Etodolac, a preferential COX-2 inhibitor, does not inhibit platelet aggregation in a randomized placebo-controlled trial

To date, platelet aggregation studies have not been formally evaluated in persons receiving Etodolac, a preferential cyclooxygenase-2 (COX-2) inhibitor. Our purpose was to investigate the influence of Etodolac in therapeutic (analgesic) doses (300 mg every 12h) on platelet aggregation as compared to placebo in healthy volunteers. Platelet aggregation, the primary efficacy variable in this trial, was performed according to the Born method with platelet rich plasma; it was evaluated as maximal platelet aggregation induced by 3 substances (adenosine diphosphate (ADP), epinephrine, collagen); each of these substances was used at 3 different concentrations. No significant difference in platelet aggregation as assessed by Born aggregometry was seen in volunteers treated with etodolac or placebo. Etodolac applied in regular analgesic doses to volunteers does not show an inhibitory effect on platelet aggregation and therefore seems an attractive analgesic substance for the perioperative setting. Norbert Zoller°, Anita Gähler, Priska Degiacomi, Wolfgang C Korte. ° Kantonsspital St. Gallen, † Center for Laboratory Medicine, St. Gallen; ‡ University of Bern, Bern, Switzerland. Corresponding author : Prof. Dr. med. Wolfgang Korte, Division of Clinical Chemistry and Hematology, Center for Laboratory Medicine, Kantonsspital, 9007 St. Gallen, Switzerland, wolfgang.korte@zlmsg.ch ; Phone:+41 – 71 – 494 39 73 ; Fax:+41 – 71 – 494 39 00 Running title Etodolac does not inhibit platelet aggregation. DOI : 10.14302/issn.2328-0182.japst-12-99 Freely Available Online www.openaccesspub.org | JAPST CC-license DOI : 10.14302/issn.2328-0182.japst-12-99 Vol-1 Issue –1 Page No3 Introduction Research into cyclooxygenase inhibition lead to the identification of a constitutional cyclooxygenase activity (cyclooxygenase 1, COX-1), which can be distinguished from a cytokine-induced cyclooxygenase activity (cyclooxygenase 2, COX-2) [1]. With the use of cyclooxygenase inhibitors as anti-inflammatory agents and analgesics, unwanted side effects such as mucosal toxicity can occur. It was postulated that such side effects are mainly associated to the effects of COX-1 inhibition [2]; and that preferential inhibition of COX-2 would therefore decrease this type of toxicity [3]. This lead to the development of preferential COX-2 inhibitors with effective anti-inflammatory and analgesic effects documented [4,5]. As postulated, it became apparent that COX-2 inhibition was indeed associated with a lower degree of mucosal toxicity [6]. It was also shown that COX-2 activity is not involved in platelet thromboxane biosynthesis [7] and that selective COX-2 inhibition thus does not effect platelet thromboxane A2 (TxA2) dependent platelet aggregation [8]. No such studies were published on the use of Etodolac (Lodine, SigmaTau Pharma AG, Zofingen, Switzerland) in humans so far. Analgesic drugs that modify enzymatic pathways can influence platelet aggregability and use of non-steroidal anti-inflammatory drugs (NSAIDs) may lead to increased perioperative bleeding risk [9,10], a side effect seen with COX inhibitors [11]. Perioperative bleeding is becoming a more important issue for various reasons, including the increased frequency of regional anesthesia. Etodolac, a COX inhibitor that was introduced in the 1980s has been marketed world-wide. In 1999, it was identified as a preferential COX-2 inhibitor [12]. Which was, however, shown not to be significantly selective towards COX-2 [13,14,15]. However, up to date in medical practice neither an increased risk of bleeding nor an increased risk of cardiovascular side effects had been observed [16-18]. Only minimal renal side effects have been described [1921], with one patient with rheumatoid arthritis developing a membranous nephropathy [22]. A previous study [23] showed that the analgesic effect of a short-term treatment with etodolac after coronary artery bypass operation is superior to tramadol. In that study, a trend toward a faster pain reduction with etodolac as compared with diclofenac was observed, suggesting that the analgesic effect of etodolac in that setting is at least as effective as that of diclofenac. Therefore, it is of interest to know in addition whether Etodolac has any effect on platelet aggregation. The objective of this study was thus to investigate the influence of Etodolac in therapeutic doses on platelet aggregation as compared to placebo in healthy volunteers as no studies on platelet aggregation with the use of Etodolac has been published so far. Experimental procedures, Materials and Methods The study was approved by the institutional review board and was registered with the swiss federal regulatory board (Swissmedic 2005DR1357). Volunteers (20 to 50 years of age, table 1) gave written informed consent. This study was designed as an open-label, crossover, randomized, prospective, monocentric, placebocontrolled study. Determination of sample size For the primary variable, a normal distribution was assumed. We anticipated a mean aggregation of 80% of the normal (± 15%) in the placebo group. A mean of 65% (± 15%) (i.e. a difference of 15%) was considered as a clinically significant deviation. The power calculation was performed as specified for AB/BA (two-stage crossover) trials. To reach a power of 80%, a sample size of 12 subjects was thus needed. The sequence of treatment allocation with randomization was blockwise (5 volunteers per block). In-/Exclusion criteria Exclusion criteria included the use of NSAIDs in the last 14 days before study entry; known hypersensitivity to any active or inactive ingredient of the study medication or placebo; history of allergic reactions to acetyl salicylic acid or other NSAIDs; use of platelet inhibiting medication during the last 30 days before study entry; diagnosis of malignancy; any history of cardiovascular, respiratory, renal, hepatic, haematological, neurological or psychiatric pathologies; a history of gastric and / or duodenal ulcers or other gastrointestinal bleeding; inflammatory bowel diseases; history of thromboses; history of bleeding, alone or in conjunction with NSAID (Continued on page 4) Freely Available Online www.openaccesspub.org | JAPST CC-license DOI : 10.14302/issn.2328-0182.japst-12-99 Vol-1 Issue –1 Page No4 use; concomitant medication (except oral contraceptives); women of child-bearing potential not willing to subject to a medically accepted method of contraception; pregnant or nursing women; and participation in another clinical trial in the 30 days preceding the study. Before enrolment, a complete medical history was taken and a physical examination was performed. Laboratory parameters evaluated at this point were liver function, renal parameters and complete blood count.


