Pharmacological Basis for the Antidiarrheal and Antispasmodic Effects of Cuminaldehyde in Experimental Animals: In Silico, Ex Vivo and In Vivo Studies.

BACKGROUND: Medicinal herbs are frequently used for the management of gastrointestinal disorders because they contain various compounds that can potentially amplify the intended therapeutic effects. Cuminaldehyde is a plant-based constituent found in oils derived from botanicals such as cumin, eucalyptus, myrrh, and cassia and is responsible for its health benefits. Despite the utilization of cuminaldehyde for several medicinal properties, there is currently insufficient scientific evidence to support its effectiveness in treating diarrhea. Hence, the present investigation was carried out to evaluate the antidiarrheal and antispasmodic efficacy of cuminaldehyde, with detailed pharmacodynamics explored. METHODS: An in vivo antidiarrheal test was conducted in mice following the castor oil-induced diarrhea model, while an isolated small intestine obtained from rats was used to evaluate the detailed mechanism(s) of antispasmodic effects. RESULTS: Cuminaldehyde, at 10 and 20 mg/kg, exhibited 60 and 80% protection in mice from episodic diarrhea compared to the saline control group, whereas this inhibitory effect was significantly reversed in the pretreated mice with glibenclamide, similar to cromakalim, an ATP-dependent K+ channel opener. In the ex vivo experiments conducted in isolated rat tissues, cuminaldehyde reversed the glibenclamide-sensitive low K+ (25 mM)-mediated contractions at significantly higher potency compared to its inhibitory effect against high K+ (80 mM), thus showing predominant involvement of ATP-dependent K+ activation followed by Ca++ channel inhibition. Cromakalim, a standard drug, selectively suppressed the glibenclamide-sensitive low K+-induced contractions, whereas no relaxation was observed against high K+, as expected. Verapamil, a Ca++ channel inhibitor, effectively suppressed both low and high K+-induced contractions with similar potency, as anticipated. At higher concentrations, the inhibitory effect of cuminaldehyde against Ca++ channels was further confirmed when the preincubated ileum tissues with cuminaldehyde (3 and 10 mM) in Ca++ free medium shifted CaCl2-mediated concentration-response curves (CRCs) towards the right with suppression of the maximum peaks, similar to verapamil, a standard Ca++ ion inhibitor. CONCLUSIONS: Present findings support the antidiarrheal and antispasmodic potential of cuminaldehyde, possibly by the predominant activation of ATP-dependent K+ channels followed by voltage-gated Ca++ inhibition. However, further in-depth assays are recommended to know the precise mechanism and to elucidate additional unexplored mechanism(s) if involved.

Effects of Omeprazole and Verapamil on the Pharmacokinetics, Safety, and Tolerability of Mavacamten: Two Drug-Drug Interaction Studies in Healthy Participants.

Two open-label, Phase 1 studies assessed the effects of omeprazole (a weak to moderate cytochrome P450 [CYP] 2C19 inhibitor) and verapamil (a moderate CYP3A4 inhibitor) on the pharmacokinetics, safety, and tolerability of mavacamten. In the omeprazole study, healthy participants received mavacamten 15 mg alone or with a 31-day course of omeprazole 20 mg once daily. In the verapamil study, healthy participants received mavacamten 25 mg alone or with a 28-day course of verapamil 240 mg once daily. In the omeprazole study, 27 of 29 randomized participants completed the study. Nine participants receiving mavacamten alone were normal metabolizers (NMs) of CYP2C19 substrates, and 6 were rapid metabolizers; 8 NMs and 6 rapid metabolizers received mavacamten + omeprazole. In both studies, mavacamten showed no safety signals and was generally well tolerated. Overall mavacamten exposure (area under the plasma concentration-time curve) increased by approximately 50% with omeprazole coadministration; maximum observed concentration (Cmax ), time to Cmax , and elimination half-life were not affected appreciably. In the verapamil study, 25 of 26 randomized participants received the study drug(s) and were included in the pharmacokinetic analyses; 24 completed the study. In the pharmacokinetic population, 12 participants received mavacamten alone (11 NMs, 1 poor metabolizer) and 13 received mavacamten + verapamil (7 NMs, 4 intermediate metabolizers, 2 poor metabolizers). Following verapamil coadministration in NMs and intermediate metabolizers, mavacamten area under the plasma concentration-time curve was minimally increased (by less than 20%), and Cmax was modestly increased (by 52%). These results suggest that mavacamten can be coadministered with weak CYP2C19 and moderate CYP3A4 inhibitors.

