Dosages Based on Body Weight

• Amount of medication per

• Weight of the patient per

• Unit of time

Dosages Based on Body Weight (cont.)

Rule 17-2Rule 17-2 Calculating dosage based on body weight:

Step A Convert: patient’s weight to kilograms

• Round to nearest tenth

Dosages Based on Body Weight (cont.)

Rule 17-2 Rule 17-2 (cont.)

Step B Calculate: the desired dose D by multiplying dose ordered by the weight in kilograms such as

dose desired kg or dose desired kg xkg

mcgx

kg

mg

Dosages Based on Body Weight (cont.)

Rule 17-2Rule 17-2 (cont.)

Step C Think!...Is It Reasonable?

Confirm whether or not the desired dose is safe by checking the label, package insert, or product literature.

Dosages Based on Body Weight (cont.)

Rule 17-2Rule 17-2 (cont.)

Perform dosage calculation.

Calculate the amount to administer, using proportion method, dimensional analysis, or the formula method.

Dosages Based on Body Weight (cont.)

Calculate the amount to administerto a 3 yr old weighing 34 lb.

Ordered: hysocyamine sulfate 5 mcg/kg subcut 1 h pre-anesthesia

On hand: hysocyamine sulfate 0.5 mg/mL

Example Example

Dosages Based on Body Weight (cont.)

Step A Convert 34 lb to kg = 15.5 kg

Step B Calculate desired dose:5 mcg / kg x 15.5 kg = 77.5 mcg

77.5 mcg = 78 mcg = D

Example Example

Dosages Based on Body Weight (cont.)

Step C Confirm desired dose is safe.

Based on PDR : 5 mg / kg is the recommended dose for a child over 2 years old.

Example (cont.) Example (cont.)

Back to Order

Dosages Based on Body Weight (cont.)

Find The amount to administer:

Step A first factor 1 mg/1000 mcg

Step B Calculate amount to administer.

A mL = 1 mg /1000 mcg x 1 mL / 0.5 mg x 78 mcg/ 1

Amount to administer = 0.156 mL = 0.16 mL

Step C

0.78 is 0.16 of 5, so 0.16 mL is reasonable.

Example (cont.) Example (cont.)

Back to Order

Dosages Based on Body Weight (cont.)

• Pediatric injection volume is limited based on the size and age of the child.

The length and gauge of the needle also varies with the age and size of the patient and the location of the injection.

Ensuring Safe Dosages

Ensuring Safe Dosages (cont.)

Rule 17-3Rule 17-3 Ensuring Safe Dosages

When working with special populations, always check the package insert, drug label, or product literature to ensure the safety of the dose to be administered.

Ensuring Safe Dosages (cont.)

Determine if dose is safe for a child weighing 38 lb. If safe, calculate the amount to administer.

Ordered: Pediazole suspension 5 mL qid

On hand: Pediazole susp (combination drug)

Erythromycin 200 mg / 5 mL

Sulfisoxazole 200 mg / 5 mL

Example Example

Ensuring Safe Dosages (cont.)

Step A Convert 38 lb to kg = 17.3 kg

Step B Calculate recommended dose.

Package insert :

recommend dose for erythromycinethylsuccinate = 50 mg/kg/d

50 mg / 1 kg x 17.3 kg = 865 mg

Example Example

Ensuring Safe Dosages (cont.)

recommended dose for sulfisoxazole acetyl = 150 mg/kg/d

150 mg/1kg x 17.3 kg = 2595 mg

Example Example

Ensuring Safe Dosages (cont.)

Step C Think!...Is It Reasonable?

Order is for 5 mL 4 times a day.

Daily dose of erythromycin = 800 mg/day

Falls under maximum dose of 865 mg/day

Daily dose of sulfisoxazole = 2400 mg/day falls under maximum dose of 2595 mg/day

Example Example

Error Alert !

Practice

Determine whether the following order is safe. If safe, calculate the amount to administer.

For a child weighing 14.5 kgOrdered: Amoxil 175 mg PO q8hOn hand: 200 mg/5 mLUsual dose 20-40 mg/kg day

Answer: Dosage falls within range.

Amount to administer is: 4.375 mL (round to 4.4 mL)

Apply Your Knowledge

True or FalseA baby who weighs 6 lb 8 oz weighs 6.8 lb.

A baby who weighs 9.5 lb weighs 9 lb 8 oz.

Answer: False

Answer: True