Antipsychotic Dose Conversion Calculator









Results

Select the medication you're converting from and its dose and the drug you're converting to, and hit submit.


Antipsychotic Cross-Taper

Days Drug Switching From Drug Switching To
1-3
4-6
7-9
10-

Methodology

A look under the hood!

I have always wanted a clinical tool that offered a blueprint for cross-tapering from one antipsychotic medication to another, and particularly one that took medication half-life into account. A drug like aripiprazole with a 75 hour half-life is going to linger much longer than a short half-life medication like quetiapine (t½ ≈ 6 hours). Therefore, a long half-life medication like aripiprazole can be stopped abruptly as it can autotaper while the new drug is being titrated upward, whereas a short half-life medication like quetiapine has to be down-tapered simultaneously with the up-taper of the new drug.

So, for those curious, I assumed the switching FROM drug was already at steady state (i.e. the patient had been on that medication for at least five half lives), and then used the formula below to calculate estimated daily clearance/elimination:

N(t) = N0(½)t/t½

Where N(t) is remaining quantity at time (t), N0 is initial serum level, and t½ is half life

Using a spreadsheet with that formula, I plugged in various antipsychotic half lives and compared the daily elimination using different down-tapers, and while aiming for about 25% level decrease every three days, a pattern became evident.

  • For long half-live medications (half lives measured in days), abrupt stoppage allowed for an autotaper that could be offset by adding 25% of the equipotent dose of the new drug every three days.
  • For medium half-life drugs (about a day), 50% dose reduction for days 1-3 could be followed by reducing to 25% of initial dose for days 4-6, before discontinuing entirely, and all offset by the same up-taper.
  • For the über-short half medications, I was able to use an intuitive crosstaper, reciprocally decreasing/increasing doses without any consideration for accumulated serum concentration of the drug that’s being discontinued (since its half life is far shorter than the dosing interval).

Long t½ Drugs

Days From To
1-3 Discontinue 25%
4-6 50%
7-9 75%
10- 100%

Medium t½ Drugs

Days From To
1-3 50% 25%
4-6 25% 50%
7-9 Discontinue 75%
10- 100%

Short t½ Drugs

Days From To
1-3 75% 25%
4-6 50% 50%
7-9 25% 75%
10- Discontinue 100%

In order to make the suggested cross-taper usable, I’ve rounded the doses (of converted TO drug) to whatever the smallest increment of that particular drug is. Any suggestions to improve this tool are welcome and appreciated.

Reference:
1. Danivas V, Venkatasubramanian G. Current perspectives on chlorpromazine equivalents: Comparing apples and oranges!. Indian J Psychiatry. 2013;55(2):207-208. doi:10.4103/0019-5545.111475
2. Inada T, Inagaki A. Psychotropic dose equivalence in Japan. Psychiatry Clin Neurosci. 2015;69(8):440-447. doi:10.1111/pcn.12275
3. Hsia SL, Leckband SG, Rao S, Jackson E, Lacro JP. Dosing strategies for switching from oral risperidone to paliperidone palmitate: Effects on clinical outcomes. Ment Health Clin. 2018;7(3):95-100. Published 2018 Mar 23. doi:10.9740/mhc.2017.05.095
4. Psychiatric Pharmacy Essentials: Antipsychotic Dose Equivalents. The College of Psychiatric and Neurologic Pharmacists.
5. Half Life Calculator

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Last updated June 21 2023 05:13:30. Disclaimer: This website does not provide medical advice, nor is it a substitute for clinical judgment.