Anchors to memorize: 1:1,000 = 0.1% (epinephrine), 1:10,000 = 0.01%.
Express 1:2,500 as a percentage. 1:2,500 means 1 g in 2,500 mL, so (1 ÷ 2,500) × 100 = 0.04% w/v.
Practice percentage & ratio strength →
The drug amount is unchanged by dilution; only concentration and volume change. Remember to QS to the final volume when the question asks for it.
How many mL of a 20% stock are needed to make 120 mL of a 2% solution? V₁ = (2% × 120) ÷ 20% = 12 mL (then QS to 120 mL with diluent).
Practice dilution →
Don't confuse the two: medial = known quantities → find strength; alternate = known strengths → find quantities.
Make 250 mL of 25% dextrose from 70% and 10% stock. Parts of 70% = 25 − 10 = 15; parts of 10% = 70 − 25 = 45; total = 60. Volume of 70% = (15 ÷ 60) × 250 = 62.5 mL (and 187.5 mL of the 10%).
Practice alligation →
Valence trap: monovalent ions (Na⁺, K⁺) → mEq = mmol; divalent ions (Ca²⁺, Mg²⁺) → 2 mEq per mmol.
How many mEq are in 1 g of KCl (MW 74.5, valence 1)? mmol = 1,000 ÷ 74.5 = 13.4; mEq = 13.4 × 1 = 13.4 mEq. Osmolarity of 0.9% NaCl = 9 g/L ÷ 58.5 × 2 × 1,000 = 308 mOsm/L.
Practice milliequivalent (meq), millimole & milliosmole →
Always round drops to a whole number, and round pump rates exactly as the question instructs.
Infuse 1,000 mL over 8 hours with a set that gives 15 drops/mL. (1,000 × 15) ÷ (8 × 60) = 15,000 ÷ 480 = 31.25 → 31 drops/min.
Practice iv infusion & drip rate →
Rounding trap: rounding BSA to one decimal too early can shift the dose by several mg — carry full precision to the end.
A patient is 170 cm and 70 kg. BSA = √(170 × 70 ÷ 3,600) = √3.306 = 1.82 m². A 175 mg/m² order → 175 × 1.82 = 318.5 mg.
Practice body surface area (bsa) & chemo dosing →
Read the ask: total vs nonprotein kcal changes whether you include the amino acid calories.
Calories from 1,000 mL of dextrose 20%? Grams = 1,000 × 20% = 200 g; 200 × 3.4 = 680 kcal.
Practice tpn & nutrition calculation →
The exam gives you the E-value — the skill is the 4-step setup, not memorizing E-values.
Make 30 mL of 1% pilocarpine HCl (E = 0.24) isotonic. (1) drug = 0.3 g; (2) 0.3 × 0.24 = 0.072 g; (3) 0.009 × 30 = 0.27 g; (4) 0.27 − 0.072 = 0.198 g.
Practice isotonicity & e-value →
Weight rule first, formula second — using actual weight when AdjBW is required is the classic error.
70-yr-old male, 5'10" (IBW = 73 kg), weighs 90 kg, SCr 1.2. Since 90 < 125% of 73, use IBW. CrCl = (140 − 70) × 73 ÷ (72 × 1.2) = 59.1 mL/min.
Practice creatinine clearance (cockcroft-gault) →
Loading dose depends on Vd; maintenance depends on clearance — a favorite mix-up.
Two levels: 40 mg/L at hour 0, 10 mg/L at hour 8. k = ln(40 ÷ 10) ÷ 8 = 1.386 ÷ 8 = 0.173 hr⁻¹, so t½ = 0.693 ÷ 0.173 ≈ 4 hr.
Practice pharmacokinetics →
Always dose-normalize both AUCs — comparing raw AUCs from different doses is the built-in trap.
IV 100 mg gives AUC 50; oral 200 mg gives AUC 60. First term: 60 ÷ 200 = 0.30; second term: 100 ÷ 50 = 2; F = 0.30 × 2 = 0.60 = 60%.
Practice bioavailability (f) →
Stability caps the day supply of an open container, and the 20% reduction only applies going NPH→glargine or Toujeo→Lantus/Basaglar — not the reverse.
Lantus 10 mL vial at 25 units/day: 1,000 ÷ 25 = 40 days, but an open glargine vial is stable 28 days → 28-day supply. Switching NPH 30 units BID to glargine: 60 × 0.8 = 48 units daily.
Practice insulin day supply & switching →
90 MME/day is the common safety-review threshold; watch route differences — the same drug by a different route has a different number.
Oxycodone 10 mg three times daily = 30 mg/day. Table: 20 mg oxycodone ≈ 30 mg morphine, so MME = 30 × (30 ÷ 20) = 45 MME/day.
Practice opioid conversion & mme →
Round down — you can't bill for a partial day. Inhalers count total actuations (puffs), not mL.
A 5 mL eye drop bottle (20 drops/mL = 100 drops), 1 drop in each eye twice daily = 4 drops/day. 100 ÷ 4 = 25 days.
Practice days supply calculation →
mg/kg/DAY vs mg/kg/DOSE is the number-one trap in this family — read which one the order specifies.
A 66 lb child on amoxicillin 45 mg/kg/day divided twice daily. kg = 66 ÷ 2.2 = 30 kg; daily = 45 × 30 = 1,350 mg; per dose = 1,350 ÷ 2 = 675 mg.
Practice weight-based (mg/kg) dosing →
Add the displacement volume to the diluent when finding concentration — ignoring it overestimates the strength.
A 1 g vial reconstituted to 100 mg/mL needs a final volume of 10 mL. If the label says to add 9.5 mL diluent, the powder volume = 10 − 9.5 = 0.5 mL.
Practice reconstitution & powder volume →
Numerically, SG equals grams per mL because it's referenced to water (1 g/mL).
Glycerin has a specific gravity of 1.25. The weight of 240 mL = 240 × 1.25 = 300 g.
Practice specific gravity →
Only correct calcium when albumin is low. For phenytoin with CrCl < 10, the 0.2 factor becomes 0.1.
Measured calcium 7.5 mg/dL, albumin 2.5 g/dL. Corrected = 7.5 + 0.8 × (4.0 − 2.5) = 7.5 + 1.2 = 8.7 mg/dL.
Practice clinical lab calculation →
Never round these to the nearest whole number. 2.19 vials is 3 vials, not 2 — and 2.25 bottles of antibiotic is 3, or the patient runs out mid-course. The leftover in the last container is waste, not an error.
An 82 kg patient needs vancomycin 20 mg/kg = 1,640 mg, stocked as 750 mg vials. 1,640 ÷ 750 ≈ 2.19, so you open 3 vials.
Practice dispensing quantity →