Sequence-Dependent Amplification of Gabapentinoid-Associated Dementia Risk by Dihydropyridine Calcium Channel Blockers: Asymmetric Pharmacodynamic Vulnerability Consistent with Homeostatic Synaptic Plasticity

Background: Concomitant gabapentinoid and dihydropyridine calcium channel blocker (DHP-CCB) use amplifies dementia risk, an interaction proposed to involve dual neuronal calcium channel blockade. Whether this risk depends on the sequence of drug initiation - and is therefore preventable by prescribing order - remains unknown. Methods: Using the Rutgers Clinical Research Data Warehouse (2015-2024), we conducted three complementary analyses. The primary analysis (Population 4) compared gabapentin versus pregabalin in 4,451 patients on chronic DHP-CCB therapy who newly initiated a gabapentinoid (55 dementia events; IPTW Cox model). The asymmetry confirmatory analysis (Population 3) compared DHP-CCB versus ACE/ARB initiation in 1,740 patients on chronic gabapentinoid therapy (29 dementia events). A sensitivity analysis replicated prior findings in a broader CCB-first cohort (N=9,383). A dementia acceleration analysis examined outcomes in 273 patients with established dementia initiating gabapentinoid. Results: In Population 4, gabapentinoid initiation on a background of chronic CCB therapy was associated with a 2.23-fold elevated dementia risk compared to pregabalin (IPTW HR 2.23, 95% CI 1.43-3.48, p=0.0004). The Population 3 asymmetry test yielded a null result: adding DHP-CCB to chronic gabapentinoid therapy carried no differential dementia risk versus adding ACE/ARB (IPTW HR 0.995, 95% CI 0.595-1.664, p=0.98). This directional asymmetry - elevated risk only when gabapentinoid is added to pre-existing CCB therapy, not the reverse - is the central finding. Lagged analyses showed HRs increasing monotonically from 2.23 to 2.87 across 0- to 180-day lag windows, reducing concern for protopathic bias. In the dementia acceleration cohort, DHP-CCB use at gabapentinoid initiation was associated with encephalopathy (IPTW HR 2.09, 95% CI 1.19-3.67, p=0.010); zero encephalopathy events occurred among non-DHP CCB users (N=16), consistent with DHP subtype specificity. Conclusions: The gabapentinoid-CCB cognitive interaction is directionally asymmetric: risk concentrates in patients adding gabapentinoid to pre-existing CCB therapy, not the reverse. This pattern is mechanistically consistent with impaired homeostatic synaptic plasticity in neurons compensating for chronic L-type calcium channel blockade. For patients already on CCB therapy requiring neuropathic pain management, pregabalin may be preferable to gabapentin, pending external validation. The asymmetry also implies that initiating a CCB in a patient already on gabapentin may not carry equivalent risk.