Background

Studies investigating or controlling for the impact of antipsychotic medications often need to quantify the amount of medication to which an individual is or has been exposed. As different antipsychotics have different potencies, the task is more complicated than using each medication’s daily dosage in milligrams, for example. Further complicating the matter is that antipsychotic medications have different formulations including oral medications, and injectable formulations that are either short- or long-acting (also called depots). A commonly used strategy to account for the differing potencies is to calculate the equivalent dose of each medication in terms of a reference medication.

Chlorpromazine (CPZ) is an antipsychotic medication most often used for this purpose. A CPZ-equivalent dose is typically defined as a dose of antipsychotic that is comparable to 100 mg of CPZ.1 The total daily dose of a medication expressed in milligrams of CPZ per day is the daily-dose equivalent, and is commonly utilized in both clinical and research settings.2 Both strategies allow the dose of one medication, such as quetiapine, to be expressed in equivalents of chlorpromazine.

There are various approaches to defining dose equivalents, including the “defined daily doses” (Methodology WCCfDS, 2013), and Delphie methods.3 Defined daily doses, which are produced by the World Health Organization, provide an estimate of the average maintenance antipsychotic daily dose required for a 70-kg adult with psychosis.4 On the other hand, the Delphi method is an approach to reach a consensus to antipsychotic dose equivalents based on a two-stage, questionnaire-based survey of experts.5 Using the doses defined through these methods, equivalency ratio for each antipsychotic can be calculated, with CPZ as a reference medication (i.e. x mg/day of antipsychotic A is equal to 1 mg/day CPZ).

While there is no single standard method to defining dose equivalence, the International Consensus Study by Gardner et al. (2010), which used the Delphi method,6 is a widely used resource to calculate equivalency ratios.

chlorpromazineR

We present here an easy-to-use R package to calculate CPZ daily dose equivalents for common oral and injectable antipsychotic medications. We do not propose to suggest which conversion factors are appropriate to use, or how to interpret the converted data. All users should also refer to the papers from which the conversion factor data originates to determine whether the use of such data is appropriate for their study.

With this package, we hope:

  • to improve transparency and consistency in calculating CPZ equivalents,
  • to reduce human error and improve accuracy,
  • and to simplify workflows for large datasets, as from chart reviews of electronic health records.

We use the data from the International Consensus Study (Gardner et al. 2010) as the default conversion “key”. We also include keys generated from the most widely cited papers on CPZ equivalence. The user can also create their own keys (and contribute them to this package), which are list objects as described below.

While the default key is gardner2010, derived from the 2010 paper by Gardner et al, no equivalency was provided for short acting vs. oral chlorpromazine, so gardner2010 only includes oral and long acting injectable conversion factors. However, the SAI equivalencies are available in terms of chlorpromazine SAI equivalents, so to use that data knowing this limitation, the key gardner2010_withsai is available if needed. The SAI values calculated could then be converted using an external reference value).

Input data structure

The data is assumed to be stored in a data.frame where each row represents a participant, and with the required variables stored in columns. The two variables always required are the antipsychotic names and the dose to convert. The generic name of the medication must be used. There are differing conventions for drug name abbreviations, and different brand names around the world, so brand names are not built into the package.

For oral medications or short-acting injectables, the dose is converted directly, i.e. not accounting for dosing frequencies, which must be done separately. The exception is for long-acting injectables (LAIs), which converts to daily equivalent oral CPZ dose by dividing by the frequency of administration in days. Thus when using LAIs, a third variable, the administration frequency in days, must be available, unless the stored doses have already been divided by the administration frequency.

Key data structure

The conversion factors are stored in “keys”. A key is a list object containing 3 named sub-lists: oral, sai and lai.

names(gardner2010)
#> [1] "oral" "sai"  "lai"

Each sub-list is itself a named list where the names are the antipsychotic names, and the values are the conversion factors.

names(gardner2010$oral)[1:5]
#> [1] "chlorpromazine" "amisulpride"    "aripiprazole"   "benperidol"    
#> [5] "clopenthixol"

The conversion factor is what a given dose needs to be multiplied by to get the CPZ-equivalent.

gardner2010$oral$aripiprazole
#> [1] 20

For example, with aripiprazole, the value is 20, meaning that the CPZ-equivalent dose of aripiprazole 5 mg is 5 * 20 = 100.

