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A serotonin-dopamine reuptake inhibitor (SDRI) is a type of drug which acts as a reuptake inhibitor of the monoamine neurotransmitters serotonin and dopamine by blocking the actions of the serotonin transporter (SERT) and dopamine transporter (DAT), respectively. This in turn leads to increased extracellular concentrations of serotonin and dopamine, and, therefore, an increase in serotonergic and dopaminergic neurotransmission.
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A closely related type of drug is a serotonin-dopamine releasing agent (SDRA).
Comparison to SNDRIs
Relative to serotonin-norepinephrine-dopamine reuptake inhibitors (SNDRIs), which also inhibit the reuptake of norepinephrine in addition to serotonin and dopamine, SDRIs might be expected to have a reduced incidence of certain side effects, namely insomnia, appetite loss, anxiety, and heart rate and blood pressure changes.
Examples of SDRIs
Unlike the case of other combination monoamine reuptake inhibitors such as serotonin-norepinephrine reuptake inhibitors (SNRIs) and norepinephrine-dopamine reuptake inhibitors (NDRIs), on account of the very similar chemical structures of their substrates, it is exceptionally difficult to tease apart affinity for the DAT from the norepinephrine transporter (NET) and inhibit the reuptake of dopamine alone. As a result, selective dopamine reuptake inhibitors (DRIs) are rare, and comparably, SDRIs are even more so.
Pharmaceutical drugs
Medifoxamine (Cledial, Gerdaxyl) is an antidepressant that appears to act as an SDRI as well as a 5-HT2 receptor antagonist. Sibutramine (Reductil, Meridia, Siredia, Sibutrex) is a withdrawn anorectic that itself as a molecule in vitro is an SNDRI but preferentially an SDRI, with 18.3- and 5.8-fold preference for inhibiting the reuptake of serotonin and dopamine over norepinephrine, respectively. However, the metabolites of sibutramine are considerably more potent and possess different ratios of monoamine reuptake inhibition in comparison, and sibutramine appears to be acting in vivo mainly as a prodrug to them; accordingly, it was found to act as an SNRI (73% and 54% for norepinephrine and serotonin reuptake inhibition, respectively) in human volunteers with only very weak inhibition of dopamine reuptake (16%).
Research chemicals
Two SDRIs that are known in research at present are RTI-83 and UWA-101, though other related compounds are also known. Based on its chemical structure, UWA-101 may actually also possess some activity as a releasing agent, and if so, unlike RTI-83, it would not be an SDRI in the purest sense and would also be an SDRA. Manning et al. presented two high-affinity MAT-ligands with good binding selectivity for SERT and DAT, namely the 4-indolyl and 1-naphthyl arylalkylamines ent-16b (Ki 0.82, 3.8, 4840 nM for SERT, DAT, NET) and ent-13b respectively.