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complex infusion rate question

by Pharmer
(NY, NY)

You receive an order for 250 mg of Aminophylline in normal saline (total volume 500 ml). The patient weighs 110 lb. The Aminophylline is to be administered at a dose of 0.4 mg/per/kg per hour. Aminophylline Injection is supplied in 10 mL vials with 25 mg/mL. The IV set to be used delivers 60gtts/ml. What will be the flow rate, in drops per minute, to administer the dose ordered?

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complex infusion rate question

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Jan 10, 2012
Solution - Broken down in 5 parts
by: Anonymous

1. Change 110lbs to kg. So weight = 50kg

2. 0.4mg/kg, so multiply 50kg by 0.4mg = 20mg/hr

3. The total amount is 500ml. The key is calculate how many vials you will need for the total volume. There are 10ml in each vial and 500ml total. Therefore you need 50 vials.

4. From #2 there are 20mg/hr. We must convert mg to ml. In the stock vials there is a concentration of 25mg/ml. So 20mg/hr divided by 25mg/ml = 0.8ml/hr. Convert hr to mins and you get 0.0133ml/min.

5. Now use your equation which is 0.0133ml/min multiply by drop factor of 60gtts/ml and you get 0.8gtts/min. Multiply this number by a factor of 50 (since that is the number of vials you will need to get the required volume) and you get 40gtts/min.

Jul 01, 2011
The trick is to use the fact Aminophylline 250mg/500ml solution (let alone Aminophylline Injection is supplied in 10mL vials with 25 mg/mL)
by: Kevin Khuu

All we need are:
Receive an order 250mg of Aminophylline in 500mL.
The patient weighs 110 lb.
Administered at a dose of 0.4 mg/kg/hr.
The IV set to be used delivers 60gtts/ml.
Now, Let's go:
Patient weighs: 110 : 2.2 = 50 kg.
Mg Amino he needs in 1 hour: 50 x 0.4 = 20 mg. or in 1 minute: 20 : 60 = 0.3333 mg. Equivalent in ml: 0.6666 x 500 : 250 = 0.6666 ml
Equivalent in gtt/min: 0.6666 x 60 = 40 gtt/min.
That's it. Thank you for your attention.

Jun 06, 2011
(2/2) I got ~40 gtts/min
by: Anonymous

5) Now we need to determine the milligrams/hour to be administered.
The Dosage is 0.4 mg/kg/hr and the Patient weighs 110 lbs, so we convert the Patient?s weight to the factor desired (kilograms).

>> 110lbs x (1kg / 2.2lbs) = 50kg

Analyzing the Dosage, we discover that the Patient needs 0.4 milligrams of medicine for every kilogram he/she weighs every hour. So, if we multiply the milligrams needed per hour by the Patient?s weight, we come up with the total amount of medicine needed (mg) per hour.

>> 0.4 mg/hr x 50kg = 20 mg/hr

6) We now have everything needed to solve the problem.
To find the Flow Rate in Drops per Minute, we first divide our Rate in Milligrams per Hour by our Concentration in Milligrams per Drop.

>> 20 mg/hr / .0083 mg/gtt = 2409.6 gtt/hr

Now we divide our Drops per Hour by 60 Minutes per Hour

>> 2409.6 gtt/hr / 60 min/hr = 40.16 gtt/min

So, Flow Rate in Drops per Minute that satisfies the conditions of the order give is approximately 40 drops per minute.

I hope that helps anyone who is puzzled by this problem. If anyone sees an error in my logic, please feel free to point it out, like I said, I am just now going over this stuff.

Jun 06, 2011
(1/2) I got ~40 gtts/min
by: Andrew

I just now started looking at the mathematics to be used on the PTCE so I could be wrong, but here's what I came up with for this problem along with my rationale:

Order: 250mg med in NS, with Total Volume at 500ml
Med vial: 10ml @ 25mg/ml
Patient weight: 110 lbs
Drop Factor: 60 gtts/ml
Dosage: 0.4 mg/kg/hr
Need to find: Flow Rate in gtts/min

1) If you need only 250mg of medicine, how many vials of medicine do you need?

>> 250mg med needed / (25mg/ml * 10ml) =
>> 250mg med needed / (250mg) = 1 Vial of Medicine Needed

2) Since a new solution has been made, it would make sense that we find the new concentration since that is essentially the only new piece of information we can get from it. What is the concentration of the solution made from 1 Vial of Medicine + NS = 500ml?

>> 250mg med / 500ml = 0.5 mg/ml
This says that every milliliter of solution contains 0.5 milligrams of medicine.

3) We know that the Drop Factor is 60 drops for every milliliter of solution and we have 500 milliliters of solution. How many drops solution do we get?

>> 500ml x 60 gtts/ml = 30,000 gtts

4) Pausing to review the information we have so far, we see that the Dosage we need is in milligrams (0.4 mg/kg/hr) and the Flow Rate we need is in drops per minute. It follows, then, that we need to determine the amount of medicine in milligrams is contained in each drop of solution. Currently, we have the volume of solution (500ml), we have determined the quantity of drops we can get from the volume of solution (30,000 gtts), and we have the concentration of the solution (0.5 mg/ml). How do we convert 30,000 gtts to # mg/gtt?

First, we need to attach a common factor to the number of drops that is found in the concentration, so we find how many milliliters of solution are in each drop.

>> 500ml / 30,000gtts = 0.016 ml/gtt

Second, we multiply by the concentration to find the number of milligrams per drop.

>> 0.016 ml/gtt x 0.5 mg/ml = 0.0083 mg/gtt

May 29, 2011
Is this correct?
by: Anonymous

I got 20gtt/min

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