Tutorial

Example for one route only

To demonstrate with a simple example using only oral medications, consider the following data:

participant_ID <- c("P01", "P02", "P03", "P04")
age <- c(42, 29, 30, 60)
antipsychotic <- c("olanzapine", "olanzapine", "quetiapine", "ziprasidone")
dose <- c(10, 12.5, 300, 60)
example_oral <- data.frame(participant_ID, age, antipsychotic, dose, 
                           stringsAsFactors = FALSE)

example_oral
#>   participant_ID age antipsychotic  dose
#> 1            P01  42    olanzapine  10.0
#> 2            P02  29    olanzapine  12.5
#> 3            P03  30    quetiapine 300.0
#> 4            P04  60   ziprasidone  60.0

In this case we have example_oral, a data.frame, with one row per participant, and a variable for the antipsychotic name, labeled antipsychotic and a variable for the dose, named dose.

To calculate CPZ-equivalent doses, use the to_cpz() function:

to_cpz(example_oral, ap_label = "antipsychotic", dose_label = "dose", 
       route = "oral")
#>   participant_ID age antipsychotic  dose cpz_conv_factor cpz_eq
#> 1            P01  42    olanzapine  10.0           30.00    300
#> 2            P02  29    olanzapine  12.5           30.00    375
#> 3            P03  30    quetiapine 300.0            0.80    240
#> 4            P04  60   ziprasidone  60.0            3.75    225

Notice that 2 new columns appear, which are named based on the default arguments in to_cpz(). The CPZ-equivalent doses are in the column labeled cpz_eq.

Example for data with oral and injectable routes

The default key from the study by Gardner et al. included dosing equivalents for oral medications, short acting injectables and long-acting injectables. If the original data includes more than one of these routes, the route argument can be set to “mixed”.

In this case, more information is required to calculate the equivalent doses. Specifically, a variable to indicate the route (“oral”, “sai”, or “lai”) is required, and if long-acting injectables are used, then the injection frequency is also required.*

*If the doses have already manually been divided by the frequency, then setting the q parameter to 1 will forgo the need to specify a variable storing the frequency information.

Here is some example data:

example_lai <- example_oral
example_lai$participant_ID <- c("P05", "P06", "P07", "P08")
example_lai$antipsychotic <- c("zuclopenthixol decanoate", 
                               "zuclopenthixol decanoate", 
                               "perphenazine enanthate", "fluspirilene")
example_lai$q <- c(14, 21, 14, 14)
example_lai$dose <- c(200, 200, 50, 6)

example_sai <- example_oral
example_sai$participant_ID <- c("P09", "P10", "P11", "P12")
example_sai$antipsychotic <- c("Chlorpromazine HCl", "Loxapine HCl", 
                               "Olanzapine tartrate", "Olanzapine tartrate")
example_sai$dose <- c(100, 50, 10, 5)

example_oral$q <- NA
example_sai$q <- NA

example_oral$route <- "oral"
example_lai$route <- "lai"
example_sai$route <- "sai"

example_mixed <- rbind(example_oral, example_sai, example_lai)

example_mixed
#>    participant_ID age            antipsychotic  dose  q route
#> 1             P01  42               olanzapine  10.0 NA  oral
#> 2             P02  29               olanzapine  12.5 NA  oral
#> 3             P03  30               quetiapine 300.0 NA  oral
#> 4             P04  60              ziprasidone  60.0 NA  oral
#> 5             P09  42       Chlorpromazine HCl 100.0 NA   sai
#> 6             P10  29             Loxapine HCl  50.0 NA   sai
#> 7             P11  30      Olanzapine tartrate  10.0 NA   sai
#> 8             P12  60      Olanzapine tartrate   5.0 NA   sai
#> 9             P05  42 zuclopenthixol decanoate 200.0 14   lai
#> 10            P06  29 zuclopenthixol decanoate 200.0 21   lai
#> 11            P07  30   perphenazine enanthate  50.0 14   lai
#> 12            P08  60             fluspirilene   6.0 14   lai

