Histazine

Uses

Histazine Theoclate Tablets are an anti-emetic (anti-sickness drug) which helps to prevent, and treat nausea and vomiting, including travel sickness, and vertigo. Histazine Theoclate contains promethazine which belongs to a group of medicines called phenothiazines. Your doctor may prescribe this medicine for giddiness or light-headedness (vertigo), or for sickness after an operation, and in such cases the tablets should be taken as instructed by your doctor.

Histazine is also used to associated treatment for these conditions: Allergic urticaria, Anaphylaxis, Cough, Dermographism, Motion Sickness, Nasal Congestion, Postoperative pain, Seasonal Allergic Conjunctivitis, Seasonal Allergic Rhinitis, Vasomotor Rhinitis, Acute Allergic Reactions, Dry cough, Perioperative nausea and vomiting, Upper respiratory symptoms, Sedative therapy, Adjunct to anesthesia and analgesia

How Histazine works

Histazine is a an antagonist of histamine H1, post-synaptic mesolimbic dopamine, alpha adrenergic, muscarinic, and NMDA receptors. The antihistamine action is used to treat allergic reactions. Antagonism of muscarinic and NMDA receptors contribute to its use as a sleep aid, as well as for anxiety and tension. Antagonism of histamine H1, muscarinic, and dopamine receptors in the medullary vomiting center make promethazine useful in the treatment of nausea and vomiting.

Dosage

Histazine dosage

To prevent travel sickness on short journeys: Histazine Theoclate should be taken at least one or two hours before travelling. Adults and children aged over 10 years should take one tablet. Children aged 5 to 10 years should be given half a tablet.

To prevent travel sickness on long journeys: Histazine Theoclate should be taken at bedtime each night during the journey, starting the night before you travel. Adults and children aged over 10 years should take one tablet. Children aged 5 to 10 years should be given half a tablet.

To treat travel sickness: Adults and children over 10 years should take one tablet as soon as you feel sick, followed by a second tablet the same evening. Take a third tablet the following evening if necessary. Children aged 5 to 10 years should treated in the same way, but with half a tablet each time.

For sickness and vomiting due to other causes, and for treating vertigo: Adults and children aged over 10 years should take one tablet up to three times a day. Children aged 5 to 10 years should be given half a tablet up to three times a day. Alternatively you should follow the instructions given by your doctor.

Side Effects

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with promethazine. Just because a side effect is stated here does not mean that all people using Histazine Theoclate will experience that or any side effect.

• Drowsiness or feeling tired.
• Dizziness.
• Restlessness.
• Headache.
• Nightmares.
• Blurred vision.
• Difficulty passing urine.
• Dry mouth.
• Confusion.
• Feeling disorientated.
• Unexpected increase in excitability in children.
• Increased sensitivity of the skin to sunlight (photosensitivity). If affected you should avoid sun lamps and direct sunlight while you are taking this medicine.
• Loss of appetite.
• Awareness of your heartbeat (palpitations).
• Abnormal heartbeats (arrhythmias).
• Low blood pressure (hypotension).
• Abnormal movements of the hands, legs, face, neck and tongue, eg tremor, twitching, rigidity (extrapyramidal effects).
• Blood disorders.

Toxicity

The intraperitoneal LD₅₀ in rats is 170mg/kg and in mice is 160mg/kg. The subcutaneous LD₅₀ in rats is 400mg/kg and in mice is 240mg/kg. The oral LD₅₀ in mice is 255mg/kg.

Patients experiencing an overdose of promethazine may present with mild central nervous system and cardiovascular depression, hypotension, respiratory depression, unconciousness, hyperreflexia, hypertonia, ataxia, athetosis, extensor-plantar reflexes, convulsions, dry mouth, flushing, gastrointestinal symptoms, and fixed, dilated pupils. Treat overdoses with symptomatic and supportive treatment, which may include activated charcoal, sodium sulfate, magnesium sulfate, controlled ventilation, diazepam, intravenous fluids, vasopressors, norepinephrine, phenylephrine, anticholinergic antiparkinsonian agents, diphenhydramine, barbiturates, or oxygen.

Precaution

Histazine Theoclate tablets can make some people feel drowsy, dizzy, confused or disorientated and this may reduce your ability to drive or operate machinery safely. Do not drive or operate machinery until you know how this medicine affects you and you are sure it won't affect your performance. If your child is affected in this way they should avoid potentially hazardous activities such as riding bikes. You should not leave your child unattended after giving them this medicine.

Avoid drinking alcohol while taking Histazine Theoclate because this is likely to make the above effects more likely or worse.

Histazine Theoclate tablets may make your skin more sensitive to sunlight than usual, so you should avoid exposing your skin to direct sunlight or sunlamps until you know how your skin reacts. If you can't avoid strong sunlight you should use a sunscreen lotion or make sure your skin is protected with clothing.

