Economic consequences of selective serotonin reuptake inhibitor use with drugs also metabolized by the cytochrome P-450 system

Selecting an appropriate medication for treating neuropathic pain in patients with diabetes: a study using the U.K. and Germany Mediplus databases

OBJECTIVE

To evaluate the appropriateness of prescribing select neuropathic pain medications to diabetes patients based on the potential for drug-drug interactions with medications diabetes patients were prescribed continuously for > or =3 months (chronic use).

METHODS

Medical records of patients with a diagnosis of diabetes or use of antidiabetic medications between January 1, 2002 and September 30, 2005 in the U.K. and Germany Mediplus databases were obtained.

PATIENTS

Medication use profiles were evaluated between April 2004 and September 2005. The metabolic pathways associated with medications that were prescribed chronically to at least 10% of study patients were compared with the metabolic pathways of neuropathic pain medications to identify potential drug-drug interactions.

RESULTS

A total of 40,448 patients in the U.K. (63.6 +/- 16.6 years, 51% male) and 31,930 patients in Germany (68.9 +/- 12.7 years, 46% male) were identified. Frequently prescribed medications in the U.K. included aspirin (33.7%), metformin (32.7%), simvastatin (25.5%), atorvastatin (19.4%), atenolol (18.1%), and in Germany hydrochlorothiazide (35.8%), aspirin (25.2%), metformin (21.6%), metoprolol (20.3%), and simvastatin (18.3%). Several neuropathic pain medications have potential for drug-drug interactions with medications prescribed to diabetes patients. Examples include (neuropathic pain medications vs. diabetes medications): duloxetine, paroxetine, and methadone (CYP2D6 inhibitors) and oxycodone HCL, hydrocodone (CYP2D6 substrates) vs. metoprolol and bisoprolol (CYP2D6 substrates); and carbamazepine (CYP3A4 inducer) vs. simvastatin, and atorvastatin (CYP3A4 substrates).

CONCLUSIONS/INTERPRETATION

Our findings underscore the need for medical vigilance when selecting medications for treating neuropathic pain in diabetes patients.

Role of efflux pumps and metabolising enzymes in drug delivery

The impact of efflux pumps and metabolic enzymes on the therapeutic activity of various drugs has been well established. The presence of efflux pumps on various tissues and tumours has been shown to regulate the intracellular concentration needed to achieve therapeutic activity. The notable members of efflux proteins include P-glycoprotein, multi-drug resistance protein and breast cancer resistance protein. These efflux pumps play a pivotal role not only in extruding xenobiotics but also in maintaining the body's homeostasis by their ubiquitous presence and ability to coordinate among themselves. In this review, the role of efflux pumps in drug delivery and the importance of their tissue distribution is discussed in detail. To improve pharmacokinetic parameters of substrates, various strategies that modulate the activity of efflux proteins are also described. Drug metabolising enzymes mainly include the cytochrome P450 family of enzymes. Extensive drug metabolism due to the this family of enzymes is the leading cause of therapeutic inactivity. Therefore, the role of metabolising enzymes in drug delivery and disposition is extensively discussed in this review. The synergistic relationship between metabolising enzymes and efflux proteins is also described in detail. In summary, this review emphasises the urgent need to make changes in drug discovery and drug delivery as efflux pumps and metabolising enzymes play an important role in drug delivery and disposition.

Economic evaluation of antidepressive agents: a systematic critique of experimental and observational studies

The purpose of this study was to examine whether experimental and observational pharmacoeconomic analyses of antidepressant drugs support the choice of one of the selective serotonin reuptake inhibitors or newer antidepressants as first-line treatment for patients with major depression. We systematically reviewed economic evaluations of two or more antidepressants completed in clinical practice. A systematic electronic search yielded 38 studies meeting the inclusion criteria, of which 23 were administrative database analyses, 12 were observational studies, and 3 were randomized clinical trials. Experimental data indicated that tricyclic antidepressants are equivalent to selective serotonin reuptake inhibitors in terms of total expenditure. While the database analyses are susceptible to bias and confounding variables, they provided an added dimension based on observations from everyday clinical practice. The majority of these studies failed to show any significant difference. Taken together, available pharmacoeconomic studies indicate that tricyclic drugs and selective serotonin reuptake inhibitors have similar cost effectiveness in the health care systems where these comparisons have been made.

The need for an iterative process for assessing economic outcomes associated with SSRIs

Pharmacotherapeutic advances in the treatment of depression have included the development of the selective serotonin reuptake inhibitors (SSRIs), thereby providing alternatives to tricyclic antidepressants. Concurrent with these events have been significant structural (e.g. pharmaceutical formularies) and regulatory (e.g. required pharmacoeconomic evaluations) changes in the delivery, financing, and oversight of healthcare programmes throughout the world. International cost-containment initiatives are increasingly mandating a demonstration of value for money, defined in terms of a measurable health and/or financial outcome, and, in the case of medicines, attributable to a given expenditure, for a given pharmacotherapeutic option. We examine the inherent strengths and weaknesses of 5 study designs used to discern and contrast financial outcomes stemming from the use of antidepressant pharmacotherapy for the treatment of depressive illness [randomised controlled trials (RCTs); meta-analyses; decision-analytical models (DAMs); retrospective database investigations; randomised naturalistic inquiry]. We argue that the economic appraisal of pharmacotherapy requires an iterative process extending from the developmental (RCTs; meta-analyses; DAMs) through to the postmarketing phase (database reviews; naturalistic inquiry), thereby resulting in a portfolio of evidence as to the safety, efficacy and effectiveness of a given pharmacotherapeutic category (e.g. SSRIs) and/or a specific medication. Database reviews, while nonrandomised, and prospective naturalistic inquiry afford greater insight into the patterns of use and financial merits of prescribing specific pharmacotherapeutic options for the treatment of depression within the context of clinical practice as compared with RCTs, meta-analyses and DAMs. The portfolio of evidence to date indicates that the first-line use of SSRIs in the treatment of depression is clinically warranted, and represents value for money.

Pharmaceuticals--cost or investment? An employer's perspective

Employers are becoming increasingly concerned about rising pharmaceutical costs. Are improved health and cost outcomes achieved as a result of increasing pharmaceutical costs? One should approach this issue with a holistic view that considers the overall impact that disease conditions have on health and productivity. To illustrate, we first identified the "top ten" most expensive physical and mental health concerns facing American businesses, using data from over 60 firms from the 1996 MarketScan Private Pay Fee-For-Service Research Database. For some of these top ten conditions, the literature already addresses the drug cost versus investment issue, with mixed results. For conditions in which uncertainty prevails and for other high-cost conditions, empirical analyses should address the drug cost versus investment issue to minimize the risk of a penny-wise and pound-foolish payment/coverage policy. A similar strategy should be applied to individual corporate diagnostic assessments.

["Clinically significant" new drug interactions]

The concomitant intake of drugs with the potential to cause drug interactions is frequent. In contrast, adverse effects due to drug interactions account for only a small fraction of all adverse effects. A reproducible evaluation of the clinical relevance of drug interactions is lacking. We now can accurately define the potential of a drug to cause interactions, primarily by comparative investigations within a drug class. Whether or not the selection of the drug based on this information is useful for the patient is unknown. Therefore, usually it is to be recommended to abandon therapeutically reasonable drug combinations with a risk for interactions only if equivalent therapeutic options are available. Several actual examples on interactions with selective serotonin re-uptake inhibitors, HMG-CoA reductase inhibitors, mibefradil, sildenafil, protease inhibitors and with grapefruit juice are discussed.