botox-dosing

Botulinum Toxin Type A (BTX-A)

Muscle Selection, Dosing, and Administration

Dosing Guidelines
BTX-A dosing is patient-specific, and dependent upon muscles involved, prior response, and functional goals. The injection of a moderate initial dose with subsequent adjustments is advised. For example, the larger lower extremity muscles appear to have a broader range of dose response. Adult patients should not be injected with more than 400 units/visit, whereas pediatric patients (under 12 years of age) should be given the lesser of 12 units/kg or a total of 400 units/visit. Reinjections should not be given before 3 months after the last visit, primarily to prevent antibody formation. Although contraindications and side effects are minimal, conditions requiring caution include patients who are hypersensitive to any ingredient in BTX-A, using aminoglycoside antibiotics, diagnosed with neuromuscular disease, pregnant or may become pregnant, or in lactation.

Muscle selection

A working knowledge of primary clinical patterns of muscle spasticity is essential to individualizing BTX-A therapy.
BTX-A injections are most effective in relieving focal spasticity around a joint or series of joints.
Even though BTX-A is a focal treatment, untreated muscles may benefit from the disruption of the synergy patterns that often replace isolated muscle control. Clinicians should realize that adjacent muscles usually have some reduction in tone.
Controlled tone reduction through BTX-A injections must not interfere with existing patient function. For example, in a non-ambulatory patient, complete weakness of the thigh adductors or gastrocsoleus may be appropriate, whereas in the ambulatory patient, only mild tone reduction may be sufficient.
Since it is not always practical to treat all muscles in one visit, the treatment team should prioritize muscles to be injected. Synergic muscles or sites remote from the original injections may need to wait for follow-up treatment.
Additional problematic muscles may be exposed by previous BTX-A injections, requiring subsequent BTX-A treatment as well.
Outcomes should be evaluated by a range of clinical measures, including rating scales and video tape recordings, that reflect clearly defined goals and objectives.

Dosing
Several dose-modifiers must be considered in making possible adjustments in the amount of BTX-A used within the given muscle range. Patients with a clinical profile that suggests a lower initial dose may begin with injections at the low end of the range and those with a higher dose profile may start at the high end. The dose used for those patients who fall in between is left to the discretion of the experienced clinician. Given the number of variables involved, clinical experience is an important factor.

Administration
The number of injection sites is primarily determined by the size of the muscle. Theoretically, it may be appropriate to inject more sites with smaller doses. More injection sites facilitate a wider distribution of BTX-A to nerve terminals. Too many injection sites, however, may contribute to the undesirable use of BTX-A on areas, such as the musculotendinous junction, where no nerve terminals exist. One should consider decreasing the number of injection sites or certain pediatric patients to minimize discomfort.

The proper targeting of muscles is a crucial factor in achieving efficacy and reducing adverse effects from BTX-A injections. Proficiency in dosing and injecting BTX-A demands skill development. Difficult-to-localize muscles often require adjunctive imaging methods (EMG, ES, CT, fluoroscopy, and ultrasound) to confirm injection sites. The objective in EMG or ES monitoring is to target the region of maximum muscle activity.