Prescribing BiDil: is it black and white?

Cytochrome P450 pharmacogenetics in African populations: implications for public health

INTRODUCTION

Africa harbors a disproportionate burden of disease when taking into account the triple challenge caused by HIV/AIDS, tuberculosis (TB) and malaria, against a backdrop of an increasing burden of noncommunicable diseases. More than 80% of therapeutic drugs used in the management of these diseases/conditions are metabolized by CYP enzymes that exhibit genetic polymorphisms.

AREAS COVERED

There is variability in the expression and activities of CYPs resulting in interindividual differences in the response to standard doses of therapeutic drugs, due to genetic polymorphisms, which exhibit both quantitative and qualitative differences between racial and between ethnic groups. The review aims to evaluate the implications of the genetic variation in CYPs on the public health of Africans. The CYPs reviewed here metabolize most of the commonly used therapeutic drugs and include CYP1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 3A4 and 3A5. Allele frequencies are compared between African ethnic groups and among populations of African, Asian and European origin. Data are obtained from our own studies and literature.

EXPERT OPINION

The variability in the pattern of genetic variation between populations translates into differences in drug response. Understanding CYP variability improves rational drug use and has public health significance.

Isosorbide dinitrate and hydralazine in a fixed-dose combination produces further regression of left ventricular remodeling in a well-treated black population with heart failure: results from A-HeFT

BACKGROUND

Isosorbide dinitrate combined with hydralazine therapy compared with placebo in patients with heart failure resulted in a sustained increase in left ventricular (LV) ejection fraction (EF) indicative of regression of LV remodeling in the first Vasodilator-Heart Failure Trial (V-HeFT-I) in patients receiving only digoxin and diuretic. In the African-American Heart Failure Trial (A-HeFT) a fixed-dose combination resulted in a 43% reduction in mortality in 1050 black patients with heart failure already treated with recommended neurohormonal inhibiting drugs. Whether the fixed-dose combination produces a further regression of LV remodeling when added to renin-angiotensin and sympathetic inhibitors has not been documented.

METHODS AND RESULTS

Echocardiograms at baseline and 6 months after randomization to placebo or a fixed-dose combination of isosorbide dinitrate/hydralazine (FDC I/H) were analyzed in 678 A-HeFT participants in a core laboratory. LVEF rose by 2.8 EF units in the FDC I/H group versus 0.8% in the control group (P < .01), LV mass index fell by 7.4 g/m2 in the FDC I/H group versus an increase of 1.4 g/m2 in the placebo group (P < .05), LV diastolic transverse diameter fell by 2.2 mm in FDC I/H and was unchanged in placebo (P < .01), and the LV systolic and diastolic sphericity indices improved in the FDC I/H group but remained unchanged in the placebo group. The mean plasma B-type natriuretic peptide (BNP) also measured in a core laboratory fell in the FDC I/H group by 39 pg/mL compared with 8 pg/mL in the placebo group (P = .05).

CONCLUSIONS

A fixed-dose combination of I/H produces regression of LV remodeling when added to background therapy with renin-angiotensin and sympathetic inhibitors in black patients with heart failure. This remodeling benefit may explain at least in part the mortality reduction in A-HeFT.

Recent developments in nitric oxide donor drugs

During the 1980s, the free radical, nitric oxide (NO), was discovered to be a crucial signalling molecule, with wide-ranging functions in the cardiovascular, nervous and immune systems. Aside from providing a credible explanation for the actions of organic nitrates and sodium nitroprusside that have long been used in the treatment of angina and hypertensive crises respectively, the discovery generated great hopes for new NO-based treatments for a wide variety of ailments. Decades later, however, we are still awaiting novel licensed agents in this arena, despite an enormous research effort to this end. This review explores some of the most promising recent advances in NO donor drug development and addresses the challenges associated with NO as a therapeutic agent.

The Evolving Role of Drug Metabolism in Drug Discovery and Development

Drug metabolism in pharmaceutical research has traditionally focused on the well-defined aspects of absorption, distribution, metabolism and excretion, commonly-referred to ADME properties of a compound, particularly in the areas of metabolite identification, identification of drug metabolizing enzymes (DMEs) and associated metabolic pathways, and reaction mechanisms. This traditional emphasis was in part due to the limited scope of understanding and the unavailability of in vitro and in vivo tools with which to evaluate more complex properties and processes. However, advances over the past decade in separate but related fields such as pharmacogenetics, pharmacogenomics and drug transporters, have dramatically shifted the drug metabolism paradigm. For example, knowledge of the genetics and genomics of DMEs allows us to better understand and predict enzyme regulation and its effects on exogenous (pharmacokinetics) and endogenous pathways as well as biochemical processes (pharmacology). Advances in the transporter area have provided unprecedented insights into the role of transporter proteins in absorption, distribution, metabolism and excretion of drugs and their consequences with respect to clinical drug-drug and drug-endogenous substance interactions, toxicity and interindividual variability in pharmacokinetics. It is therefore essential that individuals involved in modern pharmaceutical research embrace a fully integrated approach and understanding of drug metabolism as is currently practiced. The intent of this review is to reexamine drug metabolism with respect to the traditional as well as current practices, with particular emphasis on the critical aspects of integrating chemistry and biology in the interpretation and application of metabolism data in pharmaceutical research.