A preliminary comparison of the efficacy and tolerability of botulinum toxin serotypes A and B in the treatment of myofascial pain syndrome: a retrospective, open-label chart review.

BACKGROUND: Myofascial pain syndrome (MPS) is characterized by acute or chronic regional muscle pain associated with single or multiple trigger points within taut bands of muscle. Botulinum toxins have clinical utility when sustained focal muscle relaxation is required and may be a useful addition to the treatment armamentarium for MPS.

OBJECTIVE: The purpose of the present article was to compare the efficacy and tolerability of botulinum toxin serotypes A and B (BTX-A and BTX-B) in the treatment of MPS.

METHODS: This was a retrospective, open-label, single-center chart review. Charts of all patients who received either BTX-A or BTX-B for MPS between January and November 2001 were included in the review. Patients rated the intensity of their pain on a visual analog scale (VAS) from 0 = no pain to 10 = worst pain imaginable before and after receiving BTX-A or BTX-B.

RESULTS: The charts of 91 patients (74.7% female, 25.3% male; mean [SD] age, 47 [10.2] years) who received BTX-A (n = 56; mean dose, 256.9 U; range, 100-600 U) or BTX-B (n = 35; mean dose, 9000 U; range, 2500-20,000 U) were included in this retrospective review. Patients who received BTX-A had significantly greater mean reductions in VAS pain scores compared with those who received BTX-B (mean reduction, 2.7 vs 1.8, respectively; P < 0.001). Patients who received BTX-A also reported significantly longer durations of pain relief compared with those who received BTX-B (4.5 vs 2.7) months; P < 0.001). Eight of 56 patients (14.3%) in the group that received BTX-A reported mild adverse events that included flulike symptoms, injection-site pain, and weakness of the neck muscles. Seven of 35 patients (20.0%) in the group that received BTX-B reported adverse events that included mild flulike symptoms, dry eyes, severe visual disturbances, and severe dry mouth.

CONCLUSION: Patients with MPS who received BTX-A reported significantly greater reductions in pain for longer durations compared with those who received BTX-B. No patients who received BTX-A experienced severe systemic adverse events, compared with 4 patients who received BTX-B. The results of this comparison are consistent with the US Food and Drug Administration-approved labeling indicating that BTX-A is not interchangeable with any other botulinum toxin in terms of biological activity.