From the FDA Drug Label
To prepare a dilute solution containing 1 mg of ketamine per mL, aseptically transfer 5 mL from a 50 mg per mL vial to 45 mL of 0.9% Sodium Chloride Injection, USP (Normal Saline) and mix well. The amount of normal saline to be added is 45 mL to achieve a 1mg/ml solution.
From the Research
To achieve a 1mg/ml ketamine solution, you should add 45ml of normal saline to the 5ml of 50mg/5ml ketamine. This will create a total volume of 50ml containing 50mg of ketamine, resulting in the desired concentration of 1mg/ml. The calculation works as follows: the original 5ml contains 50mg of ketamine (50mg/5ml = 10mg/ml). To dilute this to 1mg/ml, you need to increase the volume while keeping the total amount of drug constant. Since 50mg ÷ 1mg/ml = 50ml total volume needed, and you already have 5ml, you need to add 45ml of normal saline. This dilution is important for precise dosing when lower concentrations are required for certain procedures or patient populations. Always verify your calculations and follow institutional protocols when preparing medication dilutions, as supported by studies on ketamine stability and usage 1.
Some key points to consider when preparing ketamine solutions include:
- The stability of ketamine solutions, which has been assessed in various studies, including one that found 10-mg/mL and 50-mg/mL ketamine solutions to be stable for at least 90 days at both ambient and refrigeration temperatures 1.
- The importance of precise dosing, which is critical in achieving the desired therapeutic effect while minimizing potential side effects.
- The various routes of administration and dosing regimens that have been explored in clinical practice, including intravenous, oral, sublingual, transmucosal, intranasal, intramuscular, and subcutaneous routes, as well as different dosing frequencies and durations 2.
However, the specific question of how much normal saline to add to 5ml of 50mg/5ml ketamine to achieve a 1mg/ml solution is primarily a matter of calculation, and the answer is based on simple arithmetic rather than complex clinical considerations. The provided studies, while informative on various aspects of ketamine use and stability, do not directly impact the calculation for diluting ketamine to a specific concentration. Therefore, the primary consideration is ensuring the accuracy of the dilution to achieve the desired concentration for safe and effective use.