Entecavir is an antiviral medication used to treat chronic hepatitis B virus (HBV) infections. It belongs to the class of drugs called nucleoside analogues and works by inhibiting the reverse transcriptase enzyme, which is essential for the replication of the virus. Entecavir is taken orally and is available in tablet form. It is generally well-tolerated, with few side effects. The most common side effects include headache, fatigue, nausea, and diarrhea. Entecavir is approved for the treatment of chronic HBV infections in adults and children aged 2 years and older and is typically used as a long-term treatment to prevent viral replication and liver damage. It should only be used under the guidance of a healthcare provider.

Usage

Entecavir is primarily used to treat chronic hepatitis B virus (HBV) infections. It works by inhibiting the reverse transcriptase enzyme, which is essential for the replication of the virus. Entecavir is typically used as a long-term treatment to prevent viral replication and liver damage in people with chronic HBV infections who have evidence of active viral replication and/or liver damage.

Entecavir is usually prescribed as a daily oral tablet, with the dose depending on a patient's age, weight, and other factors. It can be taken with or without food.

Entecavir is approved for use in adults and children aged 2 years and older. It is generally well-tolerated, with few side effects. The most common side effects include headache, fatigue, nausea, and diarrhea. In rare cases, entecavir can cause serious liver damage, particularly in people with pre-existing liver disease.

It is important to note that entecavir is not a cure for chronic HBV infections, but rather a treatment to control the virus and prevent liver damage. Therefore, it is typically used as a long-term treatment, and patients may need to continue taking the medication for several years or even for life.

Entecavir should only be used under the guidance of a healthcare provider, who will monitor a patient's liver function and viral load regularly during treatment. It is important to follow the prescribed dosing schedule and to not miss any doses, as this can lead to viral resistance and treatment failure.

Dosage

The dosage of entecavir depends on several factors, including a patient's age, weight, kidney function, and the severity of their hepatitis B virus (HBV) infection. The following information provides a general overview of the recommended dosing for entecavir:

For adults:

• For patients with normal kidney function: the recommended dose is 0.5 mg once daily.

• For patients with kidney impairment: the dose may need to be adjusted based on the patient's creatinine clearance (a measure of kidney function).

For children:

• For children aged 2 to 11 years: the recommended dose is based on body weight. For patients weighing less than 30 kg, the dose is 0.015 mg per kg of body weight (up to a maximum of 0.5 mg) once daily. For patients weighing 30 kg or more, the dose is 0.5 mg once daily.

• For children aged 12 to 17 years: the recommended dose is the same as for adults (0.5 mg once daily).

Entecavir is usually taken as a single daily dose, with or without food. It is important to take entecavir exactly as prescribed by a healthcare provider, as missing doses or taking too much can lead to viral resistance and treatment failure.

It is also important to note that the dosing for entecavir may need to be adjusted in patients with kidney impairment. In these patients, the dose may need to be reduced or the dosing frequency may need to be adjusted based on their creatinine clearance. Therefore, it is important to discuss any kidney problems with a healthcare provider before starting treatment with entecavir.

Side effects

Entecavir is generally well-tolerated, and most people do not experience significant side effects. However, like any medication, entecavir can cause side effects in some people. The following are some of the most common side effects of entecavir:

1. Headache

2. Fatigue

3. Nausea

4. Diarrhea

5. Abdominal pain

6. Dizziness

7. Insomnia

8. Rash

9. Muscle weakness

In rare cases, entecavir can cause more serious side effects, including:

1. Lactic acidosis (a buildup of lactic acid in the body)

2. Severe liver damage or liver failure (particularly in patients with pre-existing liver disease)

3. Kidney problems (such as renal impairment or failure)

4. Pancreatitis (inflammation of the pancreas)

5. Immune reconstitution inflammatory syndrome (a condition in which the immune system attacks the body's own tissues)

It is important to seek medical attention if any of the following symptoms occur:

1. Jaundice (yellowing of the skin or eyes)

2. Dark urine or light-colored stools

3. Unusual fatigue or weakness

4. Persistent nausea, vomiting, or abdominal pain

5. Swelling of the legs or feet

6. Difficulty breathing

Precaution of Entecavir

Before taking entecavir, it is important to inform your healthcare provider of any medical conditions you have, medications you are taking, and any allergies you may have. Here are some precautions to keep in mind when taking entecavir:

1. Allergic reactions: If you are allergic to entecavir or any of its ingredients, do not take the medication. Signs of an allergic reaction may include hives, difficulty breathing, and swelling of the face, lips, tongue, or throat.

