Questions about the use of antibiotics in acute pancreatitis
© De Campos et al; licensee BioMed Central Ltd. 2006
Received: 29 April 2006
Accepted: 04 July 2006
Published: 04 July 2006
Background and objective
The use of antibiotics in acute pancreatitis despite recent clinical trials remains controversial. The aim of this study is to review the latest clinical trials and guidelines about antibiotics in acute pancreatitis and determine its proper use.
Through a Medline search, we selected and analyzed pertinent randomized clinical trials and guidelines that evaluated the use of antibiotics in acute pancreatitis. We answered the most frequent questions about this topic.
Results and conclusion
Based on these clinical trials and guidelines, we conclude that the best treatment currently is the use of antibiotics in patients with severe acute pancreatitis with more than 30% of pancreatic necrosis. The best option for the treatment is Imipenem 3 × 500 mg/day i.v. for 14 days. Alternatively, Ciprofloxacin 2 × 400 mg/day i.v. associated with Metronidazole 3 × 500 mg for 14 days can also be considered as an option.
Severe acute pancreatitis (SAP) as defined by the Atlanta criteria, is present in up to 25% of patients with acute pancreatitis (AP) , with mortality of 10%–20%.
In these patients, AP develops in two phases: the first ten days are characterized by the systemic inflammatory response syndrome (SIRS), whereas in the end of the second week infection complications begin to appear .
These complications due to infection are responsible for up to 80% of deaths in patients with AP. About 40% to 75% of patients with pancreatic necrosis develop infection, 24% after the first week and 71% after the third week [3, 4], with mortality rates up to 50% [5, 6]. The mechanisms of infection in AP are bacteria translocation, via lymphatic, via hematogenic, and reflux from duodenum and biliary tree as well .
If the major problem in AP is infection of pancreatic necrosis, it makes sense to consider that the use of antibiotics in this situation could reduce the morbidity and mortality of these patients. However, at present there are still controversies about this topic.
Therefore, some questions remain unclear regarding the use of antibiotics in AP:
1-Should we use antibiotics in Acute Pancreatitis?
4-Should we wait for more studies?
1- Should we use antibiotics in Acute Pancreatitis?
Some authors observed reduction in necrosis infection after the introduction of antibiotics in the treatment of severe forms of AP, when compared with historic controls without antibiotics. Banks et al. described a decrease from 67% to 32% , while Ho & Frey observed a reduction from 75% to 20% in the infection of pancreatic necrosis .
a. Review of clinical trials
There are few randomized clinical trials about the use of antibiotics in AP. Pederzoli et al. in 1993  conducted the first of them, which analyzed 74 patients with SAP in six medical centers in Italy. The patients were randomized in two groups: one control with 33 patients and the treatment group with 41 patients that received Imipenem 3 × 500 mg/day intravenously (i.v.) during 14 days. They observed reduction in pancreatic sepsis in patients that received antibiotics (30.3% vs. 12.2%, p < 0.01). However, they did not find reduction in mortality between the groups (12% vs. 7%, respectively).
Sainio et al. carried out another study in 1995 , analyzing data from 60 patients with SAP. One group control and the other treated with Cefuroxime 3 × 1.5 g/day i.v. They observed reduction in the number of pancreatic operations (36 vs. 8, p = 0.012) and in mortality (7 vs. 1, p = 0,028) in the treatment group. However, 66.7% of patients in this group had their antibiotics changed during the treatment. Furthermore, 23 out of 30 patients in the control group received antibiotics in an average period of six days after the beginning of the treatment. The use of this cephalosporin is also questionable due to low pancreatic penetration.
Delcenserie et al. in 1996  analyzed prospectively 23 patients with alcoholic SAP that were divided into two groups: one control and one that was treated with Ceftazidime 3 × 2 g/day i.v., Amicacin 2 × 7.5 mg/kg i.v., and Metronidazole 3 × 500 mg i.v. for 10 days. They observed a decrease in septic complications in the treatment group (7 vs. 0, p = 0.03). Nevertheless, there was no difference in mortality rate between the groups. In another clinical trial, Schwarz et al. described a decrease in pancreatic infection in a group of 29 patients, utilizing Ofloxacin and Metronidazole (7% × 46%, respectively) .
Clinical studies comparing the use of antibiotics with placebo
Infected necrosis (%)
Pederzoli et al. 
