Terbinafine is a synthetic allylamine antifungal agent that was derived from naftifine through a chemical modification process that occurred in 1979. Terbinafine is an antifungal medication used to treat infections such as ringworm, athlete's foot, jock itch, and fungal nail infections. It belongs to the allylamine class and works by blocking the enzyme squalene epoxidase, which is essential for building fungal cell membranes. This interference ultimately results in the destruction of fungal cells. Terbinafine is particularly effective against dermatophytes—the fungi responsible for these common skin and nail infections—but it does not work against bacterial or viral infections.
BRAND NAMES
Lamisil, Lamisil Once, Lamisil AT, and Terbinex.
Take the tablet once a day with water. No dietary restrictions are required for its consumption. Apply a thin layer of cream, gel, or spray to the affected skin and the surrounding area. Rub in gently.
MECHANISM OF ACTION
Terbinafine, an antifungal from the allylamine class, acts by blocking the enzyme squalene epoxidase, which is essential for the synthesis of ergosterol in fungi. By targeting this pathway, terbinafine achieves a dual fungicidal and fungistatic effect.
PHARMACOKINETICS
Absorption
After oral administration, terbinafine is well absorbed but undergoes significant first-pass metabolism, which reduces its overall bioavailability. It is a highly lipophilic drug that preferentially accumulates in skin, nails, and fat tissue, where it remains for extended periods.
Distribution
At steady state, terbinafine has a mean volume of distribution of 947 liters.
Metabolism
Terbinafine is extensively metabolized in the liver by multiple cytochrome P450 (CYP) enzymes, with the resulting metabolites being inactive and primarily excreted in urine. The drug also strongly inhibits the CYP2D6 enzyme, which can cause significant and prolonged drug interactions.
Excretion
The kidneys excrete approximately 70–80% of an administered terbinafine dose, and the remaining 20% is eliminated in the feces.
PHARMACODYNAMICS
Terbinafine’s pharmacodynamic action results from its ability to inhibit fungal cell membrane synthesis by targeting the enzyme squalene epoxidase early in the ergosterol biosynthesis pathway. This inhibition causes a toxic accumulation of squalene and a reduction in ergosterol levels, disrupting the fungal cell membrane and producing a fungicidal effect that quickly kills fungal cells.
ADMINISTRATION
Terbinafine is an antifungal medication that can be administered orally or topically. The method of administration, dosage, and duration of treatment depend on the type, location, and severity of the fungal infection.
DOSAGE AND STRENGTH
Terbinafine is available in oral and topical forms.
Oral terbinafine is often taken once daily for a specified duration depending on the condition being treated.
Oral granules is typically taken once daily.
DRUG INTERACTIONS
Oral terbinafine tablets interact with numerous other medications because it blocks the enzyme CYP2D6 in the liver, which is responsible for breaking down many drugs. This can lead to increased levels of other medications in the body, raising the risk of side effects. Interactions are less common with topical terbinafine products.
FOOD INTERACTIONS
The key food interactions for oral terbinafine involve caffeine and specific mixing instructions for oral granules. Terbinafine can slow the body's processing of caffeine, so it's best to limit or avoid coffee, tea, and chocolate to prevent side effects like restlessness, headaches, or jitters. Empty the oral granules onto a spoonful of a bland, soft food, like pudding or mashed potatoes, before taking. Swallow the mixture right away without chewing. Do not use acidic or fruit-based foods like applesauce.
CONTRAINDICATIONS
Contraindications for the oral antifungal medication terbinafine include active or chronic liver disease, a history of allergic reaction, and severe kidney impairment. Terbinafine is also generally not recommended during pregnancy or breastfeeding.
SIDE EFFECTS
Gastrointestinal issues.
Headache.
Changes in taste or smell.
Skin rash and itching.
Muscle and joint pain.
Liver problems.
Severe skin reactions.
Blood disorders.
Serious allergic reaction.
Lupus-like syndrome.
Depression.
OVER DOSE
The most common symptoms associated with an overdose of oral terbinafine are related to the stomach and nervous system:
Nausea and vomiting.
Abdominal pain.
Dizziness.
Headache.
Rash.
Frequent urination.
TOXICITY
Terbinafine toxicity primarily concerns the liver and, rarely, the kidneys, blood, and other systems. While the oral antifungal drug is generally well-tolerated, rare instances of severe, and sometimes fatal, liver injury have been reported.
