Acetaminophen / dextromethorphan / diphenhydramine Side Effects

Not all side effects for acetaminophen / dextromethorphan / diphenhydramine may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

For the Consumer

Applies to acetaminophen / dextromethorphan / diphenhydramine: liquid

Check with your doctor if any of these most COMMON side effects persist or become bothersome:

Constipation; diarrhea; dizziness; drowsiness; dry mouth, nose, or throat; excitability (especially in children); headache; loss of appetite; nausea; nervousness or anxiety; upset stomach; vomiting; weakness.

Seek medical attention right away if any of these SEVERE side effects occur while taking acetaminophen / dextromethorphan / diphenhydramine:

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); dark urine or pale stools; difficulty urinating or inability to urinate; fast or irregular heartbeat; hallucinations; seizures; severe dizziness, drowsiness, lightheadedness, or headache; severe or persistent loss of appetite; stomach pain; tremor; trouble sleeping; unusual fatigue; vision changes; yellowing of the skin or eyes.

For Healthcare Professionals

Applies to acetaminophen / dextromethorphan / diphenhydramine: oral liquid

Cardiovascular

Two cases hypotension have been reported following the administration of acetaminophen. Both patients experienced significant decreases in blood pressure. One of the two patients required pressor agents to maintain adequate mean arterial pressures. Neither episode was associated with symptoms of anaphylaxis. Neither patient was rechallenged after resolution of the initial episode.

Cardiovascular side effects of acetaminophen have included two cases of hypotension.

Cardiovascular side effects of diphenhydramine have included hypotension, tachycardia, and palpitations.

Gastrointestinal

Gastrointestinal side effects of diphenhydramine have been usually mild and included nausea and dry mouth.

Gastrointestinal side effects of dextromethorphan have included stomach upset.

Genitourinary

Genitourinary side effects of diphenhydramine have included urinary retention and dysuria as a result of the anticholinergic effects of diphenhydramine.

Hematologic

Hematologic side effects of acetaminophen have included rare cases of thrombocytopenia. Methemoglobinemia with resulting cyanosis has also been observed in the setting of acute overdose.

Hematologic side effects of diphenhydramine have included rare reports of hemolytic anemia, thrombocytopenia, and agranulocytosis.

Hypersensitivity

Most commonly, hypersensitivity to diphenhydramine has manifested itself in patients receiving systemic drug after being sensitized to it by topical application. Sensitization with systemic administration has also been reported.

Hypersensitivity side effects of diphenhydramine have included rash, pruritus and eczema. Photosensitivity reactions have also been reported.

Hypersensitivity side effects of dextromethorphan have included rare reports of fixed-drug eruptions.

Nervous system

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. Dystonic reactions have been accompanied by dizziness, mental confusion, rigidity, lip and tongue protrusion, trismus, torticollis, and swallowing difficulties and generally resolve spontaneously. Toxic encephalopathy has been reported in a child with chicken pox treated generously with topical diphenhydramine. Delirium has been reported in elderly patients with mild dementia following a small oral dose of diphenhydramine.

Nervous system side effects of diphenhydramine have included frequent reports of depression with drowsiness and sedation. Motor skills may be impaired. Dystonic reactions have been reported after single doses of diphenhydramine.

Nervous system side effects of dextromethorphan have included drowsiness and dizziness. Other side effects such as excitation, mental confusion, and opioid like respiratory depression have been rare and occurred at higher dosages. In some cases of abuse, patients experienced euphoria, hyperactivity, mania, and auditory and visual hallucinations.

Ocular

Ocular side effects of diphenhydramine have included blurred vision, diplopia, and dry eyes due to anticholinergic effects.

Dermatologic

Dermatologic side effects acetaminophen have included rare reports of erythematous skin rashes. Acetaminophen associated bullous erythema and purpura fulminans have been reported. One case of toxic epidermal necrolysis associated with acetaminophen administered to a pediatric patient has been reported. Acetaminophen has been associated with a risk of rare but potentially fatal serious skin reactions known as Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and acute generalized exanthematous pustulosis (AGEP).

Hepatic

Alcoholic patients may develop hepatotoxicity after even modest doses of acetaminophen. In healthy patients, approximately 15 grams of acetaminophen is necessary to deplete liver glutathione stores by 70% in a 70 kg person. However, hepatotoxicity has been reported following smaller doses. Glutathione concentrations may be repleted by the antidote N-acetylcysteine. One case report has suggested that hypothermia may also be beneficial in decreasing liver damage during overdose.

In a recent retrospective study of 306 patients admitted for acetaminophen overdose, 6.9% had severe liver injury but all recovered. None of the 306 patients died.

One study has suggested that acetaminophen may precipitate acute biliary pain and cholestasis. The mechanism of this effect may be related to inhibition of prostaglandin and alterations in the regulation of the sphincter of Oddi.

Cases of acute pancreatitis have been reported rarely.

A 19-year-old female developed hepatotoxicity, reactive plasmacytosis and agranulocytosis followed by a leukemoid reaction after acute acetaminophen toxicity.

Hepatic side effects of acetaminophen have included severe and sometimes fatal dose dependent hepatitis in alcoholic patients. Hepatotoxicity has been increased during fasting.

Renal

Renal side effects of acetaminophen have included rare reports of acute renal failure, acute tubular necrosis, and interstitial nephritis. Adverse renal effects are most often observed after overdose, after chronic abuse (often with multiple analgesics), or in association with acetaminophen-related hepatotoxicity.

Acute tubular necrosis usually occurs in conjunction with liver failure, but has been observed as an isolated finding in rare cases. A possible increase in the risk of renal cell carcinoma has been associated with chronic acetaminophen use as well.

One case-control study of patients with end-stage renal disease suggested that long term consumption of acetaminophen may significantly increase the risk of end-stage renal disease particularly in patients taking more than two pills per day.

However, a recent cohort study of analgesia use of initially healthy men concluded that moderate use of analgesics including acetaminophen was not associated with increased risk of renal disease.

Metabolic

Metabolic side effects of acetaminophen have included metabolic acidosis following a massive overdose of acetaminophen.

In the case of metabolic acidosis, causality is uncertain as more than one drug was ingested. The case of metabolic acidosis followed the ingestion of 75 grams of acetaminophen, 1.95 grams of aspirin, and a small amount of a liquid household cleaner The patient also had a history of seizures which the authors reported may have contributed to an increased lactate level indicative of metabolic acidosis.

Respiratory

Respiratory side effects of acetaminophen have included a case of eosinophilic pneumonia.

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