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In vitro effect of dexmedetomidine on platelet aggregation

Abstracts

BACKGROUND AND OBJECTIVES: Dexmedetomidine is a selective α2-agonist. There are 250-300 α2-adrenoceptor on the surface of each human platelet and ephedrine induces platelet aggregation by binding these receptors. This study was designed to study platelet function after incubation with therapeutic concentrations of dexmedetomidine. METHODS: The study was carried out on 18 healthy, non-smoking males, ages ranging 25 to 35 years old. Because of the recommended therapeutic concentration range of dexmedetomidine obtained by intravenous infusion is 0.4-1.2 ng.mL-1, dexmedetomidine solutions were prepared in three different concentrations. The calculated value of dexmedetomidine solution and diluent without dexmedetomidine as control were added to the blood sample. Thus, we obtained 0, 0.4, 0.8 and 1.2 ng.mL-1 dexmedetomidine concentrations of plasma. Each concentration of dexmedetomidine was incubated with whole blood at 37ºC during 15 minutes. Then blood samples were centrifugated to prepare platelet-rich plasma and platelet-poor plasma. The platelet-rich plasma was diluted with the platelet-poor plasma to yield test platelet-rich plasma with a final platelet count of 250 ± 50 X 10(9).L-1. RESULTS: The platelet aggregation amplitudes and slopes were statistically similar among all groups by the aggregation test, which were performed with ADP, collagen or epinephrine. CONCLUSION: Therapeutic concentrations of dexmedetomidine had no effect on the platelet functions in healthy individuals in vitro.

Dexmedetomidine; In Vitro; Platelet aggregation


JUSTIFICATIVA E OBJETIVOS: Dexmedetomidina é um α2-agonista seletivo. Há 250-300 receptores α2-adrenérgicos na superfície de cada uma das plaquetas humanas e a efedrina induz a agregação das plaquetas por ligação desses receptores. Este estudo foi desenvolvido para estudar a função plaquetária após incubação com concentrações terapêuticas de dexmedetomidina. MÉTODOS: O estudo foi conduzido com 18 homens saudáveis, não fumantes, com idades entre 25 e 35 anos. Porque o intervalo recomendado de concentração terapêutica de dexmedetomidina, obtido por infusão intravenosa, é de 0,4-1,2 ng.mL-1, as soluções de dexmedetomidina foram preparadas em três concentrações diferentes. Os valores calculados da solução de dexmedetomidina e do diluente sem dexmedetomidina (controle) foram adicionados a uma amostra de sangue. Assim, 0; 0,4; 0,8 e 1,2 ng.mL-1 de concentrações plasmáticas de dexmedetomidina foram obtidas. Cada concentração de dexmedetomidina foi incubada com sangue total a 37ºC durante 15 minutos. Em seguida, as amostras de sangue foram centrifugadas para preparar o plasma rico em plaquetas e o plasma pobre em plaquetas. O plasma rico em plaquetas foi diluído com o plasma pobre em plaquetas para gerar o teste de plasma rico em plaquetas com uma contagem final de plaquetas de 250 ± 50 x 10(9).L-1. RESULTADOS: As amplitudes e os declives da agregação plaquetária foram estatisticamente semelhantes entre todos os grupos nos testes de agregação feitos com ADP, colágeno ou adrenalina. CONCLUSÃO:As concentrações terapêuticas de dexmedetomidina não tiveram efeito in vitro nas funções plaquetárias de indivíduos saudáveis.

