Formula sheets, the key method steps for every topic and 6 practice problems, with full solutions at the back.
During a rapid infusion of vancomycin, a patient develops flushing and a red rash on the face, neck and upper body. What is the most likely cause and action?
In adult cardiac arrest with shock-refractory ventricular fibrillation, which antiarrhythmic is commonly given?
A child weighing 10 kg is prescribed 2.5 mg/kg of a drug. The stock solution contains 25 mg/mL. Draw up the dose: what volume V do you give?
A child weighing 12 kg is prescribed 20 mg/kg per dose of an oral suspension that contains 100 mg in 5 mL. What volume V do you give?
Practice exercise (made-up values, not clinical guidance). A patient receives an IV bolus of 220 mg of gentamicin. The level back-extrapolated to time zero is 12 mg/L and the half-life is 3.5 h. Find the volume of distribution Vd.
Practice exercise (made-up values, not clinical guidance). A 91 kg patient has a phenytoin level of 4.5 mg/L; the target is 15 mg/L. The drug is given intravenously as phenytoin sodium (S = 0.92), and the volume of distribution is 0.7 L/kg. What extra loading dose LD raises the level to the target?
Answer: C · An infusion reaction; stop or slow the infusion and inform the prescriber
Rapid vancomycin infusion releases histamine, causing flushing and itching of the upper body (formerly called "red man syndrome"). It is managed by stopping or slowing the infusion, and sometimes with an antihistamine.
Answer: B · Amiodarone
Amiodarone is used for VF or pulseless VT that persists after shocks, with lidocaine as an alternative. Adenosine, digoxin and verapamil have no role in VF.
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 = 12 mL
Dose calculation: the amount to give equals what is prescribed divided by what you have, times the quantity it comes in: amount = (desired dose/stock strength) × stock volume. Always keep the units the same (convert g to mg, mg to mcg first) and check that the answer is sensible.
Answer: Vd = 18.33 L
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.
Answer: LD = 727 mg
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.
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