Drug interactions and Precautions of Opioids

Opioids: interactions and precautions

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Opioid drugs have the potential to interact with many other medications. For a full list, see standard texts.

Always confirm what other medications the patient is taking, including prescribed medications, over-the-counter medication, complementary and alternative medicine products, and any illicit compounds.

The following interactions and precautions should be considered when using opioid drugs:

• Serious adverse reactions may occur if pethidine or tramadol is administered to patients receiving monoamine oxidase inhibitors (MAOIs); these opioids should not be used during or within 14 days of MAOI use. Other opioids should be carefully titrated in patients receiving MAOI therapy due to occasional unconfirmed reports of interactions.

• Pethidine and tramadol may contribute to serotonin toxicity and should be used with caution with other serotonergic drugs (eg selective serotonin reuptake inhibitors, mirtazapine, venlafaxine, selegiline, St John’s wort).

• Concomitant central nervous system depressant drugs (eg sedatives, hypnotics, antipsychotics, antidepressants, anaesthetics, alcohol) may increase the sedative and depressant effects of opioids.

• Concomitant use of drugs with anticholinergic activity may increase the risk of severe constipation and/or urinary retention.

• Partial agonist opioid analgesics (eg buprenorphine) may reduce the analgesic effect of pure opioid agonists (eg morphine) or may precipitate withdrawal symptoms.

• Drugs that induce or inhibit the hepatic cytochrome system may affect blood levels of opioids, leading to either decreased effectiveness or toxicity. Opioids affected include methadone, tramadol, and codeine. Fluvoxamine can double plasma methadone levels. Diltiazem, erythromycin and fluconazole can all lead to increased concentrations of alfentanil.

• Prolongation of the QT interval may occur with high doses of methadone. This effect may be increased if methadone is given with other drugs that also prolong the QT interval. This can lead to arrhythmia.