Pilocarpinae Hydrochloridum, Pilocarpine Hydrochloride.
C11H17N2O2Cl = 244.616.
Pilocarpine hydrochloride, C11H16N2O2, HCl, may be prepared by dissolving the base obtained from the pure nitrate in sufficient diluted hydrochloric acid to form a neutral solution, concentrating and setting aside over sulphuric acid to crystallise. It is official in the U.S.P. It occurs in the form of colourless, odourless crystals, deliquescent in moist air. Melting-point, 204° to 205°; specific rotation, +90° to +92°. The aqueous solution has a faintly bitter taste, and is neutral or only faintly acid to litmus. Sulphuric acid dissolves it with production of hydrochloric acid gas, and the formation of a colourless liquid; on the addition of a small fragment of potassium bichromate, a bright grass-green colouration is produced. The concentrated aqueous solution gives no precipitate on addition of solution of ammonia, and only a few oily drops on the addition of aqueous solution of sodium or potassium hydroxide, but these quickly redissolve (distinction from most other alkaloids). If 1 to 2 centigrams be dissolved in 2 mils of water in a test-tube, and 2 mils of a slightly acid solution of hydrogen peroxide be added, and a small layer of benzene carefully poured on the liquid; then if 3 or 4 drops of a 0.3 per cent. solution of potassium bichromate be added and the whole shaken gently, the benzene layer will turn violet, while the aqueous solution will remain yellow. A mixture of equal parts of the salt and calomel, moistened with alcohol, becomes blackened. The salt contains no water of crystallisation. On complete ignition it leaves no residue (absence of inorganic impurities). It is usually freer from pilocarpidine than pilocarpine nitrate.
Freely soluble in water, in absolute alcohol (1 in 10); almost insoluble in ether or chloroform.
Action and Uses. The properties of pilocarpine and its salts are described under Pilocarpinae Nitras. The hydrochloride is frequently prescribed in preference to the nitrate, but it must not be ordered with the salts of silver, lead, or mercury on account of its incompatibility.
Dose.—3 to 30 milligrams (1/20 to ½ grain).