Bob Wilffert

Pharmacogenetics: from bench to byte--an update of guidelines.

Currently, there are very few guidelines linking the results of pharmacogenetic tests to specific therapeutic recommendations. Therefore, the Royal Dutch Association for the Advancement of Pharmacy established the Pharmacogenetics Working Group with the objective of developing pharmacogenetics‐based therapeutic (dose) recommendations. After systematic review of the literature, recommendations were developed for 53 drugs associated with genes coding for CYP2D6, CYP2C19, CYP2C9, thiopurine‐S‐methyltransferase (TPMT), dihydropyrimidine dehydrogenase (DPD), vitamin K epoxide reductase (VKORC1), uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1), HLA‐B44, HLA‐B*5701, CYP3A5, and factor V Leiden (FVL).

ORGANIC AND INORGANIC CALCIUM-ANTAGONISTS REDUCE VASOCONSTRICTION INVIVO MEDIATED BY POSTSYNAPTIC ALPHA-2-ADRENOCEPTORS

SummaryThe influence of various calcium antagonists and divalent metal cations on the pressor responses induced by the selective α1-adrenoceptor agonist methoxamine and the selective α2-adrenoceptor stimulating agent B-HT 920 (2-amino-6-allyl-5,6,7,8-tetrahydro-4H-thiazolo-[4,5-d]-azepine) was studied in pithed rats.1.The calcium antagonists verapamil, D 600 and nifedipine, when given intraarterially (i.a.) in doses up to 1 mg/kg did not influence the pressor effects of methoxamine. Only higher amounts of these calcium antagonistic drugs (1–3 mg/kg i.a.) somewhat reduced this pressor response.2.The vasoconstriction due to B-HT 920, as reflected by the increase in diastolic pressure, was markedly inhibited by verapamil, D 600 and nifedipine in a dose-dependent manner. In low doses a parallel displacement to the right was observed, whereas in higher amounts the shift was non-parallel.3.The divalent cations Mn2+, Ni2+ and Co2+ (0.05–0.15 mmol/kg i.a.) hardly affected the pressor effect of methoxamine, whereas B-HT 920-induced vasoconstriction was highly sensitive to these metal ions. La3+ and Mg2+ were ineffective.4.The calcium antagonists verapamil, D 600 and nifedipine displayed only minor affinities for [3H]prazosin (α1) as well as [3H]clonidine (α2) binding sites of rat brain membranes.5.It is concluded that an influx of extracellular Ca2+ is necessary for the vasoconstriction in vivo initiated by stimulation of vascular postsynaptic α2-adrenoceptors. On the other hand, vasopressor responses to α1-adrenoceptor stimulation are not directly dependent on a transmembrane influx of calcium ions.

Pharmacogenetics: From Bench to Byte

Despite initial enthusiasm, 1 , 2 , 3 the use of pharmacogenetics has remained limited to investigation in only a few clinical fields such as oncology and psychiatry. 4 , 5 , 6 , 7 , 8 The main reason is the paucity of scientific evidence to show that pharmacogenetic testing leads to improved clinical outcomes. 9 , 10 Moreover, for most pharmacogenetic tests (such as tests for genetic variants of cytochrome P450 enzymes) a detailed knowledge of pharmacology is a prerequisite for application in clinical practice, and both physicians and pharmacists might find it difficult to interpret the clinical value of pharmacogenetic test results. Guidelines that link the result of a pharmacogenetic test to therapeutic recommendations might help to overcome these problems, but such guidelines are only sparsely available. In 2001, an early step was taken to develop such guidelines for the therapeutic use of antidepressants, and these included CYP2D6‐related dose recommendations drawn from pharmacokinetic study data. 11 However, the use of such recommendations in routine clinical practice remains difficult, because they are currently outside the ambit of the clinical environment and are not accessible during the decision‐making process by physicians and pharmacists, namely the prescription and dispensing of drugs.

Pharmacogenetic differences between warfarin, acenocoumarol and phenprocoumon

Coumarin oral anticoagulant drugs have proven to be effective for the prevention of thromboembolic events. World-wide, warfarin is the most prescribed drug. In Europe, acenocoumarol and phenprocoumon are also administered. Yet it has been proven that variant alleles of the VKORC1 and CYP2C9 genotypes influence the pharmacokinetics and pharmacodynamics of these drugs. The combination of these two variant genotypes is a major cause of the inter-individual differences in coumarin anticoagulant drug dosage. Individuals who test positive for both variant genotypes are at increased risk of major bleeding. The impact of the CYP2C9 and VKORC1 genotype is most significant during the initial period of coumarin anticoagulant therapy. The effect of VKORC1 allelic variants is relatively similar for all three VKAs. The CYP2C9 polymorphism is associated with delayed stabilisation for coumarin anticoagulants. The effects of CYP2C9 polymorphisms on the pharmacokinetics and anticoagulant response are least pronounced in the case of phenprocoumon. In the long term, patients using phenprocoumon have more often international normalised ratio (INR) values in the therapeutic range, requiring fewer monitoring visits. This leads us to conclude that in the absence of pharmacogenetic testing, phenprocoumon seems preferable for use in long-term therapeutic anticoagulation. Pharmacogenetic testing before initiating coumarin oral anticoagulants may add to the safety of all coumarin anticoagulants especially in the elderly receiving multiple drugs.

