Study finds unexpected results in acid suppression between two OTC heartburn treatments

Researchers say differences can help guide appropriate medication selection

In a new study, researchers have directly compared the early therapeutic response of drugs from widely-used classes of heartburn medications, omeprazole magnesium, a proton pump inhibitor (PPI) and famotidine, a histamine-2 receptor antagonist (H2RAs), in an over-the-counter (OTC) setting. In contrast to general consensus, suggesting first day superiority of H2RAs, the results show similar acid suppression on the first day of dosing between these drugs as reported in Alimentary Pharmacology & Therapeutics.

Researchers also report evidence that with daily use, the body develops a rapid onset of tolerance to even a low dose H2RAs such as Pepcid AC®.

The findings may help physicians and consumers make better choices about which therapy to use when treating heartburn, which is caused by stomach acid flowing up into the esophagus, a condition that affects more than 50 million Americans annually.

"There have been many studies testing acid-suppression in these two classes of drugs -- PPIs and H2RAs (also known as H2-blockers or H2s) – but very few studies have compared the two types of drugs in an OTC setting where so many of these treatments are used," says Philip Miner, MD, Clinical Professor of Medicine at the University of Oklahoma and lead investigator at Oklahoma Foundation for Digestive Research.

"Because these two drugs work in fundamentally different ways to suppress acid production, we didn't expect that the PPI would work as well as the H2RAs within the first 24 hour period after treatment. In addition, while using the lower-dose H2RAs, the degree of acid suppression ability was found to significantly decrease after the first day of use. While this study measured acid suppression, it did not measure symptom relief or the speed of onset of action. However, both PPIs and H2RAs owe their clinical efficacy to their ability to suppress gastric acid secretion. This means that for people who have frequent heartburn, that is, heartburn two or more days per week, taking an over-the-counter PPI is an excellent option."

In this 14 day study, subjects were randomly assigned to one of six treatment sequences, each including three regimens: omeprazole magnesium 20.6 mg (Prilosec OTC®) once a day; famotidine 10 mg (Pepcid AC) twice a day; and famotidine 20 mg (now available over-the-counter as Maximum Strength Pepcid AC®) twice a day. 1 During the study treatment period, the amount of acid production was measured over 24-hours several times. Results indicate:

The PPI - Prilosec OTC - showed significant acid suppression on the very first day of treatment compared to baseline (Day 0) and comparable to the acid suppression of H2RAs – Pepcid AC and the medicine in Maximum Strength Pepcid AC. 1
After Day 1 of treatment, Prilosec OTC was consistently superior in acid suppression vs. the H2RAs - Pepcid AC and the medicine in Maximum Strength Pepcid AC. 1
In addition, while using the lower-dose H2RAs - Pepcid AC, the degree of acid suppression ability was found to significantly decrease after the first day of use. 1
Different medications, different mechanisms

The mechanistic activities of PPIs and H2RAs are well documented, and show that while both PPIs and H2RAs effectively reduce the amount of stomach acid, they do it in very different ways. The key point of difference happens at a cellular level in the stomach. The stomach is lined with millions of acid producing pumps. Acid producing pumps rely on three chemical signals that tell them to produce stomach acid. H2RAs are able to block one of these signals, thereby reducing the amount of acid produced and generally have a quicker onset of action than PPIs. PPIs on the other hand actually shut down the active pumps themselves. This study showed the PPI had more profound effects on stomach acid over time.

"The study results add an important aspect to the existing literature on these two medications," says Miner. "It further underscores the need for consumers to identify their needs in heartburn protection in order to select the most appropriate treatment."