Genetic polymorphisms and the impact of a higher clopidogrel dose regimen on active metabolite exposure and antiplatelet response in healthy subjects.

A double-blind crossover study was conducted in four CYP2C19 genotype-defined metabolizer groups to assess whether increase in clopidogrel dosing can overcome reduced pharmacodynamic response in CYP2C19 poor metabolizers (PMs). Ten healthy subjects in each of four metabolizer groups were randomized to a clopidogrel regimen of a 300-mg loading dose (LD) and a 75-mg/day maintenance dose (MD) for 4 days followed by 600-mg LD and 150 mg/day MD, or vice versa. The exposure levels of clopidogrel's active metabolite H4 (clopi-H4) in PMs were 71% lower on the 75-mg/day regimen and 64% lower on the 150-mg/day regimen than the corresponding exposure levels in extensive metabolizers (EMs). In PMs, the maximal platelet aggregation (MPA) induced by adenosine diphosphate (ADP) 5 µmol/l was 10.5% lower on the 75-mg/day regimen and 7.9% lower on the 150-mg/day regimen than the corresponding values in EMs. PMs who were on the clopidogrel regimen of 600-mg LD/150 mg/day MD showed clopi-H4 exposure and MPA levels similar to those in EMs who were on the regimen of 300-mg LD/75 mg/day MD. In a pooled analysis evaluating CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP3A5, CYP2D6, ABCB1, and P2RY12 polymorphisms (N = 396 healthy subjects), only CYP2C19 had a significant impact on antiplatelet response. In healthy CYP2C19 PMs, a clopidogrel regimen of 600-mg LD/150 mg/day MD largely overcomes diminished clopi-H4 exposure and antiplatelet response, as assessed by MPA levels.

Differential effects of omeprazole and pantoprazole on the pharmacodynamics and pharmacokinetics of clopidogrel in healthy subjects: randomized, placebo-controlled, crossover comparison studies.

Four randomized, placebo-controlled, crossover studies were conducted among 282 healthy subjects to investigate whether an interaction exists between clopidogrel (300-mg loading dose/75-mg/day maintenance dose) and the proton-pump inhibitor (PPI) omeprazole (80 mg) when they are administered simultaneously (study 1); whether the interaction, if any, can be mitigated by administering clopidogrel and omeprazole 12 h apart (study 2) or by increasing clopidogrel to 600-mg loading/150-mg/day maintenance dosing (study 3); and whether the interaction applies equally to the PPI pantoprazole (80 mg) (study 4). Relative to levels after administration of clopidogrel alone in studies 1,2,3, and 4, coadministration of PPI decreased the AUC(0-24) of the clopidogrel active metabolite H4 by 40, 47, 41, and 14% (P ≤ 0.002), respectively; increased maximal platelet aggregation (MPA) induced by 5 micromol/l adenosine diphosphate (ADP) by 8.0, 5.6, 8.1, and 4.3% (P ≤ 0.014), respectively; and increased the vasodilator-stimulated phosphoprotein phosphorylation-platelet reactivity index (VASP-PRI) by 20.7, 27.1, 19.0 (P < 0.0001), and 3.9% (P = 0.3319), respectively. The results suggest that a metabolic drug-drug interaction exists between clopidogrel and omeprazole but not between clopidogrel and pantoprazole.

Antithrombotic effects of S 18886, a novel orally active thromboxane A2 receptor antagonist.

Platelet activation and thrombus formation play a critical role in the onset of acute coronary syndromes. Thromboxane A2 (TxA2) is among the different chemical modulators released by activated platelets. TxA2 is considered one of the most powerful agonists for platelet activation. In addition, TxA2 exerts a vasoconstrictor effect by serving as an agonist of the thromboxane receptor (TP) on the vascular smooth muscle cell membranes. The putative effect of TxA2 on thrombosis is demonstrated by the clinical effectiveness of acetylsalicylic acid (ASA) in the prevention of acute coronary syndromes. Among the clinically used antiplatelet agents, clopidogrel has shown to be slightly more effective than ASA in the prevention of atherothrombotic events in patients with peripheral arterial disease, and is one of the most widely used after aspirin. The aims of the study were to study the antithrombotic effects of escalating doses of the TP-receptor antagonist, S 18886 and to compare its effects with those achieved by the administration of ASA (5 mg kg-1 day-1), and clopidogrel (3 mg kg-1 day-1). The study was undertaken at high and low shear rate conditions using the Badimon perfusion chamber in a porcine model. Antithrombotic effects were assessed as changes on platelet and fibrin(ogen) deposition. The doses of 30 and 100 micro g kg-1 day-1 were selected based on a previous platelet aggregation study. S 18886 shows a dose-dependent antithrombotic response. The dose of S-100 develops similar antithrombotic effects to those of clopidogrel and superior to those of aspirin. The antithrombotic effects were statistically significant at both studied shear rate conditions. Therefore, the orally active TP-receptor antagonist, S 18886, appears to be a new and effective agent to prevent atherothrombotic complications.

