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Zithromax Side Effects

Zithromax (azithromycin), commonly called Z-Pak, is a macrolide antibacterial drug prescribed to treat a variety of mild to moderate infections. Zithromax has been linked to several serious side effects, including severe or life-threatening allergic reactions, heart problems (including dangerous arrhythmias), drug-induced diarrhea and colitis, and liver failure. The U.S. Food and Drug Administration issued a new Zithromax warning in August 2018. The agency warned of an increased risk of cancer relapse and death in certain patients.

Zithromax (azithromycin) is a prescription antibiotic used to treat a variety of mild to moderate infections in patients, including some respiratory tract and soft-tissue infections. It is often a common antibiotic substitute for patients with a penicillin allergy due to its slightly wider spectrum of microorganisms (bacteria) it can fight against.

But, in clinical studies and postmarketing reports, Zithromax has been linked to several serious side effects, including severe, potentially life-threatening allergic reactions, such as anaphylaxis and various skin disorders.

In 2018, the FDA warned Zithromax could increase relapse risks for certain cancer patients.

Zithromax has also been associated with heart problems, including a prolonged QT interval, that can lead to dangerous irregular heart rhythms that have been shown to sometimes cause sudden cardiac death.

Other serious side effects include antibiotic-associated diarrhea. That is caused by an overgrowth of Clostridium difficile bacteria. It can lead to severe dehydration and metabolic abnormalities, as well as colon problems. Surgery may be required. Zithromax has been reported to result in severe liver impairment and/or liver failure. Some patients have died.

Zithromax can also cause the following serious conditions
  • Infantile hypertrophic pyloric stenosis, an intestinal obstruction in infants
  • Worsening or new onset of myasthenia gravis, a disease that causes muscle weakness
  • Masking or delay of symptoms of gonorrhea or syphilis. Zithromax should not be relied on to treat these sexually transmitted infections
  • Development of drug-resistant bacteria. This risk is greater when prescribed without a proven or strongly suspected indication of bacterial infection

Zithromax and Allergic Reactions

Serious allergic reactions have been reported in patients taking azithromycin, the active ingredient in Zithromax. These reports include fatalities resulting from hypersensitivity reactions to the antibiotic drug.


This reaction to a trigger, such as a medication, results in swelling underneath the skin. Angioedema is similar to urticaria (or hives), except hives occur in the upper dermis, or on the skin’s surface.


This is a severe, potentially life-threatening whole-body allergic reaction that can occur within seconds or minutes of exposure to an allergen, such as Zithromax.

Dermatologic Reactions

This is an allergic reaction that includes skin reactions like Acute Generalized Exanthematous Pustulosis, Stevens-Johnson Syndrome, and Toxic Epidermal Necrolysis.

Skin reactions associated with Zithromax-use include:
Acute Generalized Exanthematous Pustulosis (AGEP)
also known as pustular drug eruption and toxic pustuloderma, this skin reaction is related to the administration of certain medications in about 90 percent of cases, and it is characterized by a sudden skin eruption that appears approximately five days after treatment is started
Stevens-Johnson Syndrome
this is a serious disorder of the skin and mucous membranes that causes blistering and peeling, and is most often the result of a reaction to a medication
Toxic Epidermal Necrolysis
a potentially deadly skin reaction characterized by widespread redness of the skin or mucous membranes (erythema), death of cells in an organ or tissue (necrosis), and blistering and skin peeling that can lead to sepsis (whole-body infection)

Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS)

Some cases of drug reaction with eosinophilia and systemic symptoms (DRESS) have also been reported in patients treated with Zithromax. DRESS causes an influx of infection-fighting white blood cells called eosinophils. This higher-than-normal number of eosinophils can cause inflammation, or swelling, to occur.

Genetic factors play an important role in who is more likely (predisposed) to develop DRESS. A patient’s risk of having the drug reaction may be as high as 25 percent for individuals who have a first degree relative who have experienced the syndrome. Patients with a family member who has had DRESS are more likely to develop the condition themselves.

