Hello, if you need to prepare the solution of gentamicin 10mg/ml from gentamicin sulfate you need to take 10.8 g of gentamicin sulfate per ml to have finally 10mg/ml gentamicin solution.

Good luck!

@Karen A. Darbinyan Can you please explain the calculation?

Dear Rajat,

What is the concentration (ppm or mg/L), which you require in your culture broth? Actually, 10mg/mL sounds like fresh stock solution, which you will have to prepare in sterile water. Later, you will have to add it in the stipulated concentration (mg/L) to the culture solution. I have used ampicillin and Kanamycin for my research; the final concentrations (to be used in the culture) would be 50 ppm ampicillin and 75ppm ampicillin in my culture broth.

Dear Rajat

Molecular weight of gentamicin sulfate - 516.6 g/mol

gentamicin - 477.5 g/mol

516.6/477.5= 1.081

So for preparing 10mg/ml gentamicin

You need to take 10x1.081=10.81mg of gentamicin sulfate.

Good luck!

@ Navnit Kumar Ramamoorthy I need a working concentration of 10μg/ml

Dear friend,

For a working concentration of 10 ug/ml, you need to prepare a stock of 10 mg/ml. If you prepare in this way, it will be easy to add the antibiotic for different volumes of culture. For example, if you require 100 ml of culture, you need to add 100 ul of antibiotic to the media. Don't worry about the salt form and its molecular weight and all...

Dear Rajat,

We usually employ 15 ppm gentamycin during prokaryotic expression studies. As Mukesh says, the salt-containing formulation is not going to affect your antibiotic's potency. For your requirement, from what you have mentioned above, it is evident that you need a working concentration of 10ug/mL or 10 ppm (10mg/L). SO, just as Mukesh says, for a 1L culture broth you would have to add 1mL of the freshly prepared stock (10mg/mL), which would result in the final concentration of 10 ppm, as required by you.

I want to prepare antibiotic stock solution of Amikacin. But they have given the potency between 674-786 µg/mg. How should I calculate the exact potency for preparing stock solution?

I wish there was a comprehensive tutorial to guide us how to prepare the Antimicrobial stock solution for MIC with few examples on calculation method.