It wasn’t that long ago when I was sitting in lectures as a first-year psychiatry resident. I learned about the first- and second-generation antipsychotic medications in detail. One commandment that was always preached in my training was to never combine two antipsychotic medications because there is no additional benefit. Today we are here to explore this idea and see if there is truly no additional benefit to using two antipsychotics and explore why there is so much antipsychotic polypharmacy in serious mental illness.  

Introduction

While all training programs preach the use of mono-therapy when it comes to the use of antipsychotics in clinical practice, the reality is up to 50% of psychiatric inpatients are receiving antipsychotic polypharmacy. 

Since most guidelines discourage the use of multiple antipsychotic medications, why are many psychiatrists going against these guidelines? In most cases we are just trying to stabilize patients, get them better, and keep them out of the hospital as the goal is to provide most psychiatric care in the community. To reach these goals a single medication does not always produce the desired results. 

Patients that end up on multiple antipsychotics have some unique characteristics. They tend to have more severe psychotic symptoms, are male, unemployed, and younger. Those with frequent inpatient admissions on involuntary status are also more likely to end up on two medications. 

What To Do When a Single Medication Is Not Enough?

The use of multiple antipsychotics is an area of limitted research. However, there is a difference between rational polypharmacy and irrational polypharmacy.

We should start this discussion by saying a patient should be started on monotherapy titrated to an effective dose and continued on the medication for 6 weeks prior to making a change. If the first medications fails, then switching to another medication or long acting injectable is a reasonable next step. If after another 6 weeks of treatment the patient remains unstable and symptomatic the technical next step is to start clozapine. There are many reasons why clozapine may not be a good option for a particular patient including the strict requirements for weekly complete blood cell counts CBCs.

Assuming this process is followed and the patient is still symptomatic what’s the next step?

Consider Receptor Binding Profiles

This is the first step in prescribing two medications rationally. Most first-generation medications such as Haldol will bind tightly to D2 receptors and stay bound to the sites longer. Second-generation medications like quetiapine are known to bind to the receptors and quickly dissociate giving an on-off like effect. Tight binding and longer duration of binding can lead to extrapyramidal side effects (EPS), whereas quick on-off medications like quetiapine have limitted EPS risk. 

You should also consider other receptors the medication may target such as histamine and muscarinic cholinergic receptors. It would be best to avoid combining two medications that have high antihistamine and anticholinergic activity.

Let’s look at some scenarios where antipsychotic polypharmacy makes sense. 

Patients With Acute Agitation

This is a common problem on the inpatient unit. A patient is on a low-potency quick on-off medication like quetiapine but remains symptomatic and is engaging in dangerous behavior. 

The addition of a higher potency, higher affinity medication like Haldol makes some sense here. This will control the acute agitation, can be titrated until the psychotic aggression is controlled, and can be stopped as soon as the patient is stable on quetiapine. We can see how the receptor binding profile makes this combination reasonable.

Clozapine Refractory Patients

What do you do when a patient is on the best antipsychotic medication but remains symptomatic? 

We do have several lines of evidence that we can look at for this question. One option is to add low dose risperidone. This is a similar idea to adding Haldol to quetiapine. Clozapine has lower affinity for the D2 receptor than risperidone which has much higher affinity for D2 receptors. There were two placebo-controlled trials that support this combination. Before combining medications, I would suggest obtaining a clozapine level to make sure it’s therapeutic. 

There are two more recent studies that compared multiple antipsychotic medication combinations and used rehospitalization as a measure of effectiveness. Both studies found a significant reduction in rehospitalization for patients receiving polypharmacy compared to those receiving monotherapy. The best outcome was achieved when clozapine was combined with aripiprazole. 

Patient is On a Long Acting Injectable (LAI) but Remains Symptomatic at the Highest Dose 

This is a common problem because the doses of LAIs are limitted. For example, the LAI aripiprazole (Aristida) is limitted to a maximum dose of 20 mg/day. The oral formulations of aripiprazole allow for a maximum dose of 30 mg/day. One strategy is to give the injection early. This will usually be done on week 3 for formulations that last 4 weeks. Another option is to add another medication with a different receptor binding profile such as the clozapine aripiprazole combination that was shown to reduce the risk of rehospitalization.

Treatment of Insomnia 

The addition of low dose quetiapine to a medication like paliperidone is common in clinical practice. Once D2 receptor blockade has been maximized by reaching an effective dose of paliperidone, considering the addition of as need (PRN) quetiapine for its low potency and sedating properties is reasonable. The medication should be used PRN only and should be removed once the insomnia has resolved. Consider a sleep study if sleep apnea is possible and using other options such as short-term orexin antagonists, melatonin, and sedating antidepressant if appropriate. 

Treatment of Antipsychotic Induced Side Effects 

I know what you are going to say, adding a medication to treat a side effect of another medication doesn’t make sense. Let’s take an example to illustrate why this makes sense. If a patient is stable on risperidone and is discovered to have an elevated prolactin level you have an obligation to address it. The addition of low dose aripiprazole has been proven to reduce prolactin levels in these cases. Another possibility is using aripiprazole to reduce the metabolic burden of medications such as clozapine. There is much more limited data in this area and I would consider metformin a much better option to start with if antipsychotic induced weight gain is a problem.

In the process of Switching Medication the Patient Achieves Remission 

This is another common clinical scenario. A patient didn’t respond to a medication, and you begin decreasing the dose of the first medication while titrating the new medicine. Then suddenly they are better. You don’t know why but they are better than they have ever been and now you are afraid to make any additional changes. Ideally you would finish the process and appropriately titrate the new medicine while discontinuing the ineffective medication. There is no good data to support inadequate dosing of two antipsychotics, and it’s best to continue your taper/titration and reevaluate after it’s complete.

Conclusion

There is still limited data to support the use of multiple antipsychotic medications although it is often seen in clinical practice. There are a few places where the addition of a second medication makes sense, and we can use receptor profiles to help us make rational decisions and avoid excess side effect burden.