How can I safely transition a clinically stable patient who can swallow pills and has no contraindications to oral haloperidol from haloperidol decanoate to an equivalent oral haloperidol regimen, including dose conversion and overlap schedule?

Transitioning from Haloperidol Decanoate to Oral Haloperidol

For a clinically stable patient transitioning from haloperidol decanoate to oral haloperidol, use a conversion ratio of 10-20 times the previous daily oral dose to calculate the monthly decanoate dose, then reverse this calculation to determine the new daily oral dose, with overlap beginning 2-4 weeks before the next scheduled decanoate injection. 1, 2, 3

Dose Conversion Calculation

The most reliable conversion ratio is 10-15 times the daily oral dose equals the monthly decanoate dose. 2, 3, 4

• If the patient was on haloperidol decanoate 100 mg monthly, divide by 10-15 to estimate the equivalent daily oral dose (approximately 6.7-10 mg daily oral haloperidol) 2, 3
• Research demonstrates that a 20-fold conversion (monthly decanoate = 20 × daily oral) was adequate in most patients, though 10-15 times is more conservative and safer 2, 3
• The FDA label recommends using the parenteral dose from the preceding 24 hours as an initial approximation when switching from injectable to oral forms 1

Overlap Schedule and Timing

Begin oral haloperidol 2-4 weeks before discontinuing the decanoate to account for the 26-day elimination half-life. 5

• Start oral haloperidol at the calculated daily dose 2-4 weeks before the next scheduled decanoate injection 5
• Do not administer the next decanoate injection once oral therapy has begun 6, 4
• Steady-state plasma levels from decanoate take 3-4 months to fully dissipate, so the overlap period allows gradual transition without relapse 5
• Monitor closely during weeks 2-8 after stopping decanoate, as this is when plasma levels decline most significantly 3, 5

Dosing Strategy for Oral Haloperidol

Start with the calculated equivalent daily dose divided into 2-3 times daily administration. 1

• For moderate symptoms: 0.5-2 mg twice or three times daily 1
• For severe symptoms: 3-5 mg twice or three times daily 1
• The total daily dose should match your conversion calculation from the decanoate dose 1, 3
• Oral haloperidol should be given within 12-24 hours of the last decanoate dose if doing a rapid switch, though the gradual overlap method is preferred for stable patients 1

Monitoring During Transition

Monitor for clinical deterioration, extrapyramidal symptoms, and plasma haloperidol levels if available during the first 8 weeks. 1, 4

• Check for signs of relapse weekly during the first month, then biweekly for the next month 6, 4
• Plasma haloperidol concentrations from decanoate are typically twice as high as from equivalent oral doses, so patients may initially feel "over-medicated" then experience withdrawal symptoms as decanoate clears 2
• Extrapyramidal symptoms should be monitored, though research shows these often decrease during the transition period 6
• Adjust oral dose upward by 0.5-1 mg increments if breakthrough psychotic symptoms emerge 1

Common Pitfalls to Avoid

Do not use a simple 1:1 conversion from monthly decanoate to daily oral—this will result in severe underdosing. 2, 3

• Avoid abrupt discontinuation of decanoate without oral overlap, as relapse rates are high (one study showed patients without loading/overlap relapsed within the first month) 6
• Do not assume therapeutic equivalence based solely on dose—plasma levels from decanoate are sustained but lower than oral, yet remain clinically effective 3
• Avoid waiting for complete decanoate clearance before starting oral therapy, as the 26-day half-life means 3-4 months to steady-state elimination 5
• Do not exceed 100 mg daily oral haloperidol even if the patient was on high-dose decanoate, as safety of prolonged administration above this dose is not established 1

Special Populations

For elderly or debilitated patients, start at 0.5-2 mg twice or three times daily regardless of previous decanoate dose. 1

• Geriatric patients require lower doses and more gradual adjustments 1
• Consider that these patients may have been over-treated with decanoate and benefit from dose reduction during transition 1