This section is from the book "Practical Materia Medica And Prescription Writing", by Oscar W. Bethea. Also available from Amazon: Practical Materia Medica and Prescription Writing.

In prescription writing we use only two units-Grammes and milliliters, abbreviated Gm. and mil.

If the quantity is in mils, it is read as mils and fractions of a mil.

If a part of a Gramme is not read as a fraction it is read in round numbers of the largest denomination that applies,-as 0.375 Gramme may be read as three hundred and seventy-five milligrammes.

A bookkeeper in entering a charge does not use the dollar mark or write the word dollar or cents, but all on the left-hand side of a certain line or decimal point is understood to be dollars and all on the right-hand side to be fractions of a dollar.

In writing a prescription it is not customary to write the words Gramme or milliliter or their abbreviations, but as these are the only units used, if the drug is a solid the figures are understood to be for Grammes and fractions of a Gramme, unless specified to the contrary, and if the drug is liquid the figures stand for mils and fractions of a mil, unless otherwise specified. Arabic numerals are used.

It is certainly desirable that all prescription blanks for Metric prescriptions have a line near the right-hand margin for use instead of the prescriber having to employ decimal points which are so frequently not in line, vertically, and if imperfectly made may be mistaken or may be obliterated by the wear and tear of being carried in the pocket or being handled on the files of the druggist. It is acknowledged that this is not the general custom in those countries where the system is exclusively used, but it seems desirable and is also rather the custom here. The following illustrates the Metric inscription:

Sodii Bromidi......................................................... | 5 | ||

Elix. Aromatici................................................... | q. s. | 30 |

This would represent 5 grammes of sodium bromide and 30 mils of aromatic elixir.

It is not written

Sodii Bromidi........................................................................... | Gm. 5 | |

Elix. Aromatici................................................................... | mil. 30 | |

Or: | Gm. or mil. | |

Sodii Bromidi..................................................................... | 5 | |

Elix. Aromatici................................................................. | 30 | |

Or: | ||

Sodii Bromidi..................................................................... | V | |

Elix. Aromatici..................................................................... | XXX | |

Or: | ||

Sodii Bromidi............................................................................ | 5. | |

Elix. Aromatici........................................................................ | 30. |

If for any reason it is desired to have the liquid by weight or the solid by measure, then specify, as

Acidi Hydrochlorici........................................................ | Gm. | 10 | 00 |

Aquae.................................................................................. | Gm. | 21 | 19 |

The prescriber can almost without exception follow the regular custom by taking into consideration the specific gravity and prescribing more or less bulk should he think a definite weight of a liquid necessary. For example: should he wish about 30 Gm. of glycerin he can prescribe 24 mils, which, instead of

Glycerini....................................................................................... | Gm. 30 |

would be written

Glycerini........................................................................................... | 24 |

There seems to be no fixed rule as to the use of ciphers on the right of the decimal line. The custom of bookkeepers in making out statements, etc., is a good one for the sake of appearance. Where fractions occur in one or more items the ciphers are used for the others, as

Hydrarg. Chlor. Mitis................................................................. | 25 | |

Sacchari Lactis................................................................................ | 1 | 00 |

Or: | ||

Strychninae Sulph.................................................................... | 065 | |

Arseni Trioxidi................................................................................ | 065 | |

Ferri Reducti....................................................................................... | 4 | 000 |

Quininae Sulph................................................................................... | 4 | 000 |

It should be particularly noted that Arabic numerals are used. The Roman numerals are never employed in a Metric inscription.

Prescriptions may be readily transposed from one system to the other by remembering only two essential equivalents.

1 | Gm. | = | 15.432 grains |

1 | mil | = | 16.23 minims. |

For average work these may be used approximately as

1 | Gm. | = | 15.5 grains |

1 | mil | = | 16 minims. |

To transpose Metric weights to Apothecaries' weights multiply the number of Grammes by 15.432 (or 15.5) to find the number of grains. To transpose Apothecaries' weights to Metric weights, divide the number of grains by 15.432 (or 15.5) to find the number of Grammes. To transpose Metric measures to Apothecaries' measures, multiply the number of mils by 16.23 (or 16) to find the number of minims. To transpose Apothecaries' measures to

Metric measures, divide the number of minims by 16.23 (or 16) to find the number of mils.

It is convenient to also remember the following two approximate equivalents.

1 | fluidounce | = | 30 mils. | |||

1 | grain | = | 0.065 | Gm. | (65 milligrammes). |

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