Dosage Calculations

• Pill Identification PowerPoint: Due on June 8th (Monday). This coming Monday.

  • Involves 50 drugs, covering a comprehensive range of medications you'll encounter in practice.

  • Requires listing uses, affected system (e.g., cardiovascular, nervous), generic name, and brand name for each drug. This ensures a thorough understanding of each medication.

Calculation Guidelines

• Accuracy is crucial in medication calculations. Precise calculations prevent medication errors and ensure patient safety.

• Even small errors (e.g., 1 milliliter overdose) can be detrimental, leading to adverse effects or under-treatment. This highlights the critical nature of accurate dosage calculation.

• Importance of Neatness: Work must be organized and easy to follow to minimize errors.

  • Equal signs must be aligned vertically within calculations to maintain clarity and reduce the risk of mistakes.

• Misplaced decimals can have significant consequences (e.g., 0.25 vs. 2.5), potentially leading to ten-fold errors in dosage. Double-check all decimal placements.

• Safe dosage preparation relies on basic arithmetic skills. A strong foundation in math is essential for accurate and safe medication administration.

• When the dosage ordered differs from the dose on hand follow: Always check whether all measurements are in the same system (e.g., milligrams, grams) before proceeding with calculations.

  • Convert if necessary using known conversion factors or the ratio and proportion method. Ensure consistent units to avoid errors.

  • Write the problem in equation form using the appropriate formula and labeling all parts and completing the calculations. This structured approach helps prevent mistakes.

  • Check the accuracy of your answer for reasonableness and have someone else verify your calculations. A second check adds an extra layer of safety.

Dosage Calculation Methods

• Ratio Proportion (Fraction Form): Formula: Desired Dose \over On Hand Dose * Quantity of On Hand Dose. D/O * Q

  • Acceptable as long as it yields the same answer as other validated methods; consistency is key.

  • Components to identify: Doctor's order (desired dose) and what is on hand (available concentration, form). Correctly identifying these values is vital.

  • Example: Physician orders 162 mg of aspirin every 4 hours. On hand, you have 81 mg tablets.

  • \frac{162 \text{ mg}}{81 \text{ mg}} \times 1 \text{ tablet} = 2 \text{ tablets}

  • The importance of setting up every problem before calculating. Proper setup ensures clarity and reduces errors.

  • You should set up every problem before doing any math to avoid mistakes and maintain a clear process.

Calculations with Unit Conversions

• Medications must be in the same system and measurement before dosage calculation.

  • Example: Ampicillin 0.5 grams ordered, on hand 250 mg capsules. Grams must be converted to milligrams.

  • 0.5 \text{ grams} = 500 \text{ milligrams}

  • \frac{500 \text{ mg}}{250 \text{ mg}} \times 1 \text{ capsule} = 2 \text{ capsules}

  • It is is not possible to change the vial that's sitting on your shelf, so conversions are essential when the available form doesn't match the order.

Further Examples

• Demerol 60 mg IM ordered, vials of Demerol 75 mg in 1 ml on hand.

• \frac{60 \text{ mg}}{75 \text{ mg}} \times 1 \text{ ml} = 0.8 \text{ ml}

• Versed 3 mg preoperatively ordered, vials of 5 mg per ml on hand.

• \frac{3 \text{ mg}}{5 \text{ mg}} \times 1 \text{ ml} = 0.6 \text{ ml}

• Atropine sulfate 0.6 mg ordered, ampoules labeled atropine sulfate 0.4 mg per milliliter.

• \frac{0.6 \text{ mg}}{0.4 \text{ mg}} \times 1 \text{ ml} = 1.5 \text{ ml}

Cautions for Basic Calculation

• Label all parts of the formula, including units (mg, ml, etc.) to avoid confusion.

• Use the same label for desired dose and on-hand dose (e.g., both in grams or milligrams). Consistency prevents errors.

• Use the same label for quantity and answer (e.g., tablets, ml). This ensures the answer is in the correct unit.

• Reduce fractions to the lowest terms before dividing to simplify calculations.

• Multiply by the quantity after dividing. This step is crucial for obtaining the correct final answer.

