Sanford.Rmd

---
title: "Sanford formula"
author: "kou"
date: "12/30/2017"
output: html_document
---

## Creatinine clearance formula by Sanford

 In Sanford guideline, to calculate eGFR two different formula, *non-obase* and *obase*, is used.  

 First we need to calculate ideal body weight (IBW) and body mass index (BMI)  
* IBW  
    * male  
$$
IBW_{(male)} = 50kg + 2.3kg\times (height(inch) - 60 inch)
$$
    * female
$$
IBW_{(female)} = 45kg + 2.3kg\times (height(inch) - 60 inch)
$$

**If height <= 60inch, IBW = 50kg (male) or 60kg (female)**  
**1 inch = about 2.54 cm, 60 inch = about 152.4 cm**  

* BMI  

$$
BMI = \frac{BW(kg)}{height(m)^2}
$$
 Obese is defined as 20% over IBW or BMI > 30

* non-obese formula  
    * male
$$
CCr_{(male)}   = \frac{(140 - Age)\times IBW}{72\times Scr}
$$
    * female
$$
CCr_{(female)} = \frac{(140 - Age)\times IBW}{72\times Scr}\times 0.85
$$


* obese formula  
    * male
$$
CCr_{(male)}   = \frac{(137 - Age)\times ((0.285\times BW(kg) + (12.1\times  height(m)^2))}{51\times Scr}
$$
    
    * female
$$
CCr_{(female)}   = \frac{(146 - Age)\times ((0.287\times BW(kg) + (9.74\times  height(m)^2)}{60\times Scr}
$$

* This is reference of Sanford formula (NCBI)
    * non-obese patients
[N Engl J Med 354:2473, 2006](http://www.ncbi.nlm.nih.gov/pubmed/16760447/)  
    * obese patients
[Am J Med 84:1053, 1988](http://www.ncbi.nlm.nih.gov/pubmed/3376975/)

## Other constideration to dose adjustments of antibiotics

* For non-obese people  
use the patient's actual weight for all drugs  

* For obese people  
    * *Aminoglycosides*: adjusted weight calculation as follow  
$$
adjusted weight = (IBM + 0.4\times (BW -IBW))
$$
    * *Vancomycin*: use actual body weight whether non-obese or obese  
    * *all other drugs*: insufficient data (reference as follow)  
      [Pharmacotherapy 27:1081, 2007](http://www.ncbi.nlm.nih.gov/pubmed/17655508/)

* For slow extended daily dialysis (SLEDD) over 6-12 hours, adjust dose as for continuous renal replacement therapy (CRRT). (reference as follow)    
 [Clin Dis 49:433, 2009](https://www.ncbi.nlm.nih.gov/pubmed/19580416/)