[Xiaoling]

Hi there. I need to prepare 10 mL of 1000ppm of Neomycin standards. I bought a sigma Neomycin trisulfate salt hydrate C23H46N6O13.3H2SO4.xH2O with the following information, MW908.88, potency 600ug/mg. loss on drying:not more than 10%. Before using, I have to dry the drug in vaccum oven for 3h. But can anyone please help me on how to calculate the weight of neomycin needed to prepare the stock solution taking into consideration the potency value? Your help is greatly appreciated.

[JGK]

1. Is the potency on an "as is" basis or is it for the dried material ?

2. Is the potency for Neomycin or Neomycin trisulphate?


You will need the molecula weights of Neomycin,  Neomycin trisulphate and Neomycin trisulphate hydrate(from that you can calculate the % Neomycin in Neomycin trisulphate and Neomycin trisulphate hydrate)

If the potency is on an "as is" basis for Neomycin trisulphate  then:

wt of drug * Potency *(mw Neomycin/mw Neomycin trisulphate hydrate)  will give the neomycin level

If the potency is on an "dried" basis for Neomycin trisulphate  then:

wt of drug (dried)* Potency *(mw Neomycin/mw Neomycin trisulphate)  will give the neomycin level

other permutations (not covered) can be similarly calculated. 

[Xiaoling]

Thanks a lot, JGK, for your kind reply. The potency label goes like this .."727ug neomycin base per mg(dried basis). So i guess its for the dried material. But not sure if it is for neomycin or neomycin sulfate. I never took up pharmcology and hence has no idea on this kind of calculation. Do you have any website where I can read up more on this antibiotic calculation?

[Arkcon]

The term "base" generally means "free base" as in no sulfuric or hydrochloric acid bound to the molecule.  The bottle contains the trisulfate, so you'll have to convert the molecular weights for your calculations.  Problem is your original question doesn't say 1000 ppm of what.  They may mean neomycin, neomycin trisulfate, or neomycin trisulfate hydrate.

[Xiaoling]

Thank you Arkcon for your reply. The instruction is to prepare a 10ml of 1000ppm Neomycin Standard. The antibiotic I have in hand is a Sigma Neomycin trisulfate salt hydrate powder. MF is C23H46N6O13.3H2SO4.xH2O, MW of 908.88 (anhydrous basis), Loss on drying = 6%, Potency of 727ug Neomycin Base per mg(dry basis). Please check if my interpretation is correct:

Considering the potency,
weight of neomycin required = 10ml*1000ppm/727 = 13.76mg of pure neomycin

Since my antibiotic is neomycin trisulfate,
dried neomycin trisulfate to be weighed = 13.76*908.88/614(MW of neomycin)
                                                           = 20.37mg

But if i choose not to dry the powder but calculate out the water content(6%),

amt needed =  20.37*100/94 = 21.67mg of my Sigma Neomycin trisulfate hydrate

Is it correct??


   

[Arkcon]

OK.  Step 1: define ppm.   Often, people equate 1 ppm= 1 mg/L, which is an ok definition, given the mass of water per mL.  Your application calls for 1000 ppm, or 1 gram per liter.  That seems a little high to me, are you sure you've got the correct amount?

OK, you want 1 gram of, I assume again, neomycin base.  Your neomycin sulfate can be seen as "adulterated" or "contaminated" with sulfate, water, and other impurities, so you know one thing for sure -- you will need more.  Did you remember to include the potency -- 600ug/mg?  Maybe you did, I may have just missed it.

[JGK]

I did the calculation as follows:

10 mL of 1000 ppm (1 mg/mL) = 100mg

Adustment for water content = wt/0.94 =106.4 mg

Adjustment for base (neomycin) content (0.727mg/mg) = 146.4 mg

So, to make 10 mL of the 100ppm neomycin solution, weigh 146.4 mg,  dissolve and make up to 10 mL.

[Xiaoling]

Thanks a lot Arkcon and JGK, I think I started to grasp it. Your replies really help me alot. Thanks 

[Xiaoling]

Hi guys, I think I am hit with another problem. This time I need to prepare 10mL of 1000ppm(ug/mL) of Penicillin G. I have with me Sigma Penicillin G Sodium Salt, MF:C16H17N2NaO4S , MW: 356.37, Moisture Content:0.13% and potency of 1658 units Penicillin-G Base per mg.

As you can see, the potency given is in units per mg. I read online that in international Standard, 1 mg of pure Penicillin G Sodium has 1666 units Penicillin G per mg.

Singe I need 10mg of Penicillin G, to dissolve in 10mL buffer to yeild 1000ppm, I need 1666units * 10 = 16660units of penicillin G.


So amount to weigh = 16660 / 1658
                            = 10.05mg??

[JGK]

Yes your math is correct (assuming the potency is "as is" and not  for the dried material)

If it is for the dried the the weight would be 10.06 mg

[Xiaoling]

Hmmm, 10.05mg of my sigma pencillin G sodium will have 16660units of penicillin free base. This is equivalent to 10mg of Pure Penicillin G sodium.

Do you think I need to take 10.05mg * (MW of PenicillinG/ MW of penicillin G sodium) in order to get 10mg of pure penicillin G base only?? Kinda confusing..

[JGK]

After 20 years of translating this stuff it seems really simple now 

[Xiaoling]

Wow ...you have 20 yrs of experience..Hehe...can you teach me more?? I totally have no experience in this kinda pharmaceutical calculation. But was given work to do all this calculation for 10 antibiotics!!

[Xiaoling]

Hi JGK, can you please please help me with this one too?? The antibiotic I have is streptomycin sulfate. MF: C21H39N7O12. 1.5H2SO4  MW: 728.69   Water Content is 6%, Purity by TLC is 100% and Potency is 749units Streptomycin Base per mg (dried basis). Thanks a billion .

[JGK]

Hi JGK, can you please please help me with this one too?? The antibiotic I have is streptomycin sulfate. MF: C21H39N7O12. 1.5H2SO4  MW: 728.69   Water Content is 6%, Purity by TLC is 100% and Potency is 749units Streptomycin Base per mg (dried basis). Thanks a billion .

I'm assuming you need 10 mL of a 1000 ppm STD again (1 mg/mL, 10 mg/10 mL)?

Starting at 100% purity subtract the percentage water content 100 - 6 = 94%

With TLC purity at 100%

you just need to use the following calculation =10 x 100/94

= 10.64 mg disolved in 10 mL