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Lamasil

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Lamasil

Lamasil_CS

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Medically reviewed

Marina Burgos

Last updated on 10/01/2026

This page provides general, reference-level information compiled from official medical sources. It is not a substitute for professional medical advice, diagnosis, or treatment. For decisions about your health, please consult a qualified healthcare professional.

Overview of Lamasil

Quick Facts: Terbinafine Entity

Property Description
Active Ingredient Terbinafine (often as hydrochloride salt)
Form Tablet, Cream, Gel, Solution
Pharmacological Class Antifungal Agent (Allylamine)
General Purpose To address fungal overgrowth (Dermatomycoses)
Origin Synthetic Compound

What Type of Medicine is Lamisil (Terbinafine)?

Lamisil is a recognized trade name for a medication whose active ingredient is terbinafine, a powerful synthetic compound used specifically to treat fungal infections. It is fundamentally classified as an antifungal agent or antimycotic, placing it within the specialized pharmacological class of agents targeting microscopic fungi. The core medicinal substance is often formulated as terbinafine hydrochloride, and its unique chemical structure means it belongs to the distinct sub-class of allylamine antifungals, recognized for its action against fungal pathogens. Terbinafine is clinically recognized for its specific mechanism that differentiates it from older antifungals.

Composition and Available Forms of Terbinafine

The medication is a single active ingredient product, comprised solely of terbinafine combined with various non-active bases and excipients. It is available in multiple pharmaceutical preparations designed for different uses. The two primary dosage form(s) are the tablet, which is taken orally for systemic action, and localized preparations such as the cream, gel, or solution (often available over-the-counter), which are applied directly for topical action. The diverse drug forms ensure the delivery of the active substance can be appropriately focused, whether throughout the body or precisely where the infection is located. This class of drugs selectively interferes with the fungal cell membrane synthesis.

The General Purpose of this Antifungal Agent

The overarching general purpose of this medication is to address and halt fungal overgrowth, providing resolution for conditions collectively known as dermatomycoses. For example, it is typically used in cases where a persistent fungal infection resists simpler treatments. It functions by directly interfering with the ability of fungal cells to sustain their structural integrity. This action results in a potent fungicidal action against many pathogens, meaning the drug actively works toward the elimination of the fungus, thereby clearing the infection and restoring a healthy tissue state.

Regulatory References

  1. U.S. National Library of Medicine
  2. MedlinePlus Drug Information

What side effects are possible with Lamasil?

Possible side effects and safety information

Official regulatory documents classify the safety profile of oral terbinafine tablets (Lamisil) across several physiological systems and frequency categories. Adverse reactions are grouped using the System-Organ-Class (SOC) framework, including Hepatobiliary disorders, Nervous System disorders, Skin and subcutaneous tissue disorders, and Gastrointestinal disorders.

Frequency Classification of Adverse Reactions

The majority of documented effects are categorized as Very Common or Common. Very common reactions often include headache, arthralgia (joint pain), myalgia (muscle pain), and various gastrointestinal symptoms such as diarrhea or dyspepsia. Common effects include rash, pruritus (itching), and liver enzyme abnormalities.

Less frequent but documented effects are classified as Rare or Very Rare. These include significant risks related to vital organ systems.

Serious Adverse Reactions

The label documents warnings regarding serious adverse reactions, most notably Hepatotoxicity (liver damage), which can progress to liver failure and has been reported in individuals with and without pre-existing liver disease. Other serious risks include severe Skin Reactions (such as Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis) and Blood Dyscrasias (severe blood disorders like neutropenia).

Safety Constraints and Special Considerations

The medicine is formally contraindicated for use in individuals with active or chronic liver disease. Use is generally not recommended in patients with severe renal impairment. Furthermore, the official labeling notes that neurosensory effects, particularly taste disturbance and smell disturbance, have been documented as potentially prolonged (lasting over one year) or even permanent in some cases. This structured presentation defines the medicine’s established risk profile as required by government regulatory agencies.

