Coadministration of ciprofloxacin (750 mg single dose) and didanosine gastro-resistant capsules (400 mg single dose) had no effect on ciprofloxacin AUC or Cmax. No dose adjustment is necessary for either medicinal product.
Videx Summary of Product Characteristics, Bristol-Myers Squibb Pharmaceuticals Ltd, April 2016.

Coadministration of didanosine EC (400 mg single dose) and ciprofloxacin (750 mg single dose) to 16 HIV-negative subjects resulted in no change in the AUC and Cmax of ciprofloxacin. When the buffered formulation of ddI (200 mg twice daily for 3 days) was coadministered with ciprofloxacin (750 mg twice daily for 3 days, 2 h before ddI) to 8 HIV-infected subjects, ddI AUC and Cmax decreased by 16% and 28%, respectively.
Videx Prescribing Information, Bristol-Myers Squibb Company, December 2018.

The effect of the didanosine encapsulated enteric coated beadlet formulation (400 mg) on ciprofloxacin (750 mg) was evaluated in 16 healthy volunteers. The geometric mean Cmax and AUC values were 8.1% and 9.1% lower, respectively, when given in combination. However, 90% CI of the ratios of the geometric means fell within the criteria defined for a lack of interaction (0.75 to 1.33). Didanosine as this formulation did not affect the pharmacokinetics of ciprofloxacin and the drugs may be administered simultaneously.
Lack of effect of simultaneously administered didanosine encapsulated enteric bead formulation (Videx EC) on oral absorption of indinavir, ketoconazole and ciprofloxacin. Damle BD, et al. Antimicrob Agent Chemother, 2002, 46:385-391.

The pharmacokinetics of didanosine and ciprofloxacin were evaluated following administration of didanosine (200 mg twice daily, buffered tablets) and ciprofloxacin (750 mg twice daily) to 16 HIV-infected subjects as single agents or in combination (ciprofloxacin 2 h prior to didanosine). When coadministered, there were statistically significant decreases in ciprofloxacin AUC (26%) and urinary recovery (29%), though these were not considered to be clinically significant. Other than a decrease in didanosine AUC (16%), ciprofloxacin did not alter the pharmacokinetics of didanosine.
A multiple-dose pharmacokinetic interaction study between didanosine (Videx) and ciprofloxacin (CIPRO) in male subjects seropositive for HIV but asymptomatic. Knupp CA, et al. Biopharmac Drug Dis, 1997, 18: 65-77.

The pharmacokinetics of ciprofloxacin (500 mg) were determined in a HIV-negative subject on four occasions following administration of ciprofloxacin alone, 2 h before didanosine-placebo buffered tablets, 2 h after didanosine-placebo buffered tablets and concomitantly with didanosine-placebo buffered tablets. Administration of ciprofloxacin concurrently or 2 h after the antacids in the placebo tablet reduced ciprofloxacin concentrations to below the minimum inhibitory concentration for moderately sensitive microorganisms. Administration of ciprofloxacin 2 h before the antacids resulted in normal concentrations. The results from this single subject suggest that ciprofloxacin should be given either 2 h before or at least 6 h after administration of didanosine buffered tablets.
Avoiding the ciprofloxacin-didanosine interaction. Sahai J. Ann Intern Med, 1995, 123: 394-395. The pharmacokinetics of ciprofloxacin (750 mg) administered alone and immediately after didanosine-placebo buffered tablets were determined in 12 HIV-negative subjects. Significant decreases in ciprofloxacin Cmax (from 3.38±0.63 to 0.25±0.21 µg/ml) and AUC (from 15.5±2.69 to 0.26±0.21 µg.h/ml) were seen when coadministered with the buffered tablets. The simultaneous administration of ciprofloxacin and didanosine should be avoided.Cations in the didanosine tablet reduce ciprofloxacin bioavailability. Sahai J, et al. Clin Pharmacol Ther, 1993, 53: 292-297.