Is ciprofloxacin acidic or basic? I would expect an aqueous solution of ciprofloxacin to be basic for the following reasons:


The carboxyl group has pKa = 6.09 and the secondary amino group has pKa = 8.74. Because 8.74 is further from neutral pH than 6.09, I would expect the pH of an aqueous solution to be above 7.
The tertiary amino groups are connected to an aromatic ring, so they should be very weakly basic and not affecting pH much.


However, the PubChem Compound Summary says the following about ciprofloxacin: "pH range for the 1.0% aqueous concentrates in vials is 3.3 to 3.9; the pH range for the 0.2% ready-for-use infusion solutions is 3.5 to 4.6" (see https://pubchem.ncbi.nlm.nih.gov/compound/ciprofloxacin#section=pH)

Is an aqueous solution of ciprofloxacin solution really acidic and if it is, what is the reason?

I also found an article citing several estimates of the pKa:s and the consensus seems to be that the amino group is stronger than the carboxyl group. (Babić et al. Determination of pKa values of active pharmaceutical ingredients. Trends in Analytical Chemistry, Vol. 26, No. 11, 2007.)

Here is a picture of ciprofloxacin from Wikipedia:
Your predictions are right; the molecule has more basic character.

The drug itself is practically insoluble in water, because the big organic molecule is near it's isoelectric point at the pure water's pH. However by protonating or deprotonating it and thus making it charged it's solubility is greatly enchanced.

This is also the case with those medical ready-for-use infusions:


  ...CIPRO IV solutions are available as sterile 0.2% ready-for-
  use infusion solutions in 5% Dextrose Injection. CIPRO IV contains lactic acid as a solubilizing agent and hydrochloric acid for pH adjustment. The pH range for the 0.2% ready-for-use infusion solutions is 3.5 to 4.6. 


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