Withdrawal from drugs (principally opioids) prolongs hospital admissions and causes morbidity!
Gradual weaning of drug dosing aims to prevent the onset of withdrawal abstinence syndromes:
- regime one: 10% reduction in original dose per day weaning over 10 days or
- regime two: 20% reduction in original dose per day weaning over 5 days
- regime three: 20% reduction in original dose every 2nd day weaning over 10 days
All are equally effective and the shorter 5-day wean is not associated with any increased withdrawal symptoms requiring reinstitution of drug therapyÂ
The choice of regime is typically arbitrary based on length of therapy and clinician choice.
Dose conversion of IV and enteral:
Dose escalation and/or opioid rotation are both effective ways to combat tolerance (although there is an inevitable amount of cross tolerance) but not physical dependence.
Converting between opioids and route of administration involves documenting the total 24-hour dose being administered and then using the conversion table and calculating a total daily dose of the new drug via the new route.
| Drug | IV equivalent | IV : morphine ratio | enteral equivalent | IV : enteral ratio |
| Morphine | 10mg | 1 : 1 | 30 mg | 1 : 3 |
| Codeine | 100mg | 10 : 1 | 200mg | 1 : 2 |
| Oxycodone | 10mg | 1 : 1 | 20mg | 1 : 2 |
| Fentanyl | 100mcg | 0.01 : 1 | n/a | n/a |
| Methadone | 10mg | 1 : 1 | 20mg | 1 : 2 |
Dose conversion for IV midazolam into oral diazepam:
| [Midazolam IV [rate in mcg/kg/min] x weight x 24 ] x 0.5 = Diazepam oral |
References:
[1] Brunton, L et al (2010), Goodman and Gillman’s the Pharmacological Basis of Therapeutics 12th Edition, McGraw Hill Medical, New York
[2] Macintyre, PE et al (2010), Acute Pain Management: Scientific Evidence 3rd Edition, Australian and New Zealand College of Anaesthetists and Faculty of Pain Medicine, Melbourne
[3] Miller, RD et al (2009), Miller’s Anesthesia 9th Edition, Churchill Livingstone Elsevier, Philadelphia
[4] Peck, TE & Hill, S (2008), Pharmacology for Anaesthesia and Intensive Care 3rd Edition, Cambridge University Press, Cambridge
[5] Sasada, M & Smith, S (2003), Drugs in Anaesthesia and Intesive Care 3rd Edition, Oxford University Press, Oxford
[6] Stoelting, RK & Hillier, SE (2005), Pharmacology and Physiology in Anesthetic Practise 4th Edition, Lippincott, Williams and Wilkins, Philadelphia
[7] Pediatrics 2010 May;125(5):e1208-25: Anand et al: Tolerance and withdrawal from prolonged opioid use in critically ill children.
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