Research Reports - Amantadine effect on perceptions of irritability after traumatic brain injury

J Neurotrauma. 2015 Mar 31

Hammond FM(1), Sherer M, Malec JF, Zafonte RD, Whitney M, Bell K, Dikmen S,
Bogner J, Mysiw J, Pershad R.

This study examines the effect of amantadine on irritability in persons in the
post-acute period after traumatic brain injury (TBI). There were 168 persons ≥6
months post-TBI with irritability who were enrolled in a parallel-group,
randomized, double-blind, placebo-controlled trial receiving either amantadine
100 mg twice daily or equivalent placebo for 60 days. Subjects were assessed at
baseline and days 28 (primary end-point) and 60 of treatment using observer-rated
and participant-rated Neuropsychiatric Inventory (NPI-I) Most Problematic item
(primary outcome), NPI Most Aberrant item, and NPI-I Distress Scores, as well as
physician-rated Clinical Global Impressions (CGI) scale. Observer ratings between
the two groups were not statistically significantly different at day 28 or 60;
however, observers rated the majority in both groups as having improved at both
intervals. Participant ratings for day 60 demonstrated improvements in both
groups with greater improvement in the amantadine group on NPI-I Most Problematic
(p<0.04) and NPI-I Distress (p<0.04). These results were not significant with
correction for multiple comparisons. CGI demonstrated greater improvement for
amantadine than the placebo group (p<0.04). Adverse event occurrence did not
differ between the two groups. While observers in both groups reported large
improvements, significant group differences were not found for the primary
outcome (observer ratings) at either day 28 or 60. This large placebo or
nonspecific effect may have masked detection of a treatment effect. The result of
this study of amantadine 100 mg every morning and noon to reduce irritability was
not positive from the observer perspective, although there are indications of
improvement at day 60 from the perspective of persons with TBI and clinicians
that may warrant further investigation.

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