Introduction
Research into cyclooxygenase inhibition lead to the identification of a constitutional cyclooxygenase activity (cyclooxygenase 1, COX-1), which can be distinguished from a cytokine-induced cyclooxygenase activity (cyclooxygenase 2, COX-2) [1]. With the use of cyclooxygenase inhibitors as anti-inflammatory agents and analgesics, unwanted side effects such as mucosal toxicity can occur. It was postulated that such side effects are mainly associated to the effects of COX-1 inhibition [2]; and that preferential inhibition of COX-2 would therefore decrease this type of toxicity [3]. This lead to the development of preferential COX-2 inhibitors with effective anti-inflammatory and analgesic effects documented [4,5]. As postulated, it became apparent that COX-2 inhibition was indeed associated with a lower degree of mucosal toxicity [6]. It was also shown that COX-2 activity is not involved in platelet thromboxane biosynthesis [7] and that selective COX-2 inhibition thus does not effect platelet thromboxane A2 (TxA2) dependent platelet aggregation [8]. No such studies were published on the use of Etodolac (Lodine ® , Sigma-Tau Pharma AG, Zofingen, Switzerland) in humans so far.
Analgesic drugs that modify enzymatic pathways can influence platelet aggregability and use of non-steroidal anti-inflammatory drugs (NSAIDs) may lead to increased perioperative bleeding risk [9,10], a side effect seen with COX inhibitors [11]. Perioperative bleeding is becoming a more important issue for various reasons, including the increased frequency of regional anesthesia.
Etodolac, a COX inhibitor that was introduced in the 1980s has been marketed world-wide. In 1999, it was identified as a preferential COX-2 inhibitor [12]. Which was, however, shown not to be significantly selective towards COX-2 [13,14,15]. However, up to date in medical practice neither an increased risk of bleeding nor an increased risk of cardiovascular side effects had been observed [16][17][18].
A previous study [23] showed that the analgesic effect of a short-term treatment with etodolac after coronary artery bypass operation is superior to tramadol. In that study, a trend toward a faster pain reduction with etodolac as compared with diclofenac was observed, suggesting that the analgesic effect of etodolac in that setting is at least as effective as that of diclofenac.

