An extended-release formulation of the centrally-acting muscle relaxant cyclobenzaprine (Amrix - Cephalon) has been approved by the FDA for treatment of muscle spasms. Immediate-release (IR) cyclobenzaprine (Flexeril, and others) has been available since 1977.

Nefazodone (Serzone - Bristol-Myers Squibb) was recently approved by the US Food and Drug Administration for treatment of depression. A phenylpiperazine, nefazodone is chemically related to trazodone (Desyrel, and others).

Mirtazapine (mir taz a peen; Remeron - Organon) has been approved by the US Food and Drug Administration for treatment of depression. A tetracyclic piperazinoazepine, it is an analog of mianserin, an antidepressant available in Europe, but is structurally unrelated to antidepressants previously available in the USA.

The FDA recently cleared the AmpliChip CYP450 Test (Roche), which analyzes blood-derived DNA to detect genetic variations in the activity of cytochrome P450 (CYP) enzymes CYP2D6 and CYP2C19 and determines the metabolizer status of the patient. The test is intended to help guide clinicians in prescribing individualized drug therapy. About 25% of all drugs, including many antidepressants and antipsychotics, are substrates of either CYP2D6 or CYP2C19. The test is being promoted initially to psychiatrists.

Duloxetine (Cymbalta - Lilly) is the second drug to be approved by the FDA for treatment of fibromyalgia. Pregabalin (Lyrica), which is also approved for treatment of neuropathic pain and epilepsy, was the first. Duloxetine is a selective serotonin and norepinephrine reuptake inhibitor (SNRI) that is already marketed for treatment of depression and diabetic neuropathy.

Gabapentin (Neurontin - Pfizer), which has been available in the US since 1994, is approved by the FDA only for treatment of partial epilepsy and postherpetic neuralgia, but is widely used off-label for a number of other indications, especially neuropathic pain syndromes. According to one report, among Medicaid recipients in Florida receiving gabapentin, 71% of prescriptions were for chronic pain and 8% for seizures and neuralgia ("The Pink Sheet" February 2, 2004; 66:30).

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.

Pregabalin (Lyrica - Pfizer) is the first drug approved by the FDA for management of fibromyalgia. When it was first marketed, pregabalin, which is structurally similar to gabapentin (Neurontin, and others), was approved for treatment of neuropathic pain associated with postherpetic neuralgia and diabetic peripheral neuropathy and for adjunctive treatment of partial onset seizures in adults with epilepsy. It has also been prescribed off-label for other types of neuropathic pain such as sciatica.

Milnacipran (Savella - Forest), an oral selective serotonin and norepinephrine reuptake inhibitor (SNRI), is the third drug approved by the FDA for management of fibromyalgia. The 2 others are pregabalin, a gammaaminobutyric acid (GABA) analog also approved for treatment of diabetic neuropathy, post-herpetic neuralgia and epilepsy, and duloxetine, an SNRI also approved for treatment of depression, diabetic neuropathy and generalized anxiety disorder.

As the weather becomes warmer, physicians may see more photosensitivity reactions due to systemic or topical drugs, perfumes, cosmetics or sunscreens. Even brief exposure to sunlight in warm or cold weather can cause intense cutaneous reactions in patients with drug-induced photosensitivity, and some patients may continue to be sensitive to sunlight long after stopping use of the offending agent.