[The Big E]

acetylsalicylic acid and sodium bicarbonate are often combined by manufacturers but what happens to this solution when it reacts with HCl in a human's stomach? Isn't it better for the drug to reach the intestine and then start working? And if that's the case, then how do they prevent the ionized solution of acetylsalicylic acid and sodium bicarbonate from reacting with HCl in the stomach?

[Arkcon]

Well, acetylsalicylic acid is somewhat absorbable through the stomach walls, and anything that gets it into the bloodstream faster is what a person with a headache or backache wants, or will at least claim to want during throbbing pain. 

That assumes the stomach isn't irritated by the arrival of the aspirin, which is a different response for different people.  The capsule may be enteric coated, which will survive the stomach's digestion, until the pill reaches the small intestine. 

You can also heavily buffer the pill, so acid doesn't arrive at the wrong moment and irritate the stomach.  As I understand it, the sodium bicarb in Alka-Seltzer isn't meant to buffer the aspirin, it's meant to address stomach upset from other sources.  But then again, large amounts of antacids can upset the stomach too.

[ARGOS++]

Dear The Big E;

The manufacturers mostly use “Sodium Bicarbonate”(often in combination with “Tartrate”) or similar Substances in the “Galenics” to formulate the Tablets, and normally the Tablets reaches “your” stomach quite intact (not as a solution as you told).

Inside your Stomach the Tablet gets enough wet and “Sodium Bicarbonate” and “Tartrate” starts to dissolve and reacts together to release some CO₂. This is important.
This CO₂ is now used to explode/disintegrate the whole Tablet and “generate” an as large as possible surficial area of, ASA in your case, and that’s again important to get highest possible Release Rates (DR = Dissolution Rate) of the “Active Ingredient(s)” for the fastest transport into your blood.

That makes it ‘only’ possible, that the Tablet is able to liberate you from your pain (headache) in a shorter time then half an hour. The HCl of your stomach is mostly toooo slow for that.

I hope it helps you to understand.


Good Luck!
                    ARGOS⁺⁺