Fenistil^® (Emulsion, Drops) Instructions for Use

ATC Code

R06AB03 (Dimetindene)

Active Substance

Dimetindene (Rec.INN registered by WHO)

Clinical-Pharmacological Group

Histamine H₁-receptor blocker. Antiallergic drug

Pharmacotherapeutic Group

Systemic antihistamines; substituted alkylamines

Pharmacological Action

Mechanism of action

Dimetindene is a competitive inhibitor of histamine at H₁-receptors. At low concentrations, it stimulates histamine methyltransferase, leading to the deactivation of histamine. It has a strong affinity for H₁-receptors and is a strong mast cell stabilizer. It has local anesthetic activity. It does not affect H₂-receptors.

Dimetindene also acts as an antagonist of bradykinin, serotonin, and acetylcholine.

Dimetindene is a racemic mixture that includes R-(-)- Dimetindene, which has greater H₁-antihistamine activity; it significantly reduces the increased capillary permeability associated with allergic reactions.

When used in combination with H₂-antihistamine drugs, dimetindene maleate almost completely suppresses all hemodynamic effects of histamine.

Pharmacodynamic effects

Antihistamine, antiallergic, and antipruritic agent.

Dimetindene is an effective agent for the systemic treatment of allergic and pseudoallergic conditions, as well as other diseases associated with the release of histamine (for example, pruritus of various origins, prevention of histamine-related anaphylactic reactions caused by anesthesia or the use of histamine-releasing drugs, or insect bites). The primary response after taking the drug is expected within 30 minutes, the maximum response is expected within 5 hours. The effect of the drug on skin reactions after taking 4 mg of dimetindene as a single dose is expected up to 24 hours after administration.

Pharmacokinetics

Absorption

Rapidly and sufficiently completely absorbed after oral administration.

The systemic bioavailability of the drug is approximately 70%. C_max of dimetindene in blood plasma is reached within 2 hours after administration.

Distribution

At concentrations in the range of 0.09-2 µg/ml, plasma protein binding is 90%.

Metabolism

Metabolic reactions include hydroxylation and methoxylation of dimetindene.

Excretion

T_1/2 is 6 hours. Dimetindene and its metabolites are excreted by the liver or kidneys (90% as a metabolite, 10% unchanged).

Indications

In adults and children aged 1 month and older:

• Allergic diseases (urticaria, hay fever, perennial allergic rhinitis, angioedema, food or drug allergy);
• Skin itching of various origins (eczema, pruritic dermatoses, including atopic dermatitis, itching in measles, rubella, chickenpox, insect bites);
• Prevention of allergic reactions during hyposensitizing therapy.

ICD codes

Dosage Regimen

Emulsion

For external use.

The emulsion is applied 2 to 4 times/day to the affected areas of the skin.

In children from 1 month to 2 years, the drug is used after consultation with a doctor. The maximum duration of use without consulting a doctor is 7 days.

In case of very severe itching or a large area of skin lesion, the possibility of additional use of oral dimetindene maleate preparations should be considered.

Drops

20 drops of the drug = 1 ml of the drug = 1 mg of dimetindene.

Adults and children over 12 years: the recommended daily dose is 3-6 mg (60-120 drops), divided into 3 doses, i.e., 20-40 drops 3 times/day.

For patients prone to drowsiness, it is recommended to prescribe 40 drops at bedtime and 20 drops in the morning.

The recommended dose should not be exceeded.

The maximum duration of use of the drug without consulting a doctor is 7 days.

Children

Fenistil^® drops are contraindicated in children under 1 month of age (see section “Contraindications”).

Children aged 1 month to 12 years are recommended a daily dose based on 0.1 mg/kg of body weight, which is equivalent to 2 drops per kg of body weight. The daily dose must be divided into 3 doses.

In children aged 1 month to 1 year, the drug should be used only as prescribed by a doctor and if there are indications for the use of histamine H₁-receptor blockers.

Elderly patients (over 65 years) – dose adjustment is not required.

Method of administration

For oral administration.

The bottle may have either a regular cap or a cap equipped with a child-resistant closure system. To remove the cap equipped with a child-resistant closure system, press it down and simultaneously turn it according to the picture on the cap.

When prescribed to infants, Fenistil^® drops should be added to a bottle with warm baby food immediately before feeding. If the child is already being fed with a spoon, the drops can be given undiluted. The drops have a pleasant taste.

