Opioids are increasingly used to manage not only acute but also chronic pain and heroine addiction. These patients usually receive
many other medications that can interfere with the effects of opioids and vice versa. Patients often need combinations of drugs for
their pain management, for treating opioid-related adverse effects or for other indications including depression and anxiety. Several antibiotics
can also have interactions with opioids. It is important to understand what potential interactions exist between opioids and other
Drug interactions can occur due to pharmacokinetic interactions including effects of absorption, metabolic pathways, drug transport
through membranes and protein binding. Our knowledge of the metabolism of opioids has significantly increased over the last years and
it is now possible to appreciate the role CYP enzymes, mainly CYP 2D6 and 3A4/5, in the metabolism of many commonly used opioids
like codeine and oxycodone. Our knowledge regarding the role of the transporter proteins in drug interactions related to opioids is unfortunately
meagre. Opioids inhibit the gastrointestinal system and can thus change the absorption of other drugs.
Opioids can have synergistic or additive interactions with other drugs that have analgesic or sedative effects. Endogenous opioids control
many physiological functions and exogenous opioids can have effects on all important transmitter systems (cholinergic, GABAergic, dopaminergic
and serotonergic). The literature in this field is mainly based on case reports. Interindividual differences play an important
role. Other potential interactions include prolongation of the QT-interval and lowering of the threshold for convulsions.
Keywords: Opioid, acetylcholine, dopamine, GABA, serotonin, CYP, transporter protein, QT-interval, drug transport, threshold.
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