Citalopram interaction with other drugs

Highly suicidal patients should be given agents posing less risk of lethality with overdose and less risk of interacting with other drugs taken in an overdose attempt (i.e., sertraline, citalopram, or venlafaxine). 

All SSRIs have common 5-HT agonistic effects and because of this, SSRIs have common interactions and side effects. SSRIs are potent inhibitors of serotonin reuptake by CNS neurons and may interact with other drugs such as monoamine oxidase inhibitors (MAOIs) or circumstances which cause serotonin release. A minimum 2 weeks wash-out period should be observed between stopping a MAOI and starting an SSRI. Conversely, a MAOI should not be started for at least 1 week after an SSRI has been stopped, 5 weeks after fluoxetine, and 2 weeks for paroxetine and sertraline. Escitalopram and citalopram are hypersensitive to each other. 

Of all the SSRIs citalopram has the least inhibitory effect on cytochrome P450 enzymes and has not been associated with clinically significant interactions with other CNS drugs. 

The most common interactions with SSRIs are pharmacokinetic interactions. For example, paroxetine and fluoxetine are potent CYP2D6 inhibitors (Table 30-4). Thus, administration with 2D6 substrates such as TCAs can lead to dramatic and sometimes unpredictable elevations in the tricyclic drug concentration. The result may be toxicity from the TCA. Similarly, fluvoxamine, a CYP3A4 inhibitor, may elevate the levels of concurrently administered substrates for this enzyme such as diltiazem and induce bradycardia or hypotension. Other SSRIs, such as citalopram and escitalopram, are relatively free of pharmacokinetic interactions. The most serious interaction with the SSRIs are pharmacodynamic interactions with MAOIs that produce a serotonin syndrome (see below). 

Although venlafaxine can have more interactions than SSRIs pharmacodynamically, it is comparable with citalopram and sertraline in terms of not causing CYP enzyme mediated pharmacokinetic drug-drug interactions (Table 7-29). Thus, these three antidepressants have a distinct advantage over drugs such as fluoxetine, particularly in patients who are likely to be on other medications in aaaition to their antidepressant. 

The study of ecstasy with citalopram was primarily undertaken to find out how eestasy works, but on the basis of these results and animal studies it seems likely that patients already taking citalopram may not be able to get as high on usual doses of ecstasy, and some adverse effects may also be redueed. Furthermore, if the proposed mechanism of interaction is correct, the same is also likely to be true if they are taking any other SSRI and some cases have been reported. However, be aware of possible pharmaeokinetie interaetions with some SSRIs that are potent CYP2D6 inhibitors (e.g. fluoxetine, paroxetine), which may increase ecstasy levels. There is also a risk of increased serotonergic activity and there have been a few reports of interaetions involving other sympathomimetics and SSRIs or related drugs, see Phentermine + Fluoxetine , p.205. 

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