Question

A 70 kg patient ingested phenobarb tablets to commit
suicide. Estimate the number of tabs of phenobarbital
ingested with the following information:
– Vd = 0.75 l/kg
– Peak blood conc.= 60mg/l
– Strength of phenobarbital tab=100mg

Answer 1

To estimate the number of phenobarbital tablets ingested by the patient, you can use the following formula that relates the volume of distribution (Vd), the peak blood concentration, and the total amount of drug in the body:

\[
\text{Total amount of drug in the body (A)} = Vd \times \text{Peak blood concentration}
\]

### Step 1: Calculate the total amount of drug in the body

Given:
- \( Vd = 0.75 \, \text{l/kg} \)
- Patient's weight = 70 kg
- Peak blood concentration = 60 mg/l

First, we need to calculate \( Vd \) for the patient:

\[
Vd_{\text{patient}} = 0.75 \, \text{l/kg} \times 70 \, \text{kg} = 52.5 \, \text{l}
\]

Now, we can find the total amount of drug:

\[
A = Vd_{\text{patient}} \times \text{Peak blood concentration}
\]

\[
A = 52.5 \, \text{l} \times 60 \, \text{mg/l} = 3150 \, \text{mg}
\]

### Step 2: Calculate the number of tablets ingested

Each tablet contains 100 mg of phenobarbital. To find the number of tablets:

\[
\text{Number of tablets} = \frac{A}{\text{Strength of tablet}} = \frac{3150 \, \text{mg}}{100 \, \text{mg/tablet}} = 31.5
\]

Since the number of tablets must be a whole number, we can round down to 31 tablets or state that approximately 31 to 32 tablets were ingested.

### Final Answer
The patient ingested approximately **31 to 32 tablets** of phenobarbital.