Before Using This Medicine

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

Other medical problems—The presence of other medical problems may affect the use of efavirenz. Make sure you tell your doctor if you have any other medical problems, especially:

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