Legatrin PM Side Effects
Generic Name: acetaminophen / diphenhydramine
Note: This page contains information about the side effects of acetaminophen / diphenhydramine. Some of the dosage forms included on this document may not apply to the brand name Legatrin PM.
For the Consumer
Applies to acetaminophen / diphenhydramine: tablets
Other dosage forms:
Check with your doctor if any of these most COMMON side effects persist or become bothersome:
Seek medical attention right away if any of these SEVERE side effects occur while taking acetaminophen / diphenhydramine:
Constipation; diarrhea; dizziness; drowsiness; dry mouth, nose, or throat; excitability; headache; loss of appetite; nausea; nervousness or anxiety; upset stomach; vomiting; weakness.
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 / diphenhydramine: oral capsule, oral liquid, oral tablet
Nervous system side effects from diphenhydramine have been reported frequently. These have included depression with drowsiness and sedation in nearly all patients treated. Motor skills may be impaired. Dystonic reactions have been reported after single doses of diphenhydramine.[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.
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.[Ref]
Cardiovascular side effects including two cases of hypotension have been reported following the administration of acetaminophen.
Cardiovascular side effects of diphenhydramine have included hypotension, tachycardia, and palpitations.[Ref]
Two cases of 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.[Ref]
Hepatic side effects including severe and sometimes fatal dose dependent hepatitis have been reported in alcoholic patients with the use of acetaminophen. Hepatotoxicity has been increased during fasting. Several cases of hepatotoxicity from chronic acetaminophen therapy at therapeutic doses have also been reported despite a lack of risk factors for toxicity.[Ref]
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.
A 19 year old female developed hepatotoxicity, reactive plasmacytosis and agranulocytosis followed by a leukemoid reaction after acute acetaminophen toxicity.[Ref]
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.[Ref]
Gastrointestinal side effects have been rare with the use of acetaminophen, except in alcoholics and after overdose. Cases of acute pancreatitis have been reported rarely with the use of acetaminophen. In clinical trials of caffeine citrate, five cases of necrotizing enterocolitis were reported among the 46 infants exposed to the caffeine citrate injection.
Gastrointestinal side effects of diphenhydramine have been usually mild and included nausea and dry mouth.[Ref]
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.
A recent 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.[Ref]
Renal side effects have been rare with the use of acetaminophen and have included 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.[Ref]
Hypersensitivity side effects, including anaphylaxis and fixed drug eruptions, have been reported rarely in association with acetaminophen use.
Hypersensitivity side effects to diphenhydramine have included rash, pruritus and eczema. Photosensitivity reactions have also been reported.[Ref]
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.[Ref]
Hematologic side effects including rare cases of thrombocytopenia associated with acetaminophen have been reported. Methemoglobinemia with resulting cyanosis has also been observed in the setting of acute overdose.
Hematologic side effects such as hemolytic anemia, thrombocytopenia, and agranulocytosis have been rarely caused by antihistamines such as diphenhydramine.[Ref]
Dermatologic side effects including erythematous skin rashes associated with acetaminophen have been reported, but are rare. Acetaminophen associated bullous erythema and purpura fulminans have also been reported. Acetaminophen has been associated with a risk of rare but potentially fatal serious skin reactions know as Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and acute generalized exanthematous pustulosis (AGEP).[Ref]
Genitourinary side effects have included urinary retention and dysuria as a result of the anticholinergic effects of diphenhydramine.[Ref]
Respiratory side effects including a case of acetaminophen-induced eosinophilic pneumonia have been reported.[Ref]
1. "Product Information. Tylenol Extra Strength PM (acetaminophen-diphenhydramine)." Johnson and Johnson/Merck Consumer, Fort Washington, PA.
2. Richardson GS, Roehrs TA, Rosenthal L, Koshorek G, Roth T "Tolerance to daytime sedative effects of h1 antihistamines." J Clin Psychopharmacol 22 (2002): 511-5
3. Sexton JD, Pronchik DJ "Diphenhydramine induced psychosis with therapeutic doses." Am J Emerg Med 15 (1997): 548-9
4. Brown G "Acetaminophen-induced hypotension." Heart Lung 25 (1996): 137-40
5. Lee WM "Medical progress: drug-induced hepatotoxicity." N Engl J Med 333 (1995): 1118-27
6. Gursoy M, Haznedaroglu IC, Celik I, Sayinalp N, Ozcebe OI, Dundar SV "Agranulocytosis, plasmacytosis, and thrombocytosis followed by a leukemoid reaction due to acute acetaminophen toxicity." Ann Pharmacother 30 (1996): 762-5
7. Eguia L, Materson BJ "Acetaminophen-related acute renal failure without fulminant liver failure." Pharmacotherapy 17 (1997): 363-70
8. Kawada A, Hiruma M, Noguchi H, Ishibashi A "Fixed drug eruption induced by acetaminophen in a 12-year-old girl." Int J Dermatol 35 (1996): 148-9
9. Halevi A, BenAmitai D, Garty BZ "Toxic epidermal necrolysis associated with acetaminophen ingestion." Ann Pharmacother 34 (2000): 32-4
10. Barranco P, LopezSerrano MC, MorenoAncillo A "Anaphylactic reaction due to diphenhydramine." Allergy 53 (1998): 814
Not all side effects for Legatrin PM may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.
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