Terbinafine is a broad-spectrum antifungal agent that is absorbed well when taken orally and starts to work within a week when applied to the skin. It is important to use it for the full course of treatment as a fungal infection may take weeks or months to clear.
Oral terbinafine is an inhibitor of the hepatic enzyme CYP2D6, and patients taking concomitant medications that are metabolised by this enzyme (eg, some beta-blockers, clopidogrel, type B monoamine oxidase inhibitors) require monitoring for drug interactions.
How it works
The fungicidal properties of terbinafine help it kill the fungus rather than just stopping its growth. It blocks the fungus’ ability to build protective cell membranes by inhibiting an enzyme called squalene epoxidase. The fungus then becomes dehydrated and dies. This makes terbinafine one of the most effective antifungal treatments.
This medicine is best taken at the same time each day to keep levels of the drug consistent in your body. If you miss a dose, take it as soon as you remember. Otherwise, take it at your next regular dose. It is important to finish this treatment course, even if symptoms disappear or you feel better. Otherwise, the infection may return.
A topical application of a terbinafine cream or solution is the most popular way to get this medication to the skin and nail. However, it is possible to use a pill containing this medication as well. A popular version of this is Lamisil Once, which combines the terbinafine with a novel film forming medium to soak deep into the nails and feet to deliver a more efficient treatment.
The best tinea pedis treatment should always be combined with other strategies to improve your hygiene and the environment in which you live and work. This includes using moisture wicking socks, washing your feet in the shower with an astringent such as methylated spirits and keeping shoes and socks dry after each wear.
Dosage
Infection with the fungus that causes tinea pedis is usually successfully treated with antifungal creams and powders. But if the infection is severe or a patient experiences repeated topical treatment failure, oral terbinafine may be prescribed.
The recommended dose for adults is 250 mg taken orally once daily. The tablet can be taken with or without food and it is important to swallow the medication whole, rather than chewing it. It is a moderate inhibitor of the CYP2D6 enzyme, so it may require a reduction in dose for patients with kidney problems. Oral terbinafine is rapidly and extensively absorbed into the body, with concentrations in the skin up to 75 times higher than those in the blood. It is slowly eliminated in faeces and urine, mostly after conversion to inactive compounds by the liver.
Most fungal infections are cleared within 1 to 2 weeks of terbinafine use, although nail infections can take several months before they clear up completely. A doctor will check the progress of a patient using this medication at regular intervals and may also perform blood tests to ensure the medicine is safe for them.
Terbinafine is not recommended for use in pregnancy and while breastfeeding. Oral terbinafine can be used in children over the age of 4 years with tinea pedis or tinea manuum (fingernail) but only on prescription.
Side effects
Terbinafine is effective for most people, but there are side effects that may occur. The most common side effect is itching. You should tell your doctor if you are experiencing any itching. In rare cases, terbinafine can cause an allergic reaction. This can happen if you are allergic to foods, dyes, preservatives, or animals. It can also be dangerous if you are allergic to certain medicines. Always check with your doctor before taking any new medicine. Use of alcohol and Lamisil may be an issue.
Oral terbinafine is not recommended for pregnant women or those who are breastfeeding, since the medication can be excreted into breast milk. It is also not recommended for elderly patients, since it can cause a decrease in blood flow to the feet and legs.
This medicine can lower the number of white blood cells in your body, which increases your chances of getting an infection. Check with your doctor right away if you or your child develop any serious skin reactions, sores or ulcers on the skin, a rash that spreads, fever and chills, or cough. This medicine can also affect your sense of smell or taste. Tell your doctor if you have a change in the way you feel, such as feeling very sad or empty. This may be a sign of depression.
Overdose
Terbinafine (ter’ bin a feen) is an allylamine antifungal medicine that has potent activity against dermatophyte infections, such as tinea pedis. It works by inhibiting a fungal enzyme called squalene epoxidase, which stops the fungus from making ergosterol, an important structural component of its cell membrane. It is absorbed well when taken orally and is eliminated in the urine and faeces after being converted to inactive compounds by the liver.
It is available in New Zealand in a topical formulation (cream, gel, solution and spray) and as 250 mg tablets (Dr Reddy’s Terbinafine, fully funded by PHARMAC). Oral terbinafine may be prescribed to treat fungal infections on the skin or nails if other medicines are not suitable, or if the infection is widespread. Patients should be warned about the risk of serious liver problems from taking oral terbinafine and should inform their doctor if they have ever had hepatitis or any other liver disease.
Pharmacists are often asked to treat tinea pedis, which is also known as athlete’s foot. Pharmacists should be familiar with the symptoms of this condition, and can help patients prevent recurrence by encouraging them to keep feet dry (especially between the toes), to wash them thoroughly daily and to wear shoes made from breathable materials. They should also advise patients to take care not to transfer the infection to other parts of the body, such as the hands and groin.