The function to_cpz() is used similarly as above, with the extra variable names (route_label, q) specified:

to_cpz(example_mixed, ap_label = "antipsychotic", dose_label = "dose", 
       route = "mixed", route_label = "route", q_label = "q", key=gardner2010_withsai) 
#>    participant_ID age            antipsychotic  dose  q route cpz_conv_factor
#> 1             P01  42               olanzapine  10.0 NA  oral           30.00
#> 2             P02  29               olanzapine  12.5 NA  oral           30.00
#> 3             P03  30               quetiapine 300.0 NA  oral            0.80
#> 4             P04  60              ziprasidone  60.0 NA  oral            3.75
#> 5             P09  42       chlorpromazine hcl 100.0 NA   sai            1.00
#> 6             P10  29             loxapine hcl  50.0 NA   sai            4.00
#> 7             P11  30      olanzapine tartrate  10.0 NA   sai           10.00
#> 8             P12  60      olanzapine tartrate   5.0 NA   sai           10.00
#> 9             P05  42 zuclopenthixol decanoate 200.0 14   lai           42.00
#> 10            P06  29 zuclopenthixol decanoate 200.0 21   lai           42.00
#> 11            P07  30   perphenazine enanthate  50.0 14   lai           84.00
#> 12            P08  60             fluspirilene   6.0 14   lai          700.00
#>    cpz_eq
#> 1     300
#> 2     375
#> 3     240
#> 4     225
#> 5     100
#> 6     200
#> 7     100
#> 8      50
#> 9     600
#> 10    400
#> 11    300
#> 12    300

Participants on multiple medications

If the included participants are on multiple medications, then the name and dose of the antipsychotic should be specified as separate variables in the data.frame. In this case, to_cpz() can be used multiple times, each time specifying the appropriate variables. Run it first specifying the name and dose of the first medication, and then run it again specifying the name and dose of the second medication. Be sure to change the name of the eq_label where the result will be stored.

Checking for inclusion and matching of antipsychotic names

The software depends on an exact match (except for case) of the generic names of antipsychotics. To check if there are rows that do not match, check_ap() can be used. Here is an example of data where all the antipsychotic names match the key, showing that 0 is returned (the number of mismatches):

check_ap(example_oral, ap_label = "antipsychotic", route = "oral", key=gardner2010)
#> [1] 0

When there are mismatches, they are listed, and the number is returned:

example_sai <- example_sai
check_ap(example_sai, ap_label = "antipsychotic", route = "sai", key=gardner2010)
#> The following antipsychotics were not found in the key:
#> Chlorpromazine HCl (sai)
#> Loxapine HCl (sai)
#> Olanzapine tartrate (sai)
#> Olanzapine tartrate (sai)
#> [1] 4

As with to_cpz(), mixed routes can be used with check_ap():

example_mixed_bad <- example_mixed
example_mixed_bad[1,3] <- "olanzzzzapine"
example_mixed_bad[4,3] <- "Seroquel"
example_mixed_bad[5,3] <- "chlorpromazineHCl"
example_mixed_bad[9,3] <- "zuclo decanoate"
check_ap(example_mixed_bad, ap_label = "antipsychotic", 
         route = "mixed", route_label = "route", key=gardner2010_withsai)
#> The following antipsychotics were not found in the key:
#> olanzzzzapine (oral)
#> Seroquel (oral)
#> chlorpromazineHCl (sai)
#> zuclo decanoate (lai)
#> [1] 4

While the default gardner2010 key uses the full antipsychotic name for SAI and LAI formulations (e.g. Chlorpromazine HCl) in order to be consistent with the publication and reduce the risk of errors due to ambiguity, the use can modify the key to “trim” the antipsychotic names to just 1 word (e.g. chlorpromazine).

names(gardner2010$lai)
#>  [1] "clopenthixol decanoate"   "flupenthixol decanoate"  
#>  [3] "fluphenazine decanoate"   "fluphenazine enanthate"  
#>  [5] "fluspirilene"             "haloperidol decanoate"   
#>  [7] "perphenazine enanthate"   "pipotiazine palmitate"   
#>  [9] "risperidone microspheres" "zuclopenthixol decanoate"

To trim to 1-word antipsychotic names, we have made the trim_key() function, which takes a key and generates a new key from it with the 1-word antipsychotic labels. If you want to use the gardner2010 key but want 1-word antipsychotic names, then you can use trim_key to generate that new key, which you can then use in to_cpz(). For example:

trimmed_gardner <- trim_key(gardner2010)
#> The trim_key() function can introduce errors if used in improper
#>            circumstances. Ensure that the antipsychotic compounds in your data
#>            and in the intended keys are the same compounds. The trim function is
#>            for convenience, but would introduce errors in your data if the
#>            compounds are not equivalent.

