Ketamine has known interactions with
- Theophylline (tachycardia, reduced seizure threshold with resulting seizures)
- Levothyroxine (hypotension, tachycardia)
- Diazepam (increased plasma concentrations of ketamine, consider reducing ketamine infusion dose)
An Agilia PCA pump should be obtained. Use a luer lock 50ml syringe attached to an anti siphon line (which must be labelled as per NHS Highland guidelines) and a dedicated IV cannula. Standard aseptic precautions should be deployed.
Dose and Drug Preparation
A new drug syringe should be prepared and discarded every 24 hours. Ketamine should be prepared to a concentration of 5mg/mL using these instructions:
- Obtain ketamine hydrochloride (Ketolar) at a concentration of 10mg/mL.
- Draw 20mL of ketamine into a 50mL syringe (20mL x 10mg = 200mg). The addition of 20mL 0.9% saline gives a total of 40mL volume and a final concentration of 5mg/mL (200mg ketamine in 40mL = 5mg/mL).
- Infusions should be commenced at 1mL per hour (5mg/hour) and titrated to effect (see below for maximal infusion rates) or until side effects are experienced.
- In patients weighing more than 50kg the infusion rate should not be increased more frequently than hourly and should never exceed 5mL/25mg per hour.
- If weight less than 50kg the infusion rate should not be increased more frequently than hourly and should never exceed 3mL/15mg per hour.
- Consider an initial dosage of 0.5mL (2.5mg) per hour in the frail and elderly with cautious dose titration.
Loading doses are not recommended.
Ketamine undergoes renal excretion, however there is no requirement for dose adjustment in patients with renal dysfunction in the dose ranges suggested in this guideline.
Paracetamol and NSAIDS should be continued unless specifically contraindicated.
Concurrent prescription of adequate antiemetics should be available prior to starting the infusion to ameliorate any side effects.
A dedicated ketamine prescription chart must be used and can be obtained from the acute pain team. The prescription is not valid unless signed by the treating anaesthetist or acute pain service.
Ketamine infusions should ideally be commenced before 2pm allowing for close monitoring for side effects and toxicity within day time working hours.