临床药理学消化系统课件.ppt

1、.1治疗胃肠道疾病药物治疗胃肠道疾病药物 消化系统最常见病有：消化系统最常见病有：慢性胃炎、消化性溃疡、和消化系肿慢性胃炎、消化性溃疡、和消化系肿瘤。瘤。肠易激综合征和功能性消化不良越来肠易激综合征和功能性消化不良越来越受到关注。越受到关注。另外，肝胆系统疾病也是很常见疾病。另外，肝胆系统疾病也是很常见疾病。近年在消化性溃疡的发病机制和治疗近年在消化性溃疡的发病机制和治疗的研究都有了显著进展。幽门螺杆菌在的研究都有了显著进展。幽门螺杆菌在胃部疾病发病中的作用有了进一步的认胃部疾病发病中的作用有了进一步的认识。识。.2消化性溃疡（消化性溃疡（peptic ulcer）为消化系）为消化系统最常见疾

2、病，发病率约统最常见疾病，发病率约8%10%。为。为一种慢性疾病，可反复发作，病情持续一种慢性疾病，可反复发作，病情持续数年至数十年，可发生于消化道任何部数年至数十年，可发生于消化道任何部位，最多见于胃和十二指肠溃疡。胃溃位，最多见于胃和十二指肠溃疡。胃溃疡多位于胃小弯近幽门处，十二指肠溃疡多位于胃小弯近幽门处，十二指肠溃疡一般位于球部。疡一般位于球部。消化性溃疡消化性溃疡.3一、病因及发病机制一、病因及发病机制 溃疡病的发病机制过去过于强调胃酸和胃蛋白酶的攻击作用，后来开始重视粘膜屏障、细胞保护因子、局部血液循环等抗溃疡因素。正常情况下两者处于平衡状态，当致溃疡因素作用超过抗溃疡因素，两者不

3、平衡时就易发生溃疡。.4攻击因子（致溃疡因素）胃酸过多：各种刺激引起胃酸和胃蛋白酶分泌，产生自身消化作用。有“无酸不成溃疡”的说法。幽门螺杆菌（Helicobacter pylori,Hp）：寄生在胃粘液层之下，破坏粘液层，减弱其保护作用。是溃疡病长期不愈，反复发作的重要因素。药物：阿斯匹林及非甾体类抗炎药 胆汁和十二指肠液的反流：可破坏胃粘膜，刺激G细胞分泌胃泌素促胃酸分泌。.5防御因子（抗溃疡因素）粘膜屏障：粘液-碳酸氢盐屏障（胃腔中pH常/=3 mm in size with depth,that can involve the stomach(gastric ulcer)or duod

4、enum(duodenal ulcer).The most important contributing factors are Helicobacter pylori,nonsteroidal anti-inflammatory drugs(NSAIDs),acid,and pepsin.17 Although peptic ulcers produce a variety of symptoms,none is specific for the disease.Severe pain or a rapid increase in pain suggests an ulcer complic

5、ation or another diagnosis;associated dyspepsia symptoms include nausea,bloating,heartburn,and belching.Indeed,peptic ulcers are the most common cause of acute upper GI bleeding.18 H pylori eradication and/or antisecretory therapies are the mainstay of todays treatment strategies.19四、治疗溃疡病药物分类四、治疗溃疡

6、病药物分类（一）治疗溃疡病药物的评价治疗溃疡病主要有4个有目的：（1）控制症状；（2）促进溃疡愈合；（3）防止并发症发生；（4）防止溃疡复发。现今的所有抗溃疡药物均能达到（1）和（2）的目的，有的还可减少并发症，如出血，穿孔等。但现有的抗溃疡药物都不能彻底根治溃疡病，而杀灭幽门螺旋杆菌的药物能大大降低复发率。.20抗酸剂：氢氧化铝，三硅酸镁，碳酸钙等，起中和胃酸作用，现已很少用。抑制胃酸分泌：H2受体阻断剂：西咪替西，雷尼替丁，法莫替丁H+-K+-ATP酶抑制剂（质子泵抑制剂）：奥美拉唑，兰索拉唑其他还有M受体阻断剂和胃泌素受体阻断剂胃粘膜保护剂：前列腺素E，枸橼酸铋钾，硫糖铝杀灭幽门螺杆菌：

