Exposure to phenytoin associates with a lower risk of post-COVID cognitive deficits: a cohort study

Post-COVID cognitive deficits (often referred to as 'brain fog') are common and have large impacts on patients' level of functioning. No specific intervention exists to mitigate this burden. This study tested the hypothesis, inspired by recent experimental research, that post-COVID cognitive deficits can be prevented by inhibiting receptor-interacting protein kinase. Using electronic health record data, we compared the cognitive outcomes of propensity score-matched cohorts of patients with epilepsy taking phenytoin (a commonly used receptor-interacting protein kinase inhibitor) versus valproate or levetiracetam at the time of COVID-19 diagnosis. Patients taking phenytoin at the time of COVID-19 were at a significantly lower risk of cognitive deficits in the 6 months after COVID-19 infection than a matched cohort of patients receiving levetiracetam (hazard ratio 0.78, 95% confidence interval 0.63-0.97, P = 0.024) or valproate (hazard ratio 0.73, 95% confidence interval 0.58-0.93, P = 0.011). In secondary analyses, results were robust when controlling for subtype of epilepsy, and showed specificity to cognitive deficits in that similar associations were not seen with other 'long-COVID' outcomes such as persistent breathlessness or pain. These findings provide pharmacoepidemiological support for the hypothesis that receptor-interacting protein kinase signaling is involved in post-COVID cognitive deficits. These results should prompt empirical investigations of receptor-interacting protein kinase inhibitors in the prevention of post-COVID cognitive deficits. Little is known about the causes and treatments of post-COVID 'brain fog'. Taquet et al. report that people taking phenytoin at the time of COVID-19 infection were less likely to later develop brain fog, suggesting that the latter might be due to damage to the blood vessels in the brain, which might be preventable with medications.