Entecavir (Oral)

Although it cannot cure Hepatitis B, entecavir is effective in managing symptoms for patients who are afflicted by the disease.


Entecavir belongs to a class of drugs known as anti-viral medications, and as such, it acts to reduce or prevent the spread of the virus throughout the body. It is primarily used in the treatment of Hepatitis B, a liver infection carried out by the virus known as Hepatitis B. If left untreated, a condition like this could result in severe damage to the liver, and possibly even liver cancer or cirrhosis of the liver.

It should be noted that this medication cannot prevent the spread of the disease to other persons that the patient comes in contact with, especially through direct means such as shared needles, and/or sexual contact.

The medication itself is a liquid which is taken orally, and should only be ingested according to the specific instructions which your doctor has given you, usually in a Medication Guide. This is a very important instructional document which details proper usage of the drug, and which should be read from cover to cover each time the prescription is filled, in case anything has changed.

In general however, it is recommended that the medication be taken on an empty stomach, at least two hours after your last meal, and two hours before your next one. This helps to maintain a more or less constant level of the medication in your body, so that it can be as effective as possible in treatment.

Condition Treated

Chronic Hepatitis B Virus (HBV)

Type Of Medicine

  • Anti-viral

Side Effects

Along with the desirable effects of entecavir, there are some less desirable side effects which are sometimes experienced by patients, at various levels of severity. Some of these are serious enough that medical treatment should be sought immediately when they appear, while others are fairly mild and will simply fade away on their own, once your body adapts itself to the medication.

One of the most severe side effects is an allergic reaction, and if you suspect that you are having an allergic reaction to entecavir, you should immediately seek medical attention, because the symptoms may become worse, even life-threatening. An allergic reaction is characterized by one or more of the following symptoms:

  • Hives and/or rashes appearing on the skin
  • A sensation of tightness in the chest, or other difficulty with breathing
  • Extreme itchiness
  • Pronounced swelling, especially in the facial area, around the lips, tongue, and throat
  • Dizziness or disorientation after ingestion.

This grouping of side effects can occur in patients, with a wide range of different severities, and if you should experience any of these symptoms, you should contact your doctor, especially if the level of discomfort you feel becomes intolerable.

  • Abdominal cramping or stomach discomfort
  • Fast or irregular heartbeat
  • Sensation of bloating or fullness constantly
  • Drowsiness or constant fatigue
  • Unusual weakness
  • Disorientation or dizziness
  • Trouble with swallowing
  • Loss of appetite
  • Persistent coughing
  • Intermittent diarrhea
  • Rapid, shallow breathing
  • Rashes, hives, or extreme itching
  • Nausea and/or vomiting
  • Puffiness around the eyelids, lips, or tongue
  • Pain in the abdomen or stomach

A relatively mild grouping of side effects are those included below, and these do not necessarily call for medical attention, unless you feel extreme discomfort from them, and would prefer some kind of relief. For the most part, symptoms in this grouping will subside all by themselves without treatment, but if they do cause you concern, you should still consult with your doctor.

  • Heartburn or indigestion
  • Unusual belching
  • Headaches
  • Acid stomach or sour stomach
  • Pain or discomfort in the abdomen or stomach
  • Difficulty sleeping
  • Excessive drowsiness
  • Thinning of the hair, or hair loss.

In some unusual cases, patients have developed a medical condition known as lactic acidosis when taking entecavir. The symptoms experienced initially may not seem particularly threatening, but these symptoms can worsen as time goes by, and the condition can even prove to be fatal. That makes it very important that you seek medical attention if you should experience any of the following symptoms:

  • Sensation of lightheadedness, tiredness, or extreme weakness
  • Powerful stomach pains, often accompanied by nausea and vomiting
  • Highly irregular heartbeat, often much faster than normal
  • Extreme muscle pain or weakness
  • Numbness or tingling sensation in the legs or arms
  • Persistent difficulty with breathing.

It is also possible for entecavir to cause liver problems in some patients, even though its medical usage is to treat problems with the liver. If you should experience any of the side effects in the following group, you should immediately contact your doctor and convey exactly what you are experiencing:

  • Nausea and/or vomiting
  • Persistent and extreme itching
  • Tired feeling
  • Dark-colored urine
  • Jaundiced look around the eyes or on the skin
  • Clay -colored stools
  • Upper stomach or abdominal pains
  • Loss of appetite
  • Strong headaches
  • Dizziness or disorientation
  • Abdominal cramping or pains.


You should never take entecavir in smaller or larger amounts than those recommended by your doctor, and you must remain under the care of your doctor for the entire duration of the time you are being treated with entecavir. You should notify your doctor right away if you experience changes in weight, because one of the primary factors used to gauge an appropriate dosage is the patient's weight. This is particularly true with children between the ages of two and 18, so it is essential that weight changes are reported faithfully.