Aconitum sp. alkaloids: The modulation of voltage-dependent Na+channels, toxicity and antinociceptive properties

Alkaloids from Aconitum sp., used as analgesics in traditional Chinese medicine, were investigated to elucidate their antinociceptive and toxic properties considering: (1) binding to Na+ channel epitope site 2, (2) alterations in synaptosomal Na+ and Ca2+ concentration ([Na+]i, [Ca2+]i), (3) arrhythmogenic action of isolated atria, (4) antinociceptive and (5) acute toxic action in mice. The study revealed a high affinity group (Ki 1 microM) and a low affinity group (Ki 10 microM) of alkaloids binding to site 2. The compounds of the high affinity group induce an increase in synaptosomal [Na+]i and [Ca2+]i (EC50 3 microM), are antinociceptive (ED50, 25 microg/kg), provoke tachyarrhythmia and are highly toxic (LD50 70 microg/kg), whereas low affinity alkaloids reduce [Ca2+]i, induce bradycardia and are less antinociceptive (ED50 20 mg/kg) and less toxic (LD50 30 mg/kg). These results suggest that the alkaloids can be grouped in Na+ channel activating and blocking compounds, but none of the alkaloids seem to be suitable as analgesics because of the low LD50/ED50 values.

Effect of converting enzyme inhibition and angiotensin receptor blockade on the vasoconstriction mediated by alpha 1-and alpha 2-adrenoceptor stimulation in pithed normotensive rats

SummaryThe effect of functional impairment of the renin-angiotensin system on the vasoconstriction mediated by postsynaptic α1 and α2-adrenoceptors in pithed normotensive rats was studied. Selective α1-adrenoceptor stimulation was induced by intravenously administered cirazoline, whereas B-HT 920 was used as a selective agonists at α2-adrenoceptors. The angiotensin converting enzyme was inhibited by intravenous treatment of the pithed rats with captopril, teprotide or enalapril. Blockade of angiotensin receptors was produced by intravenously applied [Sar1 Ala8]angiotensin II (saralasin). Pretreatment with angiotensin converting enzyme inhibitors or with saralasin in doses which produced a maximal reduction in basal diastolic blood pressure, only slightly attenuated the hypertensive response to cirazoline. In contrast, these drugs provoked a most significant reduction of the α2-adrenoceptor mediated vasoconstriction. Restoration of the basal diastolic blood pressure by intravenous infusion with angiotensin II or with vasopressin completely reversed the inhibitory effect of captopril on the vasopressor response to B-HT 920. One hour after bilateral nephrectomy, captopril still reduced the α2-adrenoceptor mediated vasoconstriction. However, 18–24 h after bilateral nephrectomy, captopril had no additional inhibitory effect on the vasopressor response to selective α2-adrenoceptor stimulation. It is concluded that in pithed normotensive rats the pressor response to α2-adrenoceptor stimulation is significantly potentiated by endogenous angiotensin II, even at low circulating levels of the octapeptide. The modulatory action of angiotensin II on the α-adrenoceptor mediated vasoconstriction probably represents an effect on the basal arteriolar muscular tone rather than a specific interaction.

Pharmacoeconomic evaluations of pharmacogenetic and genomic screening programmes : A systematic review on content and adherence to guidelines

The fields of pharmacogenetics and pharmacogenomics have become important practical tools to progress goals in medical and pharmaceutical research and development. As more screening tests are being developed, with some already used in clinical practice, consideration of cost-effectiveness implications is important. A systematic review was performed on the content of and adherence to pharmacoeconomic guidelines of recent pharmacoeconomic analyses performed in the field of pharmacogenetics and pharmacogenomics.Economic analyses of screening strategies for genetic variations, which were evidence-based and assumed to be associated with drug efficacy or safety, were included in the review. The 20 papers included cover a variety of healthcare issues, including screening tests on several cytochrome P450 (CYP) enzyme genes, thiopurine S-methyltransferase (TMPT) and angiotensin-converting enzyme (ACE) insertion deletion (ACE I/D) polymorphisms.Most economic analyses reported that genetic screening was cost effective and often even clearly dominated existing non-screening strategies. However, we found a lack of standardization regarding aspects such as the perspective of the analysis, factors included in the sensitivity analysis and the applied discount rates. In particular, an important limitation of several studies related to the failure to provide a sufficient evidence-based rationale for an association between genotype and phenotype.Future economic analyses should be conducted utilizing correct methods, with adherence to guidelines and including extensive sensitivity analyses. Most importantly, genetic screening strategies should be based on good evidence-based rationales. For these goals, we provide a list of recommendations for good pharmacoeconomic practice deemed useful in the fields of pharmacogenetics and pharmacogenomics, regardless of country and origin of the economic analysis.

