Compounding Ingredient Quantities - NAPLEX

1. What is the formula to convert percent strength (%w/v) to ratio strength $1:x$?

   $x = \frac{100}{\%w/v}$. Rearranges percent strength to find x in 1:x ratio by dividing 100 by the percentage.

2. What is the formula to calculate grams from moles using molecular weight (MW)?

   $g = mol \times MW$. Determines mass in grams by multiplying moles by molecular weight.

3. What is the formula to find grams of solute for a %w/w preparation from total grams?

   $g_{solute} = \frac{\%w/w}{100} \times g_{total}$. Derives from the definition of %w/w as the mass of solute per 100 grams of total preparation.

4. What is the formula to calculate milliequivalents (mEq) from mg, MW, and valence?

   $mEq = \frac{mg \times valence}{MW}$. Computes milliequivalents accounting for ion valence and molecular weight from milligrams.

5. What is the formula to calculate mg from mEq, MW, and valence?

   $mg = \frac{mEq \times MW}{valence}$. Solves for milligrams using milliequivalents, molecular weight, and ion valence.

6. Identify the method to find ingredient amount when potency is not 100% (assay given).

   $\text{Weigh} = \frac{\text{required amount}}{\text{assay fraction}}$. Adjusts the weighed amount to compensate for less than 100% potency as indicated by assay.

7. What volume of solute is needed to prepare $80\,mL$ of a $10\%\,v/v$ solution?

   $8\,mL$. Based on %v/v: 10% means 10 mL solute per 100 mL total, for 80 mL.

8. What mass of solute is needed to prepare $120\,mL$ of a $2\%\,w/v$ solution?

   $2.4\,g$. Applies %w/v definition: 2% means 2 g per 100 mL, scaled to 120 mL.

9. What mass of solute is needed to prepare $250\,g$ of a $5\%\,w/w$ ointment?

   $12.5\,g$. Uses %w/w: 5% means 5 g solute per 100 g total, applied to 250 g.

10. What is the formula to calculate aliquot volume needed to deliver a target mass from a solution?

    $V = \frac{Dose}{C}$. Determines the volume required to deliver a specific dose based on solution concentration.

11. What is the formula for dilution using concentrations and volumes (all in consistent units)?

    $C_1V_1 = C_2V_2$. Applies the principle that the amount of solute remains constant before and after dilution.

12. What is the formula to adjust for hydrate/anhydrous forms using molecular weights?

    $g_{needed} = g_{target} \times \frac{MW_{available}}{MW_{target}}$. Corrects for differences in molecular weights between available and target forms of the compound.

13. What is the formula to convert ratio strength $1:x$ (w/v) to percent strength?

    $\%w/v = \frac{100}{x}$. Converts ratio strength where 1 part solute in x parts solution equals 100/x percent.

14. What mass should be weighed to obtain $500\,mg$ active if assay is $80\%$?

    $625\,mg$. Divides required active amount by assay fraction (0.8) to find weighed mass.

15. What is the formula to find mL of solute for a %v/v preparation from total mL?

    $mL_{solute} = \frac{\%v/v}{100} \times mL_{total}$. Stems from %v/v as the volume of solute per 100 mL of total solution volume.

16. How many milligrams of drug are in $30\,g$ of a $1.5\%\,w/w$ cream?

    $450\,mg$. Uses %w/w: 1.5% means 1.5 g per 100 g, for 30 g converted to mg.

17. What ratio strength $1:x$ is equivalent to $2\%\,w/v$?

    $1:50$. Converts 2% w/v to ratio 1:x by dividing 100 by 2.

18. What volume of a $1\,mg/mL$ solution provides a $0.25\,mg$ dose?

    $0.25\,mL$. Calculates volume as dose divided by concentration to deliver required amount.

19. What volume of a $20\%$ stock is needed to make $300\,mL$ of a $5\%$ solution?

    $75\,mL$. Uses dilution formula $C_1V_1 = C_2V_2$ to find stock volume needed.

20. How many grams of drug are in $45\,mL$ of a $4\%\,w/v$ solution?

    $1.8\,g$. Applies %w/v: 4% means 4 g per 100 mL, scaled to 45 mL.

21. What is the formula for alligation to find parts of high strength needed: $parts_{high}$?

    $parts_{high} = C_{target} - C_{low}$. In alligation, parts of higher concentration equal the difference between target and lower concentration.

22. What is the percent strength (%w/v) equivalent of ratio strength $1:250$ (w/v)?

    $0.4\%\,w/v$. Converts 1:250 ratio to percent by dividing 100 by 250.

23. What is the formula to calculate moles from grams using molecular weight (MW)?

    $mol = \frac{g}{MW}$. Calculates the number of moles by dividing mass in grams by molecular weight.

24. What is the formula for alligation to find parts of low strength needed: $parts_{low}$?

    $parts_{low} = C_{high} - C_{target}$. In alligation, parts of lower concentration equal the difference between higher and target concentration.

25. What is the formula to find grams of solute for a %w/v preparation from total mL?

    $g_{solute} = \frac{\%w/v}{100} \times mL_{total}$. Based on %w/v definition as grams of solute per 100 mL of total solution volume.

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