7、三联疗法：枸橼酸铋、甲硝唑、羟氨苄青霉素二联疗法：奥美拉唑、甲红霉素，或加羟氨苄青霉素三联疗法.21Acid Peptic Diseases Pharmacological Approach to Treatment http:/ Modulating Gastric Acid 抗酸药物的发展 Beginning with antacids,histamine type-2 receptor antagonists(H2RAs),and sucralfate,there has been a steady development of effective therapies for these

8、 conditions,culminating with the proton-pump inhibitors(PPIs).23Antacids 现已用得越来越少了，大多被H2RAs和PPIs取代。特点：They are inexpensive,readily available,and safe in most populations.Antacids work nearly instantaneously and find utility for rapid relief of mild or sporadic symptoms.The effective time for antacid

9、s to reduce stomach acidity is relatively short on an empty stomach.calcium carbonate,sodium bicarbonate,magnesium hydroxide and aluminum hydroxide.hydrotalcite铝碳酸镁.24H2-receptor Antagonists The H2RAs are reversible structural analogs of histamine that cause a decrease in the tonic activation rate o

10、f the receptor,thus,these agents act as inverse agonists with a functional antagonism of histamine activity.Cimetidine,ranitidine,famotidine and nizatidine.（西咪替丁为肝药酶抑制剂，有抗雄激素作用）.25 特点：H2RAs mainly inhibit basal rate of acid release during nonfeeding periods.This is of particular importance during th

11、e nocturnal periods of fasting,which is the rational for the use of H2RA dosing at bedtime.The H2RAs are often administered once a day prior to bedtime to maximally impact nocturnal basal acid secretion.All agents have linear pharmacokinetics and are eliminated primarily by renal mechanisms.Dose adj

12、ustments are needed for patients with renal impairment.26 H2RAs are superior to placebo,but inferior to PPIs for the treatment of esophageal reflux disease.Histamine receptor antagonists have modest efficacy in nonulcer dyspepsia,however,they are not as effective as PPIs.27Proton Pump Inhibitors PPI

13、s are weak bases that act as prodrugs and need an acidic environment in order to inhibit the H+K+-ATPase.PPIs accumulate in the secretory canaliculus of the parietal cell.The PPI becomes protonated and converted into the active sulfenamide species,which forms disulfide bonds with cysteine residues i

14、n the-subunit of the H+K+-ATPase.28 By contrast,with H2RAs,PPIs also decrease pepsin secretion,which serves to reduce mucosal damage.Morning dosing of PPIs is associated with significantly improved acid suppression.PPIs should be administered before breakfast.The effects of the PPIs increase with re

15、peated administration and,generally by the third day.29 PPIs undergo metabolism via hepatic CYP2C19.Of the PPIs,rabeprazole is unique as only 15-20%of its metabolism involves the CYP system.There is differential metabolism between individuals due to pharmacogenetic variation.Possible associations wi

16、th hip fractures,renal complications and community-acquired pneumonia have also been demonstrated.The long-term safety of the class include prolonged hypergastrinemia,the possible association of PPIs with gastric atrophy and chronic hypochlorhydria.30 PPIs should not be administered concomitantly wi

17、th H2-antagonists,prostaglandins or other antisecretory agents owing to the marked reduction in their acid inhibitory effects when administered simultaneously.31Mucosal Protective Agents Sucralfate It is a nonabsorbable medication that binds to gastric mucosa and ulcerated tissue.These properties fa

18、vor healing and provide cytoprotective effects.Sucralfate has similar efficacy in healing of duodenal ulcer and gastric ulcers when compared with H2RAs.The primary utility is in the prophylaxis of stress ulceration in critically ill patients.sucralfate is best avoided in patients with kidney failure

19、.32PPIs抗泌酸作用强，并可用于上消化道出血等 PPI infusion and high-dose oral therapy in the setting of bleeding PUD have been common practices for the last several years.The use of intravenous formulations of PPIs prior to endoscopy in patients with bleeding PUD.33PPI抑制夜间泌酸改善症状 After 1.4 months of pantoprazole(40 mg d

20、aily)therapy,any sleep disturbances had improved in more than 75%of patients,with resolution of nighttime heartburn and nighttime regurgitation in 73%and 84%of patients,respectively.34PPI新剂型增强药效 AGN,the enteric-coated novel PPI,was shown to provide faster and more profound acid suppression than esom

21、eprazole on day 1 and also at day 5,the time point that both medications should have reached steady state.Both medications were well tolerated and no adverse events were reported.Nocturnal acid suppression was also greater by 2 pH units after 5 days.35长期使用长期使用PPIs的不良反就应的不良反就应 Adverse Effects of Prot

