Did you measured the pH of two solutions? pH can influence the capacity of ciproflox to dissolve completely. 

like first thing.. are you sure that your strains are S. aureus and not another specie? perhaps you may first to do a right identification.. if with PCR it is better and than if the identification is confirmed to think at the real problem..

Thank you for your reply. May be i didn't give proper explanation of my problem. Here is my question again.

Ciproflox is in powder form which i want to dissolve in PBS at final concentration of 100mM. But when i add the powder to PBS and mix it, it was saturating and settling down after certain time. I thought it was supersaturating at 100mM concentration and hence i again dissolved ciproflox in PBS at final concentration of 2mM. But still the same problem was there. I even tried the same with phosphate buffer. But the same problem arises with that also. Then i have tried with dH2O, there it was dissolved completely at 100mM concentration also. In fact, i am doing interaction studies of ciproflox with a protein. Saturation of ciproflox was giving false results. What changes i need to do to dissolve ciproflox in any of the buffer.

Cipro is having pH dependent solubility with minimal solubility at pH 7.4.try dissolkving at pH 6.8 

If you can completely dissolve the same amount it in dH2O, but not in equal volume of buffer, you're probably having problems with ionic strength. Solubility is affected by other ions that are already in the solution, causing something (probably cipro) to precipitate.  Try using a buffer with weaker ionic strength (less salts already dissolved).

@Amit: If i am not wrong you want to perform the ITC experiment to check the interactions of your protein and Cipro. Then, in that case you can still use completely water dissolved compound for ITC. for your reference i am attaching this paper for you

If that is not the solution then you can make "total ionic strength adjustment buffer (TISAB)" which you can prepare or TISAB II which is commercially available from Sigma Aldrich. 

http://www.beilstein-journals.org/bjoc/single/articleFullText.htm?publicId=1860-5397-10-275

I have some experience dissolving ciprofloxacin.  I'm fairly sure it dissolved very well in ultrapure water.  When I measured the pH of the water it was somewhat acidic, about 5 or 6.  I believe, as someone else mentioned,  it does not dissolve well in neutral or physiological pH.  So, the solution to the problem would be to dissolve it in the water that you plan on using to make your buffer or medium,  and then once it is dissolved you can try using it to make the full solution that you intend to use.  I don't believe it will crash out of solution if done this way. 

I have faced the same problem. Ciprofloxacin was not soluble in PBS ph 7.4 but it was soluble in water. To overcome this problem, you can either use PBS ph 6.4-6.8 or you can also use less ionic strength buffer like HBSS to increase the solubility.

Hi everyone.

I am doing experiment with ciprofloxacin.

I have the problem that Ciprofloxacin was not soluble in distilled water. I have tried to dissolve ciprofloxacin in distilled water at 100 ppm. But it was not completely dissolved. I saw your answers, everyone also said that it was soluble in water. I don't know why I can not do like that. Could someone help me to solve this problem?

@Nguyen.... If you look at SigmaAldrich product page you will see that CIP is soluble in 0.1N HCl at 25 mg/ml.

I personally required a 0.1M 100ml solution so….

I dissolved 0.37ml of 37%HCL (liquid) in 99.63ml dH2O.

I then used 10ml of this 0.1M HCl solution to dissolve 10mg CIP giving me a 1mg/1ml concentrate solution. It dissolved almost immediately with no CIP crashing out.

I was using this for screening of E. coli isolates using MacConkey agar

I hope this was not too late and you find it useful.

How i can dissolved ciprofloxacin in distilled water. kindly let me know. i am unable to dissolve it is distilled water.

In my experience, you absolutely need slightly acidic water to dissolve ciprofloxacin. pH 5 or 6 worked for me. Our ultrapure water was already acidic, so it worked well, but if I tried to dissolve it in physiological buffer directly from powder it always failed. You should be able to make a concentrated stock in acidic water, just slightly acidic, then add it to your desired solution with no issues.

Y. Kumata

Dr adam

I dissoleved ceftazidum in saturated bicarbonyte as manufacture recommended but it didnt dissolve well , any suggestion

Thank you

@Abeer Ameen, do you mean ceftazidime? That is reported to dissolve at 5 mg/ml in pH 7.2 PBS. What concentration do you need to make?

@Abeer, see here:

https://www.biovision.com/ceftazidime.html

Sodium hydroxide makes it much more soluble, but I don't know how stable it is at high pH. I am surprised anyone would recommend saturated bicarbonate, since that could possibly salt out cef.

Y. Kumata

Try dissolving in lower pH or DMSO it will work

I have the same issue i.e. solubility of ciprofloxacin. However, I have tried many times by using different solvents like MeOH, Acetone, CH3OH, distilled water, pH 5.5 distilled water, but results were not fruitful. I want to entrap this drug in nanocarrier and check for drug release...Plz, give me appropriate advice, if someone is doing such that.

How long does it take for ciprofloxacin (not ciprofloxacin hydrochloride) to dissolve in ultrapure water?

For me it takes at least a day.

I tried Methanol: ultrapure water 1: 1, but it doesn't speed up the dissolution either.

Adam, if I dissolve ciprofloxacin in 0.1NHCl, mean in water slightly acidic, is that affect to cell culture during testing the cytotoxiciry through MTT assay, is that affect on the result, how I know if the cells killed by ciprofloxacin or by the acidic environment?????