This medicine may interfere with some pregnancy tests, causing false negative or false positive results.

If you are due to have any skin prick tests to diagnose allergies you should stop taking Histazine Theoclate at least 72 hours before the tests. This is because antihistamines can prevent or lessen the skin reactions that indicate an allergy, and so can make the test results unreliable.

Interaction

It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start taking Histazine Theoclate. Similarly, check with your doctor or pharmacist before taking any new medicines while taking Histazine Theoclate, to make sure that the combination is safe.

Histazine Theoclate should not be taken by anyone who has taken a type of antidepressant called a monoamine oxidase inhibitor (MAOI), eg phenelzine, tranylcypromine, isocarboxazid, in the previous 14 days.

You are more likely to feel drowsy if you take Histazine Theoclate with any of the following (which can also cause drowsiness):

• alcohol
• antipsychotic medicines, eg chlorpromazine
• barbiturates, eg phenobarbital
• benzodiazepines, eg diazepam, temazepam
• sedating antihistamines, eg chlorphenamine, brompheniramine, hydroxyzine
• sleeping tablets, eg zopiclone
• strong opioid painkillers, eg morphine, codeine, dihydrocodeine, tramadol
• tricyclic antidepressants, eg amitriptyline.

Food Interaction

• Avoid alcohol. Alcohol may increase the sedation caused by promethazine.

Histazine Alcohol interaction

[Moderate] GENERALLY AVOID:

Concurrent use of ethanol and phenothiazines may result in additive CNS depression and psychomotor impairment.

Also, ethanol may precipitate dystonic reactions in patients who are taking phenothiazines.

The two drugs probably act on different sites in the brain, although the exact mechanism of the interaction is not known.

Patients should be advised to avoid alcohol during phenothiazine therapy.

Histazine Drug Interaction

Major: escitalopram, topiramateModerate: zolpidem, diphenhydramine, duloxetine, cyclobenzaprine, pregabalin, acetaminophen / hydrocodone, albuterol, alprazolam, ondansetron, cetirizineUnknown: esomeprazole, pantoprazole, montelukast, levothyroxine, acetaminophen, cyanocobalamin, ascorbic acid, cholecalciferol

Histazine Disease Interaction

Major: acute alcohol intoxication, cardiovascular disease, CNS depression, head injury, antidopaminergic effects 1, asthmaModerate: anticholinergic effects, asthma/COPD, breast cancer, dystonic reactions, hematologic toxicity, liver disease, NMS, parkinsonism, renal dysfunction, seizure disorders, tardive dyskinesia, antidopaminergic effects 2

Volume of Distribution

The volume of distribution of promethazine is approximately 970L or 30L/kg.

Elimination Route

A 25mg dose of intramuscular promethazine reaches a C_max of 22ng/mL. Intravenous promethazine reaches a C_max of 10.0ng/mL, with a T_max of 4-10h, and an AUC of 14,466ng*h/mL. Oral promethazine is only 25% bioavailable due to first pass metabolism. Oral promethazine reaches a C_max of 2.4-18.0ng/mL, with a T_max of 1.5-3h, and an AUC of 11,511ng*h/mL.

Half Life

The elimination half life of promethazine is approximately 12-15h.

Clearance

The intravenous clearance of promethazine is approximately 1.14L/min. The renal clearance of promethazine is 5.9mL/min and the renal clearance of promethazine sulfoxide is 90.4mL/min.

Elimination Route

An intravenous dose of promethazine is 0.64% eliminated in the urine as the unchanged parent drug, 0.02-2.02% in the urine as desmethylpromethazine, 10% in the urine as promethazine sulfoxide.

Pregnancy & Breastfeeding use

If you are pregnant you should not take Histazine Theoclate without consulting your doctor first. Histazine Theoclate should only be used during pregnancy if essential, and only if the expected benefit to the mother outweighs any potential risks to the developing baby. It should not be used during the last two weeks of pregnancy, because if taken during this time it may cause irritability or excitement in the baby after birth. Seek further medical advice from your doctor.

Small amounts of Histazine Theoclate may pass into breast milk. This is not expected to be harmful to a nursing infant with occasional short-term use of Histazine Theoclate, but there is a risk that it may cause drowsiness, irritability or excitement in a newborn baby. If you are breastfeeding you should not take Histazine Theoclate without getting medical advice from your doctor first.

Contraindication

• Children under five years of age.
• People with reduced awareness, slow reactions or extreme drowsiness caused by medicines or illnesses that reduce activity in the central nervous system.
• People who have taken a type of medicine called a monoamine-oxidase inhibitor antidepressant (MAOI) in the past 14 days.
• Children and adolescents who have signs and symptoms suggestive of Reye's syndrome.
• People who are allergic to any ingredients of the tablets.
• Histazine Theoclate tablets contain lactose and should not be taken by people with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption.

Storage Condition

Store between 15-30° C. Protect from light.

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