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.

Tetrabenazine (Xenazine - Ovation Pharmaceuticals), an old drug first synthesized 50 years ago for treatment of schizophrenia, was recently approved by the FDA for the treatment of chorea associated with Huntington's disease. It has been available in other countries for decades.

Anxiety disorders (generalized anxiety disorder, panic disorder, social anxiety disorder, and various phobias) are the most common form of psychiatric illness. They can be treated effectively with cognitive behavioral therapy (CBT) and/or pharmacotherapy.

Recombinant interleukin-2 (IL-2; Proleukin - Cetus), a lymphokine that stimulates growth of T lymphocytes, is available from the National Cancer Institute on an investigational basis for treatment of renal cell carcinoma and malignant melanoma. Although recently released in many European countries, the drug has not been approved for marketing by the US Food and Drug Administration.

Consensi (Coeptis/Burke), a fixed-dose combination of the calcium channel blocker amlodipine (Norvasc, and others) and the COX-2 selective NSAID celecoxib (Celebrex, and generics), has been approved by the FDA for treatment of patients who have hypertension and osteoarthritis.

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.

The ability of grapefruit juice to increase serum concentrations of drugs was first discovered during a study of the effect of ethanol on felodipine (Plendil) pharmacokinetics. Double-strength grapefruit juice used to disguise the taste of ethanol resulted in higher than expected serum concentrations of felodipine (DG Bailey et al, Clin Invest Med 1989; 12:357).

Alprazolam, a short-acting benzodiazepine, is one of the most widely prescribed drugs in the US. It is approved by the FDA for treatment of anxiety and panic disorder. An extended-release formulation, Xanax XR, which can be taken once a day, recently became available for panic disorder.

Atovaquone (Mepron - Burroughs Wellcome), a hydroxynaphthoquinone, was recently approved by the US Food and Drug Administration (FDA) for oral treatment of mild to moderate Pneumocystis carinii pneumonia (PCP) in patients who cannot tolerate trimethoprim-sulfamethoxazole (Septra, Bactrim, and others). PCP is a common opportunistic infection and frequent cause of death in patients with AIDS.

Yohimbine hydrochloride, a presynaptic 2 -adrenergic receptor antagonist available by prescription in the USA (Yocon, Yohimex, and others), is advertised for treatment of impotence and has been used as an aphrodisiac. A pre-1938 drug, yohimbine has never been approved for marketing by the US Food and Drug Administration.