First off a word of caution--consult with your physician about amantadine and One MUST NOT "cold turkey" off amantadine. If one were to discontinue this drug for any reason, one must be weaned off it.

Let's not beat ourselves up yet, though will join with you should amantadine turn out to be a major player vis a vis anticholinergic effect. I recall (and found thru recent (yesterday and today!) research that amantadine's 2 primary modes of action are that it is a dopamine releasing drug (causes a release of dopamine in the neurons increasing concentration of dopamine in the synaptic cleft and inhibits its reuptake) and it is an NMDA antagonist (see Rick's posting about glutamate and a new way to look at PD), and several references note this anti NMDA action is its predominate antiparkinson action. It's antichonlinergic effects are reported to be "indirect" in some references(ie amantadine was found to depress NMDA evoked acetylcholine release), barely detectable in some studies, though direct in others.

The following study is cited ONLY because of the description of amantadine--this was indeed a very poorly designed study, despite the fact it came out of johns hopkins
http://psy.psychiatryonline.org/cgi/.../full/45/3/205
"The precise mechanism of amantadine's brain action is unknown. It appears to have dopamine-modulating activity in the peripheral and CNS by augmenting the release and inhibiting the cellular reuptake of dopamine.10 Amantadine is also a N-methyl-D-aspartic acid receptor antagonist, which may indirectly enhance dopaminergic transmission and confer neuroprotective effects, similar to its analogue, memantine.11 Moreover, amantadine is known to alter the function of nicotinic acetylcholine receptors in muscle and has a weak antagonist effect on mammalian hippocampal nicotinic acetylcholine receptors. This may signify protective effects in neurodegenerative disorders or in cholinergic toxicity.12"
(my total knowledge of what "nicotinic acetylcholine receptors" function happens to be is from wikipedia...)

All this contradictory information is hurting my head; i am going to bed, to take up the investigation in the morning. My husband takes amantadine; it is the first drug prescribed for him during his first consultation with a neurologist. We have emailed his neurologist for assistance.