Hi I'm Dr. Friend. I'll help you with Gracie today (that's the name of my oldest daughter, love it!).
Unfortunately, drops are NOT an appropriate way to measure anything. Drop size is extremely variable, and you can not reliably predict how much you are applying.
Rather than using drops, I recommend getting a syringe to measure the 0.4 mL accurately. You should be able to obtain one at a pharmacy. Your pharmacist may be able to give you a single syringe. Get a 1 cc syringe if possible, this size will be the easiest to measure 0.4 cc. Larger syringes will be more difficult to measure accurately.
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