proof spirit** in the UK?
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100 proof = 57.1% v/v ethanol.
87. How do you convert **proof strength** to percentage?
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In the US, percentage = proof / 2. In the UK, percentage = proof × 0.571.
88. What is the **milliequivalent** used for?
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Expressing the concentration of electrolytes in solution, such as sodium, potassium, and chloride.
89. Calculate the milliequivalents of 1 g of NaCl. (Molecular weight = 58.5, valence = 1)
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$\text{mEq} = \frac{1000 \text{ mg} \times 1}{58.5} = 17.1 \text{ mEq}$
90. What is the **body surface area (BSA)** method?
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A method to calculate pediatric doses based on the child's surface area relative to an average adult (1.73 m²).
91. State the **BSA formula** for pediatric dosing.
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$\text{Child dose} = \frac{\text{BSA of child}}{1.73} \times \text{Adult dose}$
92. What is **Young's rule**?
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$\text{Child dose} = \frac{\text{Age}}{\text{Age} + 12} \times \text{Adult dose}$
93. What is **Clark's rule**?
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$\text{Child dose} = \frac{\text{Weight (lb)}}{150} \times \text{Adult dose}$
94. What is **Dilling's formula**?
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$\text{Child dose} = \frac{\text{Age}}{20} \times \text{Adult dose}$
95. What is the **Fried's rule**?
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$\text{Infant dose} = \frac{\text{Age in months}}{150} \times \text{Adult dose}$
96. What is the **percentage error** formula?
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$\text{Percentage error} = \frac{\text{Actual value} - \text{Measured value}}{\text{Actual value}} \times 100\%$
97. What is the **least weighable quantity** for a Class II prescription balance?
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20 mg
98. What is the **sensitivity requirement** of a balance?
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The minimum weight that causes a discernible change in the balance's equilibrium point.
99. How do you calculate the **percentage error** in weighing?
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$\text{Percentage error} = \frac{\text{Sensitivity requirement}}{\text{Quantity weighed}} \times 100\%$
100. What is the **minimum measurable quantity**?
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The smallest weight that can be accurately weighed on a balance, often 20 mg for Class II balances.
101. What is the **isotonicity** of a solution?
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The property of having the same osmotic pressure as body fluids, preventing cell damage.
102. What is **hemolysis**?
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The rupture of red blood cells due to a hypotonic solution.
103. What is **crenation**?
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The shrinkage of red blood cells due to a hypertonic solution.
104. What is the **freezing point** of blood?
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$-0.52^\circ\text{C}$
105. What is the **cryoscopic method**?
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A method to determine isotonicity by measuring the freezing point depression of a solution.
106. What is the **White-Vincent method**?
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A method to make a solution isotonic by adding water to the drug until the freezing point is -0.52°C, then adding an isotonic buffer to the final volume.
107. What is the **Sprowls method**?
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A method to calculate the amount of adjusting substance needed to make a solution isotonic using the sodium chloride equivalent (E value).
108. What is a **buffer solution**?
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A solution that resists changes in pH upon addition of small amounts of acid or base.
109. What is the **Henderson-Hasselbalch equation**?
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$\text{pH} = \text{p}K_a + \log\left(\frac{[\text{A}^-]}{[\text{HA}]}\right)$
110. What is **tonicity**?
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The effective osmotic pressure of a solution relative to body fluids.
111. What is **osmotic pressure**?
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The pressure required to prevent the flow of solvent across a semipermeable membrane.
112. What is **osmolarity**?
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The concentration of osmotically active particles per liter of solution (Osm/L).
113. What is **osmolality**?
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The concentration of osmotically active particles per kilogram of solvent (Osm/kg).
114. What is the **normal osmolarity** of blood?
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Approximately 300 mOsm/L.
115. How do you calculate **osmolarity**?
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$\text{Osmolarity} = \text{Molarity} \times i$
116. What is the **van't Hoff factor**?
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The number of particles a solute dissociates into in solution.
117. Calculate the osmolarity of 0.9% w/v NaCl. (MW = 58.5)
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$0.9\% = 9 \text{ g/L}$. Molarity = $\frac{9}{58.5} = 0.154 \text{ M}$. Osmolarity = $0.154 \times 2 = 0.308 \text{ Osm/L} = 308 \text{ mOsm/L}$.
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