Onychon (Tablets) Instructions for Use

ATC Code

D01BA02 (Terbinafine)

Active Substance

Terbinafine

Clinical-Pharmacological Group

Antifungal drug

Pharmacotherapeutic Group

Antifungal agent

Pharmacological Action

Antifungal agent, belongs to the group of allylamines, has a broad spectrum of antifungal action. In low concentrations, it exerts a fungicidal effect on dermatophytes Trichophyton spp. ( Trichophyton rubrum, Trichophyton mentagrophytes, Trichophyton tonsurans, Trichophyton verrucosum, Trichophyton violaceum), Microsporum canis, Epidermophyton floccosum, molds (for example, Scopulariopsis brevicaulis), yeast fungi, mainly Candida albicans. On Candida spp. and their mycelial forms, it exerts, depending on the type of fungus, a fungicidal or fungistatic effect.

Terbinafine disrupts the early stage of biosynthesis of the main component of the fungal cell membrane, ergosterol, by inhibiting the enzyme squalene epoxidase.

When used orally, it is not effective in the treatment of pityriasis versicolor caused by Pityrosporum ovale, Pityrosporum orbiculare, Malassezia furfur.

Pharmacokinetics

When taken orally, it is well absorbed; absorption is more than 70%; the absolute bioavailability of terbinafine due to the first-pass effect is approximately 50%. After a single oral dose of 250 mg, its C_max in plasma is reached after 1.5 hours and is 1.3 µg/ml. AUC is 4.56 µg×h/ml; when taken simultaneously with food, AUC increases by 20%. With long-term use, C_max increases by 25%, AUC – by 2.3 times. Binding to plasma proteins is 99%. It is rapidly distributed in tissues, penetrates into the dermal layer of the skin and nail plates. It penetrates into the secretion of the sebaceous glands and accumulates in high concentrations in the hair follicles, hair, skin, and subcutaneous tissue. It undergoes significant metabolism; the resulting metabolites do not have antifungal activity. Excretion by the kidneys is 70%. The effective T_1/2 is 30 hours, the terminal one is 200-400 hours (indicates prolonged excretion from the skin and adipose tissue). Does not accumulate in the body.

Indications

Mycoses of the scalp (trichophytosis, microsporosis); fungal diseases of the skin and nails (onychomycosis) caused by Trichophyton spp. ( T. rubrum, T. mentagrophytes, T. verrucosum, T. violaceum), Microsporum spp. ( M. canis, M. gypseum) and Epidermophyton floccosum; severe, widespread dermatomycosis of the smooth skin of the trunk and extremities requiring systemic treatment; candidiasis of the skin and mucous membranes.

ICD codes

Dosage Regimen

Take tablets orally, with or without food.

Administer the standard adult dose as 250 mg once daily.

For children weighing over 40 kg, use the adult dose of 250 mg once daily.

For children weighing 20 kg to 40 kg, administer 125 mg once daily.

For children weighing less than 20 kg, a dose of 62.5 mg once daily is recommended.

The treatment duration is determined by the infection site and causative pathogen.

For tinea pedis, treat for 2 to 6 weeks.

For tinea corporis or tinea cruris, treat for 2 to 4 weeks.

For onychomycosis of fingernails, a 6-week course is typical.

For onychomycosis of toenails, a 12-week course is standard.

For tinea capitis in children, treat for 4 weeks; duration may be extended based on clinical response.

In patients with severe renal impairment (creatinine clearance <50 ml/min) or pre-existing liver disease, reduce the dose by 50%.

For geriatric patients, use the standard adult dose unless renal or hepatic impairment is present.

Complete the full prescribed course to prevent relapse and ensure mycological cure.

Clinical improvement in onychomycosis becomes apparent only after healthy nail regrowth, which occurs months after treatment cessation.

Adverse Reactions

From the digestive system: often – feeling of fullness in the stomach, nausea, abdominal pain, diarrhea, decreased appetite; in isolated cases ( 0.1-1%) – disturbance of taste sensations, including their loss (recovery occurs within several weeks after cessation of treatment); rarely ( 0.01-0.1%) – hepatotoxic effect (increased activity of liver enzymes, liver failure).

From the CNS often – headache, dizziness.

From the hematopoietic system very rarely ( <0.01%) – neutropenia, agranulocytosis, thrombocytopenia.

From the immune system rarely – anaphylactoid reactions, including angioedema, exacerbation of systemic lupus erythematosus.

