Antipsychotic monitoring by LC-MS/MS confirms adherence to first- and second-generation agents used for schizophrenia, bipolar disorder, and as adjuncts in depression and anxiety. Two interpretation points stand out: risperidone's active metabolite hydroxyrisperidone is paliperidone (Invega), a marketed drug in its own right, and quetiapine is a well-known cause of methadone false positives on immunoassay.1
Adherence to antipsychotics is often poor and hard to verify by history alone, and a specific LC-MS/MS result documents recent use between visits. It also resolves the quetiapine-driven methadone false positive that can otherwise appear on an immunoassay screen.3
LC-MS/MS measures specific antipsychotics and key metabolites (e.g., norquetiapine, hydroxyrisperidone). Absence in a prescribed patient may reflect non-adherence, PRN use, a drug interaction, or altered CYP metabolism. When a methadone immunoassay is unexpectedly positive in a patient on quetiapine, confirm methadone and EDDP by LC-MS/MS to exclude cross-reactivity.3
Confirms recent use. Detection indicates use within the estimated window; levels do not confirm dose or schedule.
Paliperidone may be risperidone. Hydroxyrisperidone (paliperidone) is risperidone's active metabolite; a positive can reflect prescribed risperidone.
Can explain a methadone screen. Quetiapine can cross-react on the methadone immunoassay; confirm by LC-MS/MS.3
May indicate non-adherence. Absence in a prescribed patient can reflect missed doses, PRN use, or altered metabolism.
Not on routine panels. Antipsychotics are not on standard drug screens; only targeted testing detects them.
Timing and cutoff. Absence may reflect timing of last use or levels below the cutoff.
| Antipsychotic | Urine analyte(s) | Estimated window |
|---|---|---|
| Aripiprazole | Aripiprazole (OPC-3373) | Up to ~16 days |
| Olanzapine | Olanzapine | 4-12 days |
| Quetiapine | Quetiapine, norquetiapine | 1-2 days |
| Risperidone | Risperidone, hydroxyrisperidone | Parent ~5 d; metabolite ~6 d |
| Paliperidone | Hydroxyrisperidone | ~6 days |
| Haloperidol | Haloperidol (+ metabolite) | ~5 days |
| Clozapine | Clozapine, N-desmethylclozapine | 2-3 days |
| Lamotrigine | Lamotrigine | 5-7 days |
Windows estimated from half-life (about 5x t-half); note that hydroxyrisperidone is paliperidone (Invega).