Sainio et al. 
Delcenserie et al. 
Ceftazidime + Amicacin + Metronidazole
Schwarz et al. 
Ofloxacin + Metronidazole
Results of a clinical double-blind trial about the use of antibiotics in severe acute pancreatitis 
Intention to treat (114 patients)
Pancreatic necrosis (CT) (76 patients)
Ciprofloxacin/Metronidazole (58 patients)
Placebo (56 patients)
Ciprofloxacin/Metronidazole (58 patients)
Placebo (56 patients)
b. Time of infection
Although the risk for the development of pancreatic infection is higher in the third week, microorganisms can be found in the pancreatic tissue in the first week .
De Souza et al. demonstrated in an experimental model that bacteria could be detected in the pancreatic tissue six hours after the induction of AP . Similarly, Schwarz et al. observed bacteria in the pancreatic necrosis between 8 and 16 hours after the pancreatitis induction .
These data suggest that the best time to introduce antibiotics is immediately after the diagnosis of AP and the evaluation of its severity. However, the confirmation of necrotizing pancreatitis by CT scan can take at least 72 hours since the onset of symptoms. C-reactive protein is a sensitive marker of pancreatic necrosis and it starts to increase significantly 48 hours after the onset of symptoms. Thus, C-reactive protein can be useful in the identification of patients with high possibility to develop necrosis, in particular when the value is over 150 mg/dl, and subsequently define which patients are candidates to receive early antibiotics .
Nordback et al, in a clinical trial observed advantages in the early use of Imipenem in patients with pancreatic necrosis when compared with the late use .
c. Complications of antibiotics in AP
The main arguments against the use of antibiotics are the increase of fungal infection, and the increase of bacteria resistance, with more Gram-positive infections .
There are evidences in the literature that fungal infection has to be considered as an additional factor which influences the outcome of the patients .
One paper analyzing data of 46 patients with infected pancreatic necrosis receiving antibiotics showed that 17 (37%) of them developed fungal infection. Nevertheless, the fungal infection did not contribute to increase mortality in this group of patients .
Gloor et al. analyzed 103 patients with necrotizing AP that received antibiotics (Imipenem/cilastatin) and concluded that fungal infections when treated properly do not contribute to a worst prognosis. This same paper showed that the presence of multi-resistant bacteria was rare (2.9%) .
Consensus recommendations about the use of antibiotics in acute pancreatitis
Uhl et al. 2002 
International Association of Pancreatology (Pancreatology)
Toouli et al. 2002 
Journal of Gastroenterology and Hepatology
Nathens et al. 2004 
Crit Care Med
UK working party 2005 
United Kingdom (Gut)
Clancy et al. 2005 
Journal of Gastrointestinal Surgery
Werner et al. 2005 
Bassi et al. 2003 
Chinese pancreatic disease group 2005 
Chinese society of gastroenterology (Chinese Journal of Digestive Diseases)
Takeda et al. 2006 
JPN Guidelines for the management of acute pancreatitis
Moreover, the UK guidelines for the management of AP advocate that the risk of infected necrosis is very small when there is less than 30% necrosis . Although there is no support in the literature, it is reasonable to assume that prophylactic antibiotic therapy should be considered only for patients with more than 30% pancreatic necrosis. In contrast, there is no evidence in the literature that the use of antibiotics in the absence of necrosis is beneficial.
Based on these studies we believe that the use of antibiotics is benefic to patients with SAP with more than 30% pancreatic necrosis, and starting as soon as possible.
2- Which antibiotic?
Two main aspects must drive the choice of the antibiotics: the flora and the penetration in the pancreatic tissue.
One single microorganism causes most of infections in AP. The bacteria most frequently found are E. coli (27–35%), Enterococcus (24–26%), Staphylococcus aureus (14–16%), Staphylococcus epidermidis (15%), Klebsiella (15%) Pseudomonas sp (7–11%) and Streptococos (4–7%) [7, 40, 41].
Ampicillin was one of the first antibiotics used in AP, although it has failed to show advantages to these patients, due to poor action in the flora and low penetration in the pancreatic tissue .
