610
TABLE !)—OPT!CAL DENSITY VALUES ON FIFTEEN ANT!-HCV-POSmVE SAM PlES WITH AN D WITHOUT UREA WASH
*Patient also had
hepatoma
infections is low and increases with maturation of the immune
response’ shows the reduction in OD after urea treatment. 8/9 anti-HCV-positive patients with cryptogenic cirrhosis had predominantly high-avidity antibodies (less than 50% reduction in presence of urea) whereas only 1 of 6 antibody-positive patients with other chronic liver disease had high-avidity antibody. All the livers from patients with cryptogenic cirrhosis were cirrhotic but in 1 patient there was more piecemeal and spotty parenchymal necrosis than was seen in the other 8--and this patient was the 1 with predominantly low-avidity antibody, suggesting continuing disease activity or more recent infection. In chronic liver disease non-specific low-avidity antibodies may sometimes be present and cross-react with the recombinant HCV antigen used in the assay. We recommend, in the absence of a confirmatory or specific neutralisation test, that all samples from patients with chronic liver disease which are anti-HCV positive should be retested in the presence of 8 mol/1 urea. This method is only valid for chronic infection; specific low-avidity antibody may be present for some months after acute infection or during active infection. This assay, with and without a urea wash, in conjunction with histological examination may help to distinguish recent from remote HCV infections. Table
II
Clinical Microbiology and Public Health Laboratory, Cambridge CB2 2QW, Department of Surgery, University of Cambridge; and Histopathology Laboratory, Addenbrooke’s Hospital
GRAY T. G. WREGHITT P. J. FRIEND D. G. D. WIGHT V. SUNDARESAN R. Y. CALNE
J. J.
G, Choo Q-L, Alter HJ, et al. An assay for circulating antibodies to a major etiologic virus of human non-A, non-B hepatitis. Science 1989; 244: 362-64. 2. Inouye S, Hasegawa A, Matsuno S, Katwo S. Changes in antibody avidity after virus infections: detection by an immunosorbent assay in which a mild proteindenaturing agent is employed. JClin Microbiol 1984; 20: 525-29. 3. Eisen HN, Siskind GW. Variations in affinities of antibodies during the immune response. Biochemistry 1964; 3: 996-1008. 4. Webster RG. The immune response to influenza virus III changes in the avidity and specificity of early IgM and IgG antibodies. Immunology 1968; 14: 39-52. 1. Kuo
Cyclosporin toxicity SIR,-Dr Lucey and colleagues (Jan 6, pl1) report a liver transplant patient with cyclosporin (Cy) toxicity (nephrotoxicity and neurotoxicity) with therapeutic blood concentrations, and attribute the toxicity to a metabolite which may be related to a deficiency of P450 III A enzyme. Cy is effective treatment for psoriasis.12 However, because of the side-effects of nephrotoxicity and hypertension thought to be related to dose and blood concentration
severe cases that have not responded to other Methotrexate (MTX), widely used in psoriasis, may cause hepatotoxicity, which is related to the cumulative dose. Cy is metabolised in the liver and excreted in the bile. If liver function is abnormal after MTX treatment, high blood concentrations of Cy may result even at low doses because of impaired excretion in the bile. We have seen cyclosporin toxicity (nephrotoxicity and hypertension) in psoriasis, but have measured parent drug concentrations with a monoclonal antibody assay and parent drug and metabolites with a polyclonal antibody assay. We investigated 8 female and 5 male patients with chronic plaque psoriasis treated with Cy and compared the 7 patients who had previously received MTX (group I: mean age 55 years, range 27-77) with the 6 who had not (group II: mean age 40 years, range 32-45). The average duration of Cy treatment was 2-5 years, mean dose 3 mg/kg daily (range 1-5). The average cumulative dose of MTX was 3270 mg (range 1200-3700). In group 1,5 patients had raised alkaline phosphatase and aspartate aminotransferase before starting Cy which persisted throughout the study. In group II, 2 patients had an initial transient abnormality in liver function tests. Parent drug and metabolites were measured by a polyclonal antibody (’Sandium-kit polyclonal’) in the first half of the study; the therapeutic range for transplantation was 400-800 ng/ml, above which toxicity may be expected. 5 patients in group I had blood concentrations above the therapeutic range on more than one occasion whereas none in group II had such concentrations. In group I the mean Cy blood concentration was 626 ng/ml and in group IIit was 296 ng/ml (p < 0-01). In the latter half of the study we used a monoclonal antibody assay that measures parent drug alone (’Sandimmun-R kit specific ab’). The therapeutic range for transplantation patients is 200-400 ng/ml. In only 1 patient was the concentration above the therapeutic range, and this patient was in group I. Hypertension (systolic over 160 mm Hg, diastolic over 95 mm Hg) developed in 7 patients, 6 of whom were in group I. Serum creatinine was consistently increased by over 30% of the initial concentration in 4 patients, all of whom were in group I. Although the patients in group I were significantly older than those in group II, this difference does not explain the abnormal liver function tests in the MTX-treated group. The high blood concentrations shown by the polyclonal antibody assay in patients who had received MTX suggest that this group can metabolise Cy but that excretion via the bile is impaired leading to accumulation in the blood. These results indicate that Cy metabolites are synergistic to the side-effects of the parent drug and that patients with impaired liver function from MTX treatment may be at risk of Cy toxicity. Thus it may be advisable to consider Cy as the first line oral drug for psoriasis in preference to MTX in systemic treatment.