Overdose and Emergency Response

Overdose scope

Feature Official Regulatory Statement
Documented overdose presentations Overdose following excessive oral ingestion is primarily associated with manifestations related to the gastrointestinal tract and the central nervous system.
Physiological systems affected (as stated in label) Gastrointestinal system and CNS (e.g., nausea, vomiting, dizziness, headache).
Dose-related or exposure-related factors (if applicable) Manifestations are typically associated with ingestion of excessive oral doses.
Population-specific overdose notes (if applicable) No specific population-based considerations (e.g., pediatric, geriatric) are uniquely identified as official overdose risk factors.
Emergency-response statements (as written in official documents) Management includes symptomatic and supportive treatment. Measures like gastric lavage and activated charcoal may be used.
When immediate medical help is required (label-derived phrasing only) Seek immediate medical attention or contact a Poison Control Center/emergency services immediately.

Overdose classifications (high-level)

Classification Official Regulatory Statement
Severity classification (as defined in official documents) Manifestations are generally documented as extensions of known effects, typically comprising gastrointestinal and neurological symptoms.
Regulatory basis (EMA / FDA / etc.) Information derived from government-authorized prescribing information.
Overdose-context constraints (as defined in official documents) No specific antidote is known or documented. Hospital monitoring may be required based on clinical status.

Resulting overdose structure

Official overdose statements:

  • Ingestion of excessive oral doses is associated with clinical manifestations including nausea, vomiting, abdominal pain, dizziness, and headache.
  • Management of an overdose is primarily symptomatic and supportive treatment.
  • There is no specific antidote documented in official prescribing information for Terbinafine.
  • Patients who have taken an excessive dose must seek immediate medical attention or contact emergency services immediately.

Connection to the overall overdose profile (2–4 sentences): The regulatory documents define the overdose profile based on common, predictable manifestations involving the gastrointestinal and neurological systems following excessive oral ingestion. This profile mandates the emergency-seeking condition: immediate medical assistance is required to manage the symptoms and initiate supportive care. The focus is placed on clinical observation and support until the substance is eliminated, a strategy outlined in official governmental labeling.

Therapeutic Uses of Lamasil

Terbinafine is commonly used to help with fungal infections affecting the skin, hair, and nails, primarily used in conditions associated with dermatophyte infections. Oral tablets are relevant for fungal infections of the toenails and fingernails, as well as tinea capitis (scalp ringworm), and may be applied in addressing widespread skin infections such as tinea corporis (ringworm), tinea cruris (jock itch), and severe tinea pedis (athlete's foot). This medication supports the management of symptom clusters where patients experience intense itching, scaling, and inflammation.

The primary therapeutic benefit is in its role in managing symptoms related to inflammatory or irritative states that often characterize persistent fungal disease. It may assist with the management of symptoms related to cracked or peeling skin and supports the healing process. This approach supports a sense of stability when symptoms are more noticeable.

“This medication is applied across domains where additional symptomatic support is needed, relevant in clinical settings marked by conditions presenting with systemic or localized discomfort, such as those that are deep-seated or affect multiple areas.”

Quick Fact: Management of Cutaneous Symptoms
Common Symptoms: Intense itching, redness, scaling, and skin maceration (softening and breakdown of skin).
Benefit Focus: Helps manage these symptoms that interfere with daily functioning.

Regulatory References

  1. NIH MedlinePlus Drug Information

Eligibility and Restrictions for Use

Who can and cannot use Lamisil?

Official regulatory bodies define specific population rules for the use of oral Lamisil (terbinafine) tablets.

Contraindicated Populations

The medication must not be used (contraindicated) in patients with a history of hypersensitivity or allergic reaction to terbinafine. It is also absolutely contraindicated for patients diagnosed with chronic or active hepatic disease.

Restricted and Conditional Use

Use is not recommended in patients with significant renal impairment (Creatinine Clearance less than 50 mL/min). The oral tablet is also not recommended for women who are pregnant or breastfeeding, as terbinafine is excreted into breast milk. Regulatory documents advise use with caution in individuals with pre-existing autoimmune conditions like Psoriasis or Lupus Erythematosus, due to the potential for exacerbation.

