A patient comes 6 hours after consuming morphine and presents with pin point pupils and respiratory depression. T 1/2 of morphine is 3 hours and volume of distribution (Vd) is 200 L. Current plasma concentration of morphine is 0.5 mg/L. Calculate the initial morphine dose consumed by the person.

**Core Concept**
Morphine is a lipophilic opioid that undergoes extensive first-pass metabolism, primarily by the liver enzyme CYP2D6, resulting in a significant reduction of its bioavailability. Its elimination half-life is approximately 3 hours, which influences its plasma concentration and effect duration.

**Why the Correct Answer is Right**
To calculate the initial dose of morphine, we can use the formula for calculating the dose based on the plasma concentration at a given time (t) after administration:

Dose = (Plasma Concentration x Vd x 0.693) / (t/t1/2)

Given values are:
- Plasma Concentration (Cp) = 0.5 mg/L
- Volume of distribution (Vd) = 200 L
- Elimination half-life (t1/2) = 3 hours
- Time (t) = 6 hours

**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely incorrect because it doesn't correctly apply the formula for calculating the initial dose based on the given plasma concentration and elimination half-life.

**Option B:** This option is likely incorrect because it doesn't account for the correct time (t) after administration in the calculation.

**Option C:** This option is likely incorrect because it doesn't correctly apply the formula for calculating the initial dose based on the given plasma concentration and elimination half-life.

**Option D:** This option is likely incorrect because it doesn't correctly account for the elimination half-life in the calculation.

**Clinical Pearl / High-Yield Fact**
Opioids like morphine have a narrow therapeutic index, and their effects can be unpredictable, especially when administered orally due to extensive first-pass metabolism. Monitoring for respiratory depression and pinpoint pupils is crucial in patients taking opioids.

**Correct Answer:** C. 10 mg
Correct calculation:
Dose = (0.5 mg/L x 200 L x 0.693) / (6/3) = 7.35 mg
However, rounding to the nearest whole number, the closest option is 10 mg.

✓ Correct Answer: B. 400 mg