Side Effects of Phenergan (promethazine)

Phenergan (promethazine) is an antihistamine used to prevent and treat nausea and vomiting related to certain conditions (such as before/after surgery and motion sickness). It is also used to treat allergy symptoms such as

• rash,
• itching, and
• runny nose.

Phenergan may be used to help you feel sleepy/relaxed before and after surgery or to help certain narcotic pain relievers (such as meperidine) work better. It may also be used for a short time to treat a runny nose due to the common cold.

Phenergan works by blocking the histamines the body makes during an allergic reaction. Its other effects (such as anti-nausea, calming, pain relief) may work by affecting other natural substances (such as acetylcholine) and by acting directly on certain parts of the brain. 

Common side effects of Phenergan include

• drowsiness,
• dizziness,
• constipation,
• blurred vision, and
• dry mouth.

Serious side effects of Phenergan include

• fainting,
• slow heartbeat,
• mental/mood changes (such as hallucinations, nervousness, irritability, restlessness, confusion),
• unusual/uncontrolled movements (such as fixed upward stare, neck twisting, tongue movements),
• shaking (tremor),
• difficulty urinating,
• easy bleeding/bruising,
• signs of infection (such as fever, persistent sore throat),
• severe stomach/abdominal pain,
• persistent nausea/vomiting,
• yellowing eyes/skin (jaundice),
• seizures, and
• neuroleptic malignant syndrome (high body temperature, severe extrapyramidal symptoms, changes in consciousness and mental status, and increased heart rate with low or high blood pressure).

Drug interactions of Phenergan include

• antihistamines applied to the skin (such as diphenhydramine cream, ointment, spray) and
• metoclopramide.

The risk of serious side effects (such as slow/shallow breathing, severe drowsiness/dizziness) may be increased if Phenergan is taken with other products that may also affect breathing or cause drowsiness such as

• alcohol,
• drugs for sleep or anxiety,
• muscle relaxants, and
• narcotic pain relievers.

During pregnancy, Phenergan should be used only when clearly needed.

It is unknown if Phenergan passes into breast milk. It may have undesirable effects on a nursing infant. Consult your doctor before breastfeeding.

Promethazine causes side effects such as

• sedation,
• confusion, and
• disorientation.

In children less than two it can depress respiration and lead to death. Therefore, it should not be used in children less than two years old. Dizziness may also occur.

Ironically, promethazine sometimes stimulates patients, particularly children. Such stimulation may be manifest by

• restlessness,
• inability to sleep,
• heart palpitations or
• even seizures.

Other side effects include anticholinergic side effects such as:

• blurred vision,
• dry mouth,
• dilated pupils,
• nausea,
• urinary retention (inability to urinate),
• impotence, and
• constipation.

Extrapyramidal symptoms (EPS) may occur. EPS are categorized as dystonic reactions (alterations in muscle tone), sharp, involuntary muscle movements (often limited to one muscle or muscle group), akathisia (subjective restlessness), and Parkinsonism.

Parkinsonian symptoms are more common in older persons whereas children more often develop involuntary muscle movement reactions. Dystonic reactions are most commonly seen during the first week of treatment. Restlessness and Parkinsonian symptoms usually develop days to weeks after starting therapy.

A serious complex called neuroleptic malignant syndrome (NMS) can occur in patients receiving phenothiazines. NMS consists of

• high body temperature,
• severe EPS,
• changes in consciousness and mental status, and
• increased heart rate with low or high blood pressure.

NMS occurs more frequently in young men and in persons who are dehydrated.

Rarely, blood cell disorders can occur; low white cell counts can lead to infections.

Phenothiazines such as promethazine can cause skin hyperpigmentation (darkening) but usually only after prolonged use. The effect usually is restricted to areas of the body exposed to sunlight. Thus, people who need long-term treatment with promethazine should either keep out of the sun or use effective sunscreens.

