Physiological Action.—The physiolog ical action of homatropine closely re sembles that of atropine. It dilates the pupil very rapidly and energetically, but the effect passes off in 36 to 4S hours. The mydriasis of atropine lasts for 10 to 14 days, and that of hyoscyamine for 8 to 9 days. Repeated instillations of homatropine solution (1 per cent.) causes a lowering of the pulse-rate, which is, however, only temporary. Slight hyper Troia of the conjunctiva almost invari ably follows its use. Instillations of strong solutions (4 to 5 per cent.) induce a burning sensation on the conjunctiva, and, if in large amount, its bitter taste becomes perceptible, but without the dryness of the pharynx which follows the use of atropine. rl'lle action of homat ropine on the circulation also differs from that of atropine in that the former lessens the pulse-rate and diminishes the arterial pressure. Unlike atropine, again, it does not, as atropine often does, superinduce cutaneous eruptions.
Poisoning by Homatropine.—No fatal cases of poisoning have been reported from the medicinal use of this remedy, and no toxic symptoms beyond a slight drowsiness. This, no doubt, results from the fact that the use of homatropine is almost exclusively by instillation in oph thalmology. De Schweinitz and Hare, in experiments on frogs, have found that this drug in large doses first alters the respiration to the Cheyne-Stokes rhythm, then arrests it wholly; this is succeeded by a tetanic condition; and after that by a paralysis—leaving, however, the pe ripheral nerves and muscles untouched. The heart-movement is retarded and the pulse-rate diminished. Death occurs from respiratory paralysis.
An undoubted instance of poisoning following the instillation of 1 drop of a 0.2-per-cent. solution of homatropine. C. A. Oliver (Amer. Jour. Med. Sci., Nov., '96).
Case of a girl, aged 3 years, who re ceived nine applications of a solution con taining 2 per cent. each of homatropine and cocaine to the eyes in ninety min utes. Three hours later she failed to recognize familiar faces, picked at the coverlit, tried to grasp invisible objects, babbled strangely, and persisted in get ting out of bed. Her pupils were widely dilated, her face flushed, her lips and tongue parched. There was no eruption. She recovered entirely within twenty four hours. S. Stephenson (Ophthalmic Review, July, 1900).
Treatment of Poisoning by Homatro pine.—The treatment of poisoning by this remedy is similar to thaI of atropine poisoning. The stomach, by emetics and
the stomach-tube, is to be evacuated. Tannin and animal charcoal are then ad ministered and emetics again given, fol lowed by castor-oil. Artificial respira tion, heat, stimulants, and hypodermics of strychnine are useful to support the respirations. Morphine may be given carefully as a physiological antidote.
Therapeutics.—Homatropine is almost exclusively used by ophthalmologists to dilate the pupils and paralyze the muscle of accommodation for the purpose of cor recting anomalies of refraction in healthy eyes. For this purpose it is used in solu tion (4 grains to the ounce of distilled water), which is dropped into the eye every five or ten minutes until sufficient dilatation is obtained. For therapeutic uses in ophthalmology, atropine is gener ally used, although for incipient cataract Risley prefers homatropine, especially where there is discomfort without in creased ocular tension.
Homatropine is not a reliable cyclo plegic in young subjects. Hansel] (Amer. Jour. Ophth., No. 3, vol. xii).
As complete cycloplegia secured from 6 instillations of a 2-per-cent. solution of homatropine at 5-minute intervals as from a 1-per-cent. solution of atropine used 3 times daily for 2 days. F. Mayo (Med. News, June, '96).
Homatropine is a cycloplegic of the greatest value, and the evidence upon which some have rejected it is very meagre. It does not possess the surplus power os atropine, and therefore it must be used with greater care. Carelessly used solutions of atropine will produce very marked dilatation of the pupil; if directions be given for two or three in stillations a day, and if only one of these is effective, it will probably pro duce NU mydriasis. In the last 1000 pa tients upon whom the drug was used there were 22 in whom the incomplete paralysis of accommodation was sus pected. These were examined under a stronger mydriatic, and of the 44 eyes only 6 showed a higher refractive error than was noted under homatropine.
Some samples of homatropine are irri tating. Especial care should be taken in bringing the solution in contact with the cornea not to have it strike from a considerable distance. The amount of the drug commonly employed is from to grain. This rarely produces constitutional symptoms. Edward Jack son (Annals of Ophthal., Jan., 1001).
Homatropine has been used against the night-sweats of phthisis, but other remedies are preferable.