• Take extra care with decimals; never leave a decimal "naked" (e.g., always use 0.25 instead of .25). Leading zeros are essential to prevent misinterpretation.

• Convert fractions to decimals for easier calculation, especially with complex fractions.

• Round all decimals to one decimal place after computation is complete, unless otherwise specified, to maintain accuracy without excessive precision.

• Verify the accuracy of calculations and question the answer if it's not within normal limits (e.g., less than half a tablet). Use clinical judgment to assess reasonableness.

Ratio and Proportion

• Ratio: The relationship between two numbers (e.g., 1 gram : 15 grains). Understanding ratios is fundamental to setting up proportions.

• Proportion: Two equal ratios (e.g., 1 gram : 15 grains = 2 grams : 30 grains). Proportions allow us to solve for unknown quantities.

• Always label each term in the equation to maintain clarity and accuracy.

• Terms of ratios on each side must be in the same sequence (e.g., gram first on both sides). Consistency in setup is crucial.

• Verify that all the measurements are the same system convert if you need to set up the problem as a proportion labeling all terms and complete the calculations

Formula and Steps

*Dose on hand: Known Value: Desired Dose: Unknown Value.

Practical Application of Ratio and Proportion

• Problem setup: Order reads Demerol 60 mg IV. Narcotics store has vials labeled Demerol 100 mg per 2 mL.

  • On hand: 100 mg per 2 mL (this is the concentration available).

  • Doctor ordered: 60 mg (the required dose).

  • Set up proportion: 100 \text{ mg} : 2 \text{ ml} = 60 \text{ mg} : x \text{ ml}

  • Cross-multiply: (100 \times x = 120)

  • x = 1.2 \text{ ml}

  • Line up equals to keep work neat and organized.

Checking Work: The most important step.

• 100*1.2 = 120

• 2*60 = 120

• Both sides must equal to validate the calculation.

Additional Examples

• Doctor orders Digoxin 0.1 grams. On hand, you have 0.05 grams per tablet.

• Set up: 0.05 \text{ grams} : 1 \text{ tablet} = 0.1 \text{ grams} : x \text{ tablets}

Morphine Example

• Doctor orders 5 milligrams of morphine. On hand, you have 0.005 grams per 2 ml.

• Grams must be converted to milligrams.

• 0.005 \text{ grams} = 5 \text{ milligrams}

Tetracycline Example

• Doctor orders 0.75 grams. You have on hand 250 mg per tablet.

• Grams must be converted to milligrams: 0.75 \text{ grams} = 750 \text{ milligrams}

• 250 \text{ mg} : 1 \text{ tablet} = 750 \text{ mg} : x \text{ tablets}. Set all the math up

• x = 3 \text{ tablets}

• Ensure the final answer includes the appropriate quantity (e.g., tablets, milliliters).

Key Points for Accurate Calculations

• Label every part of the calculation. Include volume and weight units for clarity.

• Write everything out clearly and organize work step-by-step.

• Do not change from what works. (e.g. setting up the equation the same way, dose on hand, doctor orders, equal signs etc.)
  

  *If tablets are given, the math must make sense. You cant give a third of a tablet for instance. Only scored tablets can be split accurately.

Zocor example.

• Doctor orders 0.0006 grams of Zocor. On hand, you have 0.4 milligrams per milliliter.

• Grams must be converted to milligrams: 0.0006 \text{ grams} = 0.6 \text{ milligrams}

• 0.4 \text{ mg} : 1 \text{ ml} = 0.6 \text{ mg} : x \text{ ml}

• X = 1.5 ml
  

  *Remember volume and wieght units are important. You must include them. This is not half but WRONG.

Reglan Example

• Doctor orders 0.6 grams of Reglan. Three hundred milligram tablets three hundred milligram equals 1 tablet

Phedrine example

• Doctor ordered one hundred milligrams, and you've got zero point zero five gram tablets on him.

Codeine Example

• The doctor ordered fifteen milligrams of codeine. And on hand, you have zero point zero three gram tablets

Norvasc example.

• Doctor orders zero point zero five grams. On hand, you have twenty five milligram tablets