22、on Pump Inhibitor Drugs:Clues and Conclusions http:/ 骨折：髋部、腕、前臂 肠道菌群失调：肠营养吸收不良：缺铁性贫血 高胃泌素血症：.36根除Hp方案的药物组成原则 合用不同机制的抗菌药物 如：阿莫西林，克拉霉素，甲硝唑 采用抗泌酸药物影响Hp的生长环境 如：PPI,H2抑制剂和铋剂.37Recommendations for Treating Peptic Ulcer Disease Helicobacter pylori infection be eradicated and antisecretory therapy,preferabl

23、y with a proton pump inhibitor(PPI),be given for 4 weeks;patients with persistent symptoms should undergo endoscopy.38根除Hp有助于病愈及防止复发 To facilitate healing and to decrease the risk for recurrence of gastric and duodenal ulcers,H pylori should be eradicated in patients with peptic ulcer disease.39PPIs

24、抗酸效果较其它药好 PPIs offer suppression of acid secretion,healing,and symptom relief in patients with peptic ulcers that are superior to those associated with other antisecretory therapies.40溃疡出血应用PPIs Patients with bleeding peptic ulcers should be treated with a PPI to decrease the need for transfusions o

25、r surgery and to reduce the duration of hospital stay.Those with bleeding peptic ulcers and positive H pylori testing should have eradication therapy prescribed.41穿孔性溃疡也应根除Hp Patients with perforated ulcers should undergo eradication of coexisting H pylori infection.Successful eradication should red

26、uce the need for long-term antisecretory therapy and additional surgery.42 Patients with peptic ulcers who are older than 55 years,have alarm symptoms,or have ulcers that fail to respond to treatment should promptly undergo upper endoscopy注意恶变注意恶变.43肠易激综合征肠易激综合征Irritable Bowel Syndrome 是一组包括腹痛、腹胀、排便

27、习惯改变和大便性状异常、粘液便等表现的临床综合征，持续存在或反复发作，经检查排除可以引起这些症状的器质性疾病。本病是最常见的一种功能性肠道疾病。.44临床表现临床表现 最主要的临床表现是腹痛与排便习惯和粪便性状的改变。腹痛腹痛 几乎所有IBS患者都有不同程度的腹痛。部位不定，以下腹和左下腹多见。腹泻腹泻 一般每日35次左右，少数严重发作期可达十数次。大便多呈稀糊状，也可为成形软便或稀水样。部分患者腹泻与便秘交替发生。便秘便秘 排便困难，粪便干结、量少，呈羊粪状，表面可附黏液。其他消化道症状 多伴腹胀或腹胀感，可有排便不尽感、排便窘迫感。全身症状 相当部分患者可有失眠、焦虑、抑郁、头昏、头痛等精

28、神症状。体征 无明显体征，可在相应部分有轻压痛，部分患者可触及腊肠样肠管，直肠指检可感到肛门痉挛、张力较高，可有触痛。.45肠易激综合征类型肠易激综合征类型 便秘型：伴有周期性便秘与较频繁的正常大便交替，大便经常有白色黏液，疼痛呈绞榨样，阵发性发作，或持续性隐痛，排便后可缓解。进食常会促发症状，也可以出现腹胀、恶心、消化不良和烧心等症状。腹泻型：特别是在进食刚开始，或结束时出现突发性腹泻。夜间腹泻很少，常有疼痛、腹胀和直肠紧迫感，也可出现大便失禁等情况。.46治治 疗疗 一般治疗 建立良好的生活习惯。饮食上避免诱发症状的食物，因人而异，一般而言宜避免产气的食物如乳制品、大豆等。高纤维食物有助改

29、善便秘。对失眠、焦虑者可适当给予镇静药。药物治疗 胃肠解痉药：抗胆碱药物，胃动力药，5-HT3拮抗剂 止泻药：洛哌丁胺，思密达、药用炭等 泻药：对便秘型患者酌情使用泻药，但不宜长期使用。半纤维素或亲水胶体，在肠腔内吸水膨胀增加肠内容物水分及容积，起到促进肠蠕动、软化大便的作用，被认为是治疗IBS便秘比较理想的药物。.47 http:/ Proton Pump Inhibitors,Irritable Bowel Syndrome,and Small Intestinal Bacterial Overgrowth the role of antibiotics vs.conventional p

