Beta-blockers in heart failure. 2. Mode of action

Impact of CYP2D6 genetic polymorphism on tramadol pharmacokinetics and pharmacodynamics

BACKGROUND AND OBJECTIVE

Tramadol is metabolized by the highly polymorphic enzyme cytochrome P450 (CYP)2D6. Patients with different CYP2D6 genotypes may respond differently to tramadol in terms of pain relief and adverse events. In this study, we compare the pharmacokinetics and effects of tramadol in Malaysian patients with different genotypes to establish the pharmacokinetic-pharmacodynamic relationship of tramadol.

STUDY DESIGN AND SETTING

All patients received an intravenous dose of tramadol 100mg as their first postoperative analgesic. Blood was sampled at 0 minutes and subsequently at 15 and 30 minutes, 1, 2, 4, 8, 16, 20, and 24 hours for serum tramadol and analyzed by high-performance liquid chromatography (HPLC). Patients were genotyped for CYP2D6*1, *3, *4, *5, *9, *10, and *17 alleles and duplication of the gene by means of an allele-specific PCR. Pain was measured using the Visual Analog Scales, and adverse effects were recorded.

RESULTS

About half of the patients had the wild-type allele (CYP2D6*1), with the 'Asian'CYP2D6*10 allele accounting for most of the rest (40%). None of the genotypes predicted poor metabolism. Twenty-seven percent of the patients were intermediate metabolizers (IM) and 2.9% were ultra-rapid (UM) metabolizers; the remaining 70% were extensive metabolizers (EM). The mean total clearance (CL) predicted by the model was lower (19 L/h) and the half-life longer (5.9 hours) than those reported in Western populations. This may due to the high frequency of the CYP2D6*10 allele amongst Malaysian patients. The UM and EM groups had 2.6- and 1.3-times faster CL, respectively, than the IM. CL was 16, 18, 23, and 42 L/h while mean half-lives were 7.1, 6.8, 5.6, and 3.8 hours among the IM, EM1, EM2, and UM groups, respectively. However, the analgesic effects of tramadol were not measured adequately among the postoperative patients to establish its full therapeutic effects. There were significant differences in the adverse-effect profiles amongst the various genotype groups, with the IM group experiencing more adverse effects than the EM, and the EM having more adverse effects than the UM.

CONCLUSION

CYP2D6 activity may play an important role in determining the pharmacokinetics of tramadol and in predicting its adverse effects. If these results can be confirmed in a larger population, genotyping may be an important tool in determining the dose of tramadol.

Angiogenesis in ischaemic and hypertrophic hearts induced by long-term bradycardia

Angiogenesis and improved left ventricular function as a consequence of long-term bradycardia were first demonstrated in normal hearts, either electrically paced (rabbits, pigs) or treated with a selective sinus blocking drug alinidine (rats). Here we review the evidence that chronic heart rate reduction can have similar effects in the heart with compromised vascular supply, due to either hypertensive or haemodynamic overload hypertrophy (rats, rabbits) or ischaemic damage (rats, rabbits, pigs). Bradycardia induced over several weeks increased capillarity in all hypertrophied hearts, and in border and remote left ventricular myocardium of infarcted hearts. In some, but not all cases, coronary blood flow was improved by heart rate reduction, suggesting enlargement of the resistance vasculature in some circumstances. Cardiac or left ventricular function indices, which were depressed by hypertrophy or ischaemic damage, were preserved or even enhanced by chronic heart rate reduction. The expansion of the capillary bed in the vascularly compromised heart induced by bradycardia may be stimulated by mechanical stretch of the endothelium and/or VEGF activated by chamber dilation and myocyte stretch. The increased number of capillaries and more homogeneous distribution of capillary perfusion would support the better pump function, even in the absence of higher coronary flow. The beneficial impact of chronic heart rate reduction on myocardial angiogenesis and function in cardiac hypertrophy and infarction may be major factor in the success of beta-blockers in treatment of human heart failure.

Genetic polymorphism of CYP2D6 in patients with cardiovascular disease -- a cohort study

BACKGROUND

Cardiovascular diseases are complex diseases that are influenced by both environmental and genetic factors. CYP2D6 found in the brain and the heart is involved in the metabolism of many environmental and some endogenous substances and neurotransmitters responsible for maintaining homeostasis. This raises an interesting hypothesis that it may have a role in the development of or protection against cardiovascular diseases.

