Pharmacy practice calcs

How do you convert from smaller units to larger units? Give an example.

Divide by 1000. For example, to change from mg to g, 42mg = 0.042g.

How do you convert from larger units to smaller units? Give an example.

Multiply by 1000. For example, to change from g to mg, 0.042g = 42mg.

How many mL are in 1 liter?

1000mL.

Define "quantity per volume" concentration. Give an example.

The strength of drugs in liquid oral preparations expressed as weight of drug/unit dose. Example: amoxicillin syrup 250mg/5mL.

What does "tds" mean?

Three times a day.

Define % w/w and give an example.

% weight in weight. 1% w/w = 1g in 100g. Example: 1% hydrocortisone cream contains 1g of hydrocortisone in 100g of cream.

Define % w/v and give an example.

% weight in volume. 1% w/v = 1g in 100mL. Example: Tegretol 2% oral suspension contains 2g of active drug in 100mL of product.

Define ratio concentration.

Expresses the number of parts of a solvent within which one part of the drug is dissolved or dispersed. A 1:1000 solution indicates that 1g of drug is dissolved in 1000mL.

A solution is 1:10,000. How many mg of drug are in 10mL of solution?

1mg.

What does scaling a formula mean?

Scaling a formula means adjusting the quantities of each ingredient in a master formula to create a different total amount of a pharmaceutical product.

How much chloral hydrate is needed to make 175mL of Chloral Elixir Paediatric BP? The formula is: chloral hydrate 200mg, water 0.1mL, blackcurrant syrup 1mL, syrup to 5mL

7g.

What is a concentrated water?

A concentrated water is diluted to produce either single strength or double strength water. Examples: Chloroform water, Peppermint water, Rose water.

What is the concentration of concentrated chloroform water, double strength chloroform water, and single strength chloroform water?

Concentrated chloroform water = 10%w/v.

Double strength chloroform water = 0.5%w/v. (1 in 20)

Single strength chloroform water = 0.25%w/v. (1 in 40)

What is the dilution factor for making single strength water from concentrated water?

1 part in 40 (or 1+39).

What is the dilution factor for making double strength water from concentrated water?

2 parts in 40, i.e., 1 in 20 (or 1+19).

How much concentrated peppermint water is required to produce 1 litre of single strength peppermint water?

25mL.

A 3-year-old child weighing 15kg requires furosemide at a dose of 2mg/kg daily. The available preparation is 40mg in 5mL. What is the daily dose in mL?

3.75 mL.

Mr. A has been prescribed metformin 500mg tablets. He is to take 500mg for 7 days, then 500mg twice a day for 7 days, then 500mg three times a day thereafter. How many tablets will he require for 4 weeks of treatment?

63.

Define "mole".

The mole is the SI unit for a substance.

What is the relationship between moles and mass?

Moles = mass (g) / molecular weight.

Millimoles = mass (mg) / molecular weight.

What is a molar solution?

A molar solution is 1 mole of solute per litre.

What is the dilution equation?

c₁ x v₁ = c₂ x v₂ (where c = concentration and v = volume).

You need to dispense 200g of betamethasone 0.25% cream, but you only have a 2% cream. What quantity of 2% cream is needed?

25g.