This guide explains how ketamine is measured and how to convert between common units, with step-by-step worked examples for typical clinical uses. It is educational only — actual dosing and administration must be done or confirmed by a qualified clinician and under appropriate monitoring.
Key units and conventions
- Mass: mg (milligrams). Small doses may be expressed in mcg (micrograms, 1 mcg = 0.001 mg).
- Weight-based dosing: mg per kg (mg/kg) — multiply by patient weight in kg to get total mg.
- Volume: mL (milliliters). Vials of injectible ketamine are given as mg per mL (mg/mL) or as percent w/v.
- Percent to mg/mL: percent w/v × 10 = mg/mL (for example 1% = 10 mg/mL, 5% = 50 mg/mL).
Common ketamine concentrations (examples)
- 1% w/v = 10 mg/mL (common for lower-concentration preparations)
- 5% w/v = 50 mg/mL (very common)
- 10% w/v = 100 mg/mL (available in some settings)
- Vial sizes vary (1 mL, 2 mL, 10 mL, etc.). Always check the label.
Basic calculation formulas
- Total dose (mg) = patient weight (kg) × dose (mg/kg)
- Volume to draw (mL) = total dose (mg) ÷ concentration (mg/mL)
- To prepare an infusion: desired concentration (mg/mL) = total mg added ÷ final volume (mL)
Typical clinical dose ranges (general educational ranges only)
- Anesthetic induction (IV): about 1 to 2 mg/kg IV bolus.
- Anesthetic induction (IM): about 4 to 6 mg/kg IM.
- Analgesia / subanesthetic IV bolus: roughly 0.1 to 0.3 mg/kg.
- Analgesic infusion: commonly 0.1 to 0.5 mg/kg/hour (some protocols vary).
- Intravenous infusion for depression (research/clinic protocols): commonly 0.5 mg/kg given over 40 minutes (clinic setting with monitoring).
- Emergency procedural sedation: doses vary, often 0.5 to 1 mg/kg IV or 2 to 4 mg/kg IM depending on context.
Worked examples
Example 1 — IV induction for a 70 kg adult at 1.5 mg/kg:
Total dose = 70 kg × 1.5 mg/kg = 105 mg If vial = 50 mg/mL, volume = 105 mg ÷ 50 mg/mL = 2.1 mL If vial = 10 mg/mL, volume = 105 mg ÷ 10 mg/mL = 10.5 mL
Example 2 — Analgesic bolus for a 60 kg patient at 0.2 mg/kg, vial 10 mg/mL:
Total dose = 60 × 0.2 = 12 mg Volume = 12 mg ÷ 10 mg/mL = 1.2 mL
Example 3 — Depression protocol: 0.5 mg/kg over 40 minutes for a 70 kg patient:
Total dose = 70 × 0.5 = 35 mg total over 40 minutes Rate = 35 mg ÷ 40 min = 0.875 mg/min = 52.5 mg/hr If you prepare infusion at 1 mg/mL, infusion rate = 52.5 mL/hr If you prepare infusion at 0.5 mg/mL, infusion rate = 105 mL/hr (Choose final concentration and pump rate to be practical and safe; clinic protocols vary.)
Example 4 — Preparing an infusion concentration:
Goal: make 1 mg/mL solution and you have a 50 mg/mL vial. To get 100 mL of 1 mg/mL solution you need 100 mg total → draw 2.0 mL from 50 mg/mL vial (2 mL × 50 mg/mL = 100 mg) and dilute to a final volume of 100 mL with appropriate diluent.
Practical tips and safety
- Always check vial concentration and volume before drawing doses; mistakes occur when mg/mL is assumed incorrectly.
- Use the formulas above step by step and double-check arithmetic, especially for weight-based doses.
- Label syringes with drug name, concentration, mg and mL drawn, time, and patient when preparing for infusion.
- Ketamine increases heart rate and blood pressure and can cause dissociation and hallucinations; monitoring (airway, breathing, circulation, and level of consciousness) is required for sedative or anesthetic doses.
- Adjunct medications (eg, benzodiazepines) may be used to blunt emergence reactions, but coadministration should follow local protocols.
- Subanesthetic and psychiatric uses require specialized clinic protocols and medical supervision — do not attempt outside of supervised care.
- This information is educational and not a substitute for institutional protocols, drug monographs, or consultation with a prescribing clinician or pharmacist.
If you want, tell me the patient weight, the intended dose (mg/kg or total mg) and the vial concentration you have, and I will walk through the calculation step by step for that specific case.