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.

Discussion.

If 1 grain is about 65 milligrammes, 15 mg. is about 1/4 grain. The extract of opium contains practically no refuse matter and is the preparation usually employed for suppositories. It contains 20 per cent. (1/5) of morphine, so to get 1 part of the alkaloid 5 parts of the extract must be employed. Five times 1/4 grain is 5/4, or 1 1/4 grains, and this much of the extract must be in each dose. If 4 doses are desired, it would be 4 times 1 1/4 grains, or 5 grains.

Heading showing doctor's name, address, registry number, etc.

•

Name and address of patient.

Date,

Ext. Opii............................................................................ | gr. v |

Ol. Theobromatis........................................................ | q. s. |

M. ft. suppos. no. iv. Sig.-Use one twice daily.

Signature.

It should be remembered that extract of opium contains other active ingredients than morphine:

While Nux Vomica and its preparations are now standardized on their total alkaloidal content, they probably contain about the percentage of strychnine as required in the U. S. P. viii, that is,

Nux vomica about 1.25 per cent. Flext. of nux vomica about 1 per cent. Extract of nux vomica about 5 per cent. Tincture of nux vomica about 0.1 per cent.

(7) A physician stated that his favorite tonic was tincture of nux vomica in 5-drop doses.

How much strychnine did his patients receive?

Discussion.

Five drops of tincture of nux vomica averages a little more than 2 minims. One minim contains about 1/1000 of a grain of strychnine, and 2 minims about 1/500 (or 1/400) of a grain of strychnine.

(8) A physician was surprised that he was able to gradually increase the dosage of tincture of nux vomica till the patient was taking 50 drops.

How much strychnine was the patient receiving?

Discussion.

Fifty drops would average between 20 and 25 minims, probably about 20. One minim contains about 1/1000 of a grain of strychnine; 20 minims contain about 20/1000, or 1/50 of a grain of strychnine.

(9) Write a prescription for tincture of nux vomica, alone, and instruct the patient to begin with enough drops to represent about 1/100 grain of strychnine and increase to about 1/40 grain.

Discussion.

If tincture of nux vomica contains about 0.1 per cent. of strychnine, 1000 minims would contain about 1 grain, 1 minim about 1/1000 of a grain, or 10 minims about 1/100 of a grain, and 25 minims about 1/40 grain (1000 divided by 40 = 1000/40 = 25). Allowing 2 drops to each minim, the prescription would be as follows:

Name. etc.

Date.

Tinct. Nucis Vomicae............................................ |

Twenty (20) to fifty (50) drops in water as directed.

Signature.

(10) Write a prescription for a tonic, in thirty capsules, containing enough extract of nux vomica to represent an average dose of strychnine.

Discussion.

Extract of nux vomica contains about 5 per cent. of strychnine, so 100 grains of the extract contains about 5 grains of the alkaloid, or 20 grains of the extract contains 1 grain of the alkaloid. The dose of strychnine is 1/40 grain, so the amount of the extract to contain this much is found by taking 1/40 of the amount that contains 1 grain (1/40 of 20 = 20/40 = 1/2} If 1/2 grain of the extract is to be given at each dose and there are 30 doses, the total is thirty times 1/2 grain or 15 grains.

Name, etc.

Date,

Arseni Trioxidi................................................................. | gr. j |

Ext. Nucis Vomicae........................................................ | gr. xv |

Mas. Ferri Carb............................................................. | gr. cl |

M. ft. cap. no. xxx.

One after each meal.

It should be remembered that nux vomica contains other active ingredients than strychnine, so about 10 grains would probably be nearer the amount wanted in the prescription.

(11) Write a prescription for an adult for a 4-fluidounce tonic containing enough tincture of nux vomica to give an average dose of strychnine.

Discussion.

The average dose of strychnine is 1/40 grain. Tincture of nux vomica contains about 0.1 per cent. of strychnine, or 1000 minims contain about 1 grain, so the number of minims for 1/40 of a grain is 1/40 of 1000

(1000/40 = 25).

Four fluidounces, teaspoonful dose, gives about 32 doses, so the total amount of the tincture is twenty-five times 32 or 800 minims, or about 13 fluidrachms or about 1 1/2 fluidounces. The prescription might be written as follows:

Name, etc.

Date,

Tinct. Nuc. Vomicae................................................ | |

Tinct. Cardam. Co..................................................... | q. s. |

M.

Teaspoonful in water before meals.

It should be remembered that nux vomica contains other active constituents besides strychnine, so the dose is not altogether as would be indicated by the strychnine content. In this prescription 1 fluidounce of the tincture would probably be nearer the correct amount.

(12) Complete the following so that the patient will get an average dose of strychnine for a child her age:

For Mary Jones (4 years).

Date,

Tinct. Nux Vomicae, | |

Liq. Ferri Pep. cum Mang............ |

M.

Teaspoonful in water after meals.

Discussion.

The tincture of nux vomica contains about 0.1 per cent. of strychnine, therefore 1000 minims contain about 1 grain.

The average dose of strychnine for an adult is 1/40 grain. A child 4 years old would usually receive 1/4 of the adult dose (Young's rule), or 1/160 grain strychnine. If 1000 minims of the tincture contains about 1 grain of the alkaloid, the number of minims for 1/160 of a grain would be found by taking 1/160 of 1000 (1000 divided by 160 = 1000/160 = about 6 minims).

The prescription contains 48 doses (teaspoonfuls), so 48 times 6 is the total amount of minims required (48x6 = 288 or about 4 1/2 or 5 fluidrachms).

It should be remembered that nux vomica is not given altogether in the dose as indicated by the strychnine content as it contains some other active ingredients. Also some claim that strychnine in full proportional doses is not well tolerated by some children.

(13) A child 2 years old received 1 drop of tincture of belladonna leaves. What is the relation to average adult dose?

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