Methapyrilene hydrochloride overdose: MedlinePlus Medical Encyclopedia

P Methapyrilene hydrochloride is an antihistamine that was used in cold or flu medicines in the past. It is not used in these medicines today. Methapyrilene hydrochloride overdose occurs when someone takes more than the normal or recommended amount of this medicine. This can be by accident or on purpose.
P This is for information only and not for use in the treatment or management of an actual overdose. DO NOT use it to treat or manage an actual overdose. If you or someone you are with overdoses, call your local emergency number (such as 911), or your local poison center can be reached directly by calling the national toll-free Poison Help hotline (1-800-222-1222) from anywhere in the United States.

T Poisonous Ingredient
P Methapyrilene hydrochloride can be poisonous in large amounts.

T Where Found
P Methapyrilene hydrochloride is found in older antihistamine medicines. It was removed from the market in 1979 because it was found to cause cancer after long-term use.

T Symptoms
P BLADDER AND KIDNEYS
- Difficulty urinating
P EYES, EARS, NOSE, AND THROAT
- Blurred vision
- Dilated pupils
- Very dry eyes
- Dry mouth
- Ringing in the ears
P HEART AND BLOOD
- Low blood pressure
- Pounding heartbeat (palpitations)
- Rapid heartbeat
P NERVOUS SYSTEM
- Agitation
- Confusion
- Convulsions
- Coma (decreased level of consciousness and lack of responsiveness)
- Delirium
- Depression
- Drowsiness
- Hallucinations (seeing things that aren't there)
- Increased sleepiness
- Nervousness
- Tremor
- Unsteadiness
P SKIN
- Dry skin
- Flushed (red) skin

T Home Care
P Seek medical help right away. Do NOT make the person throw up unless poison control or a health care provider tells you to.

T Before Calling Emergency
P Have this information ready:
- Person's age, weight, and condition
- Name of the medicine (and strength, if known)
- Time it was swallowed
- Amount swallowed
- If the medicine was prescribed for the person

T Poison Control
P Your local poison center can be reached directly by calling the national toll-free Poison Help hotline (1-800-222-1222) from anywhere in the United States. This national hotline number will let you talk to experts in poisoning. They will give you further instructions.
P This is a free and confidential service. All local poison control centers in the United States use this national number. You should call if you have any questions about poisoning or poison prevention. It does NOT need to be an emergency. You can call for any reason, 24 hours a day, 7 days a week.

T What to Expect at the Emergency Room
P Take the container with you to the hospital, if possible.
P The provider will measure and monitor the person's vital signs, including temperature, pulse, breathing rate, and blood pressure. Symptoms will be treated. The person may receive:
- Activated charcoal
- Blood and urine tests
- Breathing support, including tube through the mouth into the lungs and breathing machine (ventilator)
- Chest x-ray
- EKG (electrocardiogram, or heart tracing)
- Fluids through a vein (by IV)
- Laxative
- Medicine to reverse some effects of the drug and to treat symptoms
- Tube from the mouth into the stomach to empty the stomach (gastric lavage)

T Outlook (Prognosis)
P How well someone does depends on the amount of medicine swallowed and how quickly they receive treatment. The faster medical help is given, the better the chance for recovery.
P Recovery is likely if the person survives the first 24 hours. Complications such as pneumonia, muscle damage from lying on a hard surface for a prolonged period of time, or brain damage from lack of oxygen may cause permanent disability. Few people actually die from an antihistamine overdose, unless the overdose causes serious disturbances in heart rhythm or breathing problems.

T References
P Kirk MA, Baer AB. Anticholinergics and antihistamines. In: Shannon MW, Borron SW, Burns MJ, eds. Haddad and Winchester's Clinical Management of Poisoning and Drug Overdose. 4th ed. Philadelphia, PA: Elsevier Saunders; 2007:chap 39.
P Thornton S, Ly BT. Over-the-counter medications. In: Adams JG, ed. Emergency Medicine. 2nd ed. Philadelphia, PA: Elsevier Saunders; 2013:chap 157.
P Velez LI, Feng S-Y. Anticholinergics. In: Marx JA, Hockberger RS, Walls RM, et al, eds. Rosen's Emergency Medicine: Concepts and Clinical Practice. 8th ed. Philadelphia, PA: Elsevier Saunders; 2014:chap 150.

T Review Date 10/14/2015
P Updated by: Jacob L. Heller, MD, MHA, Emergency Medicine, Virginia Mason Medical Center, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

