Diphenhydramine, commonly known by the brand name Benadryl, is an over-the-counter antihistamine used to relieve allergy symptoms such as sneezing, runny nose, and itching. It is also found in many sleep aids due to its sedative properties. While generally considered safe when used as directed, taking more than the recommended dose can lead to an overdose. A Benadryl overdose can be lethal, underscoring the importance of understanding its risks and recognizing the signs of toxicity.
The Dangers of Benadryl Overdose
An overdose of diphenhydramine can be dangerous and potentially fatal due to its broad effects on the body. At high doses, diphenhydramine primarily acts as an anticholinergic agent, meaning it blocks the action of acetylcholine, a neurotransmitter involved in many bodily functions. This anticholinergic effect can disrupt the central nervous system, leading to severe complications. High doses can cause central nervous system depression, which may manifest as profound drowsiness, confusion, and eventually coma.
Beyond its anticholinergic properties, diphenhydramine can also block sodium and potassium channels in the heart, leading to serious cardiovascular issues. This can result in abnormal heart rhythms, such as a rapid heart rate (tachycardia) or irregular heartbeats, and even lead to QRS widening or QT prolongation on an electrocardiogram. Respiratory depression, where breathing becomes shallow or stops, is another severe risk, particularly when combined with central nervous system effects. For adults, ingestions greater than 1 gram, and especially over 1.5 grams, can result in delirium, psychosis, seizures, coma, and death. For children, fatal cases have been reported with oral doses exceeding 20 mg/kg, and ingestions over 7.5 mg/kg generally require emergency medical evaluation.
Recognizing Overdose Symptoms
Recognizing overdose symptoms is crucial for timely intervention. These symptoms often reflect the drug’s anticholinergic effects and impact on the central nervous system. Common central nervous system effects include excessive drowsiness, confusion, agitation, and disorientation. Individuals may also experience visual or auditory hallucinations, delirium, and in severe cases, seizures or a coma.
Cardiovascular signs are also prominent in an overdose. These can include a rapid heart rate (tachycardia), irregular heartbeats, and potentially low blood pressure. The anticholinergic effects also lead to a specific set of physical symptoms. These include dry mouth, dry eyes, dilated pupils causing blurred vision, and difficulty urinating due to urinary retention. The skin may appear flushed and feel hot due to impaired sweating, and a fever can develop. Less common but serious symptoms can include muscle tremors, unsteadiness, and muscle damage.
What to Do in an Overdose Emergency
Immediate action is important if a Benadryl overdose is suspected. The first step is to call emergency services, such as 911, or the Poison Control Center hotline at 1-800-222-1222. Provide as much information as possible, including the individual’s age, weight, the approximate amount of Benadryl ingested, the time of ingestion, and any symptoms observed. Do not attempt to induce vomiting without guidance from a medical professional, as this can be dangerous and potentially worsen the situation.
While waiting for professional help to arrive, ensure the person has a clear airway and is breathing. If possible, position them safely to prevent injury if they experience seizures or lose consciousness. In a hospital setting, medical interventions for diphenhydramine overdose focus on supportive care. This often includes administering activated charcoal if the ingestion occurred within one to two hours to help prevent further absorption of the drug. Intravenous fluids may be given to support blood pressure and heart function, and medications can be used to manage specific symptoms, such as benzodiazepines for seizures or agitation. Continuous cardiac monitoring is also standard to detect and manage any heart rhythm abnormalities.
Safe Use and Prevention
Preventing Benadryl overdose involves careful adherence to guidelines. Always store diphenhydramine and all other medications in a secure location, out of reach of children and vulnerable individuals. Following the dosage instructions on the product label is crucial; for adults, the typical recommended dose is 25 mg to 50 mg every 4 to 6 hours, not exceeding 300 mg in a 24-hour period. For children aged 6 to 11 years, the recommended dosage is 12.5 mg to 25 mg every 4 to 6 hours, with a maximum of 150 mg per day.
Understanding potential drug interactions is also important, particularly with other sedatives, alcohol, or medications that also have anticholinergic effects. Combining Benadryl with these substances can intensify side effects and increase the risk of toxicity. Benadryl should not be used as a routine sleep aid without consulting a healthcare professional, as tolerance can develop, and its prolonged use is not recommended due to potential side effects and impact on sleep quality.