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Dodick DW, et al. Pooled PREEMPT results. PMID 20487038

Question and design

PREEMPT pooled two closely matched multicentre, double-blind trials of onabotulinumtoxinA for chronic migraine, totaling 1,384 adults. Treatment used fixed-site/fixed-dose injections with optional follow-the-pain sites and a 12-week cycle.

Why pooling mattered

PREEMPT 1 missed its original headache-episode primary endpoint, although secondary outcomes favoured treatment (PMID 20647170). PREEMPT 2 used headache days as its primary endpoint and was positive (PMID 20647171). The prespecified pooled analysis increased precision but must be read with the component-trial endpoint history visible.

Findings

  • OnabotulinumtoxinA produced a greater reduction in headache days than placebo at week 24.
  • Multiple secondary frequency, disability and quality-of-life outcomes favoured treatment.
  • Adverse-event discontinuation was uncommon, but neck pain and muscular effects are clinically relevant.

Interpretation

The program established onabotulinumtoxinA as a chronic-migraine preventive, not as treatment for episodic migraine. The operational protocol—155–195 units across head and neck sites every 12 weeks—is part of the evidence package.

Limitations

  • The injection procedure makes blinding difficult.
  • One component trial’s primary endpoint failure matters.
  • Medication overuse was common, complicating attribution while improving real-world relevance.
  • Post-treatment disease modification was not tested.

Knowledge-base use

Anchors chronic-migraine-and-chronification.md, with component PMIDs retained to prevent pooled-result simplification.