Wellington ICU Drug Manual: Appendices

appendix 10:
Drug calculations

Wellington ICU Drug Manual - Local anaesthetic safety calculations

Calculating doses from percentage solutions

  • The underlying principle of all drug dilutions is that a 100% solution is 1 gram (gm) of drug in 1 ml of volume (a '1 in 1' solution)

  • Such a solution contains 100 gm of drug in 100 mls

Therefore a 1% solution of any drug =1:100 solution = 1 gm in 100 ml = 10 gm in 1 litre = 10 mg in 1 ml = 10,000 mcg in 1 ml

Subsequent dilutions can be derived as shown in the table below where each horizontal row contains the same amount of drug.

Wellington ICU Drug Manual - Appendix 10 Drug Calculations table

Examples of common ICU drugs

  • 0.5% bupivacaine contains 5 mg in 1 ml (100 mg in a 20 ml vial)
  • 0.2% ropivacaine contains 2 mg in 1 ml (40 mg in a 20 ml vial, 400 mg in a 200 ml bag)
  • 2% lignocaine contains 20 mg in 1 ml (100 mg in a 5 ml vial)
  • '1 in 1000' adrenaline contains 1 mg in 1 ml or 1000 mcg in 1 ml
  • 10% calcium chloride contains 1 gm in 10 ml; this is 6.8 mmol of calcium & 13.6 mmol of chloride
  • 49.3% magnesium sulfate contains 493 mg in 1 ml; a single 5 ml vial therefore contains 2.465 gm
  • 8.4% sodium bicarbonate contains 84 mg in 1 ml; this is 23 mg (1 mmol or 1 mEq) of sodium & 61 mg (1 mmol or 1 mEq) of bicarbonate
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