Age Group Eligibility

Adults are the standard labeled population. Geriatric patients may use the medicine, but with caution regarding underlying organ function. Pediatric use is established only for specific indications, and use in children under two years is generally not recommended due to insufficient safety and efficacy data.

What should I know about interactions with other medicines?

Interactions with other medicines and products

Lamisil (terbinafine) tablets can interact with certain other medicinal products, primarily by altering their metabolism in the body. The active substance, terbinafine, is known to be a potent inhibitor of the cytochrome P450 2D6 (CYP2D6) enzyme.

Potential Increase in Other Medicine Levels

Due to CYP2D6 inhibition, Lamisil may increase the concentration or effect of drugs predominantly metabolized by this enzyme. Such interacting medicines include certain tricyclic antidepressants (TCAs), some beta-blockers, selective serotonin reuptake inhibitors (SSRIs), and Class 1C antiarrhythmics (e.g., flecainide, propafenone).

Changes in Lamisil Levels

Lamisil's own clearance can be significantly affected by other drugs that influence CYP450 enzymes. Medicines that inhibit CYP450 enzymes can increase Lamisil levels in the blood, such as cimetidine (increasing concentration by 33%) and fluconazole (increasing exposure by up to 69% via CYP2C9 and CYP3A4 inhibition). Conversely, enzyme inducers like rifampicin can accelerate Lamisil's clearance by 100%, thus reducing its plasma concentration. Dosage adjustments may be necessary when co-administering these agents.

Other Documented Interactions

  • Cyclosporine: Lamisil can increase the clearance of this immunosuppressant.
  • Caffeine: Lamisil decreased the clearance of intravenously administered caffeine by 19%.
  • Oral Contraceptives: Some cases of menstrual irregularities (such as breakthrough bleeding) have been reported with concomitant use, though the incidence is within the background rate for patients using oral contraceptives alone.

Mechanism of Action

Terbinafine, an allylamine antifungal, operates via a selective fungicidal mechanism targeting the core structure of the fungal cell. The mechanism is characterized by two distinct, simultaneous consequences that result in fungal cell death (lysis).

Specific Blockade of Squalene Epoxidase

This mechanism initiates with the enzyme squalene epoxidase within the fungal cell. Terbinafine functions as a non-competitive inhibitor of this enzyme, disrupting the fungal cell's ability to produce ergosterol, the vital sterol component of its cell membrane. This specific blockade initiates the cascade that affects the fungal cell's stability.

Dual Toxicity and Fungal Cell Lysis

By inhibiting the enzyme, the drug causes a dual action: a critical deficiency in ergosterol (weakening the cell membrane) and a massive, toxic accumulation of squalene, the enzyme's unprocessed substrate, inside the fungal cell. This combined toxicity results in irreversible cellular lysis and the physiological elimination of the pathogen.

Selectivity and Mechanistic Constraints

The drug demonstrates selective affinity for the fungal enzyme over the similar mammalian enzyme, which accounts for its targeting specificity. However, this fungicidal mechanism's effectiveness is constrained against certain yeasts, such as those causing Pityriasis Versicolor, where the effect may be fungistatic (growth-inhibiting) rather than fungicidal (cell-death inducing).

Dosage and Administration Information

How to Use Lamisil: Administration Guidelines

Terbinafine, known by the trade name Lamisil, is administered through two primary approved methods: oral for systemic treatment and topical for localized application. The form used—a 250 mg tablet, oral granules, or a topical formulation—is determined by the clinical scenario.

Oral Dosing and Frequency

The standard oral dosing regimen for approved systemic infections in adults is 250 mg taken once daily. This single-dose frequency is maintained for the entire course of therapy, which varies significantly by infection site. For example, treatment typically lasts 6 weeks for fingernail onychomycosis and 12 weeks for toenail onychomycosis. In pediatric cases, a weight-based once-daily dose of oral granules is used, ranging from 125 mg to 250 mg.

Administration Context and Constraints

The oral tablet can be taken with or without food. However, the oral granules must be mixed with a soft, non-acidic food—such as pudding or mashed potatoes—and the mixture must be swallowed immediately without chewing. This requirement is a procedural constraint designed to ensure proper use.

