Formula sheets, the key method steps for every topic and 6 practice problems, with full solutions at the back.
How do SGLT2 inhibitors such as empagliflozin lower blood glucose?
Two days after starting chemotherapy for a leukaemia with a high white cell count, a patient has reduced urine output. Which lab pattern suggests tumour lysis syndrome?
A child weighing 8 kg is prescribed 2.5 mg/kg of a drug. The stock solution contains 20 mg/mL. Draw up the dose: what volume V do you give?
The prescription is 1600 units of a drug that comes as 5000 units/mL. Draw up the dose in the 1 mL syringe: what volume V do you give?
Practice exercise (made-up values, not clinical guidance). A 77 kg patient is to be loaded intravenously with phenytoin sodium to reach a phenytoin level of 15 mg/L. The volume of distribution is 0.7 L/kg and the salt factor is S = 0.92. Find the loading dose LD of phenytoin sodium in mg.
Practice exercise (made-up values, not clinical guidance). A 51-year-old man weighs 64 kg and has a serum creatinine of 2.8 mg/dL (248 µmol/L). Estimate the creatinine clearance with Cockcroft–Gault: CrCl (mL/min) = (140 − age) × weight (kg)/(72 × SCr in mg/dL), × 0.85 for women. The usual digoxin dose is 250 mcg for a creatinine clearance of 120 mL/min, and a fraction fe = 0.7 of the drug is excreted unchanged by the kidneys. Using the Dettli dose fraction Q = 1 − fe·(1 − CrCl/normal CrCl), find the adjusted dose D. Round to the nearest whole number.
Answer: C · They increase the loss of glucose in the urine
SGLT2 reabsorbs most filtered glucose in the proximal tubule. Blocking it lets glucose leave in the urine, which also explains the higher risk of genital fungal infections.
Answer: A · High potassium, high phosphate, high uric acid and low calcium
Rapid tumour cell death releases potassium, phosphate and nucleic acids (which become uric acid). Phosphate binds calcium, lowering it; prevention includes IV fluids and drugs that lower uric acid.
Answer: V = 1 mL
Drawing up a dose: volume = (prescribed dose/stock strength) × stock volume. Convert to the same units first, then check that the volume fits the syringe and lands on one of its graduations.
On this 10 mL syringe every small line is 0.2 mL.
Answer: V = 0.32 mL
Drawing up a dose: volume = (prescribed dose/stock strength) × stock volume. Convert to the same units first, then check that the volume fits the syringe and lands on one of its graduations.
On this 1 mL syringe every small line is 0.01 mL.
Answer: LD = 878.8 mg
Clearance and volume: at steady state the dosing rate equals the elimination rate, so the maintenance rate = CL × Css. A loading dose is LD = Vd × C/(S × F), with S the salt factor (fraction of active drug in the salt) and F the bioavailability (1 for IV). From two levels, k = ln(C₁/C₂)/Δt; for an IV bolus Vd = dose/C₀ and CL = k × Vd. The numbers are for practice only; at the bedside always follow local protocols and have high-risk doses double-checked.
In practice the dose is rounded to a convenient amount.
Answer: D = 116 mcg
Designing a regimen: with rapid IV doses the level falls from peak to trough during the interval, so τ = ln(Cpeak/Ctrough)/k and the dose that restores the peak is Vd × (Cpeak − Ctrough). The average steady-state level is Css,avg = S·F·dose/(CL·τ). An infusion rises as C = (R/CL)(1 − e−kt). For a drug cleared by the kidneys, the dose is scaled with the creatinine clearance. The numbers are for practice only; at the bedside always follow local protocols and have high-risk doses double-checked.
In practice the dose is rounded to a convenient amount and checked against the product information.
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