names(trimmed_gardner$lai)
#>  [1] "clopenthixol"   "flupenthixol"   "fluphenazine"   "fluphenazine"  
#>  [5] "fluspirilene"   "haloperidol"    "perphenazine"   "pipotiazine"   
#>  [9] "risperidone"    "zuclopenthixol"

Using other keys

The above examples have used the default CPZ conversion key, gardner2010, based on data extracted from Gardner et al. 2010. However, not all antipsychotic medications were included in that study. This package also includes a key extracted from the data included in the Leucht et al. 2016 publication based on the World Health Organization’s Defined Daily Doses. To explicitly change the CPZ key, use the key parameter when calling to_cpz().

to_cpz(example_oral, ap_label = "antipsychotic", dose_label = "dose", 
       route = "oral", key = leucht2016)
#>   participant_ID age antipsychotic  dose  q route cpz_conv_factor   cpz_eq
#> 1            P01  42    olanzapine  10.0 NA  oral      30.0300300 300.3003
#> 2            P02  29    olanzapine  12.5 NA  oral      30.0300300 375.3754
#> 3            P03  30    quetiapine 300.0 NA  oral       0.7500188 225.0056
#> 4            P04  60   ziprasidone  60.0 NA  oral       3.7495313 224.9719

However, the authors do not recommend using the DDD values when more scientific values are available. Therefore, it can be desirable to create a new key with data from the gardner2010 key (or your own created key) combined with the leucht2016 key, using data from gardner2010 key where possible.

For this purpose, we have created the add_key() function, which takes a preferred base key from which ALL available values are taken, and adds only the missing antipsychotic conversion values from the second key to be added. Further, there is a trim parameter, which invokes the trim_key() function on both keys, in the case as in leucht2016 where only 1-word antipsychotic names are provided.

gardner_leucht <- add_key(base = gardner2010, add = leucht2016, trim = TRUE)
#> The trim_key() function can introduce errors if used in improper
#>            circumstances. Ensure that the antipsychotic compounds in your data
#>            and in the intended keys are the same compounds. The trim function is
#>            for convenience, but would introduce errors in your data if the
#>            compounds are not equivalent.
#> The trim_key() function can introduce errors if used in improper
#>            circumstances. Ensure that the antipsychotic compounds in your data
#>            and in the intended keys are the same compounds. The trim function is
#>            for convenience, but would introduce errors in your data if the
#>            compounds are not equivalent.
#> 24 (ORAL) were added to the base key (acepromazine, acetophenazine, asenapine, bromperidol, butaperazine, chlorprothixene, dixyrazine, flupentixol, levosulpiride, lurasidone, melperone, moperone, penfluridol, perazine, periciazine, pipamperone, pipotiazine, promazine, prothipendyl, sultopride, thiopropazate, thioproperazine, tiapride, tiotixene) 
#> 
#> 30 (SAI) were added to the base key (acepromazine, aripiprazole, bromperidol, chlorpromazine, chlorprothixene, clopenthixol, clotiapine, clozapine, dixyrazine, droperidol, haloperidol, levomepromazine, melperone, mesoridazine, moperone, olanzapine, perazine, periciazine, perphenazine, prochlorperazine, promazine, prothipendyl, remoxipride, sulpiride, thioproperazine, tiapride, trifluoperazine, triflupromazine, ziprasidone, zuclopenthixol) 
#> 
#> 4 (LAI) were added to the base key (bromperidol, flupentixol, olanzapine, paliperidone)

names(gardner_leucht$sai)
#>  [1] "acepromazine"     "aripiprazole"     "bromperidol"      "chlorpromazine"  
#>  [5] "chlorprothixene"  "clopenthixol"     "clotiapine"       "clozapine"       
#>  [9] "dixyrazine"       "droperidol"       "haloperidol"      "levomepromazine" 
#> [13] "melperone"        "mesoridazine"     "moperone"         "olanzapine"      
#> [17] "perazine"         "periciazine"      "perphenazine"     "prochlorperazine"
#> [21] "promazine"        "prothipendyl"     "remoxipride"      "sulpiride"       
#> [25] "thioproperazine"  "tiapride"         "trifluoperazine"  "triflupromazine" 
#> [29] "ziprasidone"      "zuclopenthixol"

Let’s change a value in the example_oral data so that there is an antipsychotic that is not listed in the gardner2010 key: asenapine.

