Question About Dosage of Chemo Drugs

Hi ebba:

I am very sorry to hear you had to be hospitalized, and are worried about possible dosing errors.

Medication errors do occur on occasion. If you have any concern, then to address the possibility of error, you could ask your medical oncologist to conduct and/or request a review of your medical record and related hospital and pharmacy records (as applicable) to confirm that: (1) dosages for each drug were correctly determined; (2) all relevant records support that the correct doses were actually administered to you; and (3) the infusion times and sequencing of drug administration was appropriate.

I am a layperson with no medical training. The below is for background information about possible doses (i.e., addresses item (1) only). Again, if you have any concerns, please ask your medical oncologist.

Please note that the doses of these four drugs are not all determined in the same manner.

You did not provide any information regarding the intended doses. NCCN guidelines (Version 2.2017) include one example of the doses in a possible TCHP regimen:

TCH chemotherapy + pertuzumab
• Trastuzumab 8 mg/kg IV day 1 followed by 6 mg/kg IV
• Pertuzumab 840 mg IV day 1 followed by 420 mg IV
• Docetaxel 75 mg/m2 IV day 1
• Carboplatin AUC 6 IV day 1
Cycled every 21 days for 6 cycles
Followed by:
• Trastuzumab 6 mg/kg IV every 21 days to complete 1 y of trastuzumab therapy Evaluate LVEF prior to and during treatment.*

Assuming the above reflects the intended regimen, then:

(1) Herceptin dose in the above regimen depends on body weight. 121 lbs = 54.8847 kg (~55 kg):

Trastuzumab (HERCEPTIN):

Initial (loading) dose: 8 mg/kg x 55 kg = 440 mgs

NOTE if 56 kgs: 8 mg/kg x 56 kg = 448 mgs (i.e., same as your 448 mg)

Subsequent doses: 6 mg/kg x 55 kg = 330 mg (future doses)

NOTE if 56 kgs: 6 mg/kg x 56 kg = 336 mgs (future doses)

(2) The dose of Perjeta in the above regimen is not weight-adjusted. This is consistent with information on the FDA label: "The initial PERJETA dose is 840 mg administered as a 60-minute intravenous infusion, followed every 3 weeks thereafter by 420 mg administered as a 30 to 60 minute intravenous infusion. (2.1)"

Pertuzumab (PERJETA):

Initial (loading) dose: 840 mg (same as your 840 mg)

Subsequent doses: 420 mg (future doses)

(3) The dose of Docetaxel (TAXOTERE) in the above regimen is on a mgs per meter squared (mg/m2) basis, which is a type of body surface area determination. There are various methods of calculating body surface area. Both weight and height are required inputs.

Docetaxel 75 mg/m2

The "Moose and Doc" patient information site includes an on-line body surface area calculator here:

http://halls.md/body-surface-area/bsa.htm

Enter weight in pounds and height in feet (') and inches ('") and choose a method (e.g., Mostellor, Dubois), click calculate, and then scroll down to select your age range, sex, and lastly type in the dose (e.g., 75) and click calculate dose.

For example, Step 1 for a person who is 121 lbs, assuming a height of 5 feet, 5 inches (65 inches tall), the Mosteller method yields a Body Surface Area of 1.59 meters squared.

Step 2 confirms this is in Normal Range for Age (36) and Gender (F).

In Step 3, multiply BSA (m2) and Dose/m2:

1.59 m2 x 75 mg/m2 = 119.25 mg (close to your 123 mgs, if you are around 65 inches tall)

(4) Carboplatin dosing in the above regimen is on an Area Under the Curve (AUC) basis.

Carboplatin: AUC 6

There are a variety of on-line calculators, but they are targeted for physicians, require additional information and have additional special settings. See e.g., http://www.globalrph.com/carboplatin.htm Please ask your medical oncologist for help on this question.

Best,

BarredOwl