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.

Even though its effectiveness has not been established, many patients take St. John's Wort (Hypericum perforatum), an over-the-counter herbal extract, to treat symptoms of depression, often without the knowledge of their physicians. Recent reports indicate that St. John's wort interacts adversely with a number of drugs.

The FDA has approved eliglustat (Cerdelga – Genzyme), an oral glucosylceramide synthase inhibitor, for treatment of adults with type 1 Gaucher disease. Eliglustat is metabolized primarily by CYP2D6. Because patients who are CYP2D6 ultra-rapid metabolizers may not achieve therapeutic concentrations and a specific dosage cannot be recommended for indeterminate metabolizers, the FDA has approved the drug only for patients who are extensive, intermediate, or poor metabolizers of CYP2D6.

Donepezil hydrochloride (Aricept - Eisai), a piperidine-based acetylcholinesterase inhibitor, is now being marketed for oral treatment of cognitive symptoms in patients with mild to moderate dementia due to Alzheimer's disease. Donepezil is the second drug approved for this indication; tacrine hydrochloride (Cognex), also an acetylcholinesterase inhibitor, has been available in the USA for four years (Medical Letter, 35:87, 1993).

Paroxetine (Paxil - SmithKline Beecham), a new selective serotonin reuptake inhibitor (SSRI), is now available in the USA. Two other SSRIs, fluoxetine (Prozac - Medical Letter, 30:45, 1988; 32:83, 1990) and sertraline (Zoloft - Medical Letter, 34:47, 1992), were approved previously.

The physiologic changes that occur with aging can affect the pharmacokinetics and pharmacodynamics of many prescription and over-the-counter drugs, increasing the likelihood of adverse effects.

The FDA has approved Onyda XR (Tris), an extended-release (ER) oral suspension formulation of the alpha_2-adrenergic agonist clonidine, for use as monotherapy or as an adjunct to stimulant therapy for treatment of attention-deficit/hyperactivity disorder (ADHD) in children ≥6 years old. Clonidine ER tablets have been available for years for treatment of ADHD in children 6-17 years old.

Propafenone (Rythmol - Knoll), a class IC antiarrhythmic drug used in Europe for treatment of various arrhythmias for more than 10 years, was recently marketed in the USA for oral treatment of life-threatening ventricular arrhythmias such as sustained ventricular tachycardia. This restrictive labeling reflects concerns arising from the interim report of the Cardiac Arrhythmia Suppression Trial, in which post-myocardial infarction patients with asymptomatic or mildly symptomatic ventricular arrhythmias treated with the class IC antiarrhythmic drugs encainide (Enkaid) or flecainide...

Candesartan cilexetil (Atacand - Astra) is the fourth angiotensin II receptor antagonist to become available in the USA for oral treatment of hypertension.

Moricizine (mor i'; siz een) hydrochloride (Ethmozine - Du Pont), a class I antiarrhythmic drug developed in the USSR, was recently approved by the US Food and Drug Administration (FDA) for oral treatment of life-threatening ventricular arrhythmias.