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.

Venlafaxine (Effexor, Effexor XR - Wyeth), an antidepressant that inhibits both norepinephrine and serotonin reuptake, was first approved by the FDA in 1993. It has been used mainly as a second-line agent for patients who have not responded to a selective serotonin reuptake inhibitor (SSRI). Some Medical Letter consultants have had the clinical impression that venlafaxine is more effective than an SSRI, particularly for patients with severe, classic depression (melancholia), and believe it should be considered a first-line drug (Treatment Guidelines from the Medical Letter 2003, 1:69). Is...

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.

Duloxetine hydrochloride (Cymbalta - Lilly), a selective serotonin and norepinephrine reuptake inhibitor (SNRI) available for treatment of depression, has also been approved by the FDA for treatment of neuropathic pain associated with diabetic peripheral neuropathy (DPN). Duloxetine is one of two drugs approved specifically for management of neuropathic pain due to diabetes; the other, pregabalin (Lyrica - Pfizer), will be marketed soon and will be reviewed in the next issue of The Medical Letter.

Bendamustine HCl (Treanda - Cephalon), an unusual DNA-alkylating agent that has been used in Europe for many years to treat lymphoma, has now been approved by the FDA for treatment of chronic lymphocytic leukemia (CLL) and non-Hodgkin's lymphoma (NHL).

Asenapine (Saphris - Schering-Plough), a dibenzo-oxepino pyrrole, has been approved by the FDA in a sublingual tablet formulation for acute treatment of schizophrenia and manic or mixed episodes associated with bipolar disorder. It is the sixth second-generation antipsychotic approved by the FDA for use in bipolar disorder.

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.

(Med Lett Drugs Ther 2008; 50:91) In the Clinical Studies section, the complete response rate with chlorambucil for CLL was 2% (not 24%).

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.