(section 4.6.5). Atropine has been used to treat urinary urgency associated with bladder
inflammation; oxybutynin (4.13), another tertiary amine antimuscarinic, has been used
to relieve bladder spasm following urologic surgery. Tolterodine (4.14), an M3-selective
antimuscarinic, has been used for the suppression of adult urinary incontinence.
Scopolamine (4.15) is a time-honored remedy for motion sickness. A variety of antimus-
carinics (e.g., homatropine (4.16), cyclopentolate (4.17), tropicamide (4.18)) have been
used in ophthalmologic disorders (uveitis, iritis) and to enable dilation of the pupils
(mydriasis) during ophthalmoscopic examination of the retina. Finally, anticholinergics
have been used in the treatment of Parkinson’s disease (section 4.4.4), but their use has
been limited since the widespread adoption of dopaminergic therapies.
The oldest anticholinergics are the tropane alkaloids of Atropa belladonna (night-
shade). Atropine (2.1) and scopolamine (4.15) are derivatives of tropine, a fused
piperidino–pyrrolidine ring system, esterified by atropic acid. Atropine is the racemate
of (−)hyosciamine, whereas scopolamine has an epoxide ring. In large doses, all of
these anticholinergic agents have central excitatory and hallucinogenic effects and were
prominent in medieval “witches’ brews.” A synthetic homolog, homatropine (4.16), has
a shorter duration of action. These agents are mixed M 1 –M 2 antagonists.
NEUROTRANSMITTERS AND THEIR RECEPTORS 213