DRESS may start as a rash that can spread all over the body.

DRESS can also affect the body’s organs, resulting in injury to the liver, kidneys, lungs, heart or pancreas. In about 10 percent of cases, DRESS results in death of the patient, usually due to severe liver damage possibly caused by an infiltration of eosinophils.

Additionally, despite initially successful symptomatic treatment of the allergic symptoms associated with DRESS in some patients, the allergic symptoms recurred soon after symptomatic therapy was stopped, even without further drug exposure. These patients may require long-term observation and treatment.

Other signs and symptoms of the serious condition can include:
  • Fever
  • Swollen lymph nodes
  • Swollen face

Development of Allergic Reactions

Allergic reactions are a common occurrence in many people. A person’s immune response that causes an allergic reaction is similar to the response that causes hay fever, also called allergic rhinitis, which is a type of inflammation in the nose.

Hay fever, which results in cold-like signs and symptoms, including runny nose, itchy eyes, congestion, sneezing and sinus pressure, occurs when a person’s immune system overreacts to allergens in the air. Likewise, an allergic reaction is the immune system’s “overreaction” to a certain substance, called an allergen, that the body becomes exposed to.

Allergens can include:
  • Medicines, such as Zithromax
  • Animal dander
  • Bee stings, or stings or bites from other insects
  • Foods, especially nuts, fish and shellfish
  • Plants, grasses and pollens

Most allergic reactions occur soon (within seconds or minutes) after a person comes into contact with an allergen. These reactions can range from mild to life-threatening. Additionally, first-time exposure may result in a mild reaction, while repeated exposures can lead to much more severe reactions.

Allergic reactions can affect only one part of the body or many parts of the body. The most serious allergic reaction is called anaphylaxis, or anaphylactic shock. This reaction involves the release of histamines in different parts of the body, which can cause the airways to tighten and lead to other symptoms as well. Without emergency medical treatment, anaphylaxis can progress quickly, sometimes resulting in death within just 15 minutes.

While most allergic reactions have very rapid onsets, some can take several hours, or even more than a day in rare instances, to become apparent, especially when the allergen is ingested.

People with a family history of allergies are more likely to experience allergic reactions.

Signs and Symptoms of Allergic Reactions

Signs and symptoms of allergic reactions can vary based on the cause (allergen), the specific reaction, and the part or parts of the body affected. Symptoms can also differ depending on the severity of the allergic reaction.

Common symptoms of a mild allergic reaction include:
  • Hives (urticaria), especially on the neck and face
  • Itching
  • Nasal congestion
  • Rashes, or reddening of the skin
  • Watery, red eyes
Symptoms of a moderate or severe allergic reaction include:
  • Abdominal pain
  • Abnormal, or high-pitched, breathing sounds
  • Anxiety (this symptom can make other symptoms, and the patient’s overall condition, worse)
  • Chest discomfort or tightness
  • Cough
  • Diarrhea
  • Difficulty breathing, or wheezing
  • Difficulty swallowing
  • Dizziness or lightheadedness
  • Flushing or redness of the face
  • Nausea or vomiting
  • Palpitations, or perceived abnormal heart beat characterized by awareness of cardiac muscle contractions in the chest that feel hard, fast and/or irregular
  • Swelling of the face, eyes or tongue
  • Unconsciousness

Treatment of Allergic Reactions

Mild to moderate allergic reactions can be treated by avoiding the allergen and reassuring the person having the reaction in order to relieve anxiety. Over-the-counter medicines, such as hydrocortisone cream and antihistamines, can be used to relieve symptoms associated with allergic reactions, such as itching. Patients should be observed for worsening symptoms and signs of distress.

Severe allergic reactions require immediate emergency medical care.

In cases of severe allergic reactions, it is important to get emergency medical help as soon as possible. Checking the person’s airway, breathing and circulation is a good idea. Warning signs of throat swelling include a very hoarse or whispered voice, or coarse sounds when the person is attempting to breathe in air. Rescue breathing and CPR should be administered when needed.