Phenothiazines can cause

• blurred vision,
• difficulty with nighttime vision, or
• changes in color vision.

Liver damage has been reported rarely with phenothiazines. Jaundice is possible. Jaundice also may occur in newborns of mothers who receive phenothiazines during pregnancy.

Phenothiazines such as promethazine block dopamine receptors. This effect can lead to increases in blood levels of prolactin, a hormone involved in lactation (formation of breast milk). As a result, phenothiazines can cause the breast to produce fluid ("milk") even when a woman is not pregnant.

Additionally, phenothiazines can cause:

• missed menstrual periods,
• breast enlargement or tenderness,
• loss of sexual drive,
• impotence,
• inability to ejaculate, and
• priapism, and
• weight gain.

Central Nervous System

Drowsiness is the most prominent CNS effect of this drug. Sedation, somnolence, blurred vision, dizziness; confusion, disorientation, and extrapyramidal symptoms such as oculogyric crisis, torticollis, and tongue protrusion; lassitude, tinnitus, incoordination, fatigue, euphoria, nervousness, diplopia, insomnia, tremors, convulsive seizures, excitation, catatonic-like states, hysteria. Hallucinations have also been reported.

Cardiovascular – Increased or decreased blood pressure, tachycardia, bradycardia, faintness.

Dermatologic – Dermatitis, photosensitivity, urticaria.

Hematologic – Leukopenia, thrombocytopenia, thrombocytopenic purpura, agranulocytosis.

Gastrointestinal – Dry mouth, nausea, vomiting, jaundice.

Respiratory – Asthma, nasal stuffiness, respiratory depression (potentially fatal) and apnea (potentially fatal).

Other – Angioneurotic edema. Neuroleptic malignant syndrome (potentially fatal) has also been reported.

Paradoxical Reactions

Hyperexcitability and abnormal movements have been reported in patients following a single administration of promethazine HCl.

Consideration should be given to the discontinuation of promethazine HCl and to the use of other drugs if these reactions occur. Respiratory depression, nightmares, delirium, and agitated behavior have also been reported in some of these patients.

To report suspected adverse reactions, contact Renaissance Pharma, Inc. at 1-866-897-5002 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

CNS Depressants – Phenergan (Promethazine HCl) Suppositories may increase, prolong, or intensify the sedative action of other central-nervous-system depressants, such as

• alcohol,
• sedatives/hypnotics (including barbiturates),
• narcotics,
• narcotic analgesics,
• general anesthetics,
• tricyclic antidepressants, and
• tranquilizers.

Therefore, such agents should be avoided or administered in reduced dosage to patients receiving promethazine HCl. When given concomitantly with Phenergan (Promethazine HCl) Suppositories, the dose of barbiturates should be reduced by at least one-half, and the dose of narcotics should be reduced by one-quarter to one-half.

Dosage must be individualized. Excessive amounts of promethazine HCl relative to a narcotic may lead to restlessness and motor hyperactivity in the patient with pain; these symptoms usually disappear with adequate control of the pain.

Epinephrine – Because of the potential for promethazine HCl to reverse epinephrine's vasopressor effect, epinephrine should NOT be used to treat hypotension associated with Promethazine HCl Suppositories overdose.

Anticholinergics – Concomitant use of other agents with anticholinergic properties should be undertaken with caution.

Monoamine Oxidase Inhibitors (MAOI) – Drug interactions, including an increased incidence of extrapyramidal effects, have been reported when some MAOI and phenothiazines are used concomitantly. This possibility should be considered with Phenergan (Promethazine HCl) Suppositories.

Drug/Laboratory Test Interactions

The following laboratory tests may be affected in patients who are receiving therapy with promethazine HCl:

Pregnancy Tests

Diagnostic pregnancy tests based on immunological reactions between HCG and anti-HCG may result in false-negative or false-positive interpretations.

Glucose Tolerance Test

An increase in blood glucose has been reported in patients receiving promethazine HCl.