Key Features:
* Ability to choose up to 3 different opiates to convert to a final opiate.
* Ability to reduce the final output based on incomplete cross-tolerance. Several
choices are available based on the clinical needs of the patient.
* Ability to edit equianalgesic conversion factors if necessary in order to reflect
any changes in the literature.
* Option for converting final output into an equivalent fentanyl patch strength as
long as published guidelines exist for the current dose.
* Methadone conversion algorithm.
Before using this application, please review these important points:
> Published equianalgesic ratios are considered crude estimates at
best and therefore it is imperative that careful consideration is given
to individualizing the dose of the selected opioid. Dosage titration of
the new opioid should be completed slowly and with frequent
monitoring.
> Review the importance of correcting for incomplete crosstolerance. Equianalagesic conversions should NOT be considered a
simple straightforward calculation and generally a lower calculated
equianalgesic dosage should be given initially. Significant inter/intra
patient variability exists depending on the selected opiate, dosage
level, and expected response.
> Factors that must be addressed during the conversion process
include: Age of the patient or presence of coexisting conditions.
Use additional caution with elderly patients (65 years and older), and
in patients with liver, renal, or pulmonary disease.
> Conversion ratios in many equianalgesic dosing tables do not
apply to repeated doses of opioids.
> The use of high but ineffective doses of a previous opioid may
result in overestimation of the converted opioid.
> Ideally, methadone conversions (especially patients who were
previously receiving high doses of an opioid) should only be
attempted in cooperation with a pain specialist or a specialist in
palliative medicine.
> Meperidine should be used for acute dosing only and not used for
chronic pain management (meperidine has a short half-life and a
toxic metabolite: normeperidine). Its use should also be avoided in
patients with renal insufficiency, CHF, hepatic insufficiency, and the
elderly because of the potential for toxicity due to accumulation of
the metabolite normeperidine. Seizures, confusion, tremors, or mood
alterations may be seen. In patients with normal renal function, total
daily doses sho uld not exceed 600mg/24hrs.
> The amount of residual drug in the patient's system must be
accounted for. Example : fentanyl will continue to be released from
the skin 12 to 36 hours after removal of the patch. Residual effects
from discontinued long-acting formulations should also be assessed
before converting a patient to a new opioid.
Step 1) Under 'Converting from' select the first
opiate you want converted. If the patient is receiving
additional opiates, you will have the option of
entering these on the next screen.
Step 2) Enter the total daily dose of the first opiate.
You will notice a pop-up entry keyboard as soon as
you tap the entry area. The popup keyboard was
designed to provide greater efficiency in entering the
required data. Simply tap the desired numbers and
then hit the [enter] key to return to the main screen.
Fentanyl transdermal patch
To convert a patient from the fentanyl patch to
another opiate, select Fentanyl IM/IV from the drop
down menu. Next, press the [Hint] button located
near the top of the main screen to access the
screen on the right. Here you will find 24hr
equivalents for the various patch strengths that can
be entered under 'Total daily dose (mg).'
Important note: Currently, the default
equianalgesic conversion factor for fentanyl is set at
0.1, which is the most commonly published value
for this drug. This factor is based on the
injectable dosage form; therefore, it is
recommended that you change this factor to 0.2 for
all non-injectable dosage forms (e.g. transdermal
patch or buccal tablets). This higher conversion
factor results in lower converted dosages that are
more in line with the published potencies of these
other dosage forms. [See Step 5 below for further
information regarding the modification of the built-in
equianalgesic conversion factors.]
Summary:
Fentanyl IV/IM: use the default factor (0.1). All other
fentanyl dosage forms: use 0.2.
Step 3) Under 'Converting to' select the opiate you
want to convert to.
Step 4) IMPORTANT It is recommended that you
adjust for incomplete cross-tolerance. Incomplete
cross-tolerance relates to tolerance to a currently
administered opiate that does not extend completely
to other opioids. This will tend to lower the required
dose of the second opioid. This incomplete crosstolerance exists between all of the opioids and the
estimated difference between any two opiates could
vary widely. This points out the inherent dangers of
using an equianalgesic table and the importance of
viewing the tabulated data as approximations. Many
experts recommend - depending on age and prior
side effects - reducing the dose of the new opiate by
33 to 50 precent to account for this incomplete crosstolerance. (Example: a patient is receiving 200mg of
oral morphine daily (chronic dosing), however,
because of side effects a switch is made to oral
hydromorphone 25 - 35mg daily - (this represents a
33 to 50 percent reduction in dose compared to the
calculated 50mg conversion dose produced via the
equianalgesic calculator). This new regimen can then
be re-titrated to patient response. In all cases,
repeated comprehensive assessments of pain are
necessary in order to successfully control the pain
while minimizing side-effects.
