Histergan Tablets

As an antihistamine: Treatment of allergic conditions e.g. hay fever, vasomotor rhinitis, stings, urticaria, angioneurotic oedema, drug sensitivity, contact dermatitis and photosensitivity.

As a sleep aid: As a short term hypnotic.

As an antihistamine:

Adults and Children over 12 years: 1 or 2 tablets three or four times per day. In severe or chronic conditions this may be increased at the discretion of a doctor, but not to exceed 300mg in any 24 hour period.

Paediatric Population:

Not recommended for children under the age of 12.

Elderly: As for adults, use cautiously, reduce dose if required.

As a sleep aid:

Adults: 1 or 2 tablets at bedtime, or after retiring when sleep is not readily achieved

Paediatric Population:

Not recommended for children under the age of 16

Elderly: As for adults, use cautiously, reduce dose if required.

Hypersensitivity to the active substance or to any of the excipients listed in section 6.1.

Contraindicated for use in patients with the following conditions: stenosing peptic ulcer, pyloroduodenal obstruction.

When used as a sleep aid: Sedation of children under the age of 16 should only be under medical direction, consequently use as a sedative in this age group is contraindicated.

Diphenhydramine should be used with caution in patients with myasthenia gravis,epilepsy or seizure disorders, prostatic hypertrophy, urinary retention, narrow-angle glaucoma, asthma, bronchitis and chronic obstructive pulmonary disease (COPD), moderate to severe hepatic impairment and moderate to severe renal impairment.

Tolerance may develop with continuous use. Seek medical advice if sleeplessness persists, as insomnia may be a symptom of a serious underlying medical illness.

May increase the effects of alcohol, therefore alcohol should be avoided. Avoid use of other antihistamine-containing preparations, including topical antihistamines and cough and cold medicines.

Use with caution in the elderly, who are more likely to experience side-effects. Avoid use in elderly patients with confusion.

Patients with rare hereditary problems of fructose intolerance, glucose-galactose malabsorption or sucrase-isomaltase insufficiency should not take this medicine.

Patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption should not take this medicine.

Diphenhydramine may potentiate the sedative effects of alcohol and other CNS depressants (e.g. tranquillizers, hypnotics and anxiolytics).

Monoamine oxidase inhibitors (MAOIs) prolong and intensify the anticholinergic effects of diphenhydramine. The product should be used with caution with MAOIs or within 2 weeks of stopping an MAOI.

As diphenhydramine has some antimuscarinic activity, the effects of some anticholinergic drugs (e.g. atropine, tricyclic antidepressants) may be potentiated therefore medical advice should be sought before taking diphenhydramine with such medicines.

Diphenhydramine is an inhibitor of the cytochrome p450 isoenzyme CYP2D6. Therefore, there may be a potential for interaction with drugs which are primarily metabolised by CYP2D6, such as metoprolol and venlafaxine.

Diphenhydramine should not be used in patients receiving any of the above drugs unless directed by a doctor

Pregnancy

Diphenhydramine crosses the placenta. Because animal reproduction studies are not always predictive of human response and since there is inadequate experience with use of diphenhydramine in pregnant women, the potential risk for humans is unknown. Use of sedating antihistamines during the third trimester may result in reactions in the newborn or premature neonates. This drug is not recommended during pregnancy. Consult a doctor before use.

Lactation

Diphenhydramine has been detected in breast milk, but the effect of this on breastfed infants is unknown. Diphenhydramine is not recommended for use during lactation. Consult a doctor before use.

Diphenhydramine is a hypnotic and will produce drowsiness or sedation soon after the dose has been taken. It may also cause dizziness, blurred vision, cognitive and psychomotor impairment. These can seriously affect the patient's ability to drive and use machines. If affected, do not drive or operate machinery.

Specific estimation of the frequency of adverse events for OTC products is inherently difficult (particularly numerator data). Adverse reactions which have been observed in clinical trials and which are considered to be common (occurring in >1/100 to <1/10) or very common (occurring in >1/10) are listed below by MedDRA System Organ Class. The frequency of other adverse reactions identified during postmarketing use is unknown, but these reactions are likely to be uncommon (occurring in >1/1,000 to <1/100) or rare (occurring in <1/1000).

Reporting of suspected adverse reactions

Reporting suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the Yellow Card Scheme, website: www.mhra.gov.uk/yellowcard or search for MHRA Yellow Card in the Google Play or Apple App Store.

Overdose is likely to result in effects similar to those listed under adverse reactions. Additional symptoms may include mydriasis, fever, flushing, agitation, tremor, dystonic reactions, hallucinations and ECG changes. Large overdose may cause rhabdomyolysis, convulsions, delirium, toxic psychosis, arrhythmias, coma and cardiovascular collapse.

Treatment should be supportive and directed towards specific symptoms. Convulsions and marked CNS stimulation should be treated with parenteral diazepam

Pharmacotherapeutic group: Antihistamines for systemic use – diphenhydramine, ATC Code: R06AA02.

Diphenhydramine is an ethanolamine-derivative anti-histamine with anti-cholinergic (anti-spasmodic), anti-tussive and sedative activity. It acts by inhibiting the effects on H1-receptors.

Diphenhydramine is effective in reducing sleep onset (ie, time to fall asleep) and increasing the depth and quality of sleep.

Diphenhydramine is a histamine H1 receptor antagonist.

The main site of metabolism is the liver.

Absorption

Diphenhydramine hydrochloride is rapidly absorbed following oral administration. Apparently it undergoes first-pass metabolism in the liver and only about 40-60% of an oral dose reaches systematic circulation as unchanged diphenhydramine.

Distribution

Diphenhydramine is rapidly distributed throughout the whole body. Peak plasma concentrations are attained within 1-4 hours. The sedative effect also appears to be maximal within 1-3 hours after administration of a single dose. It is positively correlated with the plasma drug concentration.

Biotransformation

Diphenhydramine is approx 80-85% bound to plasma proteins. Diphenhydramine is rapidly and almost completely metabolised. It is metabolised principally to diphenylmetoxyacetic acid and is also dealkylated. The metabolites are conjugated with glycine and glutamine and excreted in urine. Only about 1% of a single dose is excreted unchanged in urine.

Elimination

The elimination half-life ranges from 2.4-9.3 hours in healthy adults. The terminal elimination half-life is prolonged in liver cirrhosis.

Not applicable.

Lactose, corn starch, povidone, magnesium stearate, Opaseal (polyvinyl acetate phthalate, ethyl acetate and stearic acid), sucrose, calcium carbonate, talc, acacia, titanium dioxide E171, Opalux Pink AS 1537 (E127 erythrosine), Opaglos 6000 (carnauba wax, beeswax), silicone fluid.

Incompatible with barbiturates and iodo compounds in solution.

36 months

Store below 25° C.

Blister packs of 8, 16 and 20 tablets.

None stated