Drug dilutions & concentrations

DrugDilutions &Concentrations

Mansoura Faculty of medicineClinical Pharmacology Department

Dr Sameh AM Abdelghany

LOGO Drug Dilutions & Concentrations

It is important for patient safety that you can :I. Accurately calculate an appropriate

dose of drug for a given patient

II. Prepare an accurate dilution of a given drug.

LOGO SI Units

Definition:o SI stands for Système Internationale and is

an alternative name for the metric system of measurement.

o The main units are those used to measure :1. Weight (kilogram, kg)2. Volume (L or l) 3. Amount of substance (mole, mol).

LOGO Equivalences of weight & Volumes:

Equivalences of weight: 1 kilogram (kg) = 1000 grams (g) 1 gram (g) = 1000 milligrams (mg) 1 milligram (mg) = 1000 micrograms

(μg) 1 microgram (μg) = 1000

nanograms (ng)Equivalences of volume: 1 litre (l) = 1000 millilitres (mL) 1 millilitre = 1000 microlitre (μL)

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Drug concentrations, when put as percentages (%), either mean:

Weight/weight (w/w %) Weight/volume (w/v %) Volume/volume (v/v %) Part/part %.

LOGO Concentrations:

x % of a drug denotes x grams of the drug (or solute) in 100 milliliters of the solution.

eg. 1% lidocaine contains 1g of lidocaine in 100 mL of solution.

LOGO Dilutions:

Anything represented in an x:y (e.g. 1:1000) fashion, is x grams of drug (or solute) divided by y milliliters of solution.

e.g. 1:1000 of an epinephrine solution contains 1g of epinephrine in 1000 mL of the solution.

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Remember that 1 ml of water weighs 1 g

So…..100% solution contains 100 g in 100 ml (or 1 g in 1 ml). This is the same as 1:1

solution.

LOGO Examples: 10% soln. ≡ 10 g/100 ml soln. (≡

100 mg/ml) ≡ 1:10 soln. 1% soln. ≡ 1 g/100 ml soln. (≡

10 mg/ml) ≡ 1:100 soln. 0.1% soln. ≡ 0.1 g/100 ml soln.

(≡ 1 mg/ml) ≡ 1:1000 soln. 0.01% soln. ≡ 0.01 g/100 ml

soln. (≡ 0.1 mg/ml) ≡ 1:10000 soln.

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Question: How many milligrams of epinephrine are present in 10 mL of a 1:1000 preparation?

Answer: 1000 mL solution contain 1 g

(= 1000 mg) epinephrine. So, 10 mL will contain 10 mg

epinephrine.

LOGO Practice:Express 0.5% (w/v) in mg/mloAnswer………………………..Express 7.5% (w/v) in mg/mloAnswer………………………..Express 1:500 in mg/ml oAnswer……………………….. Express 1:2500 in μg/mloAnswer………………………..

LOGO Question?Hydrocortisone is available in

a vial of 100 mg in 2 mL. You are to prepare 24 mL of a 5-mg/mL hydrocortisone dilution using the available stock vials. How much hydrocortisone (in milliliters) and how much diluent (in milliliters) will you need?

LOGO ANSWER:

5 mg/mL = 0.005 g/mL, a 0.5% solution 100 mg/2 mL = 0.1 g/2 mL, a 5%

solution Q1xC1=Q2xC2 X × 5(%) = 24 ml × 0.5(%)So.. X= 2.4 ml hydrocortisone(answer1) 24ml -2.4ml = 21.6ml(answer2)

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Intravenous Solutions

LOGOIntravenous solutions The rate of flow of the IV solution

is monitored by maintaining the proper number of drops per minute varies with the caliber of the IV set used

should be carefully checked by the nurse in each instance.

Calibrations may vary from 10 to 60 drops / min.

LOGOCalibrating the rate of intravenous solution:

IV bottles are supplied in 250, 500, and 1000 mL sizes.

The order may read for a specified solution to be given at stated intervals (e.g., 150 mL per hour for 8 hours), or a specified amount may be administered continuously (e.g., 500 mL is to run for a 6- hour period). In every case the proper number of drops per minute is determined by the calibration of the particular IV set used.

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LOGO Example 1: 1000 mL of 5% dextrose in

water is ordered to be given over an 8-hour period. The equipment is calibrated so that 15 drops = I mL. What should be the rate of flow in drops per minute?

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First: determine the number of milliliters per

hour. Second: determine the number of milliliters per

minutes. 1000 mL ----------------- = 2.1 mL/min 8 hr x 60 min

ANSWER:

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Third: Convert the milliliter per

minute to the drops required.

I mL = 15 drops Therefore, 2 ml = 30 drops

per minute.

LOGO Example 2: How long will it take for 250

ml of IV solution to be delivered if it is flowing at 30 drops per minute? This set is calibrated at 60-drops / ml.

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First: Convert drops to milliliters. If 60

drops = I mI, 30 drops = 0.5 mL/min.

Second: Determine how many minutes it will

take for this amount of fluid to be absorbed.

250 mL ----------------- = 500 min 0.5 mL/ min

ANSWER:

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Third: Convert minutes to hours: 500 min ------------- = 8.3 hr 60

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