Doxamil

Indications

Doxylamine is used for short-term relief of occasional difficulty falling asleep in adults. Combined with Pyridoxine (vitamin B6), it is used to treat nausea and vomiting of pregnancy when changes in diet and lifestyle have not helped enough. It is also found in some cold and allergy combination products.

How It Works

Doxylamine is an older (first-generation) antihistamine. It blocks histamine H1 receptors in the brain, which causes drowsiness, and it also has an anticholinergic effect (it blocks the chemical messenger acetylcholine). These actions help with sleep and calm the signals that cause nausea.

Dosage and Administration

• Sleeplessness, adults and children over 12: usually 25 mg about 30 minutes before bed, not more than once a day. Use for short periods only (no more than 2 weeks unless a doctor advises).
• Nausea and vomiting of pregnancy (Doxylamine 10 mg with Pyridoxine 10 mg, delayed-release tablets): usually 2 tablets at bedtime to start. The doctor may increase this up to a maximum of 4 tablets a day. Swallow whole on an empty stomach; do not crush or chew.
• Children under 12: only as prescribed.

Interactions

Alcohol, sleeping pills, sedatives, anxiety medicines, opioid painkillers, other antihistamines and some antidepressants increase drowsiness and can slow breathing. Do not use with monoamine oxidase inhibitors (MAOIs). Other anticholinergic medicines (such as Amitriptyline or Trihexyphenidyl) add to dry mouth, constipation and difficulty passing urine. Check cold and allergy products so you do not take doxylamine twice.

Contraindications

• Allergy to doxylamine, other similar antihistamines or any ingredient of the product.
• Use of an MAOI now or within the last 2 weeks.
• Narrow-angle glaucoma.
• Enlarged prostate with difficulty passing urine, or blockage of the bladder, stomach or bowel.
• Newborn and premature babies.

Side Effects

Common: drowsiness (which may last into the next day), dizziness, dry mouth, constipation, blurred vision, headache and difficulty passing urine. Older people may become confused or unsteady.

Get urgent medical help if you have a fast or irregular heartbeat, severe confusion or hallucinations, fits (seizures), you cannot pass urine, or signs of a serious allergic reaction such as swelling of the face or throat, a widespread rash or difficulty breathing.

Pregnancy and Lactation

The combination with Pyridoxine is widely used for nausea and vomiting of pregnancy under a doctor's care and is considered safe for the baby. Do not use doxylamine as a sleep aid in pregnancy unless a doctor advises it. It passes into breast milk and may make the baby drowsy, irritable or feed poorly, so avoid it while breastfeeding unless the doctor says otherwise.

Precautions and Warnings

Do not drive, operate machinery or do anything that needs alertness until you know how it affects you. Avoid alcohol. Take extra care in older people because of the risk of confusion and falls. Tell your doctor if you have glaucoma, prostate problems, asthma or chronic lung disease, a heart rhythm problem, or liver or kidney disease. If sleeplessness lasts more than 2 weeks, see a doctor rather than continuing.

Overdose

Overdose can cause severe drowsiness, confusion, agitation, widened pupils, hot and dry skin, fever, a fast heartbeat, fits and muscle damage. Children are at special risk. Seek emergency medical help straight away.

Therapeutic Class

Sedating antihistamine (H1 receptor antagonist).

Storage

Store below 30°C in a dry place, away from light and out of the reach of children.