ANALGÉSICOS, Dexmedetomidina; Agregação Plaquetária; In Vitro


JUSTIFICATIVA Y OBJETIVOS: La Dexmedetomidina es un α2-agonista selectivo. Hay 250-300 receptores α2-adrenérgicos en la superficie de cada una de las plaquetas humanas y la efedrina induce a la agregación de las plaquetas por el vínculo con esos receptores. Este estudio tuvo el objetivo de estudiar la función plaquetaria después de la incubación con concentraciones terapéuticas de dexmedetomidina. MÉTODOS: El estudio fue llevado a cabo con 18 hombres sanos, no fumadores, con edades entre los 25 y los 35 años. Como el intervalo recomendado de concentración terapéutica de dexmedetomidina obtenido por infusión intravenosa es de 0,4-1,2 ng/mL, las soluciones de dexmedetomidina fueron preparadas en tres concentraciones diferentes. Los valores calculados de la solución de dexmedetomidina y del diluyente sin dexmedetomidina (control), fueron adicionados a una muestra de sangre. Así se obtuvieron 0; 0,4; 0,8 y 1,2 ng.mL-1 de concentraciones plasmáticas de dexmedetomidina. Cada concentración de dexmedetomidina fue incubada con sangre total a 37ºC durante 15 minutos. A continuación se centrifugaron las muestras de sangre para preparar el plasma rico en plaquetas y el plasma pobre en plaquetas. El plasma rico en plaquetas se diluyó con el plasma pobre en plaquetas para generar el test de plasma rico en plaquetas con un conteo final de plaquetas de 250 ± 50 x 10(9).L-1. RESULTADOS: Las amplitudes y los declives de la agregación plaquetaria fueron estadísticamente similares entre todos los grupos en los test de agregación hechos con ADP, colágeno o adrenalina. CONCLUSIÓN: Las concentraciones terapéuticas de dexmedetomidina no tuvieron efecto in vitro en las funciones plaquetarias de individuos sanos.

ANALGÉSICOS, Dexmedetomidina; Agregación Plaquetaria; In Vitro


SCIENTIFIC ARTICLE

IDepartment of Anesthesiology and Reanimation, School of Medicine, Kirikkale University, Kirikkale, Turkey

IIDepartment of Hematology, Gulhane Military Medical Academy, Ankara, Turkey

IIIDepartment of Anesthesiology and Reanimation, Kecioren Teaching and Medical Research Hospital, Ankara, Turkey

IVDepartment of Anesthesiology and Reanimation, Gulhane Military Medical Academy, Ankara, Turkey

Corresponding author

ABSTRACT

BACKGROUND AND OBJECTIVES: Dexmedetomidine is a selective α2-agonist. There are 250-300 α2-adrenoceptor on the surface of each human platelet and ephedrine induces platelet aggregation by binding these receptors. This study was designed to study platelet function after incubation with therapeutic concentrations of dexmedetomidine.

METHODS: The study was carried out on 18 healthy, non-smoking males, ages ranging 25 to 35 years old. Because of the recommended therapeutic concentration range of dexmedetomidine obtained by intravenous infusion is 0.4-1.2 ng.mL-1, dexmedetomidine solutions were prepared in three different concentrations. The calculated value of dexmedetomidine solution and diluent without dexmedetomidine as control were added to the blood sample. Thus, we obtained 0, 0.4, 0.8 and 1.2 ng.mL-1 dexmedetomidine concentrations of plasma. Each concentration of dexmedetomidine was incubated with whole blood at 37ºC during 15 minutes. Then blood samples were centrifugated to prepare platelet-rich plasma and platelet-poor plasma. The platelet-rich plasma was diluted with the platelet-poor plasma to yield test platelet-rich plasma with a final platelet count of 250 ± 50 X 109.L-1.

RESULTS: The platelet aggregation amplitudes and slopes were statistically similar among all groups by the aggregation test, which were performed with ADP, collagen or epinephrine.

CONCLUSION: Therapeutic concentrations of dexmedetomidine had no effect on the platelet functions in healthy individuals in vitro.

Keywords: Dexmedetomidine; In Vitro; Platelet aggregation

Introduction

Dexmedetomidine is a selective α₂ agonist for which labeled indication is intensive care unit (ICU) sedation. It can produce cooperative sedation associated with minimal respiratory depression and analgesia.1,2 Those properties make it useful in many clinical situations, including the sedation of ICU patients in whom the ability to perform frequent neurologic examination is of clinical importance. Additionally, because of the same properties, using this agent may be advantageous in central nervous system related procedures such as awake craniotomy, carotid endarterectomy with regional anesthesia, carotid angioplasty and stenting.1,3 It can also be preferred as an adjuvant in general anesthesia because of the possibility of the early extubation and recovery of cognitive functions. In this way, it is possible to reveal the additional postoperative neurological deficits in early postoperative period.4 The patients who are in ICU generally received concomitant medications such as vasopressors, vasodilators, digoxin, diuretics, beta blockers, aspirin, low molecular weight heparin that have all possible effects on platelet function. On the other hand, it is known that there are 250-300 α2-adrenoceptor on the surface of each human platelet and ephedrine activates platelets and induces their aggregation by binding these receptors.5 Ephedrine is considered a weak platelet agonist, the function which is mainly to sensitize platelets to other activating agents.6-9 Due to the possibility of the increased risk of hemorrhage by drug interactions, it is important to clarify the effects of dexmedetomidine on platelet functions for other medications may have possible additive effects on platelet function. This study was designed to study platelet function after incubation with therapeutic concentrations of dexmedetomidine in healthy volunteers.

