Pharmacogenetics: Part I

Emergence and Evolution of Pharmacogenetics and Pharmacogenomics in Clinical Pharmacy over the Past 40 Years

2006 marked the 40th year of publication for The Annals. Throughout its history, The Annals has provided important contributions to the development of clinical pharmacy. In 2007, we are continuing to publish articles reflecting on the history of clinical pharmacy through the eyes of practitioners, including those pioneering clinical pharmacy, as well as those whohave more recently entered the profession and a well-established specialty. In addition, we are presenting articles and editorials from the early history of The Annals that have given direction and shape to the practice of clinical pharmacy (see page 2042).

Rates of In Vivo Methylation of Desipramine and Nortriptyline

Routine monitoring of an 81-year-old man receiving treatment with nortriptyline for generalized anxiety disorder and depression revealed plasma concentrations of both amitriptyline and nortriptyline. In humans, the tricyclic antidepressant (TCA) tertiary amines imipramine and amitriptyline are typically metabolized by demethylation to the secondary active metabolites desipramine and nortriptyline, respectively. However, to our knowledge, methylation of secondary amine TCAs has been reported in only one case report of nortriptyline overdose and in two studies involving desipramine. In a retrospective analysis of patients from five Veterans Affairs medical centers, the rate of methylation of desipramine and nortriptyline was 8.9 % (five of 56 patients) and 14.6% (36 of 247), respectively. Possible explanations for methylation include genetic polymorphisms in cytochrome P450 metabolizing enzymes, polymorphism of amine N-methyltransferase enzyme, drug-drug interactions, smoking, and alcohol consumption. However, the mechanism by which methylation occurs is unclear and warrants further investigation. Awareness of the phenomenon could help in discouraging repeated laboratory tests and unnecessary adjustments of drug therapies, resulting in cost savings and better patient outcomes.

Summary of information on human CYP enzymes: human P450 metabolism data

This chapter is an update of the data on substrates, reactions, inducers, and inhibitors of human CYP enzymes published previously by Rendic and DiCarlo (1), now covering selection of the literature through 2001 in the reference section. The data are presented in a tabular form (Table 1) to provide a framework for predicting and interpreting the new P450 metabolic data. The data are formatted in an Excel format as most suitable for off-line searching and management of the Web-database. The data are presented as stated by the author(s) and in the case when several references are cited the data are presented according to the latest published information. The searchable database is available either as an Excel file (for information contact the author), or as a Web-searchable database (Human P450 Metabolism Database, www.gentest.com) enabling the readers easy and quick approach to the latest updates on human CYP metabolic reactions.

Theophylline disposition in Korean patients with congestive heart failure

OBJECTIVE

This study proposed to determine the systemic disposition of theophylline in Korean adult patients during decompensated congestive heart failure compared with disposition after recovery.

DESIGN

An experimental, prospective, self-controlled, nonrandomized design was used.

SETTING

The study was performed in a general community hospital located in Pusan, Korea.

PATIENTS

Eight nonsmoking elderly Korean patients with decompensated congestive heart failure presenting to the emergency department were included in the study. Consecutive patients who met entrance criteria were selected. All patients completed the study.

INTERVENTIONS

A single dose of aminophylline 6 mg/kg was administered by intravenous infusion over 30 minutes. Standard methods of congestive heart failure therapy were used in each patient, including bed rest, restriction of sodium, and drug therapy including digoxin. After compensation of congestive heart failure was achieved, the theophylline infusion was repeated.

OUTCOME MEASURES

Serum theophylline concentrations were measured at 2, 6, 12, and 18 hours after completion of the dose at baseline and following treatment.

RESULTS

A clinically and statistically significant improvement in mean theophylline total body clearance was demonstrated following treatment (from 21.7 +/- 2.8 to 43.4 +/- 4.7 mL/kg/h [mean +/- SEM]; p < 0.01). Comparison of these results with a computer model based on literature averages of peoples of all nationalities showed significant underprediction of theophylline clearance both before (p < 0.05) and after (p < 0.01) treatment. The theophylline elimination half-life prior to treatment was 18.2 +/- 2.2 hours and decreased to 9.1 +/- 0.8 hours following treatment (p < 0.01). There was no statistical difference between the computer-model predicted initial theophylline half-life and the measured value, but the model significantly underpredicted the improvement following treatment.

CONCLUSIONS

The improvement in theophylline clearance demonstrated in this study appears to be greater than that reported for Western patients. This has practical application to the calculation of appropriate theophylline maintenance dosage regimens in Korean patients with cardiac failure. These data support the need for consideration of racial differences in individualizing dosage regimens. We suggest that all kinetic models, whether software supported or not, should consider incorporating ethnic origin as a demographic factor that helps select the proper model for individual patients.