Step 5) This application allows the user to change
the built-in equianalgesic conversion factors if
desired. To access the individual conversion factors,
tap the 'Modify values' button with your stylus (found
at the bottom of the first screen).
After the 'Modify values' button is pressed, you will
have access to the 'Equianalgesic dosage table.' To
modify a selected conversion factor, simply tap the
drug you are interested in. In the right hand column,
you will see an example of the codeine conversion
factors. Tapping either the parenteral or oral value
will automatically pull up the popup keyboard which
will allow you to quickly edit the value.
Important note regarding methadone:
When converting an opiate to methadone or
switching a patient from methadone to another
opiate, the conversion ratios are highly variable and
precise conversions are almost impossible.
Conversion ratios for methadone decrease (lower
converted methadone dose) as the dose of the
previous opioid increases. Also, as evidenced in the
equianalgesic table, chronic doses of methadone
[Listed as: Methadone (c)] are considered to be much
more potent (lower conversion factor) compared to
acute doses of methadone [Listed as: Methadone (a)]
in the table. To further complicate matters, the
conversions between methadone and another opiate
are not bi-directional. When converting a patient who
was previously receiving chronic doses of methadone
to another opiate, the conversion factor must be
adjusted upward in order to reduce the calculated
equianalgesic dosage of the new opioid. Currently,
there is a lack of consensus regarding an accepted
conversion ratio for substituting methadone with
another opioid. The last option listed in the
equianalgesic dosage table [Meth.(c) conv] is used
for all conversions from chronic methadone to
another opiate. By default, this value is set at 7 to
provide some margin of safety.
For additional information concerning
methadone dosing, see the specialized section
below.
Main Screen
Step 6) When you are satisfied with your initial
entries on the main screen, tap the [Next page]
button located in the lower right -hand corner of the
main screen. After tapping this button you will have
access to the second screen (see image on the
right). This second screen allows you to add
additional agents if necessary. If the patient was
previously receiving only a single agent, this screen
may be left blank. Entries/selections on this screen
are completed in the same way as described above
for the main screen. When finished, tap the
[Calculate] button in the lower right-hand corner to
Second Screen
access the results screen seen below.
Step 7) Results screen: This final screen has
several features:
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The total equianalgesic dosage of the final
opiate chosen on the main screen is listed at
the top (See the example screen on the left).
This screen also lists the equivalent chronic
morphine dosage. This value is used to
estimate the fentanyl patch equivalent. It is
also used in the 'Methadone Conversions'
option.
The fentanyl patch equivalent dosage is
listed as long as there is a published
guideline available for the final morphine
equivalent dosage listed above.
If you would like to access the advanced
methadone dosing option (User-adjusted
hybrid method), tap the [Methadone
Conversions] option with your stylus. See
details below.
If you would like to edit your previous entries
or evaluate a new patient, tap the [Start
over] button to return to the main screen.
Step 8) Optional:
The User-adjusted hybrid method (advanced
methadone dosing) screen can be accessed by
tapping the [Methadone conversions] button found on
the final results screen seen on the left.
Screen Details:
At the top of this screen you will see the calculated
equivalent chronic oral morphine dosage based on
the previous entries. Depending on where this value
falls, will determine which drop down menu is
activated. If you look closely, you will see five drop
down menus:
1) 0-99mg
2) 100-299mg
3) 300-499 mg
4) 500-999mg
5) >=1000mg.
In the example to the right, the equivalent chronic
oral morphine dosage listed is 428.6mg. Because
this value falls within the 3rd drop down menu (300499mg), the program will use by default a 12:1 ratio
to calculate the daily methadone dose. This value is
then generally divided into 2 or 3 equal doses.
A quick review of the default ratios should point out
an important trend: The higher the previous
equianalgesic morphine dose => The higher the
conversion ratio used to calculate an equivalent
methadone dose.
The default ratios listed may be adjusted to match
any locally published protocols. This screen also has
a high risk option that if checked will use a 20:1
conversion ratio regardless of the previously
calculated chronic oral morphine dose. This option
should be considered if the patient is likely to be at a
greater risk of an adverse event or toxicity based on
concomitant disease states.
Methadone dosing- Important points
SLOW TITRATION OF THE DOSAGE &
FREQUENT
PATIENT ASSESSMENT ARE KEY!
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Methadone therapy should only be
initiated in a setting that has
adequate monitoring available. This
is especially important during the
initial titration period. Profound
sedation, respiratory depression or
death may occur if the early signs of
toxicity are not monitored closely. In
many cases, toxicity may not become
apparent for several days.
Significant inter/intra patient
pharmacokinetic variability exists with
methadone making precise
conversions from another opioid to
methadone almost impossible.
Conversion ratios and dosage
titration intervals must be highly
individualized and based on frequent
assessment of the patient's response.
Physicians who are not experienced
with methadone dosing should ideally
only attempt this in cooperation with a
pain specialist or a specialist in
palliative medicine.