other_oral <- example_oral
other_oral[2,3] <- "asenapine"
other_oral[2,4] <- 10

check_ap(other_oral, ap_label = "antipsychotic", route = "oral")
#> The following antipsychotics were not found in the key:
#> asenapine (oral)
#> [1] 1

We can see that asenapine is not in the default key. We could use the leucht2016 key:

to_cpz(other_oral, ap_label = "antipsychotic", dose_label = "dose", 
       route = "oral", key = gardner_leucht)
#>   participant_ID age antipsychotic dose  q route cpz_conv_factor  cpz_eq
#> 1            P01  42    olanzapine   10 NA  oral         30.0000 300.000
#> 2            P02  29     asenapine   10 NA  oral         14.9925 149.925
#> 3            P03  30    quetiapine  300 NA  oral          0.8000 240.000
#> 4            P04  60   ziprasidone   60 NA  oral          3.7500 225.000

Note that it used the gardner2010 values where they were available (olanzapine, quetiapine, ziprasidone) and the leucht2016 key for asenapine.

To draw from values from additional keys (e.g. user-created keys), the add_key() function could be used iteratively. The first argument of add_key(), base, is always the key with values that take priority.

List of included keys

Use the built in help function to see the full reference for any key, e.g. help(davis1974). The data may need to be loaded prior to using the help function (e.g. load via chlorpromazineR::davis1974, then use help(davis1974).

Key name Reference Description
davis1974 https://doi.org/10.1016/0022-3956(74)90071-5 Classic paper on chlorpromazine equivalent doses.
gardner2010 https://doi.org/10.1176/appi.ajp.2009.09060802 Consensus study.
gardner2010_withsai https://doi.org/10.1176/appi.ajp.2009.09060802 The included SAI data result in equivalent to SAI (parenteral) chlorpromazine, not oral.
leucht2016 https://doi.org/10.1093/schbul/sbv167 WHO DDD method.
woods2003 https://doi.org/10.4088/JCP.v64n0607

Converting to equivalents of an arbitrary antipsychotic

Historically, CPZ has been used as the reference antipsychotic. However, using the same key data, any arbitrary reference antipsychotic could be used. Similar to to_cpz(), to_ap() can perform this conversion. The desired reference antipsychotic can be specified, e.g. with the parameters convert_to_ap = "olanzapine", convert_to_route = "oral".

to_ap(other_oral, convert_to_ap = "olanzapine", convert_to_route = "oral", 
      ap_label = "antipsychotic", dose_label = "dose", 
      route = "oral", key = gardner_leucht)
#>   participant_ID age antipsychotic dose  q route cpz_conv_factor  cpz_eq
#> 1            P01  42    olanzapine   10 NA  oral         30.0000 300.000
#> 2            P02  29     asenapine   10 NA  oral         14.9925 149.925
#> 3            P03  30    quetiapine  300 NA  oral          0.8000 240.000
#> 4            P04  60   ziprasidone   60 NA  oral          3.7500 225.000
#>       ap_eq
#> 1 10.000000
#> 2  4.997501
#> 3  8.000000
#> 4  7.500000

  1. Davis, J. M. (1974). Dose equivalence of the antipsychotic drugs. Journal of Psychiatric Research, 1, 65–69.

  2. Danivas, V., & Venkatasubramanian, G. (2013). Current perspectives on chlorpromazine equivalents: Comparing apples and oranges! Indian Journal of Psychiatry, 55(2), 207–208. https://doi.org/10.4103/0019-5545.111475

  3. Dalkey, N. (1969). The Delphi Method: An Experimental Study of Group Opinion | RAND. Retrieved from https://www.rand.org/pubs/research_memoranda/RM5888.html

  4. Leucht, S., Samara, M., Heres, S., & Davis, J. M. (2016). Dose Equivalents for Antipsychotic Drugs: The DDD Method. Schizophrenia Bulletin, 42(suppl_1), S90–S94. https://doi.org/10.1093/schbul/sbv167

  5. Hasson, F., Keeney, S., & McKenna, H. (2000). Research guidelines for the Delphi survey technique. Journal of Advanced Nursing, 32(4), 1008–1015.

  6. Gardner, D. M., Murphy, A. L., O’Donnell, H., Centorrino, F., & Baldessarini, R. J. (2010). International consensus study of antipsychotic dosing. The American Journal of Psychiatry, 167(6), 686–693. https://doi.org/10.1176/appi.ajp.2009.09060802