Interaction between Morphine and Gabapentin
Major Absorption

ID DDInter1244 and DDInter791
Interaction Concomitant use of opioids with gabapentinoids (e.g., gabapentin, pregabalin) may increase the risk of opioid overdose and serious adverse effects such as profound sedation, respiratory depression, syncope, and death due to potentially additive depressant effects on the central nervous system. Coadministration with opioids may increase the oral bioavailability of gabapentin.
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Management Caution is advised when opioids and gabapentinoids are coadministered, particularly in patients with additional risk factors for respiratory depression such as advanced age, renal insufficiency, or chronic lung disease. The dosage and duration of each drug should be limited to the minimum required to achieve desired clinical effect, with cautious titration and dosage adjustments when needed. Use of additional central nervous system depressants should be avoided if possible. Patients should be monitored closely for signs and symptoms of respiratory depression and sedation, and advised to avoid driving or operating hazardous machinery until they know how these medications affect them. For patients who have been receiving extended therapy with both an opioid and a gabapentinoid (either for analgesia or seizure control) and require discontinuation of either medication, a gradual tapering of dose is advised, since abrupt withdrawal may lead to withdrawal symptoms and increased seizure risk.
References
Alternative for Morphine A07D
Eluxadoline
Diphenoxylate
Difenoxin

N02A
Naloxone
Naltrexone
Alternative for Gabapentin N03A
Lacosamide

Potential Metabolism Interactions

Substrate-Substrate Interaction：If more than one drug is metabolized by the same CYP, it is possible that its metabolism is inhibited because of the competition between the drugs. That means, it can be useful to lower the dosage of the drugs in the drug-cocktail because they remain longer in the organism than in monotherapy.
Inhibitor-Inhibitor Interaction：Combining two or more inhibitors of one CYP, should be compensated by lowering the dosage of these drugs because the metabolism is reduced and the drugs remain longer in the organism than in monotherapy. Not adapting the dosage bears the risk of even more side effects.
Inhibitor-Substrate Interaction：Combining drugs that have inhibitory effect and are substrates of one particular CYP, should be compensated by lowering the dosage. They rest longer in the organism than in monotherapy. Not adapting the dosage bears the risk of even more side effects.