Please help

[aswresm]

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A pharmacist is asked to prepare a sterile fortified Tobramycin eye drops at a concentration 13.5 mg/ml using Tobrex 0.3% ophthalmic drops and Tobramycin 40 mg/ml injection. How many mls of Tobramycin shouold be added to 5ml of Tobrex drops.

 

[Pharmersmarket2017]

A pharmacist is asked to prepare a sterile fortified Tobramycin eye drops at a concentration 13.5 mg/ml using Tobrex 0.3% ophthalmic drops and Tobramycin 40 mg/ml injection. How many mls of Tobramycin shouold be added to 5ml of Tobrex drops.

This problem seems confusing since different units are being used to represent concentration. The best way to solve this problem is via alligation, but in order to do so, I converted the mg/mL concentrations into % w/v so that everything has the same units. The 40 mg/mL injection is the equivalent to 4% w/v and the desired concentration of 13.5mg/mL is equivalent to 1.35% w/v. Once you get those values, just set up the alligation with the highest concentration on top (4%), the lowest concentration on the bottom (0.3%), and the desired concentration in the middle (1.35%). Once the alligation is set up, you should get an answer of 1.49mL of the 40mg/mL Tobrex injection is needed.

 

[hiremeresidency2017]

This problem seems confusing since different units are being used to represent concentration. The best way to solve this problem is via alligation, but in order to do so, I converted the mg/mL concentrations into % w/v so that everything has the same units. The 40 mg/mL injection is the equivalent to 4% w/v and the desired concentration of 13.5mg/mL is equivalent to 1.35% w/v. Once you get those values, just set up the alligation with the highest concentration on top (4%), the lowest concentration on the bottom (0.3%), and the desired concentration in the middle (1.35%). Once the alligation is set up, you should get an answer of 1.49mL of the 40mg/mL Tobrex injection is needed.

I second this method. I got 1.5 mL as well.

 

[oncopharmbath]

The question says "How many mls of Tobramycin shouold be added to 5ml of Tobrex drops"
Using the same method described above, I got 1.98 mL :/

 

[oncopharmbath]

Not sure if I've got the wrong end of the stick though!

 

[glyxambi]

The question says "How many mls of Tobramycin shouold be added to 5ml of Tobrex drops"
Using the same method described above, I got 1.98 mL :/

That's what I got too from how I interpreted the question!