Usage instructions also address population-specific limitations: the oral form is not recommended for patients with pre-existing hepatic impairment or significant renal impairment (creatinine clearance le 50 mL/min). If a dose is missed, it should be taken as soon as remembered, but if it is less than four hours before the next scheduled dose, the missed dose should be skipped entirely to maintain the proper dosing pattern.

Recent Clinical Evidence

Research Evidence / Overview of Studies for Lamasil (Terbinafine)

Evidence Base for Oral Lamisil in Fungal Nail Infections (Onychomycosis)

The most extensive research for oral terbinafine was conducted in studies exploring the clinical management of fungal nail infections, or onychomycosis. Research primarily relied on Randomized Controlled Trials (RCTs), where participants were assigned by chance to receive terbinafine or a comparison treatment. These trials, along with large reviews of multiple studies, examined patient-reported experiences and monitored the clearance of the fungus. Studies included Adults and specific groups such as Older Adults and individuals with Diabetes Mellitus.

Researchers monitored two main outcomes: Mycological Cure (laboratory findings of fungal clearance) and Clinical Cure (visible health of the nail). Findings describe patterns observed in the studies where a frequent shift to a negative culture status was measured in the active arms of the trials. Research in this area often involves extended long-term observation, with follow-up durations extending to over a year, and in some cohorts, up to five years, to monitor for any relapse or return of the fungus.

Evidence Base for Oral Lamisil in Scalp Ringworm (Tinea Capitis)

Research exploring oral terbinafine for tinea capitis, or fungal infection of the scalp, focused primarily on pediatric patients (children). Comparative trials were used to explore outcomes against other established oral treatments. Studies primarily monitored the Complete Cure Rate, which requires both laboratory and visible resolution of symptoms. Research observed that measured outcomes varied in relation to the specific type of fungus causing the infection; for instance, patterns of clearance differed when the infection was caused by Trichophyton species compared to Microsporum species.

Evidence Base for Topical Lamisil in Skin Infections

The topical forms were evaluated in trials assessing short-term or episodic symptom patterns related to common skin infections. Studies monitored the resolution of symptoms like itching (pruritus) and scaling, alongside the measured Mycological Cure. Findings describe patterns observed in the studies related to the rapid initial resolution of skin symptoms. However, studies exploring short-term symptom changes did not evaluate the use of topical treatment alone for more chronic, widespread conditions, such as the moccasin-type of athlete's foot.

Summary of Evidence Gaps and Areas of Uncertainty

The research provides insight into short-term changes but certain areas still require further study. Findings were mixed or heterogeneous regarding the management of tinea capitis caused by certain fungal species. One key area of ongoing research is the study of antifungal resistance. Furthermore, follow-up durations were limited in studies of topical use and for skin infections generally, meaning that the full picture of long-term effects are not fully established for these common conditions.

Key Studies & References

  1. Study Details | NCT00117767 | Terbinafine Compared to Griseofulvin in Children With Tinea Capitis (Example RCT informing pediatric population data)
  2. What is the most effective treatment for tinea pedis (athlete's foot)? (Includes Cochrane data on topical agents and distinction between types)

Frequently Asked Questions (FAQ)

Common questions about Lamasil (FAQ)

Q: Do I need a blood test before taking Lamasil?

Official product information describes the recommendation for a baseline liver function test before starting treatment. This test is intended to assess any pre-existing liver conditions. Periodic monitoring of these function tests is also often recommended, typically within the first 4 to 6 weeks of the treatment course.

Q: Can I stop taking Lamasil once my symptoms go away?

Official guidance emphasizes that the medication should be taken for the full duration prescribed by a healthcare professional. Stopping the medicine early, even if symptoms appear to improve, is associated with a potential risk of the infection recurring or not being entirely eliminated from the body.

Q: Does Lamasil have known interactions with common painkillers like ibuprofen?

