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Good Rules to follow in order to avoid the dangers of incompatibility are the following,
1. Never use more than one remedy at a time, if one will serve the purpose.
2. Never use Strong Mineral Acids in combination with other agents, unless you know exactly what reaction will ensue. They decompose salts of the weaker acids and form ethers with alcohol. Never combine Free Acids with hydrates or carbonates.
3. Select the simplest solvent, diluent, or excipient you know of, remembering that the solvent power of Alcohol and Water for their particular substances decreases in proportion to the quantity of the other added.
4. Generally do not combine two or more soluble salts.
5. Never prescribe a drug in combination with any of its Tests or Antidotes.
6. Do not order Glucosides (as Santonin, Colocynthin) in combination with free acids or in emulsions.
7. Prescribe Aconite only in water, and Mercuric Chloride alone in water or simple syrup. The latter is incompatible with almost everything, even the Compound Syrup of Sarsaparilla is said to decompose it.
8. Iodide of Potassium decomposes nearly all metallic salts, and is one of the drugs which is best given alone.
9. Acacia or some other emulsifying agent should always be added to prescriptions containing resinous tinctures or fluid extracts (e. g., Tinct. Cannabis Indicæ) with aqueous solutions, to prevent the separation of the resin.
10. Silver Nitrate, and Lead Acetate and Subacetate, although incompatible with almost everything, may be combined with Opium; the latter forming with Opium a compound which, although insoluble, is therapeutically active as a lotion.
11. The following-named substances are incompatible with so many others that it is best to always prescribe them alone; they are best given in simple solution :Dilute Hydrocyanic Acid.
Liquor Potassii Arsenitis.
Liquor Ferri Nitratis.
Tinct. Ferri Chloridi.
Citrate of Iron and Quinine.
Free Chlorine in Solution.
12. Tannic Acid may be prescribed with the proto-salts of Iron, but not with its per-salts. Calumba is the best vegetable tonic to prescribe with Ferric salts, as it contains neither Tannic nor Gallic Acids.
LIQUID EXTEMPORANEOUS PREPARATIONS.
Mixtures (Mistura),-in official pharmacy are aqueous preparations containing some insoluble ingredients held in suspension by an appropriate vehicle. In extemporaneous pharmacy, however, the term Mixture is applied to every fluid compound intended for internal use, except a few which bear distinctive titles, such as Emulsions, Draughts, Enemas, Elixirs and Drinks. The simplest form of mixture in this extended sense is that in which two or more liquids are mixed together; but a great variety of substances may be prescribed in this form, chief among which are most of the soluble salts, light insoluble powders, salts which may be diffused by agitation, extracts, gum-resins, and the fixed and essential oils. They are generally ordered in 2, 3, 4, 6, 8, 10 and 12-ounce vials.
The substances suitable to the mixture-form, properly so called, are those which, though more or less insoluble in water, will mix with it by agitation, trituration, etc. Those most frequently ordered are as follows:
Diffusible by Agitation :
Miscible only oy trituration :-
Potassii et Sodii Tartras.
Potassii Cyanidum. Hydrargyri Chloridum Corrosivum. Certain salts are best ordered by prescribing such agents as will when in solution together react upon each other and produce the desired salt. Instances of this may be found in the pharmacopæial processes for most of the official Liquores; the salts so produced being the following :Ammonii Acetas.
Quinina Sulphas,-requires acidulated water for its solution, the acid used being generally Sulphuric diluted, or the Aromatic Sulphuric. This method of prescribing this salt develops its bitter taste to the utmost, and is often avoided by ordering the drug to be suspended in a viscid liquid, such as Pulv. Acaciæ in Syrup of Ginger. In such a case an officious dispenser anxious to show his smartness may add some dilute Sulphuric Acid to dissolve the Quinine and thus defeat the object of the prescriber.
Sulphate of Quinine may be prescribed with Aromatic Spirit of Ammonia, Spirit of Nitrous Ether, Tinctures or other alcoholic preparations together with Glycerin or Syrup and Water. In such cases the salt should be first dissolved in the alcoholic portion of the prescription; then the glycerin or syrup, and finally the aqueous portions should be added gradually. It may also be ordered with dilute Sulphuric Acid and some vegetable insusion containing Tan. nin, in which case a precipitate of Tannate of Quinine will be produced. This of course should not be filtered, but should be dispensed with a “ Shake-label.”
Chinoidin, Cinchonine Sulphate and Quinidine Sulphate,-also require the addition of dilute mineral acid for their solution in aqueous mixtures,
Iodine,-requires the addition of lodide of Potassium for its solution in a convenient quantity of water, as in the case of the official Liquor lodi Compositus.
Red Iodide of Mercury, requires the addition of Iodide of Potassium or Mercuric Chloride for its aqueous solution.
Potassii Bitartras, Cream of Tartar,-requires the addition of Borax or Boric Acid for its solution in water.
Benzoic Acid, -requires the addition of Borax to aid its solubility in water, an equal part of the latter making it 5 times more soluble than when alone.
Lime,- is more soluble in sweetened water than in plain water, the sugar aiding its solution.
EXCIPIENTS are substances which give form and consistence to prescriptions, and serve as vehicles for the exhibition of the other ingredients. Some of the excipients are diluents, or agents which effect the dilution or division of the active ingredients; while others act in the double capacity of diluents and flavoring agents. The excipients most generally used in mixtures may be tabulated as follows, viz. :Diluents.
Yolk of Egg (Vitellus).
Tinct. Gentianæ Comp.
Tinct. Aurantii Dulcis.
Spiritus Mentha Piperitze.
Spiritus Menthæ Viridis,
Compounding the Mixture is a matter of no slight importance, and one which is best learned at the dispensing counter, though a few directions may not be out of place. In the case of the simplest form of mixture, where two or more fluid preparations are prescribed together, the only operations required are the measuring of the several ingredients and pouring them into the designed vial. In doing this the compounder should pursue a regular and definite order of procedure. Taking in his left hand a graduate of sufficient capacity to hold the whole quantity prescribed, he should walk along the shelves, and with the right hand pour from the stock-bottles the requisite quantity of each ingredient in the order in which they are entered on the prescription. A skilful clerk will hold the graduate between the thumb and first finger, the prescription between the second and third fingers, and the stopper of the stock-bottle between the little finger and the hand, leaving his right hand free for the manipulation of the bottles containing the ingredients..
When an actively poisonous agent is ordered it should always be the last thing put into the mixture. Attention to this rule will prevent the danger of the toxic substance being put in twice.
The order in which the ingredients are put together is not of so much importance in compounding a simple mixture as in the case of an emulsion, and the order of the prescription can usually be followed, with the exception noted in the preceding paragraph. Still, when several alcoholic preparations, syrups and waters are ordered together, it is good practice to first mix the alcoholic fluids, then to add the syrups and finally the water, so as to avoid the precipitation of resinous principles which would occur if the alcoholic solutions were added to the water. Distilled water should always be used, in order to insure uniformity in taste and appearance, and also as a matter of purity and cleanliness. All mixtures should be well shaken before being labelled.
Solids which are comparatively insoluble or only slowly soluble require to be rubbed up in a mortar with one or more of the fluid ingredients. Glass mortars are much employed for this purpose, and many compounders mix all the ingredients in such a mortar before transferring them to their vial. Vegetable powders (as Rhubarb, Ipecac, etc.), or finely pulverized inorganic substances, are often ordered in intimate mixture with water, thickened with mucilage or syrup. In such cases the mixture should be made in a porcelain or wedgwood mortar, enough mucilage or syrup being added at first to make a thick paste, and after this is rubbed smooth the water may be gradually added during the continued