30、harmacotherapy in treating symptoms of irritable bowel syndrome.Aliment Pharmacol Ther 25,12711281;2007.48慢性胃炎慢性胃炎病因病机：病因病机：80%以上的成年人具有不同程度的浅表性胃炎。浅表性胃炎和糜烂性胃炎主要由烟、洒、刺激性食物和药物，胆汁反流和幽门螺杆菌等引起。萎缩性胃炎则还与自身免疫反应，胃粘膜反复受损，胃腺萎缩有关。.49主要临床表现：主要临床表现：上腹不适、胃痛、食欲不振、嗳气及腹胀等。一般无明显体征。.50分 型：浅表性胃炎：胃镜下见散在胃粘膜水肿、斑点状出血、糜烂，显示红白

31、相间。腺体与粘膜厚度多数正常，肠上皮化生很少。糜烂性胃炎：病变范围深于浅表性胃炎。粘膜上有多个5-10mm大小的疣或丘疹样隆起，中央糜烂，病变多见于胃窦部。萎缩性胃炎：胃镜下粘膜色泽红白相间，而以白相为主。粘膜萎缩变薄，腺体萎缩，胃酸低下，腺上皮化生多，可能出现恶性贫血 pernicious anemia或癌变。.51诊断依据：依靠胃镜检查和胃粘膜病检。治 疗：保护胃粘膜和对症治疗。幽门螺杆菌感染者杀菌。.52Chronic gastritis associated with Helicobacter pyloriinfection.53 Left:An antral gland of the

32、 stomach with a large colony of Helicobacter pylori in the lumen(arrow).Right:A transverse section of the gastric lamina propria is shown.In the lower part,an antral gland of the stomach is present with some Helicobacter pylori in the lumen(red-blue arrow),while in the upper part a mast cell(yellow

33、arrow)is present.54幽门螺杆菌幽门螺杆菌胃腺萎缩胃腺萎缩萎缩性胃炎萎缩性胃炎肠肠上皮上皮化生化生 胃癌胃癌幽门螺杆菌幽门螺杆菌胃窦炎、十二指肠炎胃窦炎、十二指肠炎十二指肠十二指肠溃疡、胃溃疡溃疡、胃溃疡.55对幽门螺杆菌若干问题共识意见对幽门螺杆菌若干问题共识意见（安徽桐城会议（安徽桐城会议2003）Hp感染及其相关疾病感染及其相关疾病流行病学调查证实Hp在有些国家或地区的人群中，感染率仍很高.胃是Hp在人体内定植的主要部位，我国不同地区、不同民族人群胃内Hp检出率在30-80%之间，有很大差别。1 Hp是慢性胃炎和消化性溃疡(PU)的重要致病因子。.562 Hp与胃癌的发生

34、有关:(1)Hp可增加胃癌发生的危险性.(2)Hp根除后可阻断或延缓萎缩性胃炎和肠化的进一步发展，但是否能使两种病变逆转尚需进一步研究.(3)Hp根除后可降低早期胃癌术后的复发率.(4)在亚太地区如日本、韩国和中国，绝大多数Hp菌株均为cagA阳性菌株,其在消化性溃疡、胃癌和慢性胃炎中的阳性率无显著差异。(5)胃癌的发生是一个多步骤过程，从慢性胃炎经过萎缩、肠化生和不典型增生，最后到胃癌.胃癌的发生是Hp感染、宿主因素和环境因素共同作用的结果.cytotoxin-associated gene(cag).573 Hp是胃黏膜相关淋巴组织(MALT)淋巴瘤重要的致病因素，Hp感染是MALT淋巴瘤

35、产生的原因，胃MALT淋巴瘤在Hp高发区常见、多发.根除Hp可以治愈早期胃MALT淋巴瘤，染色体分析提示胃MALT淋巴瘤的发生可能具有遗传性.4 Hp与非甾体类抗炎药(NSAID)是消化性溃疡发生的两个重要独立危险因素，单纯根除Hp不足以预防NSAID溃疡，初次使用NSAID前根除Hp可降低NSAID溃疡的发生率，使用NSAID过程中根除Hp不能加速NSAID溃疡的愈合.5 Hp与胃食管反流性疾病(GERD)的关系尚无肯定结论.6 Hp感染和功能性消化不良(FD)的关系仍未明确.58Hp感染的治疗感染的治疗一线方案一线方案:(1)PPI/RBC(标准剂量标准剂量)+A(1.0)+C(0.5)，

