The FDA has approved Akynzeo (Helsinn/Eisai), an oral fixed-dose combination of the substance P/neurokinin 1 (NK₁) receptor antagonist netupitant and the serotonin-3 (5-HT₃) receptor antagonist palonosetron, for prevention of acute and delayed nausea and vomiting associated with cancer chemotherapy in adults. Akynzeo is the first product to combine drugs from these two classes. Palonosetron (Aloxi) is also available as a single agent for prevention of chemotherapy-induced and postoperative nausea and vomiting. Netupitant is the second substance P/NK₁ receptor antagonist to be approved in the US; aprepitant (Emend) was the first.

A reader expressed disappointment that our recent listing of “Some Warfarin Drug Interactions”1 did not include acetaminophen. Perhaps it should have. Acetaminophen can increase the anticoagulant effect of warfarin, particularly with continued use, but it does so inconsistently. The mechanism of this interaction has not been established, but may be related to an acetaminophen metabolite inhibiting vitamin K-epoxide reductase, the target for warfarin’s anticoagulant effect.2

Patient susceptibility varies, possibly on a genetic basis; occasional use of acetaminophen generally has little or no effect on the international normalized ratio (INR) in patients on chronic warfarin therapy, but in some, even a few grams of the drug may cause a dramatic increase in INR. One study in healthy subjects found no effect of acetaminophen 4 g per day for 2 weeks, while another study in patients with the same acetaminophen dose for the same period of time found a moderate increase in INR.3,4 It might be prudent to monitor INR in patients on chronic warfarin therapy more closely than usual when they take more than 2 g per day of acetaminophen for more than a few days.

1. Pharmacogenetic-based dosing of warfarin. Med Lett Drugs Ther 2008; 50:39.
2. HH Thijssen et al. Paracetamol (acetaminophen) warfarin interaction: NAPQI, the toxic metabolite of paracetamol, is an inhibitor of enzymes in the vitamin K cycle. Thromb Haemost 2004; 92:797.
3. D Kwan et al. The effects of acetaminophen on pharmacokinetics and pharmacodynamics of warfarin. J Clin Pharmacol 1999; 39:68.
4. I Mahe et al. Paracetamol: A haemorrhagic risk factor in patients on warfarin. Br J Clin Pharmacol 2005; 59:371.

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Warfarin sodium (Coumadin, and others) and other coumarin anticoagulants prevent thrombosis, but patient response is highly variable and overanticoagulation can lead to hemorrhage. Genotyping patients for single nucleotide polymorphisms (SNPs) that affect coumarin metabolism and sensitivity may help clinicians estimate the therapeutic warfarin dose. The FDA has added a note to warfarin labeling recommending lowrange doses for patients with such genetic variations. Commercial tests for these variants are now available and cost about $500 per test.

Tinidazole (Tindamax - Presutti Labs), an oral antiprotozoal drug similar to metronidazole (Flagyl, and others), has been approved by the FDA for treatment of trichomoniasis in adults and for treatment of giardiasis, intestinal amebiasis and amebic liver abcess in adults and children more than 3 years old. Tinidazole has been widely used outside of the US for decades under the trade name Fasigyn (Pfizer).

Cetuximab (Erbitux - ImClone Systems/Bristol-Myers Squibb), an epidermal growth factor receptor (EGFR) inhibitor, and bevacizumab (Avastin - Genentech), the first vascular endothelial growth factor angiogenesis inhibitor, have recently been approved by the FDA for treatment of patients with metastatic colorectal cancer. Cetuximab is approved for treatment of patients with EGFR-expressing tumors, either in combination regimens with irinotecan (Camptosar)when the cancer has progressed on irinotecan-based therapy, or as monotherapy for those who cannot tolerate irinotecan. Bevacizumab is approved for first-line therapy in combination with a fluorouracil-based regimen.

Aprepitant (Emend - Merck), the first substance P/neurokinin 1 (NK₁) receptor antagonist to be approved by the FDA, is now available for oral use with corticosteroids and selective serotonin (5-HT₃) receptor antagonists to prevent nausea and vomiting caused by highly emetogenic anticancer drugs such as cisplatin.

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 drugs and their adverse effects are listed in Table II on page 46. A partial list of brand names appears on page 52.

Oxaliplatin (Eloxatin -Sanofi-Synthelabo) has been approved by the FDA for use in combination with fluorouracil (5-FU; Adrucil, and others) and leucovorin (LV; Wellcovorin) for patients with metastatic colorectal cancer whose disease has recurred or progressed despite treatment with 5-FU/LV plus irinotecan (Camptosar - Medical Letter 1997; 39:8).

Irinotecan hydrochloride (Camptosar - Pharmacia & Upjohn; formerly CPT-11) has been approved by the US Food and Drug Administration for treatment of metastatic colorectal cancer refractory to other drugs including fluorouracil (5-FU; Adrucil and others).

Gemcitabine (jem site a been) hydrochloride (Gemzar - Lilly), a nucleoside analog, has been approved by the US Food and Drug Administration for intravenous (IV) use in the first-line treatment of locally advanced or metastatic adenocarcinoma of the pancreas and in patients with pancreatic cancer previously treated with fluorouracil (Adrucil, and others). No previously available drug has had more than minor activity in treating this disease.

Several currently available antiemetic drugs can prevent vomiting caused by cancer chemotherapy. Anticancer drugs that cause vomiting are listed in the table below.

Ondansetron (on dan' se tron; Zofran - Glaxo), a serotonin (5-hydroxytryptamine) antagonist, was recently marketed in the USA for intravenous use to prevent nausea and vomiting due to cancer chemotherapy. An oral formulation is available in many other countries.

The most important prognostic variable in early breast cancer is axillary lymph node involvement. Based on past experience, after 10 years about 70% of node-negative patients will be alive and apparently free of disease; about 30% will have relapsed or died. Patients with positive nodes may have a 30% to 60% relapse rate, depending on the number of positive nodes and other prognostic factors, such as the presence of estrogen receptors (IC Henderson et al, in VT DeVita, Jr et al, eds, Cancer: Principles and Practice of Oncology, 3rd ed, Philadelphia:Lippincott, 1989, p 1197). Which of these patients should receive adjuvant treatment with cytotoxic drugs and/or endocrine therapy is controversial; a National Cancer Institute (NCI) Consensus Conference on this subject is scheduled for June.

Levamisole (Janssen), an old antiparasitic drug widely used for treatment of ascariasis in animals, is now available from the National Cancer Institute (NCI) for investigational use with fluorouracil (5-FU; Adrucil; and others) as an adjuvant for treatment of resectable colon cancer that has metastasized to regional lymph nodes (Dukes stage C).

Carboplatin (Paraplatin - Bristol-Myers), a cytotoxic platinum-containing drug chemically related to cisplatin (Platinol), was recently approved by the US Food and Drug Administration (FDA) for palliative treatment of patients with recurrent ovarian cancer, including those previously treated with cisplatin.