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.

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