Tramadol hydrochloride: pharmacokinetics, pharmacodynamics, adverse side effects, co-administration of drugs and new drug delivery systems.

Tramadol hydrochloride (TrHC) is a synthetic analgesic drug exhibiting opioid and non-opioid properties, acting mainly on the central nervous system. It has been mostly used to treat pain, although its use to treat anxiety and depression has also been documented. These properties arise from the fact that they inhibit serotonin (5-HT) reuptake augmenting 5-HT concentration on the synaptic cleft. Despite this, TrHC has also been described to have several side effects which are mainly due to its fast metabolization and excretion which in turn requires multiple doses per day. To surpass this limitation, new pharmaceutical formulations are being developed intending the protection, target and sustained delivery as well as a reduction on daily dose aiming a reduction on the side effects. In the present work we have revised the efficacy, safety, biological and adverse effects of TrHC, and the added value of developing a novel drug delivery system for topical administration.