it is
only used in
treatments.
London W2 1NY, UK
A. V. POWLES B. S. BAKER LIONEL FRY
Department of Immunology, Landsitalinn, Reykjavik, Iceland
H. VALDIMARSSON
Dermatology Department, St Mary’s Hospital,
CEM, Powles AV, McFadden J, Baker BS, Valdimarsson H, Fry L. Long cyclosporin for psoriasis. Br J Dermatol 1989; 120: 253-60 2. Van Joost TH, Box JD, Heule F, et al. Low dose cyclosporin A in severe psoriasis a double-blind study. Br J Dermatol 1988; 188: 183-90. 1. Griffiths term
Clostridium difficile
carriage after infection
SIR,-Asymptomatic stool carriage of Clostridium difficile in healthy patients has been described with rates varying from between 2 and 52% in newborn babies,1 2-8% in chronically ill elderly patientsand 20-30% in adults receiving antibiotics.3 However, the stool carriage rate of this organism following an episode of C difficile-associated diarrhoea is still unclear. We report an investigation of patients who had C difficile-associated diarrhoea during an outbreak, and excretion of the organism and/or its cytotoxin three to six weeks after the onset of diarrhoea. Between Sept 23 and Oct 27, 1989, 13 patients aged 23-70 years (mean 53) at the Queen Elizabeth Hospital, Birmingham, were
611
diagnosed as having C difficile-associated diarrhoea on the basis of clinical history, positive culture, and specific cytotoxin. 3 of these patients had pseudomembranous colitis, confirmed by histology. All 13 patients had received at least one antibiotic during the week preceding the onset of diarrhoea. 3 subsequently died, 2 of whom had pseudomembranous colitis. The remaining 10 patients were all treated with 250-500 mg vancomycin orally four times daily for seven days, and broad-spectrum antibiotics were stopped where possible. A follow-up stool specimen was obtained from each patient three to six weeks after the first cytotoxin-positive specimen. When the follow-up specimen was obtained no patient had diarrhoea. 5 of the 10 patients were excreting C difficile cytotoxin and 3 were excreting the organism when the follow-up specimens were obtained. The role of C difficile as a nosocomial pathogen has been demonstrated.’ Since a proportion of patients who have had C difficile-associated diarrhoea continue to excrete the organism and/or its cytotoxin despite apparent adequate treatment and resolution of symptoms, they are still a possible source of infection. We therefore recommend that symptom-free patients with recent C difficile-associated diarrhoea should be assumed to be potentially infective, and if the patients remain in hospital or are re-admitted shortly after discharge, appropriate precautions should be maintained until a negative result is obtained on stool microbiology. This procedure should particularly apply in areas where there are immunocompromised patients. Department of Clinical Microbiology, Queen Elizabeth Hospital, Queen Elizabeth Medical Centre, Birmingham B15 2TH, UK
M. I. ISSACK T. S. J. ELLIOTT
1. Larson ME, Barclay FE, Honour P, Hill ID. Epidemiology of Clostridium difficile in infants. J Infect Dis 1982; 146: 727-33. 2. Cefai C, Elliott TSJ, Woodhouse KW. Gastrointestinal carriage rate of Clostridium difficile m elderly, chronic care hospital patients. J Hosp Infect 1988; 11: 335-39. 3. Viscidi R, Willey S, Bartlett JG. Isolation rates and toxigenic potential of Clostridum difficile isolates from various patient populations. Gastroenterology 1981; 81: 5-9. 4. McFarland LV, Milligan ME, Kirole RYY, Stamm WE. Nosocomial acquisition of Clostridium difficile infection. N Engl J Med 1989; 320: 204-10. 5. Testore GP, Pantosti A, Cerquetti M, et al. Evidence for cross-infection in an outbreak of Clostridium difficile associated diarrhoea in a surgical unit, J Med Microbiol 1988; 26: 125-28. 6. Nolan NPM, Kelly CP, Humphreys JFH, et al. An epidemic of pseudomembranous colitis: importance of person to person spread. Gut 1987; 28: 1467-73.
SiR,—As one of those responsible for the decision that no clinical trials be done with loxtidine (and as a consultant to Glaxo now, in retirement) I would like to comment on correspondence in your issue of Feb 17. The results reported by Mr Burlinson and colleagues may be difficult to interpret but it is very unlikely that they can be accounted for simply by a rise in gastrin levels, as suggested by Professor Ekman and his colleagues. No increases in tritiated thymidine incorporation were seen with loxtidine, which, in the doses used, would have produced a degree of hypergastrinaemia equivalent to that seen with omeprazole; and a negative result was also reported for pentagastrin. Comprehensive genotoxicity tests with loxtidine have been consistently negative’ while those for omeprazole have provoked comment2 because a mouse micronucleus test at 625 and 6250 times the human dose gave a borderline result, as did an in-vivo bone marrow chromosome aberration test. Do such results indicate some possible genotoxicity? These animal tests may well have resulted in the formation of the sulphenamide, which is formed at low pH. The in-vitro tests were negative but they would not have included the sulphenamide, the active moiety, which binds covalently to the parietal cell canaliculus. However, the decision not to proceed with loxtidine was based not on genotoxicity but on the finding of malignant gastric carcinoids in mice and rats. Elsewhere3Ihave discussed the significance of these fmdings to the clinical situation. There are reasons why powerful antisecretory agents with persistent effects on parietal cells may be associated with subsequent gastric malignancy. The findings of Burlinson et al do nothing to assuage such doubts and they introduce the additional possibility of direct effects on DNA. Your accompanying editorial mentions that "eight weeks’ limited duration treatment with omeprazole is suggested for general prescribing purposes". Why eight weeks and why general prescribing? Surely prudence dictates that compounds with prolonged and persistent effects should be reserved for conditions unresponsive to established therapy. Hoddesdon, Hertfordshire, UK
DESMOND POYNTER
1. Gatehouse D, Wedd 2
DJ, Paes D, et al. Investigations into the genotoxic potential of loxtidine, a long-acting H2 receptor antagonist. Mutagenesis 1988; 3: 57-68. Transcription of Proceedings of the Gastrointestinal Drugs Advisory Committee (34th meeting, March 15, 1989). Washington, DC: Food and Drug Administration.
3.
Omeprazole and genotoxicity SiR,—Your editorial (Feb 17, p 386) presents a sensible, balanced, and cautious analysis of the possible genotoxic effects of omeprazole in an in-vitro system apparently capable of detecting unscheduled DNA synthesis (UDS) and reported by Mr Burlinson and colleagues (same issue, p 419). The necessity for further experiments to confirm the observations available so far and to further validate the technique is rightly stressed. However, two points deserve comment. The omeprazole controversy bears no resemblance to the alleged association between cimetidine and cancer which was put about soon after the introduction of that agent. That association was plainly nonsense. The work on intragastric nitrosation done subsequently has been concerned with the long-term safety of acid-lowering drugs. The present concern with effects of omeprazole has arisen as a consequence of data produced by laboratory experiments-which is very different from the speculation over cimetidine. Secondly, it is debatable whether Glaxo’s freeze on studies comparing omeprazole with ranitidine should be called premature. If the genotoxicity results do not stand up to re-examination, perhaps Glaxo could be seen as having been overcautious, but it is not a bad thing to be overcautious about drug safety. If, on the other hand, the data are confirmed the action may come to be seen as the right one. The UD S data have to be lived with until they can be fully assessed in the light of further information. Department of Gastroenterology and Nutrition, Central Middlesex Hospital, London NW10 7NS, UK
J. J. MISIEWICZ
Poynter D Some possible pathological 1990; 31: 243-44
consequences of peptic ulcer
therapy.
Gut
SIR,-Mr Burlinson and his colleagues report that omeprazole 30 mg/kg increased the incorporation of tritiated thymidine into the DNA of the gastric mucosa of treated rats. They interpret their observations as indicating that omeprazole and/or a metabolite has
potential to induce DNA damage, leading to unscheduled or repair synthesis in the gastric mucosa. In the absence of positive results from a range of conventional mutagenicity studies the observations of Burlinson et al are unique in demonstrating a potential genotoxic activity with this gastric acid inhibiting drug. Astra, the manufacturers of omeprazole, conclude that the technique used by Burlinson et all is unsound and that the observations are not clinically relevant. This demonstration of the stimulation of tritiated thymidine uptake by omeprazole requires further analysis and clarification. The test used is based upon the quantification of thymidine incorporation by scintillation counting and can be criticised because of the inability of the method to distinguish between nuclei undergoing replicative or repair DNA synthesis. The tissue extraction procedures1 may harvest a