While antacids and antiallergic drugs interfere with the function of histamines,

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everyday-life

#1

While antacids and antiallergic drugs interfere with the function of histamines,
why do these not interfere with the function of each other?
Or
Both antacids and antiallergic drugs are antihistamines but they cannot replace each other. Why?


#2

Drugs designed to cure some ailment in one organ of the body that do not produce any effect to the other because they work on different receptors.
For instance, secretion of histamine causes allergy. It also causes acidity due to release of HCl in the stomach.
Since, antiallergic and antacid drugs work on different receptors, thus antihistamines remove allergy while antacid remove acidity.