36、Bid7 d;(2)PPI/RBC(标准剂量标准剂量)+M(0.4)+C(0.5)，Bid7 d;(3)PPI/RBC(标准剂量标准剂量)+A(1.0)+F(0.1)/M(0.4)，Bid7d;.59(4)B(标准剂量标准剂量)+F(0.1)/M(0.4)+C(0.5)，Bid7 d;(5)B(标准剂量标准剂量)+M(0.4)+T(0.75-1.0)，Bid14 d;(6)B(标准剂量标准剂量)+M(0.4)+A(0.5)Bid14 d.代号说明代号说明:PPI(质子泵抑制剂质子泵抑制剂):目前有埃索米拉唑目前有埃索米拉唑(E)、雷贝拉唑、雷贝拉唑(R)、兰索拉唑、兰索拉唑(L)、奥美拉唑、奥

37、美拉唑(O);RBC(枸椽酸铋雷尼替丁枸椽酸铋雷尼替丁);A阿莫西林阿莫西林;C克克拉霉素拉霉素;M甲硝唑甲硝唑;T四环素四环素;B 铋剂铋剂(枸椽酸铋钾、枸椽酸铋钾、果胶铋等果胶铋等);F呋喃唑酮呋喃唑酮.也可以也可以H2受体阻断剂受体阻断剂(H2RA)替代替代PPI(如如:西米替丁、雷尼替丁、法莫西米替丁、雷尼替丁、法莫替丁替丁).但根除率可能会有所降低但根除率可能会有所降低.60 二线方案二线方案:(1)PPI(标准剂量标准剂量)+B(标准标准剂量剂量)+M(0.4 Tid)+T(0.75-1.0)，Bid7-14 d;(2)PPI(标准剂标准剂量量)+B(标准剂量标准剂量)+F(0.1

38、)+T(0.75-1.0)，Bid7-14 d.61Hp阳性的下列疾病阳性的下列疾病必须必须支持支持不明确不明确消化性溃疡消化性溃疡1v早期胃癌术后早期胃癌术后v胃胃MALT淋巴瘤淋巴瘤v明显异常的慢性胃炎明显异常的慢性胃炎2v计划使用计划使用NSAIDsv部分部分FD3vGERD3v胃癌家族史胃癌家族史v个人强烈要求治疗者个人强烈要求治疗者v胃肠道外疾病胃肠道外疾病v1PU:无论活动或非活动，无论有无并发症无论活动或非活动，无论有无并发症.2明显异常明显异常:指合并糜烂，指合并糜烂，中中-重度萎缩，中重度萎缩，中-重度肠化生，轻重度肠化生，轻-中度不典型增生中度不典型增生.重度不典型增重度不

39、典型增生应考虑癌变生应考虑癌变.3FD和和GERD应根除应根除Hp的理由如前所述的理由如前所述.表表2 Hp感染治疗适应证感染治疗适应证.62幽门螺杆菌感染和环氧化酶幽门螺杆菌感染和环氧化酶-2表达在表达在胃癌发生中的作用胃癌发生中的作用1 Hp感染与胃癌及癌前病变感染与胃癌及癌前病变流行病学资料提示长期Hp感染可导致胃黏膜的萎缩、肠上皮化生及异型增生，最终形成胃癌。因此，1994年世界卫生组织国际癌症研究机构已正式将Hp列为第一类生物致癌因子。近年来动物实验研究、胃黏膜上皮细胞培养和Hp根除干预实验等均证实了Hp感染致胃癌的危险性。Hp细胞毒素相关基因A(cagA)阳性菌株具有更强的毒力和危

40、险性，cagA+菌株感染后胃黏膜上皮细胞损害明显并影响壁细胞的分泌功能，导致胃酸分泌减少，胃内细菌过度生长，促使硝酸盐降解为亚硝酸盐和亚硝胺等致癌物。.632 Hp感染诱导感染诱导COX-2的表达的表达 Hp感染和COX-2表达在胃癌的发生、发展中均起重要作用，Hp作为促癌因子诱导COX-2表达，Hp感染者胃黏膜中COX-2表达明显增加。Hp感染相关的急、慢性胃窦炎的胃上皮细胞和单核细胞中COX-2蛋白表达增加.虽然根除Hp减少胃黏膜COX-2表达，但不能逆转肠上皮化生。.643 COX-2在胃癌和癌前病变中表达增加在胃癌和癌前病变中表达增加 COX-2与细胞增生和肿瘤发生密切相关，正常情况下