Entecavir should be taken on an empty stomach, two hours prior to your next meal and two hours after your previous one. All instructional information provided by your doctor, including the medication guide, should be carefully read and understood. If you have any questions about the material contained in the medication guide, you should ask your doctor before leaving the office.

When taking entecavir at home, a spoon should be used and the medicine should be carefully measured into the dosing spoon which is provided with the prescription. While pouring the medicine out of its container, you should hold spoon upright. If for some reason you did not receive a dosing spoon with your prescription, ask your doctor for one because the precise dosage is important when taking this medication. After each usage, be sure to thoroughly wash and rinse your dosing spoon so it's ready for the next regularly scheduled dosage.

To get the most benefit from this medication, you have to take it regularly without missing any doses. That makes it important to refill your prescription before you run out, so that you don't have lapses in the medication. The objective is to maintain a certain level of entecavir in your body at all times, so it can constantly be working to reduce the virus level in your body. If you start missing dosages or if you stop taking entecavir altogether, your symptoms are likely to return in full force, and may possibly even get worse.


There are some known interactions between entecavir and other drugs, and in order to avoid conflicts such as these, your doctor should have a full list of all other medications which you are taking. When you initially consult your doctor about taking entecavir, you should prepare a list of all vitamins, herbal supplements, over-the-counter drugs, and all other prescription medications which you are currently taking. On the same document, you should include the dosages of each one of these, so that your doctor has the most information possible to make an informed decision about potential interactions.

This list that you prepare will have other uses too, for instance if you should ever have to go to an emergency care clinic where your primary care doctor is not resident. If you can provide a doctor there with a listing of your medications, it will be much easier for him/her to safely treat whatever condition has brought you to the emergency care clinic.

You should not drink alcohol to excess when taking entecavir, and you should not take the drug at all if you have any kind of renal dysfunction or hemodialysis. Below is a partial listing of the medications which are known to interact with entecavir, and although this is not a complete listing, it does include the most commonly checked interactions by physicians.

  • Vitamin B6
  • Vitamin A
  • Vitamin D
  • Vitamin B12
  • Vitamin B1
  • Vitamin K1
  • Vitamin C
  • Vitamin D3
  • Zinc
  • Aspirin
  • Chlorpheniramine
  • Ginkgo biloba
  • Prilosec
  • Sulfatrim
  • Potassium chloride
  • Paracetamol
  • Metaprolol succinate ER
  • Metaprolol tartrate
  • Zofran
  • Valproate sodium
  • Synthroid.


There are a number of precautions which should be observed when taking entecavir, starting with the potential for an allergic reaction. If you already know that you are allergic to entecavir or any of the ingredients used in its manufacture, you should point this out immediately when consulting with your doctor. It would also be wise to let your doctor know if you have any other allergies at all, including reactions to pets, preservatives, foods, or fabrics.

Make sure your doctor is aware of any medical history you may have with kidney disease, HIV infection, or any other hepatitis B drugs which you may have taken in the past. Since it is possible for this drug to make you dizzy, you should not use alcohol or marijuana when taking entecavir, because both these can make any side effects much worse. You should not operate a motor vehicle or any kind of machinery while taking entecavir, because you may not be sufficiently alert to safely do so. It's also true that alcohol can seriously worsen any liver problems which you might have, so you should not be using alcohol at all if taking entecavir.

If you have any type of surgeries scheduled for the near future, even if they are dental surgeries, you should alert your doctors and/or dentists to the fact that you are taking entecavir. They may want to discontinue your usage of the drug before and after surgery, or to modify the dosage that you are taking.

It's very important that you take precautions to avoid the spread of hepatitis B to anyone that you come in contact with, so you should always use some kind of preventive method when engaging in sexual activity. Entecavir should only be used when there is a powerful reason to do so for a woman who is pregnant, or is thinking of becoming pregnant.

It is not known exactly what the impacts are for entecavir on an unborn baby, and it is also not known if entecavir helps to prevent the passage of hepatitis B from mother to baby. It is likewise not recommended that a new mother breast-feed an infant while taking entecavir, because it is unknown whether or not the medication is passed on through breast milk. Since the relationship between this medication and pregnancy and or breast-feeding is not clear, neither pregnancy and breast-feeding is advisable for any patient being treated with entecavir.


Entecavir should be stored at room temperature, in a location which does not experience extremes of temperature, or excessive humidity. It should also not be exposed to direct sunlight. This medication should be kept well out of the reach of pets and children, in a location where they cannot reach it. Until it is being used, it should be kept in its original container, and after usage, the container should be properly disposed of.


Entecavir is an antiviral medication most often used in the treatment of Hepatitis B, since it can be very effective at preventing the spread of a virus. It comes in liquid form, and can easily be ingested from a spoon, on an empty stomach, in between meals. It is a drug which must be taken in the exact amount prescribed by a doctor, and one for which you must be under a doctor's care the entire time. If you should miss dosages of entecavir, or discontinue usage altogether, it is very likely that symptoms will return, and they could even be much worse than they were originally.