In vitro, terbinafine predominantly acts as a fungicidal agent against a variety of fungal diseases, such as filamentous, dimorphic, and dermatophytes. At the squalene epoxidation site, terbinafine selectively inhibits the formation of fungal ergosterol. The intermediate squalene is quickly accumulated by treated fungal cells [1].

Terbinafine has been shown to be particularly effective against experimental dermatophytosis both when applied topically and when taken orally. Skin temperature in guinea pigs afflicted with fungus decreased significantly during the fourth terbinafine therapy [2].

Absorption, Distribution and Excretion
Oral terbinafine is >70% absorbed but only 40% bioavailable after first pass metabolism, reaching a Cmax of 1µg/mL with a Tmax of 2 hours an an AUC of 4.56µg\*h/mL. Over the course of a week, 1% topical terbinafine's Cmax increases from 949-1049ng/cm2 and the AUC increases from 9694-13,492ng/cm2/h.
Terbinafine is approximately 80% eliminated in urine, while the remainder is eliminated in feces. The unmetabolized parent drug is not present in urine.
A single 250mg oral dose of terbinafine has a volume of distribution at steady state of 947.5L or 16.6L/kg.
A single 250mg oral dose of terbinafine has a clearance of 76L/h or 1.11L/h/kg.

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Metabolism / Metabolites
Terbinafine can be deaminated to 1-naphthaldehyde by CYP2C9, 2B6, 2C8, 1A2, 3A4, and 2C19. 1-naphthaldehyde is then oxidized to 1-naphthoic acid or reduced to 1-naphthalenemethanol. Terbinafine can also be hydroxylated by CYP1A2, 2C9, 2C8, 2B6, and 2C19 to hydroxyterbinafine. Hydroxyterbinafine is then oxidized to carboxyterbinafine or N-demethylated by CYP3A4, 2B6, 1A2, 2C9, 2C8, and 2C19 to desmethylhydroxyterbinafine. Terbinafine can be N-demethylated to desmethylterbinafine. Desmethylterbinafine is then dihydroxylated to a desmethyldihydrodiol or hydroxylated to desmethylhydroxyterbinafine. Finally, terbinafine can be dihydroxylated to a dihydrodiol which is then N-demethylated to a desmethyldihydrodiol.
Terbinafine has known human metabolites that include Hydroxyterbinafine, N-Desmethylterbinafine, and 1-Naphtaldehyde.

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Biological Half-Life
Oral terbinafine has an effective half life of approximately 36 hours. However, the terminal half life ranges from 200-400 hours as it distributes into skin and adipose tissue. 1% topical terbinafine's half life increases over the first seven days from approximately 10-40 hours.

Hepatotoxicity
Drug induced liver injury due to terbinafine was identified shortly after its introduction into medical use. Oral therapy with terbinafine is associated with elevations in serum aminotransferases in less than 1% of patients and the elevations are generally asymptomatic and resolve without stopping therapy. The estimated probability of developing elevated serum aminotransferase levels requiring stopping treatment is about 0.31% for 2 to 6 weeks' treatment and 0.44% for treatment longer than 8 weeks.
Clinically apparent liver injury from terbinafine occurs rarely (1 in 50,000 to 120,000 prescriptions), but many case reports and even case series have been described in the literature. Liver injury usually arises within the first 6 weeks of therapy. The pattern of injury can be either hepatocellular or cholestatic initially, but typically evolves into a cholestatic pattern which can be prolonged (Cases 1 and 2). Some cases may progress to vanishing bile duct syndrome. Signs of hypersensitivity (rash, fever, eosinophilia) are not common and, when present, are generally mild-to-moderate in severity. Autoantibody formation is rare. In addition, cases with severe hepatocellular injury with acute liver failure have been described. These instances are marked by precipitous onset with marked elevations in serum aminotransferase levels and progressive jaundice and hepatic failure. Terbinafine has also been implicated in cases of Stevens-Johnson syndrome, in which case the hepatic injury may be overshadowed by rash and allergic symptoms.
Likelihood score: B (highly likely cause of clinically apparent liver injury).

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Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
Limited information indicates that oral maternal doses of 500 mg daily produce low levels in milk and would not be expected to cause any adverse effects in breastfed infants, especially if the infant is older than 2 months. Monitor the infant for jaundice or other signs of liver toxicity, especially in younger, exclusively breastfed infants. Some sources recommend avoiding oral terbinafine during nursing.
Topical terbinafine has not been studied during breastfeeding. Because only about 1% is absorbed after topical application, it is considered a low risk to the nursing infant. Avoid application to the nipple area and ensure that the infant's skin does not come into direct contact with the areas of skin that have been treated. Only water-miscible cream, gel or liquid products should be applied to the breast because ointments may expose the infant to high levels of mineral paraffins via licking.
◉ Effects in Breastfed Infants
Relevant published information was not found as of the revision date.
◉ Effects on Lactation and Breastmilk
Relevant published information was not found as of the revision date.

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Protein Binding
Terbinafine is >99% bound to proteins in plasma, mostly to serum albumin, high and low density lipoproteins, and alpha-1-acid glycoprotein to a lesser extent.

