Patients who use proton pump inhibitors (PPI)/histamine 2 (H2) blockers have an increased risk of receiving an ocular toxoplasmosis diagnosis, according to a study published in Ophthalmology Retina. Researchers say they have not yet elucidated the mechanism that causes PPI/H2 blockers to increase this risk.
In a retrospective, match case-control study, researchers collected outpatient medical claims between January 2000 to June 2020 to examine if PPI use is associated with increased susceptibility to toxoplasmic retinochoroiditis. The researchers used ICD-9 and ICD-10 codes and identified adult patients who were diagnosed with toxoplasmic retinochoroiditis infections. The study authors compared the patient’s with those in a control group for previous PPI use or having an ailment likely to be associated with PPI use. Demographics and systemic health of patients were also accounted for in the study.
A total of 4069 cases of toxoplasmic retinochoroiditis (mean age, 54.1±18.1 years; 39.2% men) and 19,177 unaffected controls (mean age, 54.3±18.2 years; 39.1% men) were included in this study. The researchers identified PPI/H2 blocker use in 24.3% of cases compared with 19.2% of controls. Adjusting for all covariates, the researchers note increased odds of having toxoplasmosis for PPI users compared with unaffected control participants (OR,1.28 [1.17–1.40], P <.001).
“PPIs are known to significantly reduce gastric acid levels, thereby increasing gut pH. Omeprazole, an over-the-counter PPI, has been shown to inhibit acidification of phagolysosomes in vitro. T. gondii tachyzoites are extremely susceptible to acidic conditions (low pH) and acidification of the phagosome is one of the primary defense mechanisms of the host innate immune response to toxoplasmosis invasion,” the study authors explain. “Taken together, we hypothesize that the reduction in gut acidity and neutralization of the phagolysosome resulting from PPI use may be responsible for the increased risk of being diagnosed with toxoplasmic retinochoroiditis.”
The study limitations included providers using proper diagnostic codes and the impact on strains and rate of infection which varies from country to country. PPI and H2 blockers are available over the counter, which suggests an underestimate in both cases and controls due to the inability of claims data to capture over-the-counter medication uses.
Conrady CD, Pradeep T, Yu Y, Johnson MW, VanderBeek BL. Association of proton pump inhibitor/histamine-2 blocker use and ocular toxoplasmosis. Ophthalmol Retina. Published online September 2, 2022. doi:10.1016/j.oret.2022.08.023