From the skin and subcutaneous tissue often – rash, urticaria; very rarely – psoriasis-like skin rashes, exacerbation of psoriasis, Stevens-Johnson syndrome, toxic epidermal necrolysis, hair loss, acute generalized exanthematous pustulosis.

From the musculoskeletal system often – arthralgia, myalgia.

General reactions very rarely – fatigue.

Contraindications

Acute or chronic liver diseases; children under 2 years of age; lactation period; hypersensitivity to terbinafine.

With caution

Pregnancy; renal failure; alcoholism; bone marrow hematopoiesis depression; tumors; metabolic diseases; occlusive vascular diseases of the extremities.

Use in Pregnancy and Lactation

There are no data on the safety of terbinafine use during pregnancy. Therefore, Terbinafine should be used during pregnancy only if the intended benefit to the mother outweighs the potential risk to the fetus.

Terbinafine is excreted in breast milk. Its use during breastfeeding is contraindicated.

Use in Hepatic Impairment

Contraindicated in acute or chronic liver diseases.

Use in Renal Impairment

The drug should be prescribed with caution in renal failure.

Pediatric Use

Contraindicated for use in children under 2 years of age (efficacy and safety have not been established).

Geriatric Use

For elderly patients, the drug is prescribed in the same doses as for adults.

Special Precautions

Irregular use of terbinafine or premature discontinuation of treatment may lead to a relapse of the disease.

The duration of therapy can also be influenced by factors such as the presence of concomitant diseases, the condition of the nails in onychomycosis at the beginning of the treatment course.

If after 2 weeks of treatment of a skin infection there is no improvement in the condition, it is necessary to re-determine the causative agent of the disease and its sensitivity to the drug.

Systemic use for onychomycosis is justified only in case of total damage to most nails, the presence of severe subungual hyperkeratosis, and ineffectiveness of previous local therapy.

In the treatment of onychomycosis, a clinical response, confirmed by laboratory, is usually observed several months after mycological cure and the end of the treatment course, which is due to the rate of regrowth of a healthy nail. Removal of nail plates in the treatment of onychomycosis of the hands for 3 weeks and onychomycosis of the feet for 6 weeks is not required.

In the presence of liver disease, the clearance of terbinafine may be reduced.

During treatment, it is necessary to monitor the indicators of the activity of liver enzymes in the blood serum.

In rare cases, after 3 months of treatment, cholestasis and hepatitis may occur. If signs of impaired liver function appear (weakness, persistent nausea, loss of appetite, excessive abdominal pain, jaundice, dark urine, or discolored stools), the drug should be discontinued.

In severe renal impairment ( creatinine clearance <50 ml/min or blood creatinine >300 µmol/l) and impaired liver function, the dose of terbinafine should be reduced by half.

Use with caution in patients with psoriasis requires caution, because in very rare cases the drug can provoke an exacerbation of psoriasis.

During treatment with terbinafine, general hygiene rules should be observed to prevent the possibility of re-infection through underwear and shoes. During treatment (after 2 weeks) and at the end of it, antifungal treatment of shoes, socks, and stockings should be carried out.

Drug Interactions

Inhibits the isoenzyme CYP2D6 and disrupts the metabolism of drugs such as tricyclic antidepressants and selective serotonin reuptake inhibitors (for example, desipramine, fluvoxamine), beta-blockers (metoprolol, propranolol), antiarrhythmic drugs (flecainide, propafenone), MAO-B inhibitors (for example, selegiline) and antipsychotic drugs (for example, chlorpromazine, haloperidol).

Drugs – inducers of cytochrome P450 isoenzymes (for example, rifampicin) may accelerate the metabolism and excretion of terbinafine from the body. Drugs – inhibitors of cytochrome P450 isoenzymes (for example, cimetidine) may slow down the metabolism and excretion of terbinafine from the body. When using these drugs simultaneously, a dose adjustment of terbinafine may be required.

Violation of the menstrual cycle is possible with the simultaneous use of terbinafine and oral contraceptives.

Terbinafine reduces the clearance of caffeine by 19% and prolongs its T_1/2 by 31%.

Does not affect the clearance of phenazone, digoxin, warfarin.

When used concomitantly with ethanol or drugs that have a hepatotoxic effect, there is a risk of drug-induced liver damage.

Storage Conditions

Store at 2°C (36°F) to 25°C (77°F). Keep in original packaging, protected from light. Keep out of reach of children.

Dispensing Status

Rx Only

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.