2. Liver disease: Entecavir can cause liver damage or failure, particularly in patients with pre-existing liver disease. Patients with liver disease may need to be monitored more closely while taking entecavir.

3. Kidney disease: Entecavir is eliminated from the body primarily through the kidneys, and patients with kidney disease may need to have their dosage adjusted.

4. Resistance: Taking entecavir as directed and not missing doses is important to avoid developing viral resistance, which can reduce the effectiveness of the medication.

5. Pregnancy and breastfeeding: Entecavir is not recommended during pregnancy unless the benefits outweigh the risks. It is not known if entecavir passes into breast milk, so women who are breastfeeding should consult with their healthcare provider before taking entecavir.

6. HIV co-infection: Entecavir is not recommended for patients with both chronic hepatitis B virus (HBV) and human immunodeficiency virus (HIV) infections. Patients with HBV/HIV co-infection should consult with their healthcare provider to determine the best treatment options.

7. Monitoring: Regular monitoring of liver function and HBV viral load is important while taking entecavir. Follow-up appointments with your healthcare provider are important to ensure the medication is working as intended and to monitor for any potential side effects.

Overdose

aking more than the prescribed dose of entecavir can increase the risk of side effects, including liver damage and lactic acidosis. Symptoms of an entecavir overdose may include:

• Nausea and vomiting

• Dizziness

• Headache

• Fatigue

• Muscle weakness

• Abdominal pain

• Yellowing of the skin or eyes (jaundice)

If you suspect that you or someone else has taken too much entecavir, seek medical attention immediately. In case of an overdose, the treatment will depend on the severity of symptoms. Treatment may include supportive care, such as IV fluids and medications to manage symptoms.

Drug Interactions

Entecavir can interact with other medications, including prescription and over-the-counter drugs, vitamins, and supplements. Here are some examples of drug interactions that may occur with entecavir:

1. Lamivudine: Taking entecavir with lamivudine, another antiviral medication used to treat hepatitis B, may increase the risk of developing lactic acidosis, a serious side effect.

2. Tenofovir: Concurrent use of entecavir and tenofovir, another medication used to treat hepatitis B, may increase the risk of kidney problems.

3. Ribavirin: Co-administration of entecavir and ribavirin, a medication used to treat hepatitis C, is not recommended as it can increase the risk of developing anemia.

4. Medications that affect the kidneys: Entecavir is eliminated from the body primarily through the kidneys, and medications that affect kidney function may increase the concentration of entecavir in the body. Examples of medications that may interact with entecavir in this way include nonsteroidal anti-inflammatory drugs (NSAIDs), diuretics, and certain antibiotics.

5. Immunosuppressive medications: Concurrent use of entecavir and immunosuppressive medications, such as tacrolimus or cyclosporine, may increase the risk of developing infections.

6. Medications that affect the heart: Entecavir can cause changes in heart rate and rhythm, and medications that affect the heart may increase the risk of these side effects.

7. Medications that affect the liver: Entecavir can cause liver damage, and medications that affect the liver, such as acetaminophen and certain antibiotics, may increase the risk of liver damage.

Mechanisms

Entecavir works by blocking the activity of an enzyme called reverse transcriptase, which is required by the hepatitis B virus to replicate itself. By inhibiting this enzyme, entecavir prevents the virus from multiplying and spreading to healthy liver cells.

Specifically, entecavir is a nucleoside analogue, which means that it mimics the structure of the building blocks of DNA and RNA. When the hepatitis B virus tries to replicate, it incorporates entecavir into its genetic material instead of the natural building blocks, which causes errors in the viral genetic code and prevents the virus from reproducing.

Entecavir is highly selective for the reverse transcriptase enzyme of the hepatitis B virus, which means that it has minimal effect on human DNA replication. This selectivity contributes to its effectiveness and relatively low risk of side effects.

Additionally, entecavir has a long-lasting effect in the body, which means that it can be taken once a day, unlike some other antiviral medications that may require multiple doses throughout the day.

Overall, entecavir's mechanisms of action make it an effective treatment for chronic hepatitis B by reducing the viral load and improving liver function. However, it is important to note that entecavir is not a cure for hepatitis B and does not prevent transmission of the virus to others.

Disclaimer

It is important to work closely with a healthcare provider when taking entecavir to ensure its effectiveness