Emergency allergy medicines can be injected when available. Oral allergy medications should be avoided when the patient is having trouble breathing.

To prevent shock, patients can be helped to lie flat and their feet should be raised about 12 inches. They should also be covered with a coat or blanket. When a person is having trouble breathing, they should not be propped up on a pillow as this position can block the airways.

Zithromax and Cancer Relapse

In August 2018, an FDA safety alert warned that cancer patients should not take Zithromax or other brands of azithromycin. The warning followed clinical trial findings on blood and lymph node cancer patients.

The patients were treated with donor stem cell transplants. The trial found these patients saw higher cancer relapse risks if they took azithromycin long-term.

Cancer patients undergoing this treatment may develop a condition called bronchiolitis obliterans syndrome (BOS). It scars the lungs and causes severe shortness of breath. Patients develop a dry cough.

Doctors sometimes treated BOS with Zithromax or some other azithromycin medicine. But the FDA never approved the drugs for treating BOS.

Pfizer sent out a warning letter to doctors telling them to stop the practice. The FDA warning clarified that doctors should stop using any generics as well.

Zithromax and Heart Problems

In May 2012, a study in the New England Journal of Medicine reported an increase in cardiovascular death in patients treated with azithromycin compared with patients treated with amoxicillin, ciprofloxacin or no drug.

Increased Heart Risk
Patients who take Zithromax may be at an increased risk of developing heart problems that can result in death.

The study was prompted by evidence found in FDA adverse events databases that azithromycin promotes irregular heartbeats. This evidence led study authors to hypothesize that incidences of cardiovascular death may increase for patients on the drug.

Researchers concluded that certain patients were more likely to die while taking azithromycin than patients on other antibiotics or none at all.

Patients at high risk for cardiovascular death include those:
  • With existing QT interval prolongation
  • With low blood levels of potassium or magnesium
  • With a slower than normal heart rate
  • Taking drugs to treat arrhythmias

The risk of death while on azithromycin increased proportionally with the patients’ cardiovascular risk score. The study found 245 deaths per million 5-day courses in patients with the highest risk scores, compared with just nine deaths in patients with the lowest risk scores.

The increased death rate did not continue once patients finished their five-day courses of azithromycin. The increased risk stems from the drug and lasts as long as the drug levels are high in the blood. Following this study, the FDA issued a public statement detailing the study and warning that the Z-Pak may have previously unknown side effects relating to risk of cardiovascular death.

Development of QT Prolongation and Torsades de Pointes (TdP)

Prolonged cardiac repolarization, or the restoration of normal electrical polarity, and QT interval have been seen in patients being treated with macrolides, including azithromycin, the active ingredient in Zithromax. This also carries with it the risk of developing cardiac arrhythmia (irregular heartbeat) and torsades de pointes (TdP), a deadly form of ventricular tachycardia, or a series of rapid heartbeats that start in the lower chambers of the heart (ventricles).

Cases of TdP have been reported during postmarketing surveillance in patients taking Zithromax. Once this serious heart condition develops, few patients will survive it without prompt treatment.

Prolonged QT interval is a disorder of the heart’s electrical activity that occurs between the Q and T waves as seen on an electrocardiogram (EKG). The QT interval shows the electrical activity in the heart’s lower chambers called the ventricles. In people with a prolonged QT interval, the QT interval lasts longer than normal, which can upset the careful timing of a heartbeat and result in dangerous, sometimes deadly, heart rhythms.

TdP is one of the dangerous heart rhythms associated with and often preceded by a prolonged QT interval. Most TdP episodes occur in bursts, and then recur. Sometimes, these episodes cause no symptoms. Other episodes may cause patients to experience palpitations or lightheadedness. Some patients may even faint. When symptoms are present, patients are at an increased risk for sudden cardiac death.

