Concentration of a drug = amount of drug/volume in which it is dissolved.

Concentrations can be expressed as:

• Milligrams per ml, e.g. ketamine 10 mg/ml (Fig 1)
• Ratios, e.g. adrenaline 1:10 000 (Fig 2)
• Percentage, e.g. lidocaine 1% (Fig 3)
• Millimoles or milliequivalents per ml e.g. magnesium meq/ml (Fig 4)