Re: no evidence of increased adverse drug reactions in cytochrome P450 CYP2D6 poor metabolizers treated with fluoxetine or nortriptyline

Pharmacogenomic testing: relevance in medical practice: why drugs work in some patients but not in others

Genetics may account for much of the variability in our patients' responses to drug therapies. This article offers the clinician an up-to-date overview of pharmacogenomic testing, discussing implications and limitations of emerging validated tests relevant to the use of warfarin (Coumadin), clopidogrel (Plavix), statins, tamoxifen (Nolvadex), codeine, and psychotropic drugs. It also discusses the future role of pharmacogenomic testing in medicine.

Pharmacokinetics and interactions of headache medications, part II: prophylactic treatments

The present part II review highlights pharmacokinetic drug-drug interactions (excluding those of minor severity) of medications used in prophylactic treatment of the main primary headaches (migraine, tension-type and cluster headache). The principles of pharmacokinetics and metabolism, and the interactions of medications for acute treatment are examined in part I. The overall goal of this series of two reviews is to increase the awareness of physicians, primary care providers and specialists regarding pharmacokinetic drug-drug interactions (DDIs) of headache medications. The aim of prophylactic treatment is to reduce the frequency of headache attacks using beta-blockers, calcium-channel blockers, antidepressants, antiepileptics, lithium, serotonin antagonists, corticosteroids and muscle relaxants, which must be taken daily for long periods. During treatment the patient often continues to take symptomatic drugs for the attack, and may need other medications for associated or new-onset illnesses. DDIs can, therefore, occur. As a whole, DDIs of clinical relevance concerning prophylactic drugs are a limited number. Their effects can be prevented by starting the treatment with low dosages, which should be gradually increased depending on response and side effects, while frequently monitoring the patient and plasma levels of other possible coadministered drugs with a narrow therapeutic range. Most headache medications are substrates of CYP2D6 (e.g., beta-blockers, antidepressants) or CYP3A4 (e.g., calcium-channel blockers, selective serotonin re-uptake inhibitors, corticosteroids). The inducers and, especially, the inhibitors of these isoenzymes should be carefully coadministered.

Drug interactions and fluoxetine: a commentary from a clinician's perspective

This commentary suggests that clinicians require an additional perspective to that expressed in Wernicke's review. Clinicians must consider the relative risks, because even small differences may be a reason to adjust usage of a particular drug. As early as 1993, reviews noted a 'serious' interaction potential. Also, the product information requires supplementation because it does not provide the emphasis on predictable interactions that clinicians require. An extensive basis in experimental pharmacology provides the foundations for our knowledge of cytochrome P450 interactions which predict the effects on the levels of other drugs. This work has been confirmed in human studies. Adverse outcomes related to fluoxetine interactions are relatively frequent and sometimes fatal. Patients may suffer serious and irreversible ill-effects from the increased risk of many manifestations of toxicity, and the cost of resultant medico-legal settlements is considerable. A clinician who balances risks may use fluoxetine less frequently.