41、COX-2几乎不表达或表达甚少，而在炎症因子、生长因子、内毒素和促癌剂等刺激下，COX-2表达迅速增加，并参与炎症过程和肿瘤的发生、发展16.众多研究显示，COX-2在胃癌和结直肠癌中表达增加。癌组织中COX-2 mRNA显著高于癌周正常组织。.654 COX-2的致癌和促癌机制的致癌和促癌机制 尽管COX-2与胃癌的发生发展密切相关，但COX-2表达在肿瘤发生、发展中的作用机制尚不明确。COX-2可能经多种途径促进细胞增生、抑制细胞凋亡、调节肿瘤新生血管形成和增加癌细胞的侵袭性等而发生致癌和促癌作用。COX-2表达增加PGE2合成，PGE2可诱导细胞增生并刺激Bcl-2蛋白表达，后者可抑制细

42、胞凋亡。COX-2促进VEGF相关的肿瘤血管生成，可能是其在致癌和促癌中发挥作用的另一重要途径.665 Hp感染诱导感染诱导COX-2表达的机制表达的机制 目前，Hp感染诱导胃黏膜COX-2表达的机制尚待阐明，可能是Hp感染引起胃黏膜损伤刺激COX-2表达，也可能是Hp感染及其毒素直接诱导COX-2表达。国内外研究表明，Hp细菌悬液、超声提取物甚至Hp细菌培养液均可诱导培养细胞的COX-2表达.Hp感染可能通过炎症细胞释放细胞因子的间接作用，亦可能是直接诱导胃黏膜炎症细胞表达COX-2，再通过旁分泌机制和信号传导引起上皮细胞表达COX-2。.67有关Hp感染的新进展 Helicobacter

43、pylori Infection and Current Clinical Areas of Contention http:/ 肠外疾病：特发性血小板紫癜、缺铁性贫血肠外疾病：特发性血小板紫癜、缺铁性贫血 与过敏性疾病和肥胖的关系。与过敏性疾病和肥胖的关系。.68幽门螺杆菌与非甾体抗炎药在上胃肠疾病中幽门螺杆菌与非甾体抗炎药在上胃肠疾病中的相互作用的相互作用 正在应用NSAID的十二指肠溃疡现患或既往有十二指肠溃疡者，应检测Hp并对阳性者予以根除，因为临床上不能判定溃疡是Hp、或NSAID或二者共同所致.如果患者需继续应用NSAID，则应用PPI或选择性COX-2 NSAID以预防溃疡的复发

44、。对现患胃溃疡或既往有胃溃疡病史且正应用NSAID者，应用铋剂为中心的根除Hp的治疗方案较以PPI为中心的根除方案在NSAID相关性胃溃疡的治疗和预防中有更好的疗效。.69 对Hp阳性的有胃肠症状的阿司匹林应用者，如果需要继续应用阿司匹林，根除Hp会减少患者溃疡出血的危险性;如果无消化不良症状或无溃疡病史，则没有必要检测Hp或根除Hp治疗.如果患者即将应用NSAID，检测并根除Hp将肯定会减少溃疡的危险性.应用选择性COX-2 NSAID的患者，有关Hp根除的建议与未应用NSAID者相同.在长期应用NSAID者，根除Hp和随后的PPI预防疗法将肯定减少溃疡的发生和复发，促进溃疡的愈合.70Wi

45、thdrawal of Vioxx Casts a Shadow Over COX-2 Inhibitors the COX-2 inhibitor Vioxx,off the market after an alarming pattern surfaced halfway through a 3-year colon polyp prevention study.Heart attacks and strokes had occurred at a much higher rate among the roughly 1300 volunteers on Vioxx(3.5%)than a

46、mong the 1300 taking a placebo(1.9%).http:/www.sciencemag.org/cgi/content/full/306/5695/384.71 Vioxxs propensity to trigger heart attacks and strokes isnt fully understood.But some experts believe that its valued mechanism-specifically,its ability to suppress a narrow set of molecules that mediate i

47、nflammation-may have been its downfall.Anti-inflammatory drugs like naproxen suppress both prostacyclin,which plays a role in inflammation,and thromboxane.But COX-2 inhibitors block only prostacyclin;this may tilt the balance in favor of thromboxane and,potentially,blood clotting.So far the thrombosis theory has been supported only by animal studies.72A study showed that rofecoxib(Vioxx),compared here to naproxen,could cause cardiovascular problems.ADAPTED FROM D.MUKHERJEE ET AL.,JAMA 286,8(2001).73.74.75