What should clinicians know about fluphenazine decanoate (“Prolixin Dec”)?

Fluphenazine decanoate (“Prolixin Dec”) is one of the first-generation antipsychotics long-acting antipsychotics available in the United States.

Establishing Tolerability


  • Prolixin Dec is typically given IM every two weeks; there is, however, flexibility around the injection interval and injections up to every 6 weeks have been used.
  • In patients new to Prolixin Dec, dose titration can be used but is not required. Initiate with 6.25 mg IM, followed dose adjustments in between 6.25 to 12.5 mg increments every two weeks until the target dose is reached. If using dose titration, overlap with oral fluphenazine for one to two months while building up Prolixin Dec.
  • There is no exact formulary for oral to IM conversion. 10 mg fluphenazine daily corresponds to Prolixin Dec 12.5 IM every three weeks. The highest individual dose is listed in the package insert as 100 mg IM (but see below). Patient response should always be the indicator of appropriate dosing.
  • Most patients will be well maintained on a Prolixin Dec dose of 6.25 to 25 mg IM every two weeks (covering the dose range of 5 to 20 mg oral fluphenazine daily); only a minority of patients should need high-dose regimens of 37.5 or 50 mg IM every two weeks.

Dose Conversion of Oral Fluphenazine to Fluphenazine Decanoate LAI

PO Dose - Fluphenazine

LAI/IM Dose - Fluphenazine Decanoate

Initial LAI dose

Suggested 6.25 mg every 2 weeks
(or calculated at 1.25 mgx PO dose every 3-6 weeks)

10 mg daily

12.5 mg (0.5 ml) every 3 weeks
[can be given every 2 weeks]

20 mg daily

25 mg (1 ml) every 3 weeks

30 mg daily

37.5 mg (1.5 ml) every 3-6 weeks

40 mg daily

50 mg (2 ml) every 3-6 weeks

Typical dose: 6.25-25 mg every 2-4 weeks.

General conversion formula: For each 10 mg/day PO, give 12.5 mg decanoate every 3 weeks. Increase by 12.5 mg increments if doses >50 mg needed. 

Recommended available dose formulations include 25mg/ml strength, in 5ml multiple does vials.

Dose reduction may be necessary for CYP450 interactions of side effect intolerance.

1. APP Pharmaceuticals. (2010). Fluphenazine decanoate, injection usp
2. American Psychiatric Association. (2020). The American Psychiatric Association Practice Guideline for the Treatment of Patients With Schizophrenia. American Psychiatric Association Publishing. https://doi.org/10.1176/appi.books.9780890424841 

  • Therapeutic drug monitoring (TDM) can guide dosing, but it has not commonly been useful for fluphenazine decanoate.  A fluphenazine plasma level between 1 and 10 is a therapeutic target range.

Practical issues (including administration)

  • Prolixin Dec does not need to be refrigerated or reconstituted. Prolixin Dec is directly drawn up from a 5 ml vial with a 25 mg/ml concentration that can be stored after each use and used until empty.
  • Deltoid or gluteal injections are both possible; the site can be chosen based on patient preference and body habitus. Alternate sites and use 1-inch needle for deltoid, 2-inch needle for gluteal injection.
  • Give by deep intramuscular injection and use the Z-track technique to avoid leakage.
  • Prolixin Dec is oil-based (sesame oil) which is more painful than water-based long-acting injectables. You also will need to push harder. Avoid giving more than 3 cc as a single injection.

FDA Medication Label

Information on this topic is found in the FDA medication label.  Prescribing should always be informed by the FDA medication label. Medication labels can be found by searching Drugs@FDA at the FDA website. Labels are also available using the Drugs@FDA app for Apple or Android devices.

Labels change over time, and the current label should always be consulted. Here is the most recent label, at time of writing.

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