Experimental studies were performed to determine which antibiotic would have a better pancreatic concentration [43, 44]. Mithofer et al. in a necrotizing pancreatitis model defined three groups: one treated with saline solution, the second treated with Ciprofloxacin and the third treated with Imipenem/cilastatin six hours after the induction of AP. After seven days, 75% of the animals in the saline group had infection, while 25% in the Imipenem group (p < 0.01) and 6% in the Ciprofloxacin group (p < 0.01). After 21 days, the infection rate was 71%, 33% and 35% respectively (p = n.s.). The survival in seven days was 68% in the control group, 60% in the Imipenem group (p = 0.071) and 43% in the Ciprofloxacin group (p < 0.01). After 21 days, the survival was 23% in the control group vs. 52% in the Imipenem group (p = 0.044) and 70% in the Ciprofloxacin group (p < 0.001) .
Penetration of antibiotics in the pancreatic tissue 
The pancreatic concentration of an antibiotic is determined by some factors: properties of the antibiotic, anatomy and physiology of the pancreas, alkaline pH, high ion concentration, enzymatic and hormonal regulation, pathologic changes and infection . Spicak et al., studied experimentally the penetration of five antibiotics in the pancreatic tissue of rats with AP, and observed that Cefoperazone (3rd generation cephalosporin) and Ofloxacin had adequate penetration, while Amoxicillin/Clavulanic acid, Piperacillin and Amicacin demonstrated insufficient penetration. They concluded that antibiotic penetration was not influenced by necrosis of the pancreas .
In a clinical trial, Bassi et al. compared two groups with 30 patients each, whereas the first one received Pefloxacin, and the second Imipenem. They observed a decrease in the infection of pancreatic necrosis in the Imipenem group (3 × 10, p = 0.034). There was no difference in mortality (10% contra 24%, p = 0.18) . This study showed that Pefloxacin was less effective than Imipenem in clinical practice. Although this is not a study comparing Ciproflofloxacin, it can suggest that antibiotics of this class can be less effective than Imipenem.
Based on these studies and guidelines, we conclude that the recommended antibiotic in AP is Imipenem 3 × 500 mg/day i.v. Alternatively, the use of Ciprofloxacin 2 × 400 mg/day i.v. associated with Metronidazole 3 × 500 mg/day i.v. can also be considered.
3- How long?
There are no studies evaluating how long these patients should be treated with antibiotics. This time is determined by consensus meetings that recommend a period of 10 to 14 days [32, 34, 35, 37, 38]. After this period, each patient must be evaluated individually to determine if the antibiotics will be suspended, modified or continued. The cultures for bacteria and fungus are fundamental in this phase.
4- Should we wait for more studies?
Although there is no definitive conclusion about the use of antibiotics in AP, strong evidences suggest that they are beneficial. Isenmann's study is the more adequate about the use of antibiotics, and despite of a negative conclusion, it has shown that a group of patients deserved the early use of antibiotics.
New studies are coming, hopefully with a greater number of patients and more solid conclusions. However, we should not wait for them to make a decision in the treatment of these patients.
Based on available studies and in the guidelines opinions, we conclude that the best policy currently is the use of antibiotics in patients with SAP and more than 30% pancreatic necrosis. The antibiotic recommended is Imipenem 3 × 500 mg/day i.v. for 14 days. Alternatively, Ciprofloxacin 2 × 400 mg/day i.v. associated with Metronidazole 3 × 500 mg/day for 14 days can also be considered as an option.
