In writing a prescription care should be taken not to order drugs or preparations which are incompatible.

Drugs may be incompatible therapeutically, chemically, and pharmaceutically.

Therapeutic Incompatibility occurs when drugs are combined which have antagnostic physiologic actions.

Chemical Incompatibility occurs when from the combination of two or more drugs a new and undesired chemical compound results.

Pharmaceutical Incompatibility occurs when drugs are combined which form, either immediately or later, cloudy, precipitated or decomposed solutions.

There is no excuse for an educated physician to perpetrate a therapeutic incompatibility either in a prescription or in a patient. But it is not therapeutic incompatibility to modify a too decided action of a drug with one that corrects an undesired effect. This is a part of therapeutic science.

Chemical and pharmaceutical incompatibility are so closely related as to be governed many times by the same rule. Such incompatibility is difficult to avoid, and emphasizes the advisability of adopting simplicity in prescription writing, which is really a therapeutic gain.

The following alphabetical list of drugs comprises those that should generally be given alone, especially in solutions. The chemical reasons are appended:

Acids, unless very dilute and in small amount, should be prescribed alone. They combine with bases to form salts, and are incompatible with oxides, alkalies, alkaline salts, hydrates and carbonates. They all precipitate albumin.

Alkalies and Alkaline Carbonates should rarely be prescribed in solution with other drugs. They form salts with acids and precipitate many metallic and alkaloidal salts.

Alkaloidal Salts should rarely be combined with other drugs in solutions. They are precipitated by alkalies, alkaline carbonates, earthly carbonates, preparations containing tannic acid, and by iodides in solution.

Antimony and Potassium Tartrate (Tartar Emetic) should be prescribed in solutions alone. It is incompatible with acids, alkalies, tannic acid, and preparations containing tannic acid.

Arsenic (Arseni Trioxidum, Arsenious Acid) should generally be prescribed in solutions alone.

It is precipitated by salts of iron, magnesia, and solu tions of lime.

Bromides in solution should not be combined with alka loids. They precipitate the salts of morphine, quinine, and strychnine from neutral solutions.

Ferric and Ferrous Salts should generally be prescribed alone. They are incompatible with tannic acid and all drugs containing it; with alkaline carbonates, ammonia, and acacia.

Iodides should generally be prescribed alone.

They are incompatible with salts of alkaloids and metals and with mineral acids.

Mercuric Chloride (Calomel), though insoluble, had ally be prescribed alone. It is incompatible with many drugs.

Mercurous Chloride (Calomel) though insoluble, had best not be prescribed in mixtures. In solutions containing chlorides it may be converted into the mercuric salt.

Resins, including oleoresins, and fluid extracts and tinc hires containing resins, should not be prescribed in watery solutions, though they may be ordered in emulsion by suspending them with the mucilage of acacia or tragacanth.

They are all precipitated by water.

Silver Nitrate solutions and solutions of all silver salts must be ordered alone, and kept in dark bottles. If silver salts are prescribed for internal administration they must be alone or combined with some earth, and given in capsules.

Strophanthus in the form of the tincture should not be prescribed in solutions containing water.

It slowly forms a toxic substance, when in watery solu tion.

Spirits (Spiritus) should mostly not be prescribed with watery preparations, except sweet spirits of nitre, whiskey and brandy. They became cloudy upon the addition of water.

Tannic Acid, and all drugs containing tannic acid, should not be prescribed with most drugs. They are incompatible with alkaloids, salts of iron, lead, silver and antimony.