To find the dose in ng/kg/min, we can use the following steps:

Step 1: Calculate the total dose per day in ng

The concentration of the drug is given as 60,000 ng/mL, and the rate is 76.8 mL/day.

$\text{Total dose per day (ng/day)} = 60,000 \, \text{ng/mL} \times 76.8 \, \text{mL/day}$

$\text{Total dose per day} = 4,608,000 \, \text{ng/day}$

Step 2: Convert the daily dose to a per-minute dose

There are 1,440 minutes in a day (24 hours $\times$ 60 minutes).

$\text{Dose per minute} = \frac{4,608,000 \, \text{ng/day}}{1,440 \, \text{minutes/day}}$

$\text{Dose per minute} = 3,200 \, \text{ng/min}$

Step 3: Adjust for the patient's weight (ng/kg/min)

The patient's weight is 80 kg, so we need to divide the dose per minute by the patient's weight.

$\text{Dose in ng/kg/min} = \frac{3,200 \, \text{ng/min}}{80 \, \text{kg}}$

$\text{Dose in ng/kg/min} = 40 \, \text{ng/kg/min}$

Final Answer:

The dose is 40 ng/kg/min.

Would you like further details on this calculation? Here are some related questions:

1. How would the dose change if the patient's weight increased?
2. What happens to the dose if the concentration of epoprostenol decreases?
3. How would the dose be adjusted if the infusion rate changes to 100 mL/day?
4. What units do we need to be careful with when calculating medication dosages?
5. How do we convert from mL/hour to mL/day in medical dosing?

Tip: Always double-check units when converting between rates and concentrations!