The antibiotics I will be using are sulfamethoxazole, trimethoprim and tetracycline/
However, based on the standard protocol of preparing antibiotics stock solution, I need to make calculation based on this equation W=V * C / P
I can't find the potency of these antibiotics. May you help me please? Thank you very much
Hi Shumoos,
You can ask the manufacturer for each drug potency or look into the informative sheet. If the potency matters for some drugs it is represented by Units or ug or sometime by percentage per milligram.
If the manufacturer is known to follow the international code the potency of each antibiotic must be between 90% and 140% of the number of the micrograms.
https://www.gpo.gov/fdsys/pkg/CFR-1996-title21-vol5/xml/CFR-1996-title21-vol5-sec460-153.xml
I think you can represent your data by ug/ml by choosing a well known compagnies stock solutions.
IF you have no data and you want to calculate the potency of your antibiotic you have to follow the standard guideline fo potency assays: ther are two methods: measuring the zone of inhibition on agar plate using a reference strain (the diameter is proportional to the concentration/potency. Or by using the tube based turbimetric assay that is similar.
http://pharm.lancasterlabs.com/news/newsletters/antibioticmicrobialpotency
In all scenarios you have to validate your préparations (agar and microplates) using a reference strains for each lot of your prepared plates and ensure a quality assurance.
Dear Dr. Hafid
Good Day
Thank you so much for your kind reply to my question. kindly, my project is about antibacterial activity of plant crude extracts and I am following Dr. Eloff method in the publication at: https://www.researchgate.net/publication/13355248.
I will start by running susceptibility test using the standard agar well diffusion to test the activity of the extracts, then I will run broth Micro-dilution (MIC) for those bacteria that the extracts possess antibacterial activity towards it.
However, I am using tetracycline, trimethoprim and sulfamethoxazole as positive controls in both tests. I do have the powder form of the antibiotics and I am not sure how to prepare the stock solution for these tests. It is a bit confusing.
I apologize if I am taking too much of your time, but kindly please would you recommend to me a procedure to follow regarding this matter?
I am not sure weather is it necessary to calculate potency in order to prepare the stock solution of the antibiotics when they will be used as positive controls and the MIC will not be about drug susceptibility but plant crude extracts susceptibility?
The antibiotics I will be using are :
Tetracycline T3258 SIGMA http://goo.gl/B4RsMM (12.5 mg/mL) Trimethoprim https://goo.gl/9sreG5 ( 25g per 50mL) Sulfamethoxazole https://goo.gl/mKuMbg (5g per 40mL)
Thank you very much. I'll appreciate your kind help.
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Dear Shumoos Ghanim,
You can prepare stock solution at any of these concentration 1mg/ml or 2mg/ml or 3mg/ml etc, depends on your requirement. you can directly perform MIC without calculating potency of antibiotics. because the potency of antibiotics is already determined by the manufacturer.
So, You can perform MIC by Agar dilution or Broth dilution as per recommendation of CLSI criteria.
Best Wishes,
Dr Anand
Hi Shumoos,
As Anand Said, you can prepare a stock solutions of your antibiotics and do a serails dilutions depending on your bacterial species tested (Gram + or -, mycetes, mycobacteria, actinomycètes...etc), you can see the CLSI guidelines to define the range of your dilutions of your antibiotics for each species.
For your crude extracts, you can measure the concentration of your stock solutions and do a serial dilution as well to define the susceptibility for différents microbes and compare with your positive controls.
You do not need to calculate the potency.
Good luck
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