OBJECTIVE

To study the distribution of genotypes of CYP2D6 among patients with cardiovascular diseases in Malaysia.

METHOD

We obtained DNA from 128 patients who were followed up for cardiovascular diseases. Polymerase chain reaction-based methods were used to determine common CYP2D6 alleles.

RESULTS

One hundred and twenty-eight patients were enrolled. Most of the patients also had concurrent illnesses. Eleven genotypes were identified in the patients and 41% carried CYP2D6*1/*10. The second most common genotype was homozygous for the wild type gene, followed by homozygous CYP2D6*10/*10 at 14.48 %. A small percentage of the patients were heterozygous CYP2D6*1/*4. One patient was genotyped homozygous CYP2D6*4/*4 predicting a poor metabolizer prevalence of 0.78% (95% CI +/- 1.52%). Analysis using Hardy-Weinberg equilibrium showed that all of the gnotypes were consistent with equilibrium except for CYP2D6*1/*10 (chi(2); P < 0.05).

CONCLUSION

Our study suggests a possible involvement of CYP2D6 genotypes in cardiovascular system diseases, which need to be validated by further studies.

Population pharmacokinetic modelling of tramadol with application of the NPEM algorithms

BACKGROUND AND OBJECTIVE

Although the kinetic behaviour of tramadol has been described, the present study is the first to our knowledge, to report specifically on the population pharmacokinetic modelling of tramadol hydrochloride.

METHODS

The parametric Iterative Two-stage Bayesian Population Model (IT2B) program followed by the Non-parametric Expectation Maximization Population Model (NPEM2) program was used to determine population pharmacokinetic parameter values of tramadol in 138 postoperative orthopaedic Malaysian patients. All patients had received a 100 mg intravenous dose of tramadol, infused over 2-3 min, as their first postoperative analgesic. Blood was sampled at 0 min and subsequently at 15, 30 min, 1, 2, 4, 8, 16, 20 and 24 h for serum tramadol high-performance liquid chromatography analysis.

RESULTS AND DISCUSSION

The one-compartmental model pharmacokinetic parameters--volume of distribution (Vd), elimination rate constant (kel) and the total clearance rates (ClT)--found were: mean Vd = 167.6 +/- 63.84 L; median Vd = 161.48 L; mean kel = 0.1241 +/- 0.056 h(-1); median kel = 0.1138 h(-1); ClT = 19.57 +/- 9.51 L/h; median ClT =18.12 L/h. The interindividual coefficient of variation of ClT (48.56%) was higher than that of Vd (38.09%), indicating the presence of other possible influencing factors on tramadol's ClT such as CYP2D6 polymorphism, gender and age. Overall, NPEM2 suggested more diversity in the population than did IT2B.

Relationship between Type A and B personality and debrisoquine hydroxylation capacity

AIM

A person with Type A personality is an 'aggressor' compared with the rarely harried Type B. Although debrisoquine hydroxylase (CYP2D6) capacity has been associated with personality, no study has specifically investigated its association with personality Type A and B. Therefore the aim of this research was to study the impact of CYP2D6 on Type A and B personality.

METHODS

Type A and B personality questionnaires were administered to 48 healthy patients undergoing elective orthopaedic surgery. After obtaining informed consent, patients were genotyped for the various CYP2D6 alleles by allele-specific polymerase chain reaction. Based on the genotypes, patients were grouped as extensive metabolizer (EM)1 (normal) (CYP2D6*1/*1), EM2 (intermediate) (CYP2D6*1/*4, CYP2D6*1/*5, CYP2D6*1/*9 and CYP2D6*1/*10) and EM3 (slow) (CYP2D6*4/*10, CYP2D6*5/*10, CYP2D6*10/*10 and CYP2D6*10/*17). Chi(2) was used to determine the relationship between the groups and personality types.

RESULTS

The percentages of patients who were of the EM1, EM2 and EM3 groups were 20.8%, 52.1% and 27.1%, respectively. There was a significant difference (P = 0.032) between the three groups in terms of personality type, in which EM1 showed a tendency to be of personality Type A while EM2 and EM3 tended to be of personality Type B.

CONCLUSION

The study suggests that there is a relationship between CYP2D6 activity and Type A and B personality.