The Antiarrhythmic Action of the Na+/Ca2+ Exchanger Inhibitor SEA0400 on Drug-Induced Long QT Syndrome Depends on the Severity of Proarrhythmic Conditions in Anesthetized Atrioventricular Block Rabbits.

To clarify the pharmacological properties of the Na+/Ca2+ exchanger (NCX) inhibitor SEA0400 as an antiarrhythmic agent, we assessed its effects on rapid component of delayed rectifier K+ current (IKr) blocker-induced torsade de pointes (TdP) in isoflurane-anesthetized rabbits. Atrioventricular block was induced in rabbits using a catheter ablation technique, and the monophasic action potential (MAP) of the right ventricle was measured under electrical pacing at 60 beats/min. In non-treated control animals, intravenous administration of low-dose (0.3 mg/kg) or high-dose nifekalant (3 mg/kg) prolonged the MAP duration (MAP90) by 113 ± 11 ms (n = 5) and 237 ± 39 ms (n = 5), respectively, where TdP was induced in 1/5 animals treated with a low dose and in 3/5 animals treated with a high dose of nifekalant. In SEA0400-treated animals, low- and high-dose nifekalant prolonged the MAP90 by 65 ± 13 ms (n = 5) and 230 ± 20 ms (n = 5), respectively. No TdP was induced by the low dose but 1/5 animals treated with a high dose of nifekalant developed TdP. In verapamil-treated animals, low-dose and high-dose nifekalant prolonged MAP90 by 50 ± 12 ms (n = 5) and 147 ± 30 ms (n = 5), respectively, without inducing TdP. These results suggest that SEA0400 has the potential to inhibit low-dose nifekalant-induced TdP by suppressing the MAP-prolonging action of nifekalant, whereas the drug inhibited high-dose nifekalant-induced TdP without affecting the MAP-prolonging action of nifekalant. This may reveal that, in contrast to verapamil, the antiarrhythmic effects of SEA0400 on IKr blocker-induced TdP may be multifaceted, depending on the severity of the proarrhythmogenic conditions present.

Association between hemorrhage and direct oral anticoagulants in combination with verapamil: Analysis of Japanese Adverse Drug Event Report database and electronic medical record data.

OBJECTIVE: The aim of this study was to investigate the risk of hemorrhage in concomitant therapy with direct oral anticoagulants (DOACs) and class IV antiarrhythmic drugs. MATERIALS AND METHODS: First, disproportionality analysis (DPA) was performed using the Japanese Adverse Drug Event Report (JADER) database to investigate the risk of hemorrhage with DOACs. Second, a cohort study was performed using electronic medical record data to confirm the results of the JADER analysis. RESULTS: In the JADER analysis, hemorrhage was significantly associated with treatment with edoxaban and verapamil (reporting odds ratio = 1.66; 95% confidence interval (CI) = 1.04 - 2.67). The cohort study revealed that hemorrhage incidence significantly differed between the verapamil-treated group and the bepridil-treated group, with a higher risk for hemorrhage in the verapamil group (log-rank test: p < 0.001). The multivariate Cox proportional hazards model also showed that the verapamil and DOAC combination was significantly associated with hemorrhage events compared with the bepridil and DOAC combination (hazard ratio (HR): 2.87, 95% CI: 1.17 - 7.07, p = 0.022). Furthermore, creatinine clearance (Ccr) ≥ 50 mL/min was significantly associated with hemorrhage events (HR: 2.72, 95% CI: 1.03 - 7.18, p = 0.043), and verapamil was significantly associated with hemorrhage in patients with Ccr ≥ 50 mL/min (HR: 3.58, 95% CI: 1.36 - 9.39, p = 0.010) but not in patients with Ccr < 50 mL/min. CONCLUSION: Verapamil increases the risk of hemorrhage in patients on DOACs. Dose adjustment of DOACs based on renal function may prevent hemorrhage when verapamil is concomitantly administered.

Effect of Verapamil on Pancreatic Beta Cell Function in Newly Diagnosed Pediatric Type 1 Diabetes: A Randomized Clinical Trial.

