Drug Dose conversions & formulas

KCl Solution (Oral) to Tablets

KCl 10% = 20 mEq/15 mL

Calcium Salts elemental equivalence

Calcium carbonate = 40% elemental calcium

Calcium citrate = 21% elemental calcium

Aminophylline <-> Theophylline

Aminophylline to Theophylline: Multiply by 0.8 (remember: ATM)

Theophylline to Aminophylline: Divide by 0.8

Statin Dose Equivalencies

Pharmacists Rock At Saving Lives, Preventively Frequently

• Pitavastatin — 2 mg

• Rosuvastatin — 5 mg

• Atorvastatin — 10 mg

• Simvastatin — 20 mg

• Lovastatin — 40 mg

• Pravastatin — 40 mg

• Fluvastatin — 80 mg

Levothyroxine dose form equivalencies?

IV:PO = 0.75:1

Metoprolol Dose Form Equivalencies?

IV:PO = 1:2.5

Loop Diuretics equivalencies

Insulin conversions

Usually, 1:1 conversion

• Exceptions:

  • Going from NPH to Glargine 

    • NPH is dosed BID, whereas glargine is dosed daily; use 80% of NPH dose

    • Calculation Example: Patient takes NPH 30 units in the morning and 20 units at night (TDD=50 units).

      • Convert to Glargine daily: 50 units×0.80=40 units once daily.

  • Going from Toujeo to other forms of glargine: use 80% of Toujeo dose

    • Calculation: Patient takes Toujeo 50 units daily.

      • Convert to Lantus (U-100) daily: 50 units×0.80=40 units once daily.

Steroids equivalencies?

Cortisone 25 mg

Hydrocortisone 20 mg

Prednisone 5 mg 

Prednisolone 5 mg 

Methylprednisolone 4 mg

Triamcinolone 4 mg

Betamethasone 0.6 mg

Dexamethasone 0.75 mg

Lithium syrup and mEq conversions?

300 mg lithium carbonate= 5 mL lithium citrate syrup =  8 mEq Li+ ion

What do the different percent strengths represent?

Weight in volume (% w/v): the number of grams (g) of drug dissolved in 100 millilitres (mL) of liquid or solution.

• A 2% w/v means there is 2 g of drug dissolved in 100 mL of liquid or solution.

Weight in weight (% w/w): the number of g of drug in 100 g of the preparation.

• A 6% w/w means there is 6 g of drug in 100 g of the preparation.

Volume in volume (% v/v): the # number of mL of a drug in 100 mL of liquid or solution.

• A 10% v/v means there is 10 mL of drug in 100 mL of liquid or solution.

Convert from ratio to % strength:

100/ratio strength

Convert from % strength to ratio:

100/% strength

Convert PPM to % strength:

Move decimal to the LEFT 4 spaces

Convert % strength to PPM:

Move decimal to the RIGHT 4 spaces

Specific gravity

How to approach Dilution and concentration questions?

Q1*C1=Q2*C2

Units on both sides must match 

• Pure active ingredient = 100% concentration.

• Diluent (e.g., petrolatum, lanolin, alcohol, ointment base, lactose) = 0% concentration because it contains none of the active drug.

If the question asks "What is the final weight/volume of the new mixture?" → Answer is Q2​.

If the question asks "How much diluent/base must be added?" → Answer is Q2​−Q1​.

How to approach Alligation problems?

This is used when dealing with three concentrations 

Osmolarity formula

How to determine number of dissociation particles?

• Dextrose and Mannitol : 1

• Calcium Chloride: 3

• Sodium citrate: 4

• Everything else is 2

How to calculate sodium chloride equivalent?

How to determine dissociation factor?

• Dextrose and Mannitol : 1

• Calcium Chloride: 3

• Sodium citrate: 4

• Everything else is 2

How to approach Isotonicity problems?

Moles

millimoles

mEq

Do not need to convert MW if its in g/mol

Total Energy Expenditure 

TEE: BEE x Activity factor x stress factor 

Activity Factors: 

Confined to bed: 1.2

Out of Bed: 1.3

Fluid requirements for TPN: 

1,500 mL + (20 mL)(weight in kg - 20); use Total Body Weight 

Fats, Carbohydrates, and Protein conversions

Nitrogen Balance 

Nitrogen Balance = grams of protein(AA)/6.25 

Non-Protein Calories to Nitrogen ratio 

1. Find nitrogen balance 

2. Divide the total non-protein calories(dextrose and lipids) by the grams of the nitrogen 

What is there to know about Fats/lipids?

Corrected Calcium

How to reduce the risk of calcium and phosphate precipitation in parental nutrition?

• Use calcium gluconate over calcium chloride 

• Add phosphate first 

• The calcium and phosphate added together should not exceed 45mEq in one liter 

• Maintain proper pH  and refrigerate once bag is prepared 

How to approach problems involving electrolytes?

1 Find the Single-Source Requirement: Look at the requirement that can only come from one bottle (e.g., Acetate). 

2. Apply the conversion ratio 

• 1:1 Ratio for Na and K+: That same mEq number is automatically how many mEq of the "passenger" ion (Sodium) you just added.

• Phosphate: multiply volume you received by mEq

3. Subtract from the Total: Take the total requirement for that second ion (Total Sodium) and subtract the mEq you got in Step 2.

4. Convert Remaining mEq to Volume (mL): Divide the remaining mEq by the stock concentration of your second bottle (NaCl) to get your final volume.

Note: Phosphate will be written in mmol instead of mEq 

Which drug products should not be administered in the feeding tube?

• Enteric coating 

• Delayed or XR products 

• SL/ Buccal products 

• Hazardous drugs 

What is the rule for preventing drug/enteral feeding interactions?

Hold Feedings 1 hour before and 2 hours after drug administration