Drug Calculation ?

bmccns07 · Sep 9, 2007

These two questions are giving me the beans:-

1. Give 50 mg of tobramycin in 100ml of D5W over 30 min. The drop factor is 15=drops=1 mL. You would piggyback this medication into the main IV and set the drip rate at _____ gtt/min

2. The physician prescribed morphine sulfate 1 gram in 100mL D5 NSS to infuse at 10mg per hour. Calculate the flow rate in gtt/min. You would give ________ gtt/min using a microdrip

I like to use Dimension & Analysis a lot. Put the givens into the equation and cross off the factors = answers that you're looking for!

Answer

Question 1

gtt = 15gtt x 100mL (cross off mL and divide) = 50 gtt/min

min 1 mL 30 min

Note: You don't need to use 50 mg; this is just to throw you off.

Question 2

microdrip = 60gtt/mL

gtt = 60gtt x 100mL x 1 g x 10mg = 1 gtt/min

min 1 mL 1gram 1000mg 60 min (1hr)

Daytonite, BSN, RN · Sep 12, 2007

1. give 50 mg of tobramycin in 100ml of d5w over 30 min. the drop factor is 15=drops=1 ml. you would piggyback this medication into the main iv and set the drip rate at _____ gtt/min

you want to end up with

gtts/min

. the problem already gives you the information you need to complete the problem:

100 ml/30 minutes

(amount to give)

x 15 gtts/1 ml

(drop factor of tubing)

=

50gtts/minute

(drip rate)

2. the physician prescribed morphine sulfate 1 gram in 100ml d5 nss to infuse at 10mg per hour. calculate the flow rate in gtt/min. you would give ________ gtt/min using a microdrip

again, you want to end up with

gtts/min

. this problem requires you to apply two conversion factors along with the information you have been given to complete the problem. in setting this up and working it by dimensional analysis, it is also important to recognize that certain "relationships" among the terms must remain together in ratios, or fractions, of the problem and it doesn't matter which number and its label in the relationship ends up in the numerator or the denominator so long as the relationship is maintained. in other words, 100 ml/hour is the same flow rate as 1 hour/100 ml. also, you need to know that the drop factor of microdrip tubing is 60gtts/ml. this is a straight

dose desired divided by dose on hand

formula problem.

10 mg/hour

(dose desired, dose to be infused)

x 100 ml/1 gram

(dose on hand)

x

60 gtts/ml

(drop factor of tubing being used)

x 1 gram/1000 mg

(conversion factor)

x 1 hour/60 minutes

(conversion factor)

=

1 gtt/minute

the answer may look wrong because it is so low (1 gtt/minute). however, it is correct for iv morphine.