Importance: In preclinical studies, thioredoxin-interacting protein overexpression induces pancreatic beta cell apoptosis and is involved in glucotoxicity-induced beta cell death. Calcium channel blockers reduce these effects and may be beneficial to beta cell preservation in type 1 diabetes. Objective: To determine the effect of verapamil on pancreatic beta cell function in children and adolescents with newly diagnosed type 1 diabetes. Design, Setting, and Participants: This double-blind, randomized clinical trial including children and adolescents aged 7 to 17 years with newly diagnosed type 1 diabetes who weighed 30 kg or greater was conducted at 6 centers in the US (randomized participants between July 20, 2020, and October 13, 2021) and follow-up was completed on September 15, 2022. Interventions: Participants were randomly assigned 1:1 to once-daily oral verapamil (n = 47) or placebo (n = 41) as part of a factorial design in which participants also were assigned to receive either intensive diabetes management or standard diabetes care. Main Outcomes and Measures: The primary outcome was area under the curve values for C-peptide level (a measure of pancreatic beta cell function) stimulated by a mixed-meal tolerance test at 52 weeks from diagnosis of type 1 diabetes. Results: Among 88 participants (mean age, 12.7 [SD, 2.4] years; 36 were female [41%]; and the mean time from diagnosis to randomization was 24 [SD, 4] days), 83 (94%) completed the trial. In the verapamil group, the mean C-peptide area under the curve was 0.66 pmol/mL at baseline and 0.65 pmol/mL at 52 weeks compared with 0.60 pmol/mL at baseline and 0.44 pmol/mL at 52 weeks in the placebo group (adjusted between-group difference, 0.14 pmol/mL [95% CI, 0.01 to 0.27 pmol/mL]; P = .04). This equates to a 30% higher C-peptide level at 52 weeks with verapamil. The percentage of participants with a 52-week peak C-peptide level of 0.2 pmol/mL or greater was 95% (41 of 43 participants) in the verapamil group vs 71% (27 of 38 participants) in the placebo group. At 52 weeks, hemoglobin A1c was 6.6% in the verapamil group vs 6.9% in the placebo group (adjusted between-group difference, -0.3% [95% CI, -1.0% to 0.4%]). Eight participants (17%) in the verapamil group and 8 participants (20%) in the placebo group had a nonserious adverse event considered to be related to treatment. Conclusions and Relevance: In children and adolescents with newly diagnosed type 1 diabetes, verapamil partially preserved stimulated C-peptide secretion at 52 weeks from diagnosis compared with placebo. Further studies are needed to determine the longitudinal durability of C-peptide improvement and the optimal length of therapy. Trial Registration: ClinicalTrials.gov Identifier: NCT04233034.

Ethanol Extract of Glycyrrhiza uralensis Fisch: Antidiarrheal Activity in Mice and Contraction Effect in Isolated Rabbit Jejunum.

OBJECTIVE: To evaluate the antidiarrheal effect of ethanol extract of Glycyrrhiza uralensis Fisch root (GFR) in vivo and jejunal contraction in vitro. METHODS: In vivo, 50 mice were divided into negative control, positive control (verapamil), low-, medium- and high-dose GFR (250, 500, 1,000 mg/kg) groups by a random number table, 10 mice in each group. The antidiarrheal activity was evaluated in castor oil-induced diarrhea mice model by evacuation index (EI). In vitro, the effects of GFR (0.01, 0.03, 0.1, 0.3, 1, 3, and 10 g/L) on the spontaneous contraction of isolated smooth muscle of rabbit jejunum and contraction of pretreated by Acetylcholine (ACh, 10 µmol/L) and KCl (60 mmol/L) were observed for 200 s. In addition, CaCl2 was accumulated to further study its mechanism after pretreating jejunal smooth muscle with GFR (1 and 3 g/L) or verapamil (0.03 and 0.1 µmol/L) in a Ca2+-free-high-K+ solution containing ethylene diamine tetraacetic acid (EDTA). RESULTS: GFR (500 and 1,000 mg/kg) significantly reduced EI in castor oil-induced diarrhea model mice (P<0.01). Meanwhile, GFR (0.01, 0.03, 0.1, 0.3, 1, 3, and 10 g/L) inhibited the spontaneous contraction of rabbit jejunum (P<0.05 or P<0.01). Contraction of jejunums samples pretreated by ACh and KCl with 50% effective concentration (EC50) values was 1.05 (0.71-1.24), 0.34 (0.29-0.41) and 0.15 (0.11-0.20) g/L, respectively. In addition, GFR moved the concentration-effect curve of CaCl2 down to the right, showing a similar effect to verapamil. CONCLUSIONS: GFR can effectively against diarrhea and inhibit intestinal contraction, and these antidiarrheal effects may be based on blocking L-type Ca2+ channels and muscarinic receptors.