Materials and methods

After obtaining local ethic committee approval and informed consent, we carried out the study on 18 healthy, non-smoking males, ages ranging 25 to 35 years old (mean ± SD = 28.32 ± 4.35 years). We did not include subjects who had an abnormal platelet count, a history of thrombosis or abnormal bleeding, active neoplasia or active inflammatory disease. All studies were done in the morning with the volunteers fasting overnight and we ascertained that no drugs had been taken within 2 weeks before testing. The venous blood samples were drawn without a tourniquet with a 20-gauge needle from the antecubital vein. We anti-coagulated the samples with 3.8% 0.130 M sodium citrate solution (blood to anticoagulant ratio: 9/1). There was no hemolysis in samples. We kept them at room temperature and tested within 60 minutes of collection. We counted platelets using an automated cell counter device (Abbott Cell-Dyne 4000; Abbott Park, Chicago, IL, USA).

Given the recommended therapeutic concentration range of dexmedetomidine obtained by intravenous infusion is 0.4-1.2 ng.mL-1 (Precedex® SPC; Abott Laboratories, Abbott Park, IL), we prepared dexmedetomidine solutions in three different concentrations which would yield 0.4 ng.mL-1, 0.8 ng.mL-1 and 1.2 ng.mL-1 dexmedetomidine by using 0.9% sodium chloride as diluent. We used the diluent not including dexmedetomidine as control. After the determination of hematocrit values, we divided the blood samples into four equal parts. According to the amount of plasma (derived from the hematocrit), we added the calculated value of dexmedetomidine solution and diluent without dexmedetomidine as control to blood sample (1 µL solution for 1 mL of plasma) and obtained 0, 0.4, 0.8 and 1.2 ng.mL-1 dexmedetomidine concentrations of plasma. Each concentration of dexmedetomidine was incubated with whole blood at 37ºC. After incubation for 15 minutes, blood samples were centrifugated (100 g, 10 minutes) to isolate platelet-rich plasma (PRP) from supernatant. We centrifuged the remainder of blood again (2,400 g, 20 minutes) to prepare platelet-poor plasma (PPP). The PRP was diluted with the PPP to yield test PRP with a final platelet count of 250 ± 50 X 109.L-1. Aggregation was performed using a turbidometric method (Chrono-log Corporation, Model 560-Ca; Havertown, PA, USA) according to the protocol of Chrono-log Corporation. We randomly changed the sequence by which different dilutions were studied in the aggregation, which was unknown to the persons performing the studies. We evaluated platelet aggregation response with adenosine diphosphate (ADP) (5 and 10 µM final concentrations), collagen (3 µg.mL-1 final concentrations) and epinephrine (10 µM final concentration). We obtained aggregating agents from Chrono-log Corporation. The device calculated dose-response cures automatically and evaluated them using amplitude and slope.

Statistical analysis

We analyzed data using the SPSS 11.5 (SPSS Inc. Software, Chicago, Illinois, USA) statistical software. Because the data were not normally distributed and the variations were not homogenous among all groups, we used Friedman repeated measure analysis of variance to compare platelet aggregation response to ADP, collagen or epinephrine between control and each dexmedetomidine solution. All data were presented as median and range. We considered p < 0.05 statistically significant.

Results

The platelet aggregation amplitudes and slopes were statistically similar among all groups by the aggregation test, performed with ADP, collagen or epinephrine (Table 1).