severe acute pancreatitis
systemic inflammatory response syndrome
- Imrie CW: Severe acute pancreatitis. Hepatobiliary and Pancreatic Surgery. Edited by: Poston J, Blumgart L. 2003, London, UK: Martin Dunitz, 393-405. 1Google Scholar
- Büchler MW, Gloor B, Muller CA, Friess H, Seiler CA, Uhl W: Acute necrotizing pancreatitis: treatment strategy according to the status of infection. Ann Surg. 2000, 232: 619-26. 10.1097/00000658-200011000-00001.PubMed CentralView ArticlePubMedGoogle Scholar
- Gloor B, Muller CA, Worni M, Stahel PF, Redaelli C, Uhl W, Buchler : Pancreatic infection in severe pancreatitis : the role of fungus and multiresistant organisms. Arch Surg. 2001, 136: 592-596. 10.1001/archsurg.136.5.592.View ArticlePubMedGoogle Scholar
- Olah A, Belagyi T, Issekutz A, Gamal ME, Bengmark S: Randomized clinical trial of specific lactobacillus and fibre supplement to early enteral nutrition in patients with acute pancreatitis. Br J Surg. 2002, 89: 1103-1107. 10.1046/j.1365-2168.2002.02189.x.View ArticlePubMedGoogle Scholar
- Puolakkainen P, Kemppainen E, Leppaniemi A, Sainio V, Hietaranta A, Haapiainen R: Current principles of treatment in acute pancreatitis. Ann Chir Gynaecol. 1998, 87: 200-203.PubMedGoogle Scholar
- Schmid SW, Uhl W, Friess H, Malfertheiner P, Buchler MW: The role of infection in acute pancreatitis. Gut. 1999, 45: 311-316.PubMed CentralView ArticlePubMedGoogle Scholar
- Beger HG, Rau B, Isenmann R, Schwarz M, Gansauge F, Poch B: Antibiotic prophylaxis in severe acute pancreatitis. Pancreatology. 2005, 5: 10-19. 10.1159/000084485.View ArticlePubMedGoogle Scholar
- Tenner S, Banks PA: Acute pancreatitis: nonsurgical management. World J Surg. 1997, 21: 143-148. 10.1007/s002689900206.View ArticlePubMedGoogle Scholar
- Bradley EL: A clinically based classification system for acute pancreatitis: summary of the Atlanta symposium. Arch Surg. 1993, 128: 586-590.View ArticlePubMedGoogle Scholar
- Ranson JHC, Rifkind KM, Turner JW: Prognostic signs and nonoperative peritoneal lavage in acute pancreatitis. Surg Gynecol Obstet. 1976, 143: 209-219.PubMedGoogle Scholar
- Gotzinger P, Sautner T, Kriwanek S, Beckerhinn P, Barlan M, Armbruster C, Wamser P, Fugger R: Surgical treatment for severe acute pancreatitis: extent and surgical control of necrosis determine outcome. World J Surg. 2002, 26: 474-478. 10.1007/s00268-001-0252-8.View ArticlePubMedGoogle Scholar
- Balthazar EJ, Robinson DL, Megibow AJ, Ranson JH: Acute pancreatitis: value of CT in establishing prognosis. Radiology. 1990, 174: 331-336.View ArticlePubMedGoogle Scholar
- Robert JH, Frossard JL, Mermillod B, Soravia C, Mensi N, Roth M, Rohner A, Hadengue A, Morel P: Early prediction of acute pancreatitis: prospective study comparing computed tomography scans, Ranson, Glasgow, acute physiology and chronic evaluation II scores, and various serum markers. World J Surg. 2002, 26: 612-619. 10.1007/s00268-001-0278-y.View ArticlePubMedGoogle Scholar
- Banks PA, Gerzof SG, Langenvin RE, Silverman SG, Sica GT, Hughes MD: CT-guided aspiration of suspected pancreatic infection. Int J Pancreatol. 1995, 18: 265-270.PubMedGoogle Scholar
- Ho HS, Frey CF: The role of antibiotic prophylaxis in severe acute pancreatitis. Arch Surg. 1997, 132: 487-493.View ArticlePubMedGoogle Scholar
- Pederzoli P, Bassi C, Vesentini S, Campedelli A: A randomized multicenter clinical trial of antibiotic prophylaxis of septic complications in acute necrotizing pancreatitis with imipenem. Surg Gynecol Obstet. 1993, 176: 480-483.PubMedGoogle Scholar