Ethanol Extract of Glycyrrhiza uralensis Fisch: Antidiarrheal Activity in Mice and Contraction Effect in Isolated Rabbit Jejunum / 中国结合医学杂志

OBJECTIVE@#To evaluate the antidiarrheal effect of ethanol extract of Glycyrrhiza uralensis Fisch root (GFR) in vivo and jejunal contraction in vitro.@*METHODS@#In vivo, 50 mice were divided into negative control, positive control (verapamil), low-, medium- and high-dose GFR (250, 500, 1,000 mg/kg) groups by a random number table, 10 mice in each group. The antidiarrheal activity was evaluated in castor oil-induced diarrhea mice model by evacuation index (EI). In vitro, the effects of GFR (0.01, 0.03, 0.1, 0.3, 1, 3, and 10 g/L) on the spontaneous contraction of isolated smooth muscle of rabbit jejunum and contraction of pretreated by Acetylcholine (ACh, 10 µmol/L) and KCl (60 mmol/L) were observed for 200 s. In addition, CaCl2 was accumulated to further study its mechanism after pretreating jejunal smooth muscle with GFR (1 and 3 g/L) or verapamil (0.03 and 0.1 µmol/L) in a Ca2+-free-high-K+ solution containing ethylene diamine tetraacetic acid (EDTA).@*RESULTS@#GFR (500 and 1,000 mg/kg) significantly reduced EI in castor oil-induced diarrhea model mice (P<0.01). Meanwhile, GFR (0.01, 0.03, 0.1, 0.3, 1, 3, and 10 g/L) inhibited the spontaneous contraction of rabbit jejunum (P<0.05 or P<0.01). Contraction of jejunums samples pretreated by ACh and KCl with 50% effective concentration (EC50) values was 1.05 (0.71-1.24), 0.34 (0.29-0.41) and 0.15 (0.11-0.20) g/L, respectively. In addition, GFR moved the concentration-effect curve of CaCl2 down to the right, showing a similar effect to verapamil.@*CONCLUSIONS@#GFR can effectively against diarrhea and inhibit intestinal contraction, and these antidiarrheal effects may be based on blocking L-type Ca2+ channels and muscarinic receptors.

Effect of intra-arterial vasodilator administration during radial artery access on systemic blood pressure in patients receiving moderate sedation.

PURPOSE: The hemodynamic effects of intra-arterial vasodilator administration for the prevention of radial artery spasm during transradial access have not been well characterized. This study evaluates the effect of intra-arterial Verapamil and Nitroglycerine administration on systemic blood pressure and its correlation with timing of moderate sedation administration. MATERIALS AND METHODS: Institutional review board approval was granted. Patients who underwent transradial access from 4/2018 to 4/2019 and received both intra-arterial vasodilators and moderate sedation were identified and their electronic medical records reviewed. Patients were divided into three cohorts based on the timing of sedation and intra-arterial vasodilator administration. Decrease in systolic blood pressure (SBP) was expressed as means with standard deviation which were then compared using Student's t-test. RESULTS: A total of 84 patients who met inclusion criteria demonstrated an overall mean decrease in SBP of 16.45 mmHg ± 15.45 mmHg. Patients receiving sedation and intra-arterial vasodilators within their expected peak SBP effect times had similar SBP change following the intra-arterial vasodilators as those in whom the interval was greater than 10 min (4.2 mmHg; 95% CI (-4.11 to 12.52), p = 0.3171). Two patients experienced asymptomatic hypotension. CONCLUSIONS: Patients undergoing transradial access for procedures utilizing moderate sedation can safely receive intra-arterial Verapamil and Nitroglycerine for prevention of radial artery spasm.

Comparative efficacy and safety of verapamil and triamcinolone in keloid and hypertrophic scar treatment: a meta-analysis.

