In the U.S.—

• Antiviral (systemic)

Efavirenz ( ef-FAH-ver-enz) is used with other medicines in the treatment of the infection caused by the human immunodeficiency virus (HIV). HIV is the virus that causes acquired immune deficiency syndrome (AIDS).

Efavirenz will not cure or prevent HIV infection or AIDS; however, it helps keep HIV from reproducing and appears to slow down the destruction of the immune system. This may help delay the development of problems that usually result from AIDS or HIV disease. Efavirenz will not keep you from spreading HIV to other people. People who receive this medicine may continue to have some of the problems usually related to AIDS or HIV disease.

This medicine is available only with your doctor's prescription, in the following dosage form(s):

Oral
• Capsules (U.S.)

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For efavirenz, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to efavirenz. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy—Efavirenz has not been studied in pregnant women. However, studies in animals have found that it causes birth defects and other problems. A pregnancy test is recommended before starting treatment with efavirenz. In addition, it is recommended that women with the potential to become pregnant use two methods of contraception. One method of contraception should be a reliable barrier contraceptive, such as condoms, and the other method should be an oral or other hormone contraceptive. Before taking efavirenz, make sure your doctor knows if you are pregnant or if you may become pregnant.

Breast-feeding—It is not known whether efavirenz passes into the breast milk. However, breast-feeding is not recommended in patients with HIV infection because of the risk of passing the virus on to the nursing infant.

Children—Children have a higher risk of developing a rash, which is sometimes severe, while taking this medicine. Your doctor may suggest that an additional medicine, an antihistamine, be taken to prevent a rash from occurring. The appearance of a rash should be reported to your doctor as soon as possible.

Older adults—Many medicines have not been studied specifically in older people. Therefore, it may not be known whether they work exactly the same way they do in younger adults or if they cause different side effects or problems in older people. There is no specific information comparing use of efavirenz in the elderly with use in other age groups.

Other medicines—Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. It is important that you inform your health care professional of any prescription or nonprescription (OTC) medicine you are taking, especially if you are taking any of the following:

• Amprenavir (e.g., Agenerase)—Efavirenz may decrease the amount of this medicine in the body

• Astemizole (e.g., Hismanal) or
• Cisapride (e.g., Propulsid)—Efavirenz may increase the amount of these medicines in the body, which may cause cardiac arrythmias (irregular heartbeat)

• Ergot derivatives (e.g., Gerimal, Hydergine, Hydergine LC, Ergotrate, Methergine, Bellergal-S)—Efavirenz may increase the amount of these medicines in the body, which could lead to breathing problems

• Indinavir (e.g., Crixivan)—Efavirenz may decrease the amount of this medicine in the body

• Midazolam (e.g., Versed) or
• Triazolam (e.g., Halcion)—Efavirenz may increase the amount of these medicines in the body, which may lead to severe drowsiness

• Rifabutin (e.g., Mycobutin)—Efavirenz may decrease the amount of this medicine in the body

• Ritonavir (e.g., Norvir)—Taking efavirenz with this medicine may increase the chance of side effects

• Saquinavir (e.g., Invirase)—Efavirenz may decrease the amount of this medicine in the body

• Warfarin (e.g., Coumadin)—Efavirenz may either increase or decrease the amount of warfarin in the body

• Hepatitis B or C (history of) or
• Liver disease—Efavirenz may cause unwanted effects in the liver

Take this medicine exactly as directed by your doctor. Do not take it more often, and do not take it for a longer time than your doctor ordered. Also, do not stop taking this medicine without checking with your doctor first.

Keep taking efavirenz for the full time of treatment even if you begin to feel better. It is also important that you continue taking all other medicines for HIV infection your doctor has instructed you to take.

Efavirenz may be taken with or without meals. However, meals high in fat should be avoided because the amount of efavirenz absorbed into the body may be increased, which might increase the chance of side effects.

The central nervous system (CNS) side effects that may occur with this medicine usually lessen after you have taken the medicine for a while. Also, taking efavirenz at bedtime, especially during the first 2 to 4 weeks, may lessen these side effects.

Dosing—

The dose of efavirenz 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 efavirenz. If your dose is different, do not change it unless your doctor tells you to do so.

The number of capsules that you take depends on the strength of the medicine.

