Challenges recruiting to a proof-of-concept pharmaceutical trial for a rare disease: the trigeminal neuralgia experience

Trials. 2018 Dec 27;19(1):704. doi: 10.1186/s13063-018-3045-1.


Background: This study aimed to describe recruitment challenges encountered during a phase IIa study of vixotrigine, a state and use-dependent Nav1.7 channel blocker, in individuals with trigeminal neuralgia.

Methods: This was an international, multicenter, placebo-controlled, randomized withdrawal study that included a 7-day run-in period, a 21-day open-label phase, and a 28-day double-blind phase in which patients (planned n = 30) were randomized to vixotrigine or placebo. Before recruitment, all antiepileptic drugs had to be stopped, except for gabapentin or pregabalin. After the trial, patients returned to their original medications. Patient recruitment was expanded beyond the original five planned (core) centers in order to meet target enrollment (total recruiting sites N = 25). Core sites contributed data related to patient identification for study participation (prescreening data). Data related to screening failures and study withdrawal were also analyzed using descriptive statistics.

Results: Approximately half (322/636; 50.6%) of the patients who were prescreened at core sites were considered eligible for the study and 56/322 (17.4%) were screened. Of those considered eligible, 26/322 (8.1%) enrolled in the study and 6/322 (1.9%) completed the study. In total, 125 patients were screened across all study sites and 67/125 (53.6%) were enrolled. At prescreening, reasons for noneligibility varied by site and were most commonly diagnosis change (78/314; 24.8%), age > 80 years (75/314; 23.9%), language/distance/mobility (61/314; 19.4%), and noncardiac medical problems (53/314; 16.9%). At screening, frequently cited reasons for noneligibility included failure based on electrocardiogram, insufficient pain, and diagnosis change.

Conclusions: Factors contributing to recruitment challenges encountered in this study included diagnosis changes, anxiety over treatment changes, and issues relating to distance, language, and mobility. Wherever possible, future studies should be designed to address these challenges.

Trial registration:, NCT01540630 . EudraCT, 2010-023963-16. 07 Aug 2015.

Keywords: Clinical trial; Sodium channel blocker; Underrepresentation; Vixotrigine.

Publication types

  • Clinical Trial, Phase II
  • Multicenter Study
  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Aged
  • Analgesics / adverse effects
  • Analgesics / therapeutic use*
  • Double-Blind Method
  • Europe
  • Humans
  • Middle Aged
  • NAV1.7 Voltage-Gated Sodium Channel / drug effects
  • NAV1.7 Voltage-Gated Sodium Channel / metabolism
  • Pain Measurement
  • Patient Selection*
  • Rare Diseases / diagnosis
  • Rare Diseases / drug therapy*
  • Rare Diseases / metabolism
  • Rare Diseases / physiopathology
  • Sample Size
  • Sodium Channel Blockers / adverse effects
  • Sodium Channel Blockers / therapeutic use*
  • South Africa
  • Time Factors
  • Treatment Outcome
  • Trigeminal Nerve / drug effects*
  • Trigeminal Nerve / metabolism
  • Trigeminal Nerve / physiopathology
  • Trigeminal Neuralgia / diagnosis
  • Trigeminal Neuralgia / drug therapy*
  • Trigeminal Neuralgia / metabolism
  • Trigeminal Neuralgia / physiopathology
  • Young Adult


  • Analgesics
  • NAV1.7 Voltage-Gated Sodium Channel
  • SCN9A protein, human
  • Sodium Channel Blockers

Associated data