Keloids and hypertrophic scars are harmful to physical and psychological health. The study aims to compare the efficacy and safety of verapamil and triamcinolone in the treatment of keloids and hypertrophic scars. Relevant publications were searched from PubMed, Embase, Cochrane library, CNKI, Weipu, and Wanfang databases. Results were expressed as weighted mean differences (WMDs) or the relative ratios (RRs) with 95% confidence interval (CI). Pooled estimates were calculated using random-effects or fixed-effects models according to the heterogeneity among studies. The pooled results indicated that the triamcinolone treatment showed significantly better effectiveness in height (at 12, 15, 18, 21, and 24 weeks), pliability (at 3, 6, 9, 21, and 24 weeks) and vascularity (at 3, 6, 9, and 12 week) than that of verapamil (P < .05). Moreover, the side effects such as skin atrophy (RR = 0.13, 95% CI: 0.04 to 0.42, P = .001), telangiectasia (RR = 0.08, 95% CI: 0.02 to 0.28, P < .001), and hyperpigmentation (RR = 0.12, 95% CI: 0.03 to 0.44, P = .001) of verapamil were significantly less than those in triamcinolone. This meta-analysis showed that triamcinolone had a better therapeutic efficacy than verapamil, while verapamil was more safety.

Bradycardia Shock Caused by the Combined Use of Carteolol Eye Drops and Verapamil in an Elderly Patient with Atrial Fibrillation and Chronic Kidney Disease.

Ophthalmic carteolol is often used to treat glaucoma. Elderly patients with atrial fibrillation (AF) and chronic kidney disease (CKD) are common among the super-elderly in Japan. Because these patients are exposed to polypharmacy, they are at a high-risk of adverse drug interactions. We herein report an elderly patient with CKD who suffered bradycardia shock after the combined use of carteolol eye drops and verapamil for glaucoma and paroxysmal AF. This case highlights the fact that eye drops have a similar systemic effect to oral drugs, and especially in elderly patients with polypharmacy, drug interactions can unwittingly lead to serious events.

Comparing the Efficacy and Safety of Intralesional Verapamil With Intralesional Triamcinolone Acetonide in Treatment of Hypertrophic Scars and Keloids: A Meta-Analysis of Randomized Controlled Trials.

BACKGROUND: Clinical treatment of hypertrophic scars (HSs) and keloids is often unsatisfactory. Intralesional injections of triamcinolone acetonide (TAC) and verapamil are widely used to treat HSs and keloids, but their efficacy and safety are controversial. OBJECTIVES: The aim of this study was to conduct a meta-analysis of the effectiveness and safety of verapamil and TAC in the treatment of HSs and keloids. METHODS: Embase, Google Scholar, and PubMed were searched for randomized controlled trials (RCTs) from inception to February 2020. RCTs that evaluated treatment effects with the Vancouver Scar Scale or reported adverse effects were included. The continuous data and the dichotomous variables were analyzed as mean difference (MD) and relative risk (RR), respectively. RESULTS: Seven RCTs (461 patients) were included. Compared with verapamil, TAC rapidly changed the ∆height (MD = 0.07; P < 0.05) and ∆pliability (MD = 0.23; P < 0.05) after the first session, but subsequent treatments resulted in no significant differences in the ∆height, ∆pigmentation, ∆vascularity, and ∆pliability. Although total adverse effects (RR = 0.42; P = 0.1) were not significantly different, in the subgroup analysis the incidence of telangiectasia (RR = 0.04; P < 0.05) and skin atrophy (RR = 0.10; P < 0.05), but not pain (RR = 1.27; P = 0.77), was significantly lower with verapamil than with TAC. CONCLUSIONS: Verapamil may be an effective substitute for TAC. Although total adverse effects did not change, the incidence of telangiectasia and skin atrophy was lower with verapamil than with TAC.

[Therapeutic effects of target artery infusion of verapamil and chemotherapy drugs on advanced non-small cell lung cancer].

Objective: To investigate the effects of targeted artery perfusion of verapamil and chemotherapy drugs on advanced non-small cell lung cancer (NSCLC). Methods: Sixty patients with advanced NSCLC who were admitted to the Central Hospital of Zhumadian from April 2016 to April 2018 were selected as the research subjects. They were divided into the observation group (26 cases) and the control group (34 cases) according to the treatment method. Patients in the observation group were treated with targeted artery perfusion of verapamil and chemotherapy drugs while the control group were treated with target artery perfusion of chemotherapy drugs alone.Both groups were treated continuously for more than 2 months. The short-term curative effect, adverse reactions, changes in immune function, levels of serum tumor markers and Karnofsky Performance Scale (KPS) scores before and after treatment as well as the prognosis were compared between the two groups. Results: The response rate and control rate in the observation group were 80.8% and 96.2%, higher than 55.9% and 76.5% in the control group (P<0.05). After treatment, CD4(+) levels and CD4(+) /CD8(+) in the observation group were (25.43±2.76)% and (0.88±0.11), lower than (27.56±2.79)% and (0.95±0.13) in the control group (P<0.05). After treatment, serum levels of CEA and CA50 in the observation group were (11.57±2.32)ng/ml and (16.62±3.28)U/ml, also lower than (15.87±2.66)ng/ml and (20.31±3.42)U/ml in the control group (P<0.05). There was no significant difference in adverse reactions between the two groups (P>0.05). After treatment, KPS score of the observation group was (81.44±2.76) points, higher than (79.62±2.38) points of the control group (P<0.05). The median survival time and progression-free median survival time of the observation group were 16.0 months and 7.5 months, respectively, significantly better than 10.0 months and 5.0 months of the control group (P<0.05). Conclusions: The treatment with target arterial perfusion of verapamil and chemotherapy drugs for advanced NSCLC can effectively improve the short-term curative effect, reduce serum levels of tumor markers, improve life quality and prolong the survival time. However, it has a certain inhibitory effect on the patient's immune function.

