Foscarnet is an antiviral compound. Laboratory studies have shown it to be active against HIV. However, only 12 - 22 percent of an oral foscarnet dose is absorbed by the body. Ranitidine suppresses gastric acid output, increasing gastric pH. Thus by increasing gastric pH (decreasing stomach acidity), less foscarnet is expected to be decomposed or broken down in the stomach. Thus, more foscarnet should be absorbed into the body.