Posology: The study of the dosages of medicines and drugs

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Post   » Fri Nov 28, 2003 9:06 pm

Posology: The study of the dosages of medicines and drugs.

Dosage: The amount of drug to be administered per quantity of body weight, usually given in mg/kg (less frequently as mg/lb).

Dose: The amount of drug administered to the cavy at one time, usually given as mg. The amount of the drug in mg is calculated by multiplying the (Body Weight) times the (Dosage). Since many drugs are in a liquid suspension*, it is usually necessary to determine the dose by dividing this number by the concentration of the drug.

  • Convert all units to the same unit of measure. [In most cases weight must be converted to kg as mg/kg and mg/ml are commonly used.]
    • For example, if dosage is in mg/kg, convert the weight in pounds to kilos
      by dividing the pound weight by 2.2 (Y lb ÷ 2.2 lb/kg = X kg).
    • Guinea pig weighs 3.3 pounds.
      3.3 pounds ÷ 2.2 pounds/kg = 1.5 kg
  • Multiply the weight of cavy (now in kg's) times the dosage expressed in mg/kg.
    • Example, topical ivermectin: 1.5kg X 0.5mg/kg = 0.75mg ivermectin.
  • Divide this number by the concentration of the drug (concentration listed on label)
    • Example: Concentration of injectable ivermectin 1% solution is 10mg/ml
      0.75mg divided by 10mg/ml = 0.075ml
*Suspensions: Many drugs are administered as liquid suspensions. A suspension is a mixture in which fine particles are suspended in a fluid supported by buoyancy. Some of the liquid vehicles used are propylene glycol, glycerol formal, and even water. Since some drugs tend to settle out, shaking the suspension before drawing the dose is recommended.

Let's say the manufacturer wishes to create an ivermectin suspension of 10mg/cc. To make 1cc of this solution, one needs to put 10mg ivermectin in a 1cc container, fill with an inert liquid vehicle like propylene glycol, and mix throughly.

10mg/cc is the typical ivomec injection suspension.

To create a suspension of 1 mg/cc, one can dilute the above 10mg/cc suspension by combining 1 part of the ivermectin solution to 9 parts of a liquid vehicle. This yields a solution of 1mg/cc, very handy for accurately measuring the small doses guinea pigs require.

1 cc of a 10mg/cc + 9 cc liquid vehicle = a 10 cc solution with 10 mg ivermectin (a solution of 1mg/cc)

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Post   » Sun Dec 14, 2003 7:55 am

Calculating Concentration From Percentage (thanks to Josephine)

1% should be 1 gram (1000 mg) per 100 mls. That equals 100 mg per 10 mls or 10 mg/ml. [note, this is the typical concentration used for injectable ivermectin -- Lynx]

10% is 10 grams per 100 mls. 1 gram per 10 mls. 1000 mg per 10 mls. 100 mg/ml.

For percent solution it is always the same. The percentage is the number of grams of any substance dissolved in 100 mls of whatever the solvent is.

1% solution=10 mg/ml
and so on...

You only have to know it is an "x" percent solution to figure out mgs/ml.

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