DIFFERENTIAL EFFECT OF CALCIUM ENTRY BLOCKERS ON ALPHA-1-ADRENOCEPTOR-MEDIATED VASOCONSTRICTION INVIVO

SummaryThe effects of the calcium entry blockers nifedipine, (−)-verapamil and the dihydropyridine derivative PY 108-068 were evaluated on the increase in diastolic pressure of pithed normotensive rats caused by the selective α1-adrenoceptor agonists cirazoline, (−)-phenylephrine, (±)-erythro-methoxamine, (−)-amidephrine and St 587 [(2-chloro-5-trifluoromethylphenylimino)-2-imidazolidine] as well as by the mixed α1/α2-adrenoceptor agonists clonidine and DPI [(3,4-dihydroxyphenylimino)-2-imidazolidine]. The calcium entry inhibitors (up to 3 mg/kg) caused 3- to 5-fold, parallel rightward shifts of the log dose-pressor effect curves to cirazoline, (−)-phenylephrine, (±)-erythro-methoxamine and (−)-amidephrine accompanied by only a slight depression of the maximal pressor response. In contrast, the calcium entry inhibitors produced a dose-dependent profound depression of both maximum and slope of the log dose-pressor response curves to St 587 and clonidine. For DPI about 10-and 100-fold parallel displacements to the right without reduction of the maximum were found following treatment with 1 and 3 mg/kg of nifedipine, respectively. Infusion of vasopressin to counteract the vasodilatory action produced by the calcium entry inhibitors did not significantly change the pattern of interference observed under the conditions of decreased baseline diastolic pressure. The results indicate that α1-adrenoceptor-mediated vasoconstriction in the pithed normotensive rat, which is characterized by its sensitivity to blockade by prazosin and its relative insensitivity to antagonism by yohimbine or rauwolscine, can be subdivided into two distinct processes which are differentially influenced by blockade of calcium entry. It is suggested that cirazoline, (−)-phenylephrine, (±)-erythro-methoxamine and (−)-amidephrine initiate vasoconstriction predominantly by a mechanism independent of extracellular calcium influx. On the other hand, St 587 and clonidine increase arterial pressure via a mechanism which seems to be mainly governed by an entry of extracellular calcium ions. DPI probably triggers both processes of vasoconstriction in the intact circulatory system of the pithed normotensive rat.

Captopril impairs the vascular smooth muscle contraction mediated by postsynaptic α2-adrenoceptors in the pithed rat

Since two different types of α-adrenoceptors (α1- and α2-) subserve vasoconstriction in pithed rats and noradrenaline behaves as a non-selective agonist of both receptors (for review see Timmerman and van Zwieten, 1981), we have investigated this interaction between noradrenaline and captopril in more detail to identify the class of α-adrenoceptor involved. This study confirms the findings reported recently (Antonaccio and Kerwin, 1981; Clough et al., 1981) that captopril inhibits postjunctional vasocontrictor responses to noradrenaline in pithed rats. However, captopril interfered with the vasoconstriction elicited by noradrenaline only in those animals in which the vascular postsynaptic α2-adrenoceptor system could be triggered (saline-and prazosin-treated rats). Captopril was without effect after removal of the contribution of post-synaptic α2-adrenoceptor stimulation to the in vivo vascular smooth muscle contraction due to (-)-noradrenaline (rauwolscine-treated rats). These results indicate that captopril selectively impairs the vasoconstriction subserved in vivo by postjunctinal α2-adrenoceptors. The vasoconstrictor process initiated by α1-adrenoceptor activation is not affected by captopril.

Tardive dyskinesia and DRD3, HTR2A and HTR2C gene polymorphisms in Russian psychiatric inpatients from Siberia.

BACKGROUND Pharmacogenetics of tardive dyskinesia and dopamine D3 (DRD3), serotonin 2A (HTR2A), and 2C (HTR2C) receptors has been examined in various populations, but not in Russians. PURPOSE To investigate the association between orofaciolingual (TDof) and limb-truncal dyskinesias (TDlt) and Ser9Gly (DRD3), -1438G>A (HTR2A), and Cys23Ser (HTR2C) polymorphisms in Russian psychiatric inpatients from Tomsk, Siberia. METHODS In total, 146 subjects were included. Standard protocols were applied for genotyping. TDof and TDlt were assessed with AIMS items 1-4 and 5-7, respectively. Two-part model, logistic and log-normal regression analyses were applied to assess different variables (e.g., allele-carriership status, age, gender, and medication use). RESULTS TDlt, but not TDof, exhibited an association with Ser9Gly and Cys23Ser (with 9Gly and 23Ser alleles exhibiting opposite effects). However, -1438G>A was not associated with TDof and Dlt. CONCLUSIONS This is the first pharmacogenetic report on tardive dyskinesia in Russians. Subject to further replication, our findings extend and support the available data.