Hyoscine hydrobromide - Scopolamin

Hyoscine crosses the blood-brain barrier more rapidly than atropine, therefore some of the side effects are more pronounced with hyoscine. These include drowsiness, blurred vision, dizziness, dry mouth, and difficulty with micturition, while confusion may occur in the elderly. Efficacy in PONV is only moderate, and it is now rarely used. It is, however, a well-proven remedy for motion sickness, and an effect on the vestibular apparatus may contribute to its action. Here, it is given in the form of the hydrobromide (scopolamine), 1 mg of which contains 0.7 mg of the laevo-hyoscine base. Commercially available seasickness tablets usually contain 0.3 mg and one or two are recommended for protection for short journeys. Side effects preclude the long-term use of hyoscine for travel sickness. 

Scopolamine (hyoscine) is isolated from the mother liquor remaining after the isolation of hyoscyamine, and is marketed as its hydrobromide. Scopolamine is readily race-mized to atroscine, when subjected to treatment with dilute alkali. 

The isolation of the levorotatory hyoscine from the mother liquors from the preparation of i-hyoscyamine from Hyoecyamus muticu L. was reported in 1881. From early analyses (20) the new base was assigned the formula CitHjsOjN but this was subsequently revised to Ci7H2i04N (25, 52). In 1892 a second alkaloid, scopolamine (52), with the formula Ci7Hji04N, was isolated from Scopolia atropoides Bercht and Presl. However, the conversion of hyoscine and scopolamine to the same hydrobromide (25) established that they were one and the same base. 

Except for a much shorter duration of action, the effects of scopolamine are, for practical ophthalmic purposes, the same as those of atropine. The toxic effects of hyoscine hydrobromide are similar to those of atropine, but with hyoscine bradycardia instead of tachycardia occurs and central stimulation rarely precedes depression. Drowsiness leading to coma is the main central symptom. Idiosyncratic reactions are more l ely to occur with scopolamine than with atropine, and ordinary doses occasionally induce severe reactions. Contact dermatitis of the eyelids is less common with scopolamine than with atropine. 

---