Analyzing a Prescription for the Correct Dose
Date: 04/27/2005 at 12:24:46 From: Alicia Subject: Converting tsp. to ml 1 Tsp of Proventil syrup is ordered three times a day for a 5 year old child with asthma. It is supplied as 2mg/5ml. How much Proventil is he getting per dose? A safe starting dose is 0.1 mg/kg (of weight) three times a day. The child weighs 46 pounds. Is the prescribed dosage safe?
Date: 04/28/2005 at 15:31:43 From: Doctor Wilko Subject: Re: Converting tsp. to ml Hi Alicia, Thanks for writing to Dr. Math! To find the conversions, I went to www.google.com and typed: "1 Tsp = ? ml" and "1 lb = ? kg" Google gave the answers as: 1 US Tsp = 4.92892161 ml (or about 5 ml) and 1 lb = 0.45359237 kg It looks like I'm ready to start solving my problem! Before I start trying to do the math, I want to read back through the problem and make sure I understand everything. 1 Tsp of Proventil syrup is ordered three times a day for a 5 year old child with asthma. The age and asthma aren't really important, just 1 Tsp three times a day. Good so far? It is supplied as 2mg/5ml. For every 5 ml of the syrup, the patient will get 2 mg of the actual medicine. Do you agree? How much Proventil is he getting per dose? From Google, I found that 1 Tsp is about 5 ml. It was given that each 5 ml of syrup delivers 2 mg of medicine, so the patient is getting 2 mg of Proventil _per dose_ (because one dose is one Tsp, which is 5 ml). A safe starting does is 0.1 mg/kg (of weight) three times a day. The child weighs 46 pounds. Is the prescribed dosage safe? You were given that a safe dose is 0.1 mg of medicine for every 1 kg of body weight. It was given that the patient weighs 46 lbs. First thing is to convert pounds (lb) to kilograms (kg): 1 lb = 0.4536 kg (approximately), so therefore 46 lbs = 46 * 0.4536 or 20.8652 kg A safe dose is 0.1 mg of medicine for every 1 kg of body weight, so a safe dose for this specific 46 lb (20.8652 kg) patient is: 0.1 mg 20.8652 kg -------- * ---------- = 2.0865 mg (per dose) 1 kg 1 Since the patient is getting 2 mg of medicine per dose, it looks like the prescribed dosage is safe because it's within limits (from the conversion above, the patient could receive up to 2.0865 mg of medicine per dose and still be safe). The main thing with these types of problems is making sure you understand exactly what's being asked and getting the proper conversions _before_ you start trying to solve the problem. Even if the problem sounds wordy or like it has a lot of math, if you break it down line by line like I did above, you'll find that the problem becomes much more manageable. Does this help? Please write back if you have further questions. - Doctor Wilko, The Math Forum http://mathforum.org/dr.math/
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