Benylin Multi-Symptom Side Effects
Generic name: diphenhydramine / pseudoephedrine
Medically reviewed by Drugs.com. Last updated on Jun 30, 2022.
Note: This document contains side effect information about diphenhydramine / pseudoephedrine. Some of the dosage forms listed on this page may not apply to the brand name Benylin Multi-Symptom.
Central nervous system (CNS) depression commonly occurs with diphenhydramine administration, resulting in drowsiness and sedation in nearly all patients treated. Motor skills may be impaired. Dystonic reactions have been reported after single doses of diphenhydramine.
Pseudoephedrine produces nervous system stimulation, resulting in tremor, anxiety, and nervousness. Insomnia is reported in up to 30% of pseudoephedrine-treated patients. Headache may also occur in patients receiving pseudoephedrine.[Ref]
The CNS depressant effect of diphenhydramine parallels its plasma concentrations. The plasma concentration threshold for sedation is 30 to 42 ng/mL, and to cause mental impairment is 58 to 74 ng/mL. Patients should be warned against driving while taking diphenhydramine, and should avoid concomitant ingestion of alcohol.
Dystonic reactions to diphenhydramine have been accompanied by dizziness, mental confusion, rigidity, lip and tongue protrusion, trismus, torticollis, and swallowing difficulties. These reactions generally resolve spontaneously. Toxic encephalopathy has been reported in a child with chicken pox treated generously with topical diphenhydramine.
Pseudoephedrine causes vasoconstriction which generally does not produce hypertension, but may be problematic for patients with pre-existing hypertension. Arrhythmias may be produced in predisposed patients. Rarely, pseudoephedrine has been reported to cause coronary artery spasm and chest pain.[Ref]
Cardiovascular adverse effects more commonly may be associated with pseudoephedrine. Pseudoephedrine generally causes a significant rise in heart rate. Hypertension and arrhythmias may be problematic in susceptible patients.[Ref]
Hypersensitivity reactions to pseudoephedrine may also occur. Fixed drug eruptions secondary to pseudoephedrine have been reported.[Ref]
Most commonly, hypersensitivity to diphenhydramine manifests itself in patients receiving systemic drug after being sensitized to it by topical application. Sensitization with systemic administration has also been reported.[Ref]
Gastrointestinal adverse effects of pseudoephedrine may include anorexia and gastric irritation in approximately 5% of patients. Dry mouth, nose, or throat may occur in up to 15% of patients.[Ref]
Ocular affects of diphenhydramine may include blurred vision, diplopia, and dry eyes due to its anticholinergic effect.[Ref]
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