[1]. Terbinafine: mode of action and properties of the squalene epoxidase inhibition. Br J Dermatol. 1992 Feb;126 Suppl 39:2-7.

[2]. Preclinical evaluation of terbinafine in vivo. Clin Exp Dermatol. 1989 Mar;14(2):104-7.

[3]. Mupirocin vs terbinafine in impetigo.Indian J Pediatr. 2002 Aug;69(8):679-82.

Terbinafine is a tertiary amine that is N-methyl-1-naphthalenemethylamine in which the amino hydrogen is replaced by a 3-(tertbutylethynyl)allyl group. An antifungal agent administered orally (generally as the hydrochloride salt) for the treatment of skin and nail infections. It has a role as an EC 1.14.13.132 (squalene monooxygenase) inhibitor, a P450 inhibitor and a sterol biosynthesis inhibitor. It is a tertiary amine, an acetylenic compound, a member of naphthalenes, an enyne and an allylamine antifungal drug. It is a conjugate base of a terbinafine(1+).
Terbinafine hydrochloride (Lamisil) is a synthetic allylamine antifungal. It is highly lipophilic in nature and tends to accumulate in skin, nails, and fatty tissues. Like other allylamines, terbinafine inhibits ergosterol synthesis by inhibiting the fungal squalene monooxygenase (also called squalene epoxidase), an enzyme that is part of the fungal cell wall synthesis pathway. Terbinafine hydrochloride was granted FDA approval on 30 December 1992.
Terbinafine is an Allylamine Antifungal.
Terbinafine is an orally and topically active allylamine fungicidal agent which is used to treat superficial fungal infections of the skin and nails. Terbinafine has been clearly linked to rare instances of acute liver injury that can be severe and sometimes fatal.
Terbinafine is a synthetic allylamine derivative with antifungal activity. Terbinafine exerts its effect through inhibition of squalene epoxidase, thereby blocking the biosynthesis of ergosterol, an important component of fungal cell membranes. As a result, this agent disrupts fungal cell membrane synthesis and inhibits fungal growth.
A naphthalene derivative that inhibits fungal SQUALENE EPOXIDASE and is used to treat DERMATOMYCOSES of the skin and nails.
See also: Terbinafine Hydrochloride (active moiety of); Betamethasone Acetate; Florfenicol; Terbinafine (component of); Florfenicol; Mometasone furoate; Terbinafine (component of) ... View More ...

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Drug Indication
Terbinafine hydrochloride is indicated to treat fungal skin and nail infections caused by _Trichophyton_ species, _Microsporum canis_, _Epidermophyton floccosum_, and _Tinea_ species. Terbinafine hydrochloride also treats yeast infections of the skin caused by _Candida_ species and _Malassezia furfur_.
FDA Label

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Mechanism of Action
Terbinafine inhibits the enzyme squalene monooxygenase (also called squalene epoxidase), preventing the conversion of squalene to 2,3-oxydosqualene, a step in the synthesis of ergosterol. This inhibition leads to decreased ergosterol, which would normally be incorporated into the cell wall, and accumulation of squalene. Generation of a large number of squalene containing vesicles in the cytoplasm may leach other lipids away from, and further weaken, the cell wall.

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Pharmacodynamics
Terbinafine is an allylamine antifungal that inhibits squalene epoxidase (also known as squalene monooxygenase) to prevent the formation of ergosterol and cause an accumulation of squalene, weakening the cell wall of fungal cells. Terbinafine distributes into tissues and has a long terminal elimination half life, so the duration of action is long. Overdose with terbinafine is rare, even above the therapeutic dose, so the therapeutic index is wide. Patients taking oral terbinafine should have liver function tests performed prior to treatment to reduce the risk of liver injury.

C21H25N

291.4299

291.198

91161-71-6

Terbinafine hydrochloride;78628-80-5;Terbinafine-d3 hydrochloride;1310012-15-7;Terbinafine-d7;1185240-27-0;Terbinafine lactate;335276-86-3

1549008

White to yellow solid powder

1.0±0.1 g/cm3

417.9±33.0 °C at 760 mmHg

183.7±22.3 °C

0.0±1.0 mmHg at 25°C

1.586

6.61

0

1

5

22

428

0

CC(C)(C)C#C/C=C/CN(C)CC1=CC=CC2=CC=CC=C21

DOMXUEMWDBAQBQ-WEVVVXLNSA-N

InChI=1S/C21H25N/c1-21(2,3)15-8-5-9-16-22(4)17-19-13-10-12-18-11-6-7-14-20(18)19/h5-7,9-14H,16-17H2,1-4H3/b9-5+

(E)-N,6,6-trimethyl-N-(naphthalen-1-ylmethyl)hept-2-en-4-yn-1-amine

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : ≥ 100 mg/mL (~343.14 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (8.58 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: 2.5 mg/mL (8.58 mM) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), suspension solution; with ultrasonication.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: 2.5 mg/mL (8.58 mM) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution; with ultrasonication.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 4: 16.25 mg/mL (55.76 mM) in 0.5% CMC-Na/saline water (add these co-solvents sequentially from left to right, and one by one), suspension solution; with ultrasonication.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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 (Please use freshly prepared in vivo formulations for optimal results.)