Common Registration Assessment, Part 1
Ethanol content of liquid preparations
Three original questions on alcohol in liquid medicines, with the working shown and the usual traps pointed out.
Published 4 October 2026. Independent revision material, not GPhC questions, not for patient care.
Liquid medicines can contain ethanol, stated as % v/v: millilitres of ethanol per 100 mL of product. The NHS counts one unit of alcohol as 10 mL, or 8 g, of pure alcohol, and units = strength (ABV) × volume (mL) ÷ 1,000.
These questions ask how much ethanol, in mL, grams or units, a dose or a day of treatment actually delivers.
The method
- Write the % v/v as mL of ethanol per 100 mL of product.
- Scale to the dose volume to get mL of ethanol per dose.
- Multiply by doses per day for the daily ethanol volume.
- Convert to units with volume × ABV ÷ 1,000, or to grams using 10 mL = 8 g.
- Sanity-check the figure against everyday measures like one unit per small glass of wine.
Three practice questions
Work each one on paper first, then open the answer. All drugs and patients are fictional.
Question 1
An elixir contains 5% v/v ethanol. The dose is 10 mL three times daily. How many grams of ethanol does the patient take each day, using 10 mL ethanol = 8 g?
Show the answer
Answer: 1.2 g
Working: 10 mL of a 5% product contains 0.5 mL ethanol. Three doses give 1.5 mL per day. 1.5 ÷ 10 × 8 = 1.2 g.
Question 2
A tincture contains 10% v/v ethanol. How many units of alcohol are in a single 15 mL dose?
Show the answer
Answer: 0.15 units
Working: Units = 10 × 15 ÷ 1,000 = 0.15 units per dose.
Question 3
A sedative mixture contains 12% v/v ethanol, taken as 10 mL once daily. How many units of alcohol does the patient receive in a week, to one decimal place?
Show the answer
Answer: 0.8 units
Working: Per dose: 12 × 10 ÷ 1,000 = 0.12 units. Over 7 days: 0.12 × 7 = 0.84, which rounds to 0.8 units.
How this is examined
Read whether the question wants mL, grams or units before you start. All three come from the same % v/v figure but the conversions differ.
Where marks are lost
- Treating % v/v as grams per 100 mL: it is a volume measure.
- Forgetting to multiply the per-dose figure by the number of daily doses.
- Dropping the ÷ 1,000 step in the units formula and overestimating a hundredfold.
Frequently asked questions
Why does ethanol content matter clinically?
Even small daily amounts matter for patients avoiding alcohol, for children, and when several ethanol-containing liquids are taken together.
Is % v/v the same as ABV?
Yes for this purpose: a 5% v/v product has an ABV of 5, so the standard units formula applies directly.
Sources
The questions above are original and use fictional drugs. PreRegExamPrep is not affiliated with or endorsed by the General Pharmaceutical Council.
Practise until the method is automatic
Try 15 free questions with worked answers. No sign-up required.
More calculation topics
- Dose by weight calculations for the GPhC assessment
- Volume to give: liquid medicine calculations
- Percentage strength calculations: w/v, w/w and ratios
- Dilution calculations with C1V1 = C2V2
- Infusion rate calculations in mL per hour
- Drip rate calculations: drops per minute
- Body surface area calculations
- Creatinine clearance (Cockcroft-Gault) calculations
- Moles and millimoles calculations
- Displacement volume calculations for reconstitution
- Quantity to supply calculations
- Using a provided formula in calculations
- Dose information from packaging and labels
- Diluting a stock to a lower strength
- Medicine cost and switch calculations
- Rounding rules in calculations
- Enteral feed rate calculations
- Electrolyte content over time
- Infusion dose per kg per hour
- Rounding doses to measurable volumes
- Relative risk and relative risk reduction
- Absolute risk reduction and number needed to treat
- Odds ratio and confidence intervals
- Relative versus absolute risk reduction
- Loading dose and volume of distribution
- Top-up doses from measured drug levels
- Salt correction factors
- Mass and molar drug concentrations
- Half-life and falling drug levels
- Steady-state concentration and infusion rate
- Bioavailability and equivalent oral doses
- Oral maintenance dose and dosing interval
- Elimination rate constant and half-life
- Accumulation towards steady state
- Ratio strengths and one in X
- Serial dilution factors
- Mixing solutions of different strengths
- Tablet quantities for reducing regimens
- Equivalent doses from provided conversion tables
- Thresholds and dose-banding algorithms
- Unit conversions for mass and volume
- Units and units per mL
- Reconstituting powders and final concentration
- Millimoles and milliequivalents
- Infusion time and volume remaining
- Days supply from pack sizes
- Percentage w/v and w/w conversions
- Ideal and adjusted body weight from formulae
- Diluting creams and ointments by weight
- Scaling a formula to a batch size
- Age-band doses from a provided table
- Tablet fractions and split doses
- Stones, pounds, inches and metric conversions
- Micrograms per minute from mg per hour
- Percentage change and mark-up
- Molar solutions and mass per volume
- Osmolarity from component concentrations
- Direct proportion and cross-multiplication
- Scientific notation and very small quantities
- Stock use and reorder quantities
- Parts per million and very dilute solutions
- Sodium chloride equivalents and isotonic solutions
- Density and specific gravity conversions
- Doses per day and hours between doses
- Finding the volume of diluent to add
- Capping a dose at a stated maximum
- Whole vials and ampoules to draw up
- Reading values from a provided graph
- Micrograms per kg per minute infusions
- Percentage composition of a compound preparation
- Suppository displacement values
- Isotonicity by freezing point depression
- Energy content of parenteral nutrition
- Syringe driver rate calculations
- Area under the curve calculations
- Renal dose adjustments using provided bands
- Insulin units and infusion calculations
- Working backwards from a stated dose
- Doses and days from multi-dose devices
- Combined additives in one infusion
- BMI calculations for the GPhC assessment
- Fewest tablets to make a dose
- Clearance from half-life and volume of distribution
- Maintenance fluid requirements by weight
- Sodium load from effervescent tablets
- Oxygen cylinder duration calculations
- Urine output and fluid balance calculations
- Quantities for titration packs
- Infusion line priming and dead space
See also the formula sheet, the eight sample questions and the approved calculator page.