Efficacy and safety of verapamil vs triamcinolone acetonide for keloids and hypertrophic scars: A systematic review and meta-analysis.

The treatment of keloids and hypertrophic scars remains a challenge. Although triamcinolone acetonide (TAC) is one of the most common and effective treatments for keloids and hypertrophic scars, TAC is not effective in some patients, and some may even experience adverse outcomes. Verapamil might be considered a safe alternative to TAC. The aim of this study was to compare the efficacy and safety of verapamil and TAC for the treatment of keloids and hypertrophic scars. Three databases (Medline, EMBASE, and CENTRAL database) were electronically searched from 1997 to December 2019. Article selection was limited to randomized controlled trials (RCTs) and controlled clinical trials (CCTs). Two authors independently assessed the selection of studies, risk of bias, and extracted the data. Mean differences (MDs) were computed for continuous variables, risk ratios (RRs) were computed for dichotomous variables, and 95% confidence intervals (CIs) were calculated for both assessments. Five RCTs were included, comprising a total of 215 patients (273 scars). Vancouver Scar Scale (VSS) parameters (such as height, vascularity, pliability, and pigmentation) were reported as the outcome measures and provided detailed values in four studies. No significant differences were observed between verapamil and TAC in the reduction of height (MD 0.57, 95% CI -0.94 to 2.08, P = .46), vascularity (MD 0.30, 95% CI -0.42 to 1.02, P = .41), pliability (MD 0.67, 95% CI -1.12 to 2.47, P = .46), and degree of pigmentation (MD 0.14, 95% CI -0.41 to 0.69, P = .61). Adverse outcomes were reported in four studies. The results showed that the incidence of telangiectasia and skin atrophy that used verapamil was significantly lower than that for TAC. Concerning the treatment of keloids and hypertrophic scars, even though verapamil was safer than TAC, TAC worked faster than verapamil. Furthermore, we did not find any clear evidence that verapamil was more or less effective than TAC. Considering the high degree of safety of verapamil, we suggest that verapamil might be used as an alternative treatment when TAC results in adverse outcomes.

Calcium dosage in the lipid emulsion used to treat verapamil toxicity.

No Abstract Keywords.

P-Glycoprotein Inhibition Exacerbates Paclitaxel Neurotoxicity in Neurons and Patients With Cancer.

Paclitaxel-induced peripheral neuropathy (PIPN) is a common and dose-limiting adverse event. The role of P-glycoprotein (P-gp) in the neuronal efflux of paclitaxel was assessed using a translational approach. SH-SY5Y cells were differentiated to neurons and paclitaxel toxicity in the absence and presence of a P-gp inhibitor was determined. Paclitaxel caused marked dose-dependent toxicity in SH-SY5Y-derived neurons. Paclitaxel neurotoxicity was exacerbated with concomitant P-gp inhibition by valspodar and verapamil, consistent with increased intracellular accumulation of paclitaxel. Patients with cancer treated with paclitaxel and P-gp inhibitors had a 2.4-fold (95% confidence interval (CI) 1.3-4.3) increased risk of peripheral neuropathy-induced dose modification while a 4.7-fold (95% CI 1.9-11.9) increased risk for patients treated with strong P-gp inhibitors was observed, and a 7.0-fold (95% CI 2.3-21.5) increased risk in patients treated with atorvastatin. Atorvastatin also increased neurotoxicity by paclitaxel in SH-SY5Y-derived neurons. Clinicians should be aware that comedication with P-gp inhibitors may lead to increased risk of PIPN.