Dosage Calculation - Dosage By Weight Questions

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Dosage By Weight Questions
Given the weight of a patient and a dosage specified in terms of weight, calculate the necessary dosage. These problems are a type of pediatric dosage calculations.
Formula:

$$\boxed{\mathbf{Weight\; in\; Kg}x\mathbf{Dosage\; Per\; Kg}=\mathbf{Y(Required\; Dosage)}}$$

Example: A doctor orders 200 mg of Rocephin to be taken by a 15.4 lb infant every 8 hours. The medication label shows that 75-150 mg/kg per day is the appropriate dosage range. Is this doctor's order within the desired range?

$$\mathbf{Weight\; in\; Kg}x\mathbf{Dosage\; Per\; Kg}=\mathbf{Y(Required\; Dosage)}$$

Convert 15.4 lb to kg.
    lb → kg    ( ÷ by 2.2 )
    15.4 lb ÷ 2.2 = 7 kg

7 kg x 75 mg/kg = 525 mg (Minimum Desired Dosage)
7 kg x 150 mg/kg = 1,050 mg (Maximum Desired Dosage)
24 hours in one day and the medication is ordered every 8 hours.

    24 hrs / 8 hrs = 3 times per day doctor ordered medication
    200 x 3 = 600 mg ordered per day
    600 mg is within the desired range of 525-1,050 mg

$$\boxed{\mathbf{\text{Yes}}}\mathbf{\text{doctor has ordered a dosage within the desired range.}}$$

Example: Solumedrol 1.5 mg/kg is ordered for a child weighing 74.8 lb. Solumedrol is available as 125 mg / 2mL. How many mL must the nurse administer?

$$\mathbf{Weight\; in\; Kg}x\mathbf{Dosage\; Per\; Kg}=\mathbf{Y(Required\; Dosage)}$$

Convert 74.8 lb to kg.
    lb → kg    ( ÷ by 2.2 )
    74.8 lb ÷ 2.2 = 34 kg

$$\mathbf{34\; kg}x\mathbf{1.5\; mg/kg}=\mathbf{51\; mg}$$

This is now an ordinary Mass/Liquid For Liquid Question. 51 mg is ordered and the medication is available as 125 mg / 2 mL.

$$\frac{\mathbf{Ordered}}{\mathbf{Have}}x\mathbf{Volume\; Per\; Have}=\mathbf{Y(Liquid\; required)}$$

$$\frac{\mathbf{51\; mg}}{\mathbf{125\; mg}}x\mathbf{2\; mL}=\boxed{\mathbf{0.82\; mL}}$$

Alternatively, 125 mg = 2mL
Therefore 51 mg = 2/125 x 51 = 0.82 mL

Question (6): (From Ngee Ann Polytechnics Dosage Calculation Worksheet)
ORDER: Drug G 5 mg per kg body weight P.O.
AVAILABLE: Drug G 250 mg per 5 mL
BODY WEIGHT: 500 kg

$$\mathbf{\text{GIVE:}}\underline{}\mathbf{\text{mL}}$$

$$\mathbf{Weight\; in\; Kg}x\mathbf{Dosage\; Per\; Kg}=\mathbf{Y(Required\; Dosage)}$$

$$\mathbf{50\; kg}x\mathbf{5\; mg/Kg}=\mathbf{250\; mg}$$

$$\frac{\mathbf{Ordered}}{\mathbf{Have}}x\mathbf{Volume\; Per\; Have}=\mathbf{Y(Liquid\; required)}$$

$$\frac{\mathbf{250\; mg}}{\mathbf{250\; mg}}x\mathbf{5\; mL}=\boxed{\mathbf{5\; mL}}$$

Alternatively, 250 mg = 5 mL
Therefore 250 mg = 1/250 x 250 = 5 mL

Question (10): (From Ngee Ann Polytechnics Dosage Calculation Worksheet)
ORDER: Drug N 15 mg per kg body weight P.O.
AVAILABLE: Drug N 60 mg per mL
BODY WEIGHT: 100 kg

$$\mathbf{\text{GIVE:}}\underline{}\mathbf{\text{mL}}$$

$$\mathbf{Weight\; in\; Kg}x\mathbf{Dosage\; Per\; Kg}=\mathbf{Y(Required\; Dosage)}$$

$$\mathbf{100\; kg}x\mathbf{15\; mg/Kg}=\mathbf{1,500\; mg}$$

$$\frac{\mathbf{Ordered}}{\mathbf{Have}}x\mathbf{Volume\; Per\; Have}=\mathbf{Y(Liquid\; required)}$$

$$\frac{\mathbf{1,500\; mg}}{\mathbf{60\; mg}}x\mathbf{1\; mL}=\boxed{\mathbf{25\; mL}}$$

Alternatively, 60 mg = 1 mL
Therefore 1,500 mg = 1/60 x 1,500 = 25 mL
 
Continue (Go to IV Terms & Abbreviations)



Reference 
[1] Advanced Formatting, Ry’s MathML Tutorial, http://rypress.com/tutorials/mathml/advanced-formatting.
[2] MathML, Presentation MathML, https://en.wikipedia.org/wiki/MathML.
[3] MathJax in Blogger (II), Posted on Tuesday, 12 July 2011, http://irrep.blogspot.sg/2011/07/mathjax-in-blogger-ii.html
[4] MathJax, http://docs.mathjax.org/en/latest/start.html

[5] MathML Fundamentals (Colours), W3C recommendation, http://www.w3.org/TR/MathML/chapter2.html

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