Official drug interaction guidelines generally indicate no known major interaction between oral Lamasil and common non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen or other over-the-counter painkillers like paracetamol. Terbinafine is predominantly involved in different metabolic pathways than these medicines.

Q: Why does Lamasil treatment often last several weeks or months?

The extended duration of therapy is based on findings from clinical trials. These studies indicate that this length of time is necessary to ensure the fungus is cleared and to allow for the complete growth of healthy tissue, particularly in the fingernails (6 weeks) or toenails (12 weeks), which grow slowly.

Q: What should I do if I get a rash while using Lamasil?

Official warnings state that if a progressive skin rash or signs of a severe allergic reaction occur, Lamasil treatment is discontinued immediately, and medical attention is sought. These severe skin reactions are listed in regulatory documents as rare or very rare adverse events.

Q: Are there any specific warnings about using Lamasil with alcohol?

There is no known direct interaction listed between Lamasil and alcohol. However, because Lamasil carries a known risk of liver problems (hepatotoxicity), cautionary information suggests limiting or avoiding alcohol consumption to prevent placing added strain on the liver during the course of therapy.

Q: Does taking Lamasil make you more sensitive to the sun?

Official adverse reaction documents list photosensitivity reactions (increased sensitivity to light) as an uncommon or very rare side effect. Due to this possibility, official cautions advise minimizing excessive sun exposure while using this medicine.

Q: What is the shelf life of Lamasil tablets?

The shelf life of the tablets is determined by the manufacturer and is printed as the expiration date on the original container or packaging. Official instructions specify that the medication is generally required to be stored at a controlled room temperature.

Q: Are there restrictions on driving or operating machinery while taking Lamasil?

Official product information notes that Lamasil may cause central nervous system side effects like dizziness or fatigue in some people. The product label recommends avoiding driving or operating machinery if these effects are experienced.

Q: Does Lamasil cause hair loss?

Official post-marketing experience reports list alopecia (hair loss) as a very rare side effect associated with the use of oral terbinafine. This is included in official regulatory summaries detailing the complete range of adverse events.

Q: Does Lamasil have any known drug interactions with antacids?

Studies and regulatory documents indicate that there is no known clinically significant interaction between oral Lamasil and general antacid medications, such as those containing aluminum or magnesium hydroxide. The medicine's absorption is not significantly affected by antacids.

Q: Is there a generic version of Lamasil?

Yes. The active ingredient in Lamasil, terbinafine hydrochloride, is widely available as an FDA-approved generic prescription product. This is confirmed by regulatory product listings and commercial databases.

Q: Does Lamasil affect the immune system?

Official warnings specify caution in patients with pre-existing autoimmune conditions, such as lupus erythematosus or psoriasis, as cases of symptom exacerbation have been reported. Furthermore, very rare cases of severe blood disorders (blood dyscrasias) are noted in official regulatory documents.

Q: Can Lamasil interact with herbal supplements like St. John's Wort?

General drug interaction guidelines indicate that St. John's Wort is known as a potent enzyme inducer. Due to this action, the supplement may accelerate the breakdown of terbinafine in the body, which could potentially reduce the concentration of the medicine and affect its effectiveness, based on theoretical interactions.

How should Lamasil be stored and disposed of?

How to Store and Dispose of Lamisil (Terbinafine)

Official regulatory guidelines define strict conditions for the storage and disposal of Lamisil to maintain its effectiveness and ensure safety.

Storage Requirements

Condition Requirement
Temperature Store at Controlled Room Temperature, typically 20 C to 25 C (68 F to 77 F).
Prohibitions Do not freeze. Avoid excess heat and moisture (e.g., do not store in the bathroom).
Protection Keep the medication in its tightly closed, original container, protected from light.
Child Safety Store all medication out of the sight and reach of children.

Disposal Instructions

Do not dispose of unused or expired Lamisil by flushing it down a toilet or pouring it into a drain. The product must be disposed of according to local environmental requirements due to its potential toxicity to aquatic life. Consult a healthcare professional or local authority for a drug take-back program or recommended disposal procedure.

Attention! Always consult to a doctor or pharmacist before using pills or medicines.

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