Tertiary-amine muscarinic receptor antagonists

Some of these agents are particularly useful in ophthalmology included in this category are homatropine hydrobromide (Isopto homatropine) (a semisynthetic derivative of atropine) cyclo-pentolate hydrochloride (Cyclogyl), and tropicamide (Mydriacyl). These agents are preferred to atropine or scopolamine because of their shorter duration of action. 

Tertiary-amine muscarinic receptor antagonists gain access to the central nervous system and are therefore the anticholinergic drugs used to treat parkinsonism and the extrapyramidal side effects of antipsychotic drugs. Specific agents used primarily for these conditions include benztropine mesylate (Cogentin) and trihexyphenidyl hydrochloride (Artane, others). 

Tertiary amines used for their antispasmodic properties are dicyclomine hydrochloride (Ben-tyl, others), oxyphencyclimine hydrochloride (daricon), flavoxate hydrochloride (Uripas), and oxyburynin chloride (Ditropan). The latter two are indicated specifically for urological disorders. These agents appear to exert some nonspecific direct relaxant effect on smooth muscle. In therapeutic doses they decrease spasm of the gastrointestinal tract, biliary tract, ureter, and uterus characteristic atropine-like effects on the salivary glands and the eye also are seen with oxybutynin. 

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Atropine is the prototype drug of this group and will be described first. Other named agents will be mentioned only in so far as they differ from atropine. All act as non-selective and competitive antagonists of the various muscarinic receptor subtypes (Ml-3). Atropine is a simple tertiary amine certain others (see Summary) are quaternary nitrogen compounds, a modification that is important as it intensifies antimuscarinic potency in the gut, imparts ganglionblocking effects and reduces CNS penetration. 

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