This section is from the book "The Art Of Dispensing", by Peter MacEwan. See also: Calculation of Drug Dosages.
Quinine salts give rise to so many curious complications when dispensed in mixture form that some special remarks are necessary regarding them. The complications usually arise from ignorance of the peculiarities of the alkaloid, whose salts have a wide range of solubility, and our remarks in regard to them largely apply to other alkaloids. On page 70 the chemical and physical properties of quinine salts are given, from which it will be seen that the acid salts of quinine are much more soluble in water than the basic salts. Messrs. Howards & Sons, Ltd., publish a useful dispensing-counter table showing the percentage of alkaloid in each salt, its solubility, and the equivalent value to one of sulphate. As regards the last, the following may be noted:
Sulphate .... | 1.00 |
Hydrochloride................... | 0.9 |
Bihydrochloride ,............... | 1.02 |
Hydrobromide.................. | 0.96 |
Bihydrobromide ............... | 1.23 |
Bisulphate .................. | 1.24 |
Phosphate .... | 0.96 |
As to the solution of quinine sulphate in acids, the fact that the mineral acids, strong or dilute, make presentable pill-masses with quinine salts indicates that an acid should not be poured direct upon any salt, but that the salt should be well diffused in water before the acid is added. Very often, however, no acid is ordered in the prescription. In such a case it is extremely unwise to depart from the letter of the physician's order. The only admissible manner of compounding is to reduce the quinine salt to fine powder and diffuse it in the liquids. In some cases, as when spirit of ether is an ingredient, the quinine tends to adhere to the bottle, but this may be avoided by the addition of a little mucilage of acacia to the mixture. Some dispensers advocate that the quinine should be dissolved in such circumstances, and the view is one for which there is much to be said; but quinine in solution is more bitter than when in suspension, and this fact throws the balance of opinion in favour of the suspension method.
Valerianate..................... | 1.01 |
Lactate ........................................... | 0.94 |
Salicylate ....................... | 1.05 |
Hydrochloro-sulphate ........ | 0.99 |
Arsenate......................... | 1.06 |
Tannate ........................ | 3.67 |
The greater number of difficulties with quinine mixtures occur through the precipitation of the quinine after it has been brought into solution. The simplest of these, apart from those due to ordinary alkaloidal precipitants, are caused by the formation of less soluble salts, owing to double decomposition -for example, in the case of ammonium-acetate solution and a solution of sulphate of quinine there is double decomposition, and the quinine acetate formed is rapidly hydrolysed, with the result that quinine hydrate crystallises out in bulky acicular crystals. Such mixtures sometimes become quite solid, and this was considered to be due to insoluble quinine acetate until Messrs. Kidd and Hill demonstrated the hydration (The Chemist and Druggist, 1899, 11. 1073 ; 1900, 1. 664). Salicylates also form sparingly soluble compounds with soluble quinine salts.
The amount of any pharmacopoeial dilute mineral acid required to dissolve quinine sulphate is reckoned as 1 minim for each grain of sulphate. As a rule this holds good and provides permanent solutions if no body is present which reacts with the soluble quinine salt to form a less soluble one, or if the soluble salt is not 'salted out.'
Quininae sulphatis .... | . Эj. |
Acid, hydrobromic. dil. | 3j. |
Glycerini ...... |
|
Potassii bromidi ..... | 3j. |
AEtheris chlorici ..... | 3ij. |
Aquam ...... | ad |
This formed a perfectly clear mixture at first, but in a few minutes quinine sulphate began to separate in silky crystals, the amount of sulphate being the surplus unconverted into hydro-bromide and insoluble in the liquid.
 
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