What happened

Shares of Pfizer (PFE -1.07%) slipped 3.3% lower as of the market close on Thursday. The decline resulted from investors' concerns about litigation related to Zantac. The U.S. Food and Drug Administration (FDA) called for the heartburn drug to be pulled from the market in 2020 due to safety concerns. 

So what

GSK (GSK 0.09%) originally developed Zantac. By 1988, it ranked as the world's best-selling drug. Pfizer marketed an over-the-counter version of Zantac for several years. However, the company sold the U.S. rights to the OTC drug to Sanofi (SNY 0.02%) in 2006 and hasn't marketed it since then. 

Pfizer does have some legal exposure related to the increased risk of cancer associated with taking Zantac. GSK and Sanofi could be more at risk than Pfizer is because they sold Zantac for longer periods. However, it's too soon to know what the negative impact, if any, will be for any of these companies.

Now what

There's a much more important question for investors to focus on with regard to Pfizer than its part in the Zantac litigation. The fortunes for the big pharma stock hinge largely on the demand for its COVID-19 vaccine Comirnaty and COVID-19 therapy Paxlovid. The two products together generated nearly all of Pfizer's growth in the second quarter of 2022.

Pfizer's expected launch of boosters targeting the coronavirus omicron variant within a few months could provide a catalyst. The Biden administration has also warned about a potential major COVID-19 wave in the fall and winter. Another surge in cases could drive higher demand for both Comirnaty and Paxlovid.