Question

1. The prescriber ordered phenergan (promethazine HCl) 20 mg IM q6h prn nausea for a child who weighs 45 kg. The recommended dosage of this antiemetic drug is 0.25-0.5 mg/kg q4h-6h prn (max 25mg/dose). The label reads 25mg/ml.

Is the dosage safe?

If the dose is safe, how many milliliters will you administer?

Answer 1

Ordered dose of Phenergan = 20 mg IM q6h

Child weight = 45 kg

Recommended dosage of Phenergan = 0.25 - 0.5 mg/Kg q4h - 6h

Lowest recommended dose of Phenergan= 0.25mg/Kg

Calculation for lowest safe dose :-

By ratio and proportion method :-

0.25 mg : 1 kg : : X mg : 45 kg

X = 45 × 0.25 = 11.25 mg

Highest recommended safe dose of Phenergan = 0.5mg/ Kg

Calculation for highest safe dose of Phenergan :-

By ratio and proportion method :-

0.5 mg : 1 kg :: X mg : 45 kg

X = 0.5 × 45 = 22.5 mg

Yes, the prescribed dose is safe .

Available dose of Phenergan = 25 mg/ ml

By ratio and proportion method :-

25 mg : 1 ml :: 20 mg : X ml

X = 20/25 = 0.8 ml

Hence, 0.8 ml of Phenergan will be administered to the child.