As of February 2015 national retailers such as Walmart, Walgreens, CVS Pharmacy, Target and Amazon.com sell over-the-counter Zantac, according to the drug maker's official website. The heartburn medication comes in several types, including a 75-milligram dose, a 150-milligram dose and a 300-milligram dose.
The active ingredient in Zantac is rantidine, notes the official website. One tablet swallowed whole every 12 hours represents a single dosage of the medication. Zantac prevents or relieves heartburn related to acid indigestion. The drug maker asserts that the medicine begins to work within 30 to 60 minutes and that relief lasts up to 12 hours.
Rantidine works by reducing the amount of acid that the stomach produces during digestion, similar to other classes of drugs known as histamine-2 blockers, says Drugs.com. In some cases Zantac prevents ulcers and treats acid reflux disease. It is possible for Zantac to make patients more vulnerable to pneumonia. It is necessary for people who have porphyria or issues with their livers or kidneys to speak with their doctors before taking this drug.
More powerful tablets of Zantac contain 336 milligrams, according to RxList.com. One milliliter of Zantac syrup contains 16.8 milligrams of rantidine. Patients are instructed to stop using Zantac and to seek medical attention if an allergic reaction occurs with symptoms including swelling of the face, itching or difficulty breathing.