Therefore, it is of interest to know in addition whether
Etodolac has any effect on platelet aggregation. The objective of this study was thus to investigate the influence of Etodolac in therapeutic doses on platelet aggregation as compared to placebo in healthy volunteers as no studies on platelet aggregation with the use of Etodolac has been published so far.

Experimental procedures, Materials and Methods
The study was approved by the institutional review

Determination of sample size
For the primary variable, a normal distribution was assumed. We anticipated a mean aggregation of 80% of the normal (± 15%) in the placebo group. A mean of 65% (± 15%) (i.e. a difference of 15%) was considered as a clinically significant deviation. The power calculation was performed as specified for AB/BA (two-stage crossover) trials. To reach a power of 80%, a sample size of 12 subjects was thus needed.
The sequence of treatment allocation with randomization was blockwise (5 volunteers per block).

Outcome parameters
The primary efficacy variable in this trial was the extent of platelet aggregation during treatment with Etodolac (Continued on page 5) 1.25µg/ml, 5µg/ml, 10µg/ml).
As the measurement method remained the same in all instances, the model was performed with the mean value of the measurements of the 3 substances at each point in time.

Statistical analysis
All statistical tests were interpreted on the 5% significance level. or dropped out of the study prematurely) population.
Mean age ± standard deviation (SD) in this population was 37.1 ± 9.5 years.
No abnormal laboratory value was observed in any volunteer during the study.
Of the ITT population comprising 19 subjects; one volunteer was taken off study after visit 1 due to possible adjudication bias (this person was referred by Only one adverse event (abdominal discomfort) according to the study protocol was observed; it was judged to be possibly related to the study medication, but not to be clinically relevant. Of the four volunteers that were not included in the PP population, two each were in the placebo (cross over to etodolac) and the etodolac (cross over to placebo) group. The ITT population comprised 9 volunteers in the etodolac group and 10 volunteers in the placebo group (see figure 4).

Discussion
The main finding of our study is that etodolac at regular  [26][27][28][29][30], but this has not been undisputed [31]. COX-2 inhibiting drugs might be appropriate tools to provide a perioperative analgesic approach without the risk of increased bleeding. These observations with a seemingly well tolerated drug [16][17] might be particularly interesting since Rofecoxib, a selective COX-2 inhibitor, was withdrawn from the market due to its cardio-vascular and renal side effects [32], reigniting the debate on the safety of selective COX-2 inhibitors [33][34][35].
Others have shown that neither short-nor long-term exposure to etodolac was associated with cardionegative or -protective effects as compared to ibuprofen, rofecoxib and celecoxib [18].
As NSAIDs are frequently used postoperatively for analgesic treatment [36,37], side effects from these Born showed a better ability to detect differences in platelet aggregation when compared with the VASP assay [43].
As data from this study (and in accordance with animal studies) show that etodolac has no influence on platelet aggregation in healthy volunteers at regular doses, it seems that this substance might be an important addition to the analgesic armentarium in the perioperative setting. Others have shown that etodolac is efficacious in postoperative pain control in cardiac surgery [23], where platelet aggregation inhibition is an important issue with regard to catheters used for analgesic therapy. In the aforementioned animal study [41], no additional effect of etodolac on top of aspirin in inhibiting platelet aggregation was found. It would be interesting to further investigated this combination in a clinical study.
We believe that our study adds to the body of knowledge suggesting that etodolac is indeed advantageous in situations where nonsteroidal analgesics are desirable but where adequate hemostasis is a concern at the same time.

Conclusion
Our study shows that etodolac -applied in regular analgesic doses to volunteers -does not show an        further conflicts of interest are to be reported.

The current affiliation of Norbert Zoller is "Geriatrische
Klinik St. Gallen".