Thanks Paula for finding this Movement Disorders abstract! I thought the following excerpt from the full-text article was very interesting. As reported in the abstract, " Famotidine increased ‘‘good on-time’’ by 28%."
It then goes on to say, " In comparison, clinical use of the COMT inhibitor, entacapone
and MAO-B inhibitor, rasagiline, in large RCTs in advanced PD patients appear less effective.
For instance, the LARGO study27 demonstrated a significant
effect of rasagiline and entacapone on increasing
daily on-time without troublesome dyskinesia from
baseline (i.e., ‘‘good on-time’’) by 0.85 hours for both
(this equates to an increase of only 9.3%). These data
suggest that histamine H2 antagonism might be more
effective than currently available therapies to extend
good on-time..."

It sure seems to merit further studies.