Dose-effect relationship for several coagulation markers during administration of the direct thrombin inhibitor S 18326 in healthy subjects.

AIMS: We conducted a phase I placebo-controlled trial with two i.v. doses (0.5 mg h-1 and 3 mg h-1) of S 18326, a selective thrombin inhibitor that interacts with the catalytic site of thrombin, with the aim to study the relationships between increasing plasma levels of S 18326 and changes in coagulation tests and thrombin generation markers. METHODS: Thirty-six healthy male volunteers were divided into three groups. In each group, 10 volunteers were randomly assigned to receive S 18326 and two to receive a placebo. Following a bolus of 4.5 mg, doses were 0.5 mg h-1 in the first group and 3 mg h-1 in the two other groups, administered as an i.v. infusion for 24 h. Blood was drawn repeatedly up to 36 h after the bolus, and tested for the activated clotting time (ACT) and activated partial thromboplastin time (APTT). The APTT reagent was chosen among five commercial reagents to yield a linear increase in the clotting time among possible therapeutic S 18326 concentrations in vitro. To accurately measure the thrombin-inhibiting effects of low doses of S 18326 (< 0.5 microm), we developed a specific chromogenic assay. We also measured F1 + 2 prothrombin fragment levels to assess the effect of S 18326 on thrombin generation in vivo. RESULTS: A two-compartment pharmacokinetic model was fitted to the S 18326 plasma concentration vs time data by using population pharmacokinetic methods. Results of the pharmacodynamic-pharmacokinetic relationships showed that both the ACT and APTT methods yielded a linear increase according to the S 18326 concentration measured using a highly sensitive analytical method. At the end of infusion, ACT was prolonged 1.20 and 1.95-fold in the 0.5 mg h-1 and the 3 mg h-1 groups, respectively, and APTT was prolonged 1.27 and 2.75-fold. Thrombin inhibition plateaued above 0.5 microm of S 18326 according to an Emax model, confirming that the test was highly sensitive. F1 + 2 levels fell significantly after the 24 h S 18326 infusion (0.83 nm to 0.6 nm and 0.80 nm to 0.44 nm in the 0.5 mg h-1 and the 3 mg h-1 groups, respectively), but remained stable after the placebo infusion. CONCLUSIONS: Our results support specific monitoring of the thrombin inhibitor S 18326 with ACT and APTT to establish the safety range of the drug in further studies. Moreover, the fall in F1 + 2 prothrombin fragments suggests that S 18326 effectively reduces the retroactivation of factors V and VIII by thrombin.

Rilmenidine normalizes fructose-induced insulin resistance and hypertension in rats.

OBJECTIVE: The aim of this study was to determine the effects of rilmenidine (an antihypertensive drug that lowers blood pressure by decreasing sympathetic outflow) in an animal model of hypertension associated with insulin resistance, i.e. rats fed on a high-fructose diet. DESIGN: Wistar rats were fed for 4 weeks either on a standard diet (S group) or on a high-fructose diet (F group; 34.5% fructose). In half of the rats in the F group, rilmenidine (1 mg/kg per day) was added to the drinking water for the last 2 weeks of the diet (FR group). RESULTS: Body weight gain was higher in the F than in the S rats (66+/-8g versus 45+/-8g, P< 0.05), but was prevented by rilmenidine treatment (32+/-2g). Arterial systolic blood pressure was increased in F rats (162+/-2 versus 155+/-2 mmHg, P< 0.05), rilmenidine reduced this value to normal (149+/-3 mmHg). Glucose tolerance, glucose turnover rate, and insulin secretion were not modified by the diet or by the drug. However, during a euglycemic hyperinsulinemic clamp, glucose utilization was lower (10+/-1 versus 14+/-1.5 mg/min per kg; P< 0.05) and hepatic glucose production higher (1+/-0.01 versus 0 mg/min per kg, P< 0.01) in F than in S rats. These changes in insulin action were totally abolished by rilmenidine. CONCLUSIONS: These data demonstrate that rilmenidine can ameliorate the deleterious effects of a high-fructose diet, i.e. weight gain, hypertension, and resistance to the effects of insulin.

