Terbinafine Actions

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Actions of Terbinafine in details

The action of the drug on the human body is called Pharmacodynamics in Medical terminology. To produce its effect and to change the pathological process that is happening the body and to reduce the symptom or cure the disease, the medicine has to function in a specific way. The changes it does to the body at cellular level gives the desired result of treating a disease. Drugs act by stimulating or inhibiting a receptor or an enzyme or a protein most of the times. Medications are produced in such a way that the ingredients target the specific site and bring about chemical changes in the body that can stop or reverse the chemical reaction which is causing the disease.
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Terbinafine is hypothesized to act by inhibiting squalene monooxygenase, thus blocking the biosynthesis of ergosterol, an essential component of fungal cell membranes. This inhibition also results in an accumulation of squalene, which is a substrate catalyzed to 2,3-oxydo squalene by squalene monooxygenase. The resultant high concentration of squalene and decreased amount of ergosterol are both thought to contribute to Terbinafine's antifungal activity.

How should I take Terbinafine?

Apply enough Terbinafine cream to cover the affected and surrounding skin areas and rub in gently.

Apply enough Terbinafine solution to wet and cover the affected and surrounding skin areas. Allow it to dry.

Keep Terbinafine away from the eyes, nose, mouth, and other mucous membranes. The solution may be especially irritating to the eyes.

Terbinafine spray solution contains alcohol and should not be applied to the face.

Do not apply an occlusive dressing (airtight covering, such as a tight bandage or plastic kitchen wrap) over Terbinafine unless you have been directed to do so by your doctor.

Dosing

The dose of Terbinafine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of Terbinafine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

To help clear up your infection completely, it is very important that you keep using Terbinafine for the full time of treatment, even if your symptoms begin to clear up after a few days. Since fungus infections may be very slow to clear up, you may have to continue using Terbinafine every day for several weeks or more. If you stop using Terbinafine too soon, your symptoms may return. Do not miss any doses.

Missed Dose

If you miss a dose of Terbinafine, apply it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule.

Storage

Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.

Keep out of the reach of children.

Do not keep outdated medicine or medicine no longer needed.

Terbinafine administration

Administration of drug is important to know because the drug absorption and action varies depending on the route and time of administration of the drug. A medicine is prescribed before meals or after meals or along with meals. The specific timing of the drug intake about food is to increase its absorption and thus its efficacy. Few work well when taken in empty stomach and few medications need to be taken 1 or 2 hrs after the meal. A drug can be in the form of a tablet, a capsule which is the oral route of administration and the same can be in IV form which is used in specific cases. Other forms of drug administration can be a suppository in anal route or an inhalation route.
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Administer tablets without regard to meals. Administer granules with food; sprinkle granules on a spoonful of pudding or other soft, nonacidic food (eg, mashed potatoes); swallow entire spoonful without chewing; do not mix granules with applesauce or other fruit-based foods.

Terbinafine pharmacology

Pharmacokinetics of a drug can be defined as what body does to the drug after it is taken. The therapeutic result of the medicine depends upon the Pharmacokinetics of the drug. It deals with the time taken for the drug to be absorbed, metabolized, the process and chemical reactions involved in metabolism and about the excretion of the drug. All these factors are essential to deciding on the efficacy of the drug. Based on these pharmacokinetic principles, the ingredients, the Pharmaceutical company decides dose and route of administration. The concentration of the drug at the site of action which is proportional to therapeutic result inside the body depends on various pharmacokinetic reactions that occur in the body.

Mechanism of Action

Terbinafine is an allylamine antifungal.

Pharmacodynamics

The pharmacodynamics of Terbinafine tablets is unknown.

Pharmacokinetics

Following oral administration, Terbinafine is well absorbed (>70%) and the bioavailability of Terbinafine tablets as a result of first-pass metabolism is approximately 40%. Peak plasma concentrations of 1 mcg/mL appear within 2 hours after a single 250 mg dose; the AUC is approximately 4.56 mcg•h/mL. An increase in the AUC of Terbinafine of less than 20% is observed when Terbinafine tablets are administered with food.

In plasma, Terbinafine is >99% bound to plasma proteins and there are no specific binding sites. At steady-state, in comparison to a single dose, the peak concentration of Terbinafine is 25% higher and plasma AUC increases by a factor of 2.5; the increase in plasma AUC is consistent with an effective half-life of ~36 hours. Terbinafine is distributed to the sebum and skin. A terminal half-life of 200 to 400 hours may represent the slow elimination of Terbinafine from tissues such as skin and adipose. Prior to excretion, Terbinafine is extensively metabolized by at least 7 CYP isoenzymes with major contributions from CYP2C9, CYP1A2, CYP3A4, CYP2C8, and CYP2C19. No metabolites have been identified that have antifungal activity similar to Terbinafine. Approximately 70% of the administered dose is eliminated in the urine. In patients with renal impairment (creatinine clearance ≤50 mL/min) or hepatic cirrhosis, the clearance of Terbinafine is decreased by approximately 50% compared to normal volunteers. No effect of gender on the blood levels of Terbinafine was detected in clinical trials. No clinically relevant age-dependent changes in steady-state plasma concentrations of Terbinafine have been reported.

Microbiology

Terbinafine, an allylamine antifungal, inhibits biosynthesis of ergosterol, an essential component of fungal cell membrane, via inhibition of squalene epoxidase enzyme. This results in fungal cell death primarily due to the increased membrane permeability mediated by the accumulation of high concentrations of squalene but not due to ergosterol deficiency. Depending on the concentration of the drug and the fungal species test in vitro, Terbinafine may be fungicidal. However, the clinical significance of in vitro data is unknown.

Terbinafine has been shown to be active against most strains of the following microorganisms both in vitro and in clinical infections:

Trichophyton mentagrophytes

Trichophyton rubrum

The following in vitro data are available, but their clinical significance is unknown. In vitro, Terbinafine exhibits satisfactory MIC’s against most strains of the following microorganisms; however, the safety and efficacy of Terbinafine in treating clinical infections due to these microorganisms have not been established in adequate and well-controlled clinical trials:

Candida albicans

Epidermophyton floccosum

Scopulariopsis brevicaulis


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References

  1. DailyMed. "TERBINAFINE: DailyMed provides trustworthy information about marketed drugs in the United States. DailyMed is the official provider of FDA label information (package inserts).". https://dailymed.nlm.nih.gov/dailyme... (accessed September 17, 2018).
  2. NCIt. "Terbinafine: NCI Thesaurus (NCIt) provides reference terminology for many systems. It covers vocabulary for clinical care, translational and basic research, and public information and administrative activities.". https://ncit.nci.nih.gov/ncitbrowser... (accessed September 17, 2018).
  3. EPA DSStox. "Terbinafine: DSSTox provides a high quality public chemistry resource for supporting improved predictive toxicology.". https://comptox.epa.gov/dashboard/ds... (accessed September 17, 2018).

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Information checked by Dr. Sachin Kumar, MD Pharmacology

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