- Sainio V, Kemppainen E, Puolakkainen P, Taavitsainen M, Kivisaari L, Valtonen V, Haapiainen R, Schroder T, Kivilaakso E: Early antibiotic treatment in acute necrotising pancreatitis. Lancet. 1995, 346: 663-667. 10.1016/S0140-6736(95)92280-6.View ArticlePubMedGoogle Scholar
- Delcenserie R, Yzet T, Ducroix JP: Prophylatic antibiotics in treatment of severe acute alcoholic pancreatitis. Pancreas. 1996, 13: 198-201.PubMedGoogle Scholar
- Schwarz M, Isenmann R, Meyer H, Beger HG: Antibiotic use in necrotizing pancreatitis. Results of a controlled study. Dtsch Med Wochenschr. 1997, 122: 356-361.View ArticlePubMedGoogle Scholar
- Ashley SW, Perez A, Pierce EA, Brooks DC, Moore FD, Whang EE, Banks PA, Zinner MJ: Necrotizing pancreatitis – contemporary analysis of 99 consecutive cases. Ann Surg. 2001, 234: 572-580. 10.1097/00000658-200110000-00016.PubMed CentralView ArticlePubMedGoogle Scholar
- Isenmann R, Runzi M, Kron M, Kahl S, Kraus D, Jung N, Maier L, Malfertheiner P, Goebell H, Beger HG: German Antibiotics in Severe Acute Pancreatitis Study Group: Prophylactic antibiotic treatment in patients with predicted severe acute pancreatitis: a placebo-controlled, double-blind trial. Gastroenterology. 2004, 126: 997-1004. 10.1053/j.gastro.2003.12.050.View ArticlePubMedGoogle Scholar
- Bassi C, Falconi M: Discussion on prophylactic antibiotic treatment in patients with predicted severe pancreatitis: a placebo-controlled, double-blind trial. Gastroenterology. 2004, 127: 1015-1016. 10.1053/j.gastro.2004.07.045.View ArticlePubMedGoogle Scholar
- Pezzilli R: Antibiotic prophylaxis in acute necrotizing pancreatitis: yes or no?. JOP. 2004, 5: 161-164.PubMedGoogle Scholar
- Beger HG, Bittner R, Block S, Buchler M: Bacterial contamination of pancreatic necrosis. A prospective clinical study. Gastroenterology. 1986, 91: 433-438.PubMedGoogle Scholar
- de Souza L, Sampietre SN, Figueiredo S, Yria Y, Machado MC, Pinotti HW: Bacterial translocation in acute pancreatitis. Rev Hosp Clin Fac Med Sao Paulo. 1996, 51: 116-120.PubMedGoogle Scholar
- Schwarz M, Thomsen J, Meyer H, Buchler MW, Beger HG: Frequency and time course of pancreatic and extrapancreatic bacterial infection in experimental acute pancreatitis in rats. Surgery. 2000, 127: 427-432. 10.1067/msy.2000.104116.View ArticlePubMedGoogle Scholar
- Werner J, Hartwig W, Uhl W, Muller C, Buchler MW: Useful markers for predicting severity and monitoring progression of acute pancreatitis. Pancreatology. 2003, 3: 115-127. 10.1159/000070079.View ArticlePubMedGoogle Scholar
- Nordback I, Sand J, Saaristo R, Paajanen H: Early treatment with antibiotics reduces the need for surgery in acute necrotizing pancreatitis – a single-center randomized study. J Gastrointest Surg. 2001, 5: 113-118. 10.1016/S1091-255X(01)80021-4.View ArticlePubMedGoogle Scholar
- Grewe M, Tsiotos GG, Luque de Leon E, Sarr MG: Fungal infection in acute necrotizing pancreatitis. J Am Coll Surg. 1999, 188: 408-441. 10.1016/S1072-7515(98)00334-2.View ArticlePubMedGoogle Scholar
- De Waele JJ, Vogelaers D, Blot S, Colardyn F: Fungal infections in patients with severe acute pancreatitis and the use of prophylactic therapy. Clin Infect Dis. 2003, 37: 208-213. 10.1086/375603.View ArticlePubMedGoogle Scholar
- Uhl W, Warshaw A, Imrie C, Bassi C, McKay CJ, Lankisch PG, Carter R, Di Magno E, Banks PA, Whitcomb DC, Dervenis C, Ulrich CD, Satake K, Ghaneh P, Hartwig W, Werner J, McEntee G, Neoptolemos JP, Buchler MW: IAP guidelines for the surgical management of acute pancreatitis. Pancreatology. 2002, 2: 565-573. 10.1159/000071269.View ArticlePubMedGoogle Scholar
- Toouli J, Brooke-Smith M, Bassi C, Carr-Locke D, Telford J, Freeny P, Imrie C, Tandon R: Guidelines for the management of acute pancreatitis. J Gastroenterol Hepatol. 2002, 17 (Suppl): S15-39. 10.1046/j.1440-1746.17.s1.2.x.View ArticlePubMedGoogle Scholar