Cardiac vagal effects of rilmenidine in the dog: comparison with clonidine.

1. The cardiac vagal effects of rilmenidine (5 micrograms kg-1 min-1) and clonidine (0.5 micrograms kg-1 min-1) were studied in chloralose anaesthetized dogs. 2. Rilmenidine and clonidine progressively reduced the vagal stimulation-induced bradycardia. As indicated by the ED70, rilmenidine was about 23 times less potent than clonidine in this respect. Concomitantly, both drugs dose-relatedly decreased heart rate and mean blood pressure with potency ratios of rilmenidne to clonidine of about 1:23 and 1:12, respectively. 3. Importantly, the heart rate values observed under vagal stimulation during drug infusion never exceeded the values under basal vagal stimulation, and with both drugs large interindividual variations occurred under vagal stimulation. 4. These results show that the vagal bradycardia inhibition produced by rilmenidine and clonidine results from their true bradycardic effects and not from actual cardiac vagolytic properties.

[Effects of rilmenidine on rats made insulin resistant and hypertensive by a high fructose diet]. / Effets de la rilménidine chez le rat rendu insulinorésistant et hypertendu par un régime riche en fructose.

This study was aimed to determine the effects of rilmenidine, an hypertensive drug, in an animal model of hypertension associated with insulin resistance, i.e. rats fed on a high fructose diet. Wistar rats were fed during four weeks either on a standard diet (S) or on a high fructose diet (F, 34.5% de fructose). In half of the F groups, rilmenidine (1 mg/kg/day) was added to the drinking water during the two last weeks of the diet (FR). Arterial blood pressure as well as insulin efficiency were determined at the end of the four weeks. Body weight gain was higher in F than in S rats (66 +/- 8 g versus 45 +/- 8 g; p < 0.05), this was prevented by rilmenidine treatment (32 +/- 2 g). Arterial systolic blood pressure was increased in F rats (162 +/- 2 vs 155 +/- 2 mmHg; p < 0.05), rilmenidine brought this value back to normal (149 +/- 3 mmHg). During the euglycemic hyperinsulinemic clamp, glucose utilization was lower (10 +/- 1 vs 14 +/- 1.5 mg/min/kg; p < 0.05) and hepatic glucose production higher (1 +/- 0.01 vs 0 mg/min/kg; p < 0.01) in F than in S rats. These changes in insulin action were totally abolished by rilmenidine. These data demonstrate that rilmenidine can ameliorate the deleterious effects of a high fructose diet, i.e. weight gain, hypertension and resistance to the effects of insulin Rilmenidine could represent a potential therapeutic agent for the treatment of hypertension associated with metabolic disorders such as syndrom X and obesity.

Interactions of the cardiac chronotropic effects of rilmenidine with the autonomic nervous system in conscious dogs: comparison with clonidine.

1. The cardiac chronotropic effects of rilmenidine (10-100 micrograms kg-1) and clonidine (1-10 micrograms kg-1) were studied in conscious dogs with chronic atrioventricular block. 2. Rilmenidine and clonidine initially (< 3 min) decreased atrial rate, although the effect was not related to dose. More lastingly, ventricular rate was decreased in a dose-related manner (ratio, 1:21). Rilmenidine lowered mean blood pressure only at 100 micrograms kg-1, while clonidine had the same effect at doses of 5 micrograms kg-1 upward (ratio, 1:15). 3. When administered after atropine and pindolol, rilmenidine (50 micrograms kg-1) produced a decrease in atrial rate, with an identical intensity but longer duration than under basal conditions. When clonidine (2.5 micrograms kg-1) was given after atropine, no chronotropic atrial effect was observed. However, when clonidine (2.5 micrograms kg-1) was given after pindolol, it produced a decrease in atrial rate that was more marked, both in intensity and duration, than under basal conditions. After phenoxybenzamine, rilmenidine decreased atrial rate with a more marked and lasting effect than observed under basal conditions. Clonidine produced a bradycardic atrial effect identical to the basal effect. After yohimbine, rilmenidine and clonidine decreased atrial rate with an intensity similar to that under basal conditions, although the time course was totally different. 4. When given after atropine, rilmenidine (50 micrograms kg-1) and clonidine (2.5 micrograms kg-1) decreased ventricular rate as under basal conditions, whereas after pindolol and phenoxybenzamine, both drugs decreased ventricular rate less markedly than under basal conditions, both in intensity and duration. After yohimbine, rilmenidine and clonidine produced no chronotropic ventricular effect. 5. These results show that (a) the initial atrial bradycardia caused by rilmenidine results from both a decrease in sympathetic tone and an increase in cholinergic activity; while the effect of clonidine is caused mainly by the enhancement of cholinergic activity. For both drugs, alpha 2-adrenoceptors are involved at least in the initiation of the effect; (b) the very short duration of atrial bradycardia may result from reflex buffering in response to ventricular bradycardia. This buffering is less effective when heart rate was high; and (c) the ventricular bradycardia caused by both drugs is mainly the result of a decrease in sympathetic tone in response to the stimulation of alpha 2-adrenoceptors. The results also suggest that negative chronotropic postsynaptic alpha 2-adrenoceptors could be involved in the ventricular bradycardia.

