Anticholinergics are a diverse group of medications. The majority of the anticholiner-gic medications have good oral absorption, but precise figures on many are not known. In general, most have half-lives requiring at least twice and usually three times a day dosing. The antiparkinsonian effect of anticholinergics is largely attributed to centrally acting acetylcholine receptors (74). Most synthetic (tertiary) anticholinergics used in
PD are predominantly in this class: biperiden (Akineton®), trihexyphenidyl (Artane®), benztropine (Cogentin®), procyclidine (Kemadrin®). Benztropine was formulated as a combination of the anticholinergic, atropine, and an antihistamine, diphenhydramine (Benadryl®). Benztropine, has useful central effects that can be used for PD management, is more potent than trihexyphenidyl, but has less sedating effects than antihistamines (75). Recommended doses and choice of particular anticholinergic vary by practitioner, but one rule is to start with a low dose and increase slowly and conservatively (Table 1).
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