Discussion

Dexmedetomidine, the dextro enantiomer of medetomidine, is a potent and highly selective α₂-adrenoreceptor agonist.1-3 It is 8 to 10-fold more potent than clonidine for the α2-adrenoceptors. By virtue of this potency, dexmedetomidine is considered to be a full agonist of the α2-adrenoceptors, which might permit its application in relatively high doses for sedation and analgesia without the unwanted vascular effects from activation of α1-adrenoceptors.1-3 In addition to the administration in ICU as a sedative-analgesic agent, there have been a number of studies of lower doses of dexmedetomidine as an adjunct to anesthesia in cardiac and noncardiac surgical operations.10,11 On the other hand, human platelets have 250-300 α₂-adrenoreceptor on their surfaces. Ephedrine activates platelets and induces their aggregation by binding these receptors.5 Alpha-adrenergic receptors of human platelets are exclusively α2A subtype.11 In vitro, stimulation of platelet β2-adrenoreceptors blunts aggregation by increase of intracellular c AMP, and aggregatory response to epinephrine may be enhanced by non-selective blockage because of unopposed α₂-adrenoreceptor stimulation.13,14 It was speculated that catecholamine surge might trigger a hypercoagulable state and enhance the odds of overt thrombosis in patients with atherosclerotic disease and hypertension.15-18 Martins et al. evaluated effects of dexmedetomidine on blood coagulation by thromboelastography and concluded that dexmedetomidine had significantly increased reaction time and decreased coagulation index in final curves as compared to initial values. They reported that, although dexmedetomidine had a mild hypocoagulative effect, coagulation remained within normal ranges.19 Although it is wise to think that dexmedetomidine may have a decreasing effect on thrombotic events during an operation which stimulates sympathetic nervous system and leads to increased catecholamine levels, it is never used as a sole agent, not in patients undergoing surgery nor in the ICU. Hence, it is important to clarify the effects of dexmedetomidine on platelet functions for other medications, which may have possible additive effects on platelet function. We designed this study because of the fact that we could not find any published investigation related to the effects of dexmedetomidine on platelet functions in English medical literature.

A study that investigated the effects of clonidine and its analogue para-aminoclonidine showed that both agents potentiated platelet aggregation induced by a submaximal concentration of ADP and epinephrine-induced aggregation in a dose-dependent fashion. Stamp et al. concluded that these two agents are partial agonists for the α2-adrenergic receptors on blood platelets and that this receptor exists predominantly in the low-affinity state in the intact cell.20 Similarly, Petrusewicz et al. tested sixteen imidazole derivative drugs with regards to their aggregatory and antiaggregarory effects on human blood platelets and found a significant inhibition of the epinephrine induced aggregation in a dose dependent fashion by using clonidine in their study.21 In another study, it was shown that aggregation induced by ADP was potentiated by clonidine greater than or equal to epinephrine.22 In the present study, we used the recommended therapeutic dose range of dexmedetomidine in vitro and we could not find any statistically significant difference in platelet aggregation response to ADP (5 and 10 final concentrations), collagen (3 µg.mL-1 final concentrations) or epinephrine (10 µM final concentrations). While it is 8 to 10 fold more potent than clonidine for the α2-adrenoceptors, the lack of the potentialisation of the platelet aggregation by using dexmedetomidine can be explained by the low doses of dexmedetomidine. Additionally, it is notable that the increased platelet aggregation by which obtained clonidine in previous studies was also dose-dependent. Recent reports show that imidazole α-adrenergic agents inhibit epinephrine-induced aggregation in canine platelets more effectively than non-imidazole ones.23 In a previous report, nonadrenergic imidazole-prefered binding sites were shown in human platelets.24 Because both clonidine and dexmedetomidine have an imidazole structure, the imidazole structure could not be responsible for this situation. Although the results of platelet aggregation tests were not different with the therapeutic dose range of dexmedetomidine when compared with the control group in this study, these results may show an increased platelet aggregation with the usage of increased doses of the agent like clonidine. We preferred to study only the recommended dosage of this agent because of the fact that dexmedetomidine can cause unwanted cardiovascular effects with the usage of overdoses in clinical administration.

In conclusion, when used in similar concentrations to recommended dose-range, dexmedetomidine had no effect on the platelet functions in healthy individuals in vitro. However, platelet functions can be affected by several additional pathological and physiological mechanisms in clinical administration. Hence, it should be used cautiously especially if there is concomitant administration of the other medications, which can alter the platelet functions.

Conflicts of interest

The authors declare no conflicts of interest.

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  • In vitro effect of dexmedetomidine on platelet aggregation

    Emine Arzu KoseI; Oral NevruzII; Mehtap HoncaIII; Vedat YildirimIV
  • Publication Dates

    • Publication in this collection
      13 Nov 2013
    • Date of issue
      Oct 2013

    History

    • Received
      27 Aug 2012
    • Accepted
      11 Sept 2012
    Sociedade Brasileira de Anestesiologia R. Professor Alfredo Gomes, 36, 22251-080 Botafogo RJ Brasil, Tel: +55 21 2537-8100, Fax: +55 21 2537-8188 - Campinas - SP - Brazil
    E-mail: bjan@sbahq.org