Adverse Reactions

The frequency of adverse reactions was determined in accordance with the WHO classification: very common (≥1/10), common (≥1/100 but <1/10), uncommon (≥1/1000 but <1/100), rare (≥1/10000 but <1/1000), very rare (<1/10000), frequency unknown (cannot be estimated from the available data).

Contraindications

• Hypersensitivity to dimetindene or to any of the excipients included in the drug;
• Children under 1 month of age, especially in premature patients;
• Breastfeeding period (see section “Pregnancy and Lactation”);
• Closed-angle glaucoma;
• Bronchial asthma;
• Prostatic hyperplasia;
• Use in elderly patients suffering from confusion.

With caution

• Chronic obstructive pulmonary diseases;
• Epilepsy;
• Pregnancy;
• Children aged 1 month to 1 year;
• Elderly age (over 65 years).

Use in Pregnancy and Lactation

Pregnancy

There is insufficient clinical data on the use of dimetindene maleate during pregnancy. Animal studies have not shown direct or indirect adverse effects on the course of pregnancy or the health of the fetus/newborn. The use of the drug during pregnancy is not recommended, except in cases where the benefit to the mother outweighs the potential risk to the fetus and only under medical supervision.

Breastfeeding period

It is assumed that dimetindene maleate may be excreted in breast milk. The drug is contraindicated during breastfeeding.

Fertility

There is insufficient data on the effect of dimetindene maleate on female fertility. No effect of the drug on fertility was observed in animal studies, nevertheless, caution should be exercised when prescribing the drug to patients planning pregnancy.

Pediatric Use

Contraindicated for use in children under 1 month of age. The drug should be used with caution in children from 1 month to 1 year of age because the sedative effect may be accompanied by episodes of nocturnal apnea.

Geriatric Use

For elderly patients (over 65 years), dose adjustment is not required.

Special Precautions

The drug is ineffective for itching associated with cholestasis.

Fenistil^® drops should not be exposed to high temperatures.

The drug should be used with caution in children from 1 month to 1 year of age because the sedative effect may be accompanied by episodes of nocturnal apnea. In this group of patients, the use of the drug is recommended after consultation with a doctor and only for medical indications requiring treatment with antihistamines.

In young children, particularly under 6 years of age, antihistamines can cause increased excitability.

The drug should be used with caution in elderly patients due to an increased likelihood of adverse reactions such as excitability and fatigue. The use of the drug is contraindicated in elderly patients suffering from confusion.

Effect on the ability to drive vehicles and operate machinery

Like other antihistamines, Fenistil^® drops may impair attention, so it should be taken with caution when driving, operating machinery, or performing other tasks that require increased attention.

Overdose

Symptoms CNS depression and drowsiness (mainly in adults), CNS stimulation and m-anticholinergic effects (especially in children and elderly patients), including agitation, ataxia, tachycardia, hallucinations, tonic-clonic convulsions, mydriasis, dry mouth, facial flushing, urinary retention, fever, decreased blood pressure, collapse, and coma.

Treatment activated charcoal and a saline laxative should be prescribed; medications to maintain cardiac and respiratory system activity (analeptic agents should not be used).

Drug Interactions

Concomitant use of two or more drugs that depress CNS function enhances CNS depression, which can lead to undesirable and even life-threatening consequences. Thus, concomitant use of the drug and opioid analgesics, anticonvulsants, tricyclic antidepressants, MAO inhibitors, antihistamines, antiemetics, neuroleptics, anxiolytics, hypnotics, scopolamine, ethanol is not recommended.

Tricyclic antidepressants and m-anticholinergics (bronchodilators, gastrointestinal antispasmodics, mydriatic drops, etc.) increase the antimuscarinic effect, increasing the risk of exacerbation of glaucoma or urinary retention.

It is also necessary to avoid the concomitant use of antihistamines and procarbazine to reduce the effect of CNS function depression and possible potentiation.

Storage Conditions

The drug should be stored in the original packaging, in a place inaccessible to children, at a temperature not exceeding 25°C (77°F).

Shelf Life

Shelf life – 2 years.

Dispensing Status

The drug is available without a prescription.

Important Safety Information

This information is for educational purposes only and does not replace professional medical advice. Always consult your doctor before use. Dosage and side effects may vary. Use only as prescribed.