• For oral dosage form (capsules):
  • For treatment of HIV infection:
    • Adults—600 milligrams (mg) once a day, taken with other medicines.
    • Children 3 years of age and older (by weight)—
      • 10 to 15 kilograms (22 to 33 pounds) of body weight: 200 mg once a day, taken with other medicines.
      • 15 to 20 kilograms (33 to 44 pounds) of body weight: 250 mg once a day, taken with other medicines.
      • 20 to 25 kilograms (44 to 55 pounds) of body weight: 300 mg once a day, taken with other medicines.
      • 25 to 32.5 kilograms (55 to 71.5 pounds) of body weight: 350 mg once a day, taken with other medicines.
      • 32.5 to 40 kilograms (71.5 to 88 pounds) of body weight: 400 mg once a day, taken with other medicines.
      • 40 kilograms (88 pounds) of body weight or over: 600 mg once a day, taken with other medicines.
    • Children up to 3 years of age—Use and dose must be determined by your doctor.

Missed dose—

If you miss a dose of this medicine, take it as soon as you remember. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage—

To store this medicine:

• Keep out of the reach of children.
• Store away from heat and direct light.
• Do not store in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

Efavirenz may cause dizziness, difficulty in concentrating, or drowsiness. Make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are dizzy or are not alert.

Check with your physician before taking efavirenz with alcohol or other medicines that affect the central nervous system (CNS). The use of alcohol or other medicines that affect the CNS with efavirenz may worsen the side effects of this medicine, such as dizziness, poor concentration, drowsiness, unusual dreams, and trouble in sleeping. Some examples of medicines that affect the CNS are antihistamines or medicine for hay fever, other allergies, or colds; sedatives, tranquilizers, or sleeping medicine; medicine for depression; medicine for anxiety; prescription pain medicine or narcotics; barbiturates; medicine for attention deficit and hyperactivity disorder; medicine for seizures; muscle relaxants; or anesthetics, including some dental anesthetics.

Efavirenz does not decrease the risk of transmitting the HIV infection to others through sexual contact or by contamination through blood.

Women of childbearing potential should use two forms of birth control while taking this medicine, a barrier method of contraception and an oral or other hormonal method of contraception.

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• More common
  • Depression;  skin rash or itching 
  
  

• Less common
  • Blood in urine;  difficult or painful urination;  pain in lower back and/or side 
  
  

• Rare
  • Abdominal pain;  changes in vision;  blistering;  clumsiness or unsteadiness ;  confusion;  convulsions (seizures);  cough;  dark urine;  delusions;  double vision;  fainting;  fast or pounding heartbeat;  fever or chills;  headache (severe and throbbing);  hives ;  inappropriate behavior;  loss of appetite;  mood or mental changes (severe) ;  muscle cramps or pain;  nausea or vomiting;  nerve pain;  open sores;  pain, tenderness, bluish color, or swelling of leg or foot;  rapid weight gain;  seeing, hearing, or feeling things that are not there;  sense of constant movement of self or surroundings;  sores, ulcers, or white spots in mouth or on lips;  speech disorder;  swelling and/or tenderness in upper abdominal or stomach area;  swelling of hands, arms, feet, or legs;  thoughts of suicide or attempts at suicide;  tightness in chest;  tingling, burning, or prickling sensations;  tingling, burning, numbness, or pain in the hands, arms, feet, or legs;  tremor;  troubled breathing;  unusual tiredness;  weight loss;  wheezing;  yellow eyes or skin 
  
  

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. However, check with your doctor if any of the following side effects continue or are bothersome:

• More common
  • Diarrhea;  dizziness;  drowsiness;  fatigue;  headache ;  increased sweating;  poor concentration;  trouble in sleeping 
  
  

• Less common or rare
  • Abnormally decreased sensitivity, particularly to touch;  agitation or anxiety;  belching;  change in sense of taste or smell;  dry mouth;  excessive gas;  false sense of well-being;  flaking and falling off of skin;  flushing;  general feeling of discomfort;  heartburn;  indigestion;  joint pain;  lack of feeling or emotion;  loss of hair;  loss of memory;  loss of sense of reality ;  mood changes;  nervousness ;  pain;  painful, red, hot or irritated hair follicles;  ringing in the ears ;  stomach discomfort;  unusual dreams;  weakness 
  
  

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.