Question

John weighs 14 lbs. Order reads: Phenobarbital 35 mg PO bid.

Recommended dosage guideline: 4-6 mg/kg/dose PO BID. Supplied: 4 mg/ml.

Step 1: Weight in kg:                                                             _______________

Step 2: Safe dosage range:                                                     ________________

Step 3: Maximum safe dose for 24 hours:                             ________________

Step 4: Amount ordered for 24 hours:                                               ________________

Step 5: Is the ordered dose safe?                                          ________________

Step 6: How many mg/kg/day is the patient receiving:            ________________

Step 7: Calculate amount to be given for single dose:            ________________

Answer 1

Given data:-

John weighs 14 lbs. Order reads: Phenobarbital 35 mg PO bid(twice a day)

Recommended dosage guideline: 4-6 mg/kg/dose PO BID(twice a day)

Supplied: 4 mg/ml.

Weight of John= 14 lbs

= 14× 0.454 kg [as, 1 lb = 0.454 kg so, 14 lb = 0.454 × 14 kg]

= 6.356 kg

Now, recommended dose = 4-6 mg /kg

Overall recommended dose= recommended dose × weight of patient

=( 4 to 6 mg/kg) × 6.356 kg

=(4 mg/kg to 6 mg/kg) ×6.356 kg

=4 mg/kg ×6.356 kg to 6 mg/kg × 6.356 kg

=25.42 mg to 38.14 mg

Therefore, safe dosage range= 25.42 mg to 38.14 mg

Now, maximum safe single dose = 38.14 mg

Dose is given twice a day.

Hence, maximum safe dose for 24 hrs= 2× 38.14 mg= 76.28 mg

Ordered dose(single dose) = 35 mg per dose

Dose is given twice a day.

Hence, ordered dose for 24 hr= 2×35 mg

= 70 mg

Therefore, the dose is safe. ( less than maximum recommended dose)

Now, overall ordered dose for the patient= 70 mg per day

Patient weight= 6.356 kg

So, dose receiving = overall dose / patient weight

= (70 mg/day)/6.356 kg

= 11 mg/kg/day

Now, supplied: 4 mg/ml

Using unitary method:-

4 mg present in 1 ml

1 mg present in= 1/4 ml

35 mg present in=( 1/4) ×35 ml

= 8.75 ml

So, amount to be given for single dose = 8.75 ml

Step 1: Weight in kg: 6.356 kg

Step 2: Safe dosage range: 25.42 mg to 38.14 mg

Step 3: Maximum safe dose for 24 hours: 78.28 mg

Step 4: Amount ordered for 24 hours: 70 mg

Step 5: Is the ordered dose safe? Safe.

Step 6: How many mg/kg/day is the patient receiving: 11 mg/kg/day

Step 7: Calculate amount to be given for single dose: 8.75 ml