- Nathens AB, Curtis JR, Beale RJ, Cook DJ, Moreno RP, Romand JA, Skerrett SJ, Stapleton RD, Ware LB, Waldmann CS: Management of the critically ill patient with severe acute pancreatitis. Crit Care Med. 2004, 32: 2524-2536. 10.1097/01.CCM.0000148222.09869.92.View ArticlePubMedGoogle Scholar
- Working Party of the British Society of Gastroenterology; Association of Surgeons of Great Britain and Ireland; Pancreatic Society of Great Britain and Ireland; Association of Upper GI Surgeons of Great Britain and Ireland: UK guidelines for the management of acute pancreatitis. Gut. 2005, 54: iii1-iii9. 10.1136/gut.2004.057059.Google Scholar
- Clancy TE, Benoit EP, Ashley SW: Current management of acute pancreatitis. J Gastrointest Surg. 2005, 9: 440-452. 10.1016/j.gassur.2004.09.027.View ArticlePubMedGoogle Scholar
- Werner J, Feuerbach S, Uhl W, Buchler MW: Management of acute pancreatitis: from surgery to interventional intensive care. Gut. 2005, 54: 426-436. 10.1136/gut.2003.035907.PubMed CentralView ArticlePubMedGoogle Scholar
- Bassi C, Larvin M, Villatoro E: Antibiotic therapy for prophylaxis against infection of pancreatic necrosis in acute pancreatitis. Cochrane Database Syst Rev. 2003, 4: CD002941-PubMedGoogle Scholar
- Pancreatic Disease Group, Chinese Society of Gastroenterology & Chinese Medical Association: Consensus on the diagnosis and treatment of acute pancreatitis. Chin J Dig Dis. 2005, 6: 47-51. 10.1111/j.1443-9573.2005.00188.x.View ArticleGoogle Scholar
- Takeda K, Takada T, Kawarada Y, Hirata K, Mayumi T, Yoshida M, Sekimoto M, Hirota M, Kimura Y, Isaji S, Koizumi M, Otsuki M, Matsuno S: JPN Guidelines for the management of acute pancreatitis: medical management of acute pancreatitis. J Hepatobiliary Pancreat Surg. 2006, 13: 42-47. 10.1007/s00534-005-1050-8.PubMed CentralView ArticlePubMedGoogle Scholar
- Barie PS: A critical review of antibiotic prophylaxis in severe acute pancreatitis. Am J Surg. 1996, 172 (6A): 38s-43s. 10.1016/S0002-9610(96)00349-2.View ArticlePubMedGoogle Scholar
- Pederzoli P, Falconi M, Bassi C, Girelli R, Vesentini S, Martini N, Messori A: Ofloxacin penetration into bile and pancreatic juice. J Antimicrob Chemother. 1989, 23: 805-807.View ArticlePubMedGoogle Scholar
- Craig RM, Dordal E, Myles L: The use of ampicillin in acute pancreatitis. Ann Intern Med. 1975, 83: 831-835.View ArticlePubMedGoogle Scholar
- Trudel JL, Wittnich C, Brown RA: Antibiotics bioavailability in acute experimental pancreatitis. J Am Coll Surg. 1994, 178: 475-479.PubMedGoogle Scholar
- Mithofer K, Fernandez-Del Castillo C, Ferraro M, Lewandrowski K, Rattner DW, Warshaw AL: Antibiotic treatment improves survival in experimental acute necrotizing pancreatitis. Gastroenterology. 1996, 110: 232-240. 10.1053/gast.1996.v110.pm8536862.View ArticlePubMedGoogle Scholar
- Büchler MW, Malfertheiner P, Friess H, Isenmann R, Vanek E, Grimm H: Human pancreatic tissue concentration of bactericidal antibiotics. Gastroenterology. 1992, 103: 1902-1908.PubMedGoogle Scholar
- Spicák J, Martínek J, Závada F, Moravek J, Melenovsky V: Penetration of antibiotics into the pancreas in rats: an effect of acute necrotizing pancreatitis. Scand J Gastroenterol. 1999, 34: 92-97. 10.1080/00365529950172899.View ArticlePubMedGoogle Scholar
- Bassi C, Falconi M, Talamini G, Uomo G, Papaccio G, Dervenis C: Controlled clinical trial of Pefloxacin versus Imipenem in severe acute pancreatitis. Gastroenterology. 1998, 115: 1513-1517. 10.1016/S0016-5085(98)70030-7.View ArticlePubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.