3.3. Fexofenadine antacids interaction by HPLC
10 mL fexofenadine solution and 0.2 g antacid were taken in a
conical flask and the flask was shaken for 2 h at 37 C, afterward
the aliquots were filtered through a 0.45 lm Millipore
filter paper. The mobile phase was prepared by mixing methanol
and 6.8 g monobasic potassium phosphate in 1000-ml
water and pH was adjusted to 7.4 with potassium hydroxide.
The composition was methanol: phosphate buffer, 35:65 (v/
v), respectively. The injection volume was 10 lL and the run
time was 5.0 min. The mobile phase was filtered using a 0.45-
lm membrane filter (Millipore) and degassed in ultrasonic
bath. The mobile phase flow rate was 1.0 ml min1. Samples
were injected through a 20 lL loop at ambient and the retention
time for fexofenadine was 3.65–3.75 min (Arayne et al.,
2009). Peak area and percentage of fexofenadine recovered
have been discussed in Table 4. Peak areas were in contrast
with standard fexofenadine solutions to evaluate the degree
of interaction of fexofenadine with antacids. The chromatograms
of adsorption studies carried out at HPLC have been
shown in Figs. 7 and 8. In simulated gastric juice the percentage
recovery of the fexofenadine increased in case of sodium
bicarbonate (110.3%), magnesium carbonate (121.7%) and in all other antacids it decreased while in simulated intestinal
juice the percent recovery of fexofenadine increased in case
of sodium bicarbonate (115.03%), megaldrate (109.29%),
Magnesium trisilicate (110.38%) and calcium hydroxide
(106.01%). Fexofenadine (Fig. 6) has piperidine nitrogen and
at tertiary carbon it has a carboxylic group and that is why
it subsists as a zwitter ion in aqueous media at physiological
pH. These two possible sites are responsible for complex formation
and fexofenadine–antacid interaction takes place.