The following statistics were determined regarding sudden cardiac deaths as stated by a medical journal publication republished by the National Institues of Health (NIH):
  • Sudden cardiac deaths are responsible for about 50 percent of all deaths from cardiovascular diseases and 20 percent of deaths overall in the U.S.
  • Sudden cardiac death most often occurs in individuals who are not identified as being at risk in the general population
  • The majority (80 to 85 percent) of sudden cardiac deaths is caused by acute ventricular arrhythmia, most likely resulting from QT prolongation

Zithromax and Clostridium difficile-Associated Diarrhea (CDAD)

Clostridium difficile-associated Diarrhea (CDAD) is a side effect reported with nearly all antibiotics, including Zithromax. It can range in severity from mild diarrhea to fatal colitis, or inflammation of the colon. Treatment with antibacterial agents alters the normal gut flora, or the good and bad bacteria that live in the digestive tract and colon. This can lead to an overgrowth of a certain bacteria called Clostridium difficile, or C. difficile.

Symptoms of CDAD include:
  • Watery diarrhea (at least three bowel movements per day for two or more days)
  • Fever
  • Loss of appetite
  • Nausea
  • Abdominal pain and/or tenderness

About one to two percent of patients affected by antibiotic-associated diarrhea caused by C. difficile bacteria will die.

C. difficile infections result in about 3 million cases of diarrhea and colitis in the U.S. each year, according to the American Academy of Family Physicians. This condition results in death in about 1 to 2.5 percent of those affected. Patients taking antibiotics who are also elderly, suffer from other severe underlying diseases or have faulty immune systems are at an increased risk of developing CDAD.

Treatment Options

Certain hypertoxin-producing strains of C. difficile can cause an increased risk for severe illness, injury and/or death, as these strains may be resistant to traditional treatments, requiring a colectomy, or surgical bowel removal and resection of the colon.

Other Treatments for CDAD include:
  • Appropriate fluid and electrolyte management
  • Protein supplementation
  • Surgical evaluation

If CDAD is suspected or diagnosed in patients, ongoing antibiotic-use should be discontinued, except when the antibiotic therapy is directed at the treatment of C. difficile infection.

Although fever should resolve within the first two days and diarrhea should resolve within two to four days, treatment is typically continued for 10 to 14 days. Failure or success of treatment is not evaluated until at least day five.

In about 20 to 25 percent of patients, C. difficile infection will return. This recurrence is rarely caused by strains resistant to treatment, but rather it is due to C. difficile spores that persist in the colon after treatment or reinfection. Up to 5 percent of patients have more than six recurrences.

Fecal transplants have been shown to be the most effective method for helping patients with repeat C. difficile infections. A fecal transplant involves transplanting stool from a healthy individual to the colon of a patient with recurring C. difficile infections. This procedure may not be widely available, however, and its long-term safety has not been established, according to the Centers for Disease Control and Prevention (CDC).

Zithromax and Liver Injury

Zithromax use has also been linked to severe liver injury called hepatotoxicity, which refers to chemical- (or medication-) driven liver damage. Liver damage associated with the antibiotic drug has sometimes resulted in death.

Conditions of Liver Impairment and/or injury reported in patients include:
  • Abnormal liver function
  • Hepatitis – inflammation of the liver
  • Cholestatic jaundice – yellowing of the skin caused by thickening of bile (waste), obstruction of liver ducts or changes in liver cell function, usually due to toxic effects of a drug
  • Hepatic necrosis – acute, toxic injury to the liver with sudden and severe onset, and early signs of liver failure with little or no jaundice
  • Liver failure

Please seek the advice of a medical professional before making health care decisions.

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Kristin Compton's background is in legal studies. She worked as a paralegal before joining Drugwatch as a writer and researcher. She was also a member of the National Association of Legal Assistants. A mother and longtime patient, she has firsthand experience of the harmful effects prescription drugs can have on women and their children. Some of her qualifications include:

  • Bachelor of Arts in Legal Studies | Pre-Law from University of West Florida
  • Past employment with The Health Law Firm and Kerrigan, Estess, Rankin, McLeod & Thompson LLC
  • Personal experience battling severe food allergies, asthma and high-risk pregnancies
Edited By

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