In vitroevaluation of the effects of 4-aminopyridine on cytochrome P450 enzymes

Abstract

BackgroundDalfampridine extended release tablets (dalfampridine-ER, known as prolonged-, modified, or sustained-release fampridine tablets in some countries) are approved for the improvement of walking in patients with multiple sclerosis (MS). Dalfampridine-ER is an extended release formulation of 4-aminopyridine (4-AP). Dalfampridine-ER is incorporated into MS management strategies that may include disease-modifying and symptomatic therapies. Since several symptomatic therapies are partially or fully metabolized by enzymes of the hepatic cytochrome P450 system (CYP450) it is important to evaluate drug–drug interactions through potential effects of dalfampridine-ER on CYP450.MethodsThe ability of 4-AP to inhibit CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4/5 in a direct and time-dependent manner was evaluated using pooled human liver microsomes. 4-AP concentrations were 0.03, 0.1, 0.3, 1, 3, 10, and 30 μM, representing 0.1–100-times the average plasma 4-AP concentration (30 ng/mL; 0.32 μM) at therapeutic dosing; the concentration inhibiting 50% of each enzyme activity (IC50) was determined. The ability of 4-AP (0.025, 0.25, 2.5, and 25 μM) to induce the expression of CYP1A2, 2B6, 2C9, 2C19, 2E1, and 3A4/5 enzymes was evaluated using primary cultures of freshly isolated human hepatocytes from non-transplantable livers. The enzyme-inducing effects of 4-AP were compared with the prototypical inducers. Metabolites were assayed using high-performance liquid chromatography-tandem mass spectrometry techniques. All inhibition and induction assays included positive controls.Results4-AP did not directly inhibit CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, or CYP3A4/5, but at a concentration of 30 μM, CYP2E1 was inhibited by 12%, resulting in an estimated IC50 value of 125 μM. None of the enzymes demonstrated time-dependent inhibition by 4-AP. There was little or no effect by 4-AP on enzyme induction, with enzyme activities approximately equivalent to vehicle control. A main limitation was the inability to estimate effectiveness of 4-AP relative to prototypical CYP450 inducers.ConclusionThe likelihood of drug–drug interactions is remote in patients with MS who may be taking dalfampridine-ER concomitantly with medications that are metabolized by CYP450 pathways.

Central Nervous System Stimulants Limit Caffeine Transport at the Blood–Cerebrospinal Fluid Barrier

“…Based on the assumption that CYP1A2 exists in human choroid plexus epithelial cells, it is possible that methamphetamine also activates CYP1A2 in humans and increases caffeine metabolism, resulting in differences in caffeine concentrations between blood and CSF. However, another study reported that 4-AP, which was used as an alternative to stimulants, neither inhibited nor induced CYP1A2 [36]. In the culture experiments of this study, the inhibition of caffeine transfer to the CSF in the BCSFB was stronger when 4-AP was simultaneously added instead of stimulants, suggesting that the inhibition of caffeine transfer was caused by triggers other than metabolic enzyme activity.…”

Effect of Voltage-Gated K+Channel Inhibition by 4-aminopyridine in Spinal Cord Injury Recovery in Zebrafish

“…There is limited metabolism of 4-AP in humans with ~90% excreted unchanged in the urine. However, 4-AP has been shown to inhibit CYP2E1 with an IC50 value of 125 μM (Caggiano and Blight 2013). Zebrafish have two homologous P450 enzymes, Cyp2y3 and Cyp2p6 (Tsedensodnom et al 2013).…”

Development of dalfampridine, a novel pharmacologic approach for treating walking impairment in multiple sclerosis

“…The pharmacokinetics of 4‐AP and its extended‐release formulation have been well characterized . The drug exhibits dose proportionality, and excretion is through renal elimination primarily as unchanged drug (≥90%), with a low likelihood of drug–drug interactions mediated through hepatic cytochrome P450 metabolic pathways . However, oral administration of immediate‐release formulations results in rapid attainment of maximum plasma concentration ( T max : approximately 1 h), and a short elimination half‐life ( t 1/2 : approximately 3.5 h) .…”