DIPHENHYDRAMINE (BENADRYL)

Class

Antihistamine

Pharmacology and Actions

1. An antihistamine that blocks action of histamine released from the cells during an allergic reaction.
2. Direct CNS effects, which may be a stimulant or, more commonly, a depressant, depending on individual variation.
3. Anticholinergic, antiparkinsonian effect, which is used to treat acute dystonic reactions to antipsychotic drugs (Haldol,  Thorazine, Compazine, etc.). These reactions include oculogyric crisis, acute torticollis, and facial grimacing.

Indications

1. Moderate allergic reaction.
2. The second-line drug in anaphylaxis and severe allergic reactions (after epinephrine).
3. To prevent or counteract extrapyramidal reactions from antipsychotic medications.
4. For use in intractable vomiting.

Contraindications

1. Asthma (relative)
2. Nursing mothers

Precautions

1. May have additive effect with alcohol or depressants.

Administration

1. Adult: 25 mg slow IV/IO push or 50 mg IM
2. Children 8 years and younger: 1 mg/kg slow IV (not to exceed 25 mg total).

Side Effects and Special Notes

1. May cause CNS stimulation in children.
2. Side effects include dry mouth, dilated pupils, flushing, and drowsiness.
3. Diphenhydramine should be used with caution in patients with asthma/COPD, glaucoma, and bladder obstruction, as all of these conditions can be exacerbated by its administration.
4. If an IV has been or will be established for other reasons, the IV route is preferred over the IM route.