Special circumstances in OST Part 2

Special circumstances in OST Part 2
This episode of Cracking Addiction tackles how to manage some of the special circumstances in opioid substation therapy.

Hepatic impairment:
With regards to Methadone the pharmacokinetics of Methadone are largely unchanged in mild to moderate cirrhosis and the patient's usual Methadone dose may be continued in stable patients without decompensated liver disease. If there are concerns about the patient's liver function or the patient has either decompensated liver disease or severe liver dysfunction please seek specialist review. The general principles of Methadone dose titration in hepatic impairment are 'start low and go slow' and consider halving the initial starting dose and doubling the normal time you would up-titrate the dose.
Buprenoprhine is almost exclusively biliary excreted and is contraindicated in severe liver disease. It is important to seek prompt specialist advise and as with Methadone with regards to dose titration 'start low and go slow'.

Renal impairment:
20% of Methadone is excreted in the urine with Methadone largely being metabolised in the liver and is generally considered safe in chronic kidney disease. One should exercise caution at the time of induction however.
Buprenoprphine similarly is metabolised in the liver with urinary excretion of inactive metabolites and is generally considered safe in chronic kidney disease.

Concomitant use of hypnosedative medications whilst patients are using OST need to viewed with caution and avoided where possible. The combination of opioids and benzodiazepines increase the risks of respiratory depression and can increase the risks of death. Opioids impair the hypercarbic respiratory drive with patient subsequently relying on their hypoxic drive which can then be impaired by benzodiazepines. Thus the use of hypnosedative medications should be avoided where possible in patients on OST.

Pain management:
OST is used to treat opioid use disorder and is not a form of analgesia. Patients on OST who experience acute pain need adequate treatment of their acute pain. Furthermore, patients on OST are opioid tolerant wand will likely need an increased amount of analgesia to adequately manage their pain symptoms. This is not drug seeking behaviour but a patient in acute pain seeking adequate treatment. The first step in management of patients on OST with acute pain is to consider split dosing the OST as the duration of the anti-craving effect of OST is usually over 24 hours but the analgesic effect of OST is between 6-12 hours.

After split dosing with Methadone one could then use short acting opioid medication as required in addition to Methadone. In the case of buprenorphine one could utilise hydromorphone, fentanyl or morphine medications to aid in managing acute pain symptoms.

Author: Dr Thileepan Naren
Thileepan is an Addiction Medicine Advanced Trainee and experienced general practitioner with a demonstrated history of working with disadvantaged and marginalized groups.