Cardiac electrophysiological effects of rilmenidine, a novel antihypertensive agent, in the conscious dog: comparison with clonidine.

The cardiac electrophysiological effects of rilmenidine, a novel antihypertensive agent, and clonidine were studied in the conscious dog. Sinus rate, corrected sinus recovery time (CSRT) and Wenckebach point (WP) were measured in seven intact dogs. Atrial rate and atrial effective refractory period (AERP) were measured in six atrioventricular (AV)-blocked dogs with ventricular pacing. In both groups, blood pressure was also monitored. Each dog received with at least a three-day interval rilmenidine as dihydrogen phosphate and clonidine as hydrochloride in four successive intravenous injections, 30 min apart. In intact dogs, rilmenidine was administered at 50, 50, 100 and 200 micrograms/kg and clonidine at 2.5, 2.5, 5 and 10 micrograms/kg. In AV-blocked dogs, doses of rilmenidine were 25, 25, 50 and 100 micrograms/kg, those of clonidine 5, 5, 10 and 20 micrograms/kg. Rilmenidine and clonidine decreased sinus rate and atrial rate from the first dose. In this regard, rilmenidine was respectively 24 and 23 times less potent than clonidine. A lengthening of CSRT was observed at all doses with rilmenidine and at the last three doses with clonidine (ratio: 17) and a lowering of WP at all doses with rilmenidine and clonidine (ratio: 22). A shortening of AERP was also seen with rilmenidine and clonidine from the second dose (ratio: 6). All these effects may at least partly be explained by a cholinergic activation mechanism. In intact dogs both drugs produced a lowering of mean blood pressure (ratio: 17), whereas in AV-blocked dogs, in which ventricular rate was kept constant by pacing, pressure effects were more complex, being the resultant of hypotensive and hypertensive effects, the latter due to alpha vascular stimulation. Taken together, these results indicate that in the conscious dog, rilmenidine and clonidine exert qualitatively identical electrophysiological effects, but with different potency ratios.

Endothelin modulates dihydropyridine receptor decreased binding in hippocampal slices from normotensive and spontaneously hypertensive rats.

Previous studies in rats have demonstrated both the link between voltage-operated calcium channels and endothelin and their cerebral involvement in the pathophysiology of spontaneous hypertension. In the present study, the interaction of endothelin with specific dihydropyridine (DHP) binding sites was investigated using the brain slices model. In rat hippocampal slices, pre-incubation with Bay K 8644 decreased [3H] (+) PN 200-110 binding. There was no difference in agonist-induced decrease of DHP binding in normotensive and spontaneously hypertensive (SH) rats. The effect of Bay K 8644 was partially inhibited by endothelin but not by angiotensin in both normotensive and hypertensive rats. These data compared to those of other studies suggest that DHP binding sites which are regulated by endothelin are post-synaptic. We conclude that brain slices provide a good in vitro model to study DHP receptor regulation and to explore endothelin interactions with DHP-sensitive Ca2+ channels.

Intrathecal somatostatin in terminally ill patients. A report of two cases.

Intrathecal morphine has been shown to be reliable in producing analgesia in patients with intractable cancer pain. Recently, we have demonstrated that intrathecal somatostatin is as effective in the treatment of cancer pain as intrathecal morphine. This report presents 2 cases in whom analgesia could be maintained for 60 and 25 days, respectively, under continuous intrathecal infusion of somatostatin by means of infusion devices.