Indications
Dimethothiazine (also called fonazine) is an older antihistamine medicine. It is used to relieve allergic conditions such as itchy skin rashes (urticaria), itching from other causes and allergic rhinitis, and it has also been used to help prevent recurrent headaches such as migraine.
How It Works
Dimethothiazine belongs to the phenothiazine family. It blocks histamine (H1) receptors and also blocks serotonin, two natural chemicals involved in allergic reactions, itching and the blood vessel changes linked to some headaches. This reduces itching, swelling, sneezing and headache attacks.
Dosage and Administration
Take by mouth as prescribed by your doctor. The dose is usually divided through the day and adjusted to your response, starting low to reduce drowsiness. Do not take more than prescribed. Children should take it only if a doctor prescribes it.
Interactions
- Alcohol, sleeping tablets, opioid painkillers, other antihistamines and anxiety medicines: increased drowsiness.
- Anticholinergic medicines such as Atropine or tricyclic antidepressants: more dry mouth, constipation and urine retention.
- Blood pressure medicines: may cause a greater fall in blood pressure.
- MAO inhibitors and medicines that prolong the QT interval: avoid unless a doctor advises.
Contraindications
Do not take if you are allergic to Dimethothiazine or other phenothiazines, or if you are in a coma or heavily sedated. Avoid in narrow-angle glaucoma, difficulty passing urine due to an enlarged prostate, and serious liver disease unless a doctor advises.
Side Effects
Common side effects include drowsiness, dizziness, dry mouth, blurred vision, constipation and tiredness. Low blood pressure on standing, stomach upset and skin sensitivity to sunlight can occur.
Get urgent medical help for swelling of the face or throat, difficulty breathing, fainting, an irregular heartbeat, uncontrolled muscle movements or stiffness, high fever with muscle rigidity, yellowing of the skin or eyes, or fever with sore throat.
Pregnancy and Lactation
Safety in pregnancy and breastfeeding has not been established. Use only if a doctor decides it is needed. It may cause drowsiness in a breastfed baby.
Precautions and Warnings
It may make you drowsy: do not drive or use machines until you know how it affects you, and avoid alcohol. Use with caution in older people, and in people with epilepsy, heart disease, liver or kidney problems, or Parkinson’s disease. Protect skin from strong sunlight.
Overdose
Overdose may cause deep sleepiness, confusion, low blood pressure, fast heartbeat, seizures and loss of consciousness, especially in children. Seek emergency medical help.
Therapeutic Class
Phenothiazine antihistamine with antiserotonin activity.
Storage
Store below 30°C in a dry place, away from light and out of the reach of children.
Prepared by the Oshud Alo team from standard drug references. For information only; always follow your doctor's advice.