# percentage mass

## percentage mass

calculation to convert drug concentration in solution (%) to mass (in mg); based on the principle that 1% solution contains 10mg of drug per 1mL of solution (*see*

**Table 1**)

Solution strength expressed as a percentage | Solution strength expressed as percentage mass (mg/mL)(A ) | Example of volume administered (B ) | Total mass of drug administered (A × B ) |

0.25% | 2.5mg | 10mL | 25mg |

2.5mg | 20mL | 50mg | |

0.5% | 5mg | 15mL | 75mg |

5mg | 20mL | 100mg | |

1% | 10mg | 5mL | 50mg |

10mg | 10mL | 100mg | |

2% | 20mg | 4mL | 80mg |

20mg | 10mL | 200mg | |

Note: 1% solution contains 10mg of solute per millilitre of solution. The percentage mass is used in the calculation of the maximum safe dose (MSD) of an administered drug (where MSD is the maximum dose that can be administered in 24 hours, in relation to the body mass of the patient, the volume of drug injected and the strength [%] of the drug in solution; the MSDs of individual anaesthetic drugs vary – |

Agent (brand name) | Maximum safe dose (70-kg adult) | Dose per kg of body mass |

Lidocaine (Xylocaine) | 200mg | 3mg/kg |

Bupivacaine (Marcain) | 150mg | 2mg/kg |

Levo-bupivacaine (Chirocaine) | 150mg | 2mg/kg |

Mepivacaine (Scandonest) | 400mg | 6mg/kg |

Prilocaine (Citanest) | 400mg | 6mg/kg |

Ropivacaine (Naropin) | 250mg | 3.5mg/kg |