# Med/Calc

Christina Hernandez

Created on September 16, 2024

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## Transcript

### Med/CalcCalculation

### Why????

Safely administering medications requires the ability to compute medication doses accurately and measure medications correctly. A careless mistake in placing a decimal point or adding a zero to a dose can lead to a fatal error. Check every dose carefully before giving a medication.

### Metric System

##### As a decimal system, the metric system is the most logically organized.

#### Need to know Conversions:

- 1 tsp (teaspoon) = 5 mL (milliliters)
- 1 tbs (tablespoon) = 15 mL
- 1 oz (ounce) = 30 mL
- 1 c (cup) = 8 oz = 240 mL
- 1 kg (kilogram) = 2.2 lb (pound)
- 1,000 mcg (microgram) = 1 mg (milligram)
- 1,000 mg = 1 g (gram)
- 1,000 mL (milliliter) = 1 L (liter)

When working with decimal points, always use a zero before the decimal point – this is called a “leading zero.” This leading zero draws attention to the fact that this is not a whole number – it helps the reader note that there is a decimal.Example – 0.5 mg

Leading and Trailing Zeros

### Leading and Trailing Zeros

- Do not use a decimal point then a zero after a whole number – this is called a “trailing zero.” A trailing zero may make a number look like a bigger number.

- Example – “6” should not be written as “6.0” “6.0” looks like “60” – This would be a ten-fold error!

### Ratio and Proportion in Dosage Calculation

- A proportion is a relationship comparing two ratios.
- The two numbers are separated by a colon (:)
- The two numbers may also be expressed as a fraction.

##### Whether a ratio is expressed as a proportion (in a linear fashion or written across in a line) or as a fraction, like units have to be in the same position on each side of the equal sign.

##### Ratio and Proportion in Dosage Calculation

### Ratio and Proportion in Dosage Calculation

- When calculating a ratio written as a fraction, cross-multiply.
- When calculating a ratio written in a line, as a proportion, multiply the means (the two middle numbers) and multiply the extremes (the two end numbers).
- When using ratio and proportion, you will be given 3 of the 4 values, and will have to solve for the fourth value.
- Use “X” to represent the unknown quantity.

### Read carefully!

##### You may be asked to determine number of milligrams, number of tablets, number of milliliters number of units (especially with heparin and insulin), number milliequivalents…always look first at what you are given in the problem. Is it mg/tablet, or units/mL, or mg/mL? You will always be working with some unit of measure per another unit of measure.

- Always note the VALUE that you are using in a problem when you write out the problem – that way you will not confuse the value label when noting your answer.
- For example:
- The order is for 500 mg of med. You have available 100 mg/mL. How much will you give? ( When you set up the problem, note which are mg and which are mL.)

### Hint

### PRACTICE

##### Example: a medicine has a dosage strength of 50 mg per 1 mL, and the prescriber has ordered a dose of 25mg.How many mL do you administer?

What is the known?

What is the unknown?

### PRACTICE

##### Example: a medicine has a dosage strength of 50 mg per 1 mL, and the prescriber has ordered a dose of 25 mg. How many mL do you administer?

Fraction method

Ratio Method

### PRACTICE

##### Example: a medicine has a dosage strength of 50 mg per 1 mL, and the prescriber has ordered a dose of 25 mg. How many mL do you administer?

Order: 500 mg p.o. of a medicationAvailable: 1 g tabletsHow many tablets will you give?

#### Practice

Order: 0.25 mg IM of a medicationAvailable: 0.5 mg per mLHow many mL will you give?

Order: 40 mg p.o. of a medicationAvailable: 20 mg tabletsHow many tablets will you give?

### 1 g = 500 mg1 tablet X tablet

#### A ratio expressed as a proportion 3:4 = 6:8

The known is....

- 50 mg per 1 mL
- is stated first
- is placed on the left side of the equal sign

100 mg = 500 mg 100 X = 500 1 mL X mL = 5 mL (not mg)

- Desired amount
- Placed on the right side of the equal sign.

• 50 mg = 25 mg numerator labels must match 1 mL X mL denominator labels must match 50X = 25 cross multiply X = 0.5 mL

• 50 mg = 25 mg numerator labels must match 1 mL X mL denominator labels must m 50X = 25 cross multiply X = 0.5 mL

A ratio expressed as a fraction 3 = 6 4 8

• 50 mg = 25 mg numerator labels must match 1 mL X mL denominator labels must match 50X = 25 cross multiply X = 0.5 mL

They occur when a decimal placement is written incorrectly or misread. Decimal errors can result in a 10-fold, 100-fold, or even 1,000-fold overdose or underdose.

https://www.drugtopics.com/view/tenfold-errors-can-lead-tragedy