Daily Oral Haloperidol Equivalent of 200mg Haloperidol Decanoate
The daily oral haloperidol equivalent of 200mg haloperidol decanoate is approximately 10-14mg per day, using a conversion factor of 14-20:1 (depot:oral ratio).
Conversion Methodology
The conversion from haloperidol decanoate to oral haloperidol is based on established pharmacokinetic studies that demonstrate specific dose ratios:
Standard Conversion Factors
- The most commonly validated conversion ratio is 14-20 times the daily oral dose when converting from oral to depot formulations 1, 2
- Working backwards: 200mg depot ÷ 14-20 = 10-14mg daily oral haloperidol
- The 20-fold schedule (20:1 ratio) appeared adequate in most stabilized patients, meaning 200mg depot ≈ 10mg daily oral 1
- The mean ratio observed in clinical practice was 14.1:1, suggesting 200mg depot ≈ 14mg daily oral 2
Pharmacokinetic Justification
- Haloperidol decanoate produces sustained plasma levels over 28 days with an elimination half-life of approximately 21-26 days 3, 4, 5
- Plasma concentrations from depot formulations are typically lower but more stable than equivalent oral dosing, with reduced peak-to-trough fluctuations 2
- Steady-state plasma levels after depot injection are approximately 2 times higher than during previous oral treatment at equivalent calculated doses, but the clinical effect remains comparable 1
Clinical Application Algorithm
Step 1: Calculate the baseline conversion
- 200mg haloperidol decanoate monthly ÷ 20 = 10mg daily oral (conservative estimate)
- 200mg haloperidol decanoate monthly ÷ 14 = 14mg daily oral (based on mean observed ratios)
Step 2: Consider patient-specific factors
- Start with 10-12mg daily oral haloperidol for most patients as a safe initial equivalent 1, 2
- For elderly or frail patients, reduce to 5-10mg daily and titrate based on response 6, 7
- Haloperidol efficacy shows diminishing returns above 10-15mg daily, so doses exceeding this range require careful justification 6
Step 3: Monitor and adjust
- Assess clinical response over 1-2 weeks, as oral formulations reach steady-state faster than depot 2
- Watch for extrapyramidal symptoms, which may be more pronounced initially with oral dosing 3
- QTc monitoring is essential, as both formulations can prolong the QTc interval 8, 7
Important Caveats
Bioavailability Differences
- Depot formulations bypass first-pass metabolism, resulting in higher bioavailability compared to oral administration 2, 5
- This explains why the conversion ratio is not 1:1 and why plasma levels differ between routes despite clinical equivalence 1
Individual Variability
- The conversion factor range (14-20:1) reflects significant inter-patient variability in metabolism and response 1, 2
- Smoking status, ethnicity, and hepatic function affect haloperidol metabolism and may require dose adjustments 4
Common Pitfall
- Do not simply divide 200mg by 30 days (6.7mg daily) - this ignores the pharmacokinetic differences between depot and oral formulations and will result in underdosing 1, 2
- The depot formulation releases medication slowly over the entire month, not at a constant daily rate 2, 5