Serious adverse interactions between drugs continue to be reported. Many of these are due to inhibition or induction of cytochrome P450 (CYP) enzymes, particularly CYP3A4. CYP3A is thought to be involved in the metabolism of more than 50 percent of currently prescribed drugs.2 CYP3A4, which is more abundantly expressed than CYP3A5, accounts for most CYP3A activity in vivo.

Adjuvant hormone therapy with anti-estrogen drugs has been shown to reduce disease recurrence and mortality in postmenopausal women with estrogen receptor (ER)-positive breast cancer. In recent years, aromatase inhibitors (AI) have become the preferred first-line hormonal treatment over tamoxifen for such patients.1,2

Changes caused by one drug in the absorption, distribution, metabolism or excretion of another may lead to a pharmacokinetic adverse drug interaction (DN Juurlink et al, JAMA 2003; 289:1652). Additive drug interactions, such as vasodilation caused by both sildenafil (Viagra) and nitrates, can also have adverse effects.

In addition to surgery and radiation therapy, a variety of drugs are used both singly and in combination to treat breast cancer. This article summarizes the principles of adjuvant therapy and treatment for metastatic disease. A summary of individual drugs and their adverse effects begins on page 3.

The antiestrogen toremifene (Fareston - Schering) and the selective aromatase inhibitor letrozole (Femara - Novartis) have been approved by the FDA for treatment of advanced breast cancer in postmenopausal women.

The tables in this article list drugs used for treatment of cancer in the USA and Canada and their major adverse effects. The choice of drugs in Table I is based on the opinions of Medical Letter consultants. Some drugs are listed for indications for which they have not been approved by the US Food and Drug Administration. In some cases, such as elderly patients or those with many co-morbid illnesses, the regimen of choice might not be suitable. For many of the cancers listed, surgery and/or radiation therapy may be the treatment of choice or may also be part of the management. Anticancer...

Many commonly used drugs can interfere with sexual function in both men and women, causing loss of libido, interfering with erection or ejaculation in men, and delaying or preventing orgasm in women. Drug-related effects on sexual function may be difficult to distinguish from the effects of depression or disease, but most are reversible when drug use is stopped and sometimes when dosage is decreased. Since many patients are reluctant to talk about sexual difficulties, physicians may wish to ask about the possibility of drug-induced sexual dysfunction, particularly when they have...