Calculations Lecture 2

If the dose of a drug is 200 mg, how many doses are contained in 10 g?

10 g x 1000 mg/ 1 g x 1 dose/ 200 mg = 50 doses

The usual initial dose of chlorambucil is 150 mcg/kg of body weight. How many milligrams should be administered to a person weighing 154 Ib?

154 Ib x 1kg/ 2.2Ib x 150mcg/ 1 kg x 1 mg/ 1000mcg = 10.5 mg

A certain injectable contains 2 mg of a drug per milliliter of solution. What is the ratio strength (w/v) of the solution?

2 mg of drug = 0.002 g of drug 0.002 g/ 1 mL = 1 g/ x x = 500 Ratio Strength = 1: 500

The concentration of a drug additive is an animal feed is 12.5 ppm. How many milligrams of the drug should be used in preparing 5.2 kg of feed?

5.2 kg (feed) x 1000 g(feed)/ 1 kg(feed) x 12.5g (drug)/ 1,000,000g (feed) x 1000 mg (drug)/ 1g (drug) = 65 mg

If 1500 g of a solution contains 75 g of a drug substance, what is the percentage strength (w/w) of the solution?

75g/1500g x 100% = 5%

Infant

I month - 1 year

Formula for calculating the number of doses.

Total quantity/ size of dose

PPM

Parts Per Million *Number of parts of a substance per 1 million parts of the whole

PPB

Parts per billion *Number of parts of a substance per 1 billion parts of the whole

how do you convert a patients drug dose in kg to mg?

Patient dose (mg) = Patients weight (kg) x Drug dose (mg)/ 1 (kg)

Maintenance Dose

Similar to usual doses, administered to sustain the desired drug blood levels or drug effects

Specific gravity formula

grams= mL x sg

Neonate

newborn- 1 month

if a patient is changed from a daily standard dose postmenopausal product containing 0.625 mg of conjugated estrogens (CE) to a low- dose formulation containing 0.35 mg CE, how many mg less of CE would the patient take per week?

(0.625 - 0.25) = 0.275 mg difference in dose per day 0.275 mg x 7 days = 1.925 mg

(v/v)

*Percent volume in volume *Number of milliliters of a constituent in 100mL solution *Aromatic waters, topical solutions, and emulsions *mL of preparation x % concentration = mL of component

(w/v)

*Percent weight in volume *Number of grams in a constituent in 100mL solution *Solutions & lotions *mL of preparation x % concentration= g of component

(w/w)

*Percent weight in weight *Number of grams of a constituent in 100 grams of solution *Ointments, creams, and gels *g of preparation x % concentration = g of component

If the dose of a drug is 50 micrograms, how many doses are contained in 0.020 g?

0.02 g x 1000mg/ 1 g x 1 dose/ 50 micrograms x 1000 micrograms/ 1 mg = 400 doses

Express 0.02% as a ratio strength.

0.02/ 100 = 1/ x x= 5000 1:5000

How many milligrams of hydrocodone bitartrate will be contained in each dose of the following prescription: Hydrocodone bitartrate 0.12 g Guaifenesin 2.4 g Cherry Syrup ad 120 mL

0.12 g/ 120 mL x 1 teaspoonful/ 1 dose x 5mL/ teaspoonful x 1000 mg/ 1 g = 5 mg/ dose

How many teaspoonfuls would be prescribed in each dose of an elixir if 180 mL contained 18 doses?

1 dose x 180 mL/ 18 doses x 1 teaspoonful/ 5 mL = 2 teaspoonfuls

How many milligrams of gentian violet should be used in preparing the following solution? Gentian Violet Solution 500 mL 1: 10,000

1 g/ 10,000 mL = x/ 500 mL x = 0.05 g

If one tablespoon is prescribed as a dose, approximately how many doses will be contained in 1 pint of the medicine?

1 tablespoon = 15 mL 1 pint = 473 mL 473 mL/ 15 mL = 31.5 = 31.5 doses

Early childhood

1 year - 5 years

An OTC cough remedy contains 12o mg of dextromethorphan in a 60 mL bottle of product. The label states the dose as 1.5 teaspoonfuls for a child 6 years of age. How many milligrams of dextromethorphan are contained in the child's dose?

1.5 teaspoonfuls = 7.5 mL 120mg/ 60mL = x/7.5mL x = 15mg

Convert 1:2500 to a percent.

1/ 2500 = x/ 100% x = 0.04%

How should you prepare 100 mL of 2% (w/w) solution of a drug substance in a solvent having a specific gravity of 1.25?

100 mL = 100 g 100 g x 1.25 = 125 g, weight of 100 mL solvent 100% - 2% = 98% 2%/98% = x/ 125g x = 2.55 g in 125 g (or 100 mL) solvent

How many grams of a drug substance should be added to 240 mL of water to make a 4% (w/w) solution?

100% - 4% = 96% 240 mL = 240 g 4%/96% = x/ 240 g x = 10 g

How many grams of a drug substance are required to make 120 mL of a 20% (w/w) solution having a specific gravity of 1.15?

120 mL x 1.15g/ 1 mL x 20%/100% = 27.6 g

Adolescence

13 years - 17 years

How many drops would be prescribed in each dose of a liquid medicine if 15 mL contained 60 doses? the dispensing dropper calibrates 32 drops/ mL

15 mL/60 doses x 32 drops/ 1 mL = 8 drops/ dose

Convert 1:10,00 (w/v) to mg/mL

1g/ 10,000mL x 1000mg/ 1g = 1 mg/ 10mL

How many mL of a liquid medicine would provide a patient with 2 tablespoonfuls twice a day for 8 days?

2 tablespoonfuls/ 1 dose x 15 mL/ 1 tablespoonful x 2 doses/ 1 day x 8 days = 480 mL

How many milliliters of liquefied phenol should be used in compounding the following prescription? Liquefied Phenol 2.5% Calamine Lotion ad 240 mL

240 mLCL x 2.5 mL LP/ 100 mLCL = 6 mL LP

How many grams of potassium permanganate should be used in compounding the following prescription: Potassium Permanganate 0.02% Purified water ad 250mL

250 mL x 0.02g/100 mL = 0.05 g

How many milliliters of a 3% solution can be made from 27 grams of ephedrine sulfate?

3%/100% = 27g/ x x= 900 mL

It takes approximately 4g of ointment to cover an adult patient's leg. If a physician prescribed an ointment for a patient with total leg eczema to be applied twice a day for 1 week, which of the following product sizes should be dispensed: 15g, 30g, or 60g?

4 g/ 1 dose x 2 doses/ day x 1 days/ 1 week = 56 grams 60 grams should be dispensed

If a pharmacist counted 40 drops of a medication in filling a graduate cylinder to the 2.5 mL mark, how many drops per mL did the dropper deliver?

40 drops/ 2.5 mL = x/ 1 mL x = 16 drops

How many grams of dextrose are required to prepare 4000mL of a 5% solution?

4000 mL x 5g/ 100ml = 200 g

Convert 4% (w/v) to mg/mL

4g/ 1000 mL x 1000 mg/ 1 g = 40 mg/mL

Late childhood

6 years - 12 years

How many grams of aminobenzoic acid should be used in preparing 8 fluid ounces of a 5% solution in 70% alcohol?

8 fl. Oz. x 29.57 mL/ 1 fl. Oz = 236.56 mL 236.56 mL x 5g/100mL= 11.83 g

What is the percentage strength of (w/v) of a solution of urea, if 80 mL contains 12 g?

80 mL = 80 g 12 g/ 80 g= x/ 100% x= 15%

What is the percentage strength v/v of a solution of 800 g of a liquid with a specific gravity of 0.8 in enough water to make 4000 mL?

800 g water = 800 mL SG= Weight of substance/ Weight of equal volume of water 800 mL/ 0.8 = 1000 mL of active ingredient 1000 mL/ 4000 mL = x/ 100% x = 25%

If ibuprofen tablets are permitted to contain not less than 90% and not more than 110% of the labeled amount of ibuprofen, what would be the permissible range in content of the drug, expressed in milligrams, for ibuprofen tablets labeled 200 mg each?

90% of 200 mg = 180 mg 110% of 200 mg = 220 mg Range: 180- 220mg

Single dose

Amount taken at one time

Total Dose

Amount taken during the course of therapy

Daily dose

Amount taken over a given day

Median Effective Dose

Amount that produces the desired intensity of effect un 50% of the individuals tested

Median Toxic Dose

Amount that produces toxic effects in 50% of the individuals tested

A patient attempted to split in half 20 mg unsecured tablets of a drug, resulting in "half tablets" differing by 1.5 mg in drug content. Assuming a whole tablet was uniform in drug content, calculate the amount of drug in each "half- tablet"

L = Large half S = Small half L + S = 20mg L - S = 1.5mg 2L = 21.5mg L = 10.75mg S= 20mg - 10.75mg = 9.75mg

Priming or loading dose

Larger than usual initial dose to achieve the desired blood drug level

Milligram percent

Number of mg of a substance in 100mL of a liquid

Dose

Qualitative amount administered for the intended medicinal effect

How many grams of phenol should be used to prepare 240 grams of 5% (w/w) solution in water?

Weight of solution (g) x % (expressed as a decimal) = g of solute 240 g x 0.05 = 12 g