How soon after taking 2 Gas-X chewable tablets is ok to take 2 more?

It is best not to repeat the dose any sooner then 6 hours.

The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

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* For symptoms of too much gas:
o For oral dosage forms (capsules or tablets):
+ Adults and teenagers—Usual dose is 60 to 125 milligrams (mg) four times a day, after meals and at bedtime. The dose should not be more than 500 mg in twenty-four hours.
+ Children—Dose must be determined by the doctor.
o For oral dosage form (chewable tablets):
+ Adults and teenagers—Usual dose is 40 to 125 mg four times a day, after meals and at bedtime or the dose may be 150 mg three times a day, after meals. The dose should not be more than 500 mg in twenty-four hours.
+ Children—Dose must be determined by the doctor.
o For oral dosage form (suspension):
+ Adults and teenagers—Usual dose is 40 to 95 mg four times a day, after meals and at bedtime. The dose should not be more than 500 mg in twenty-four hours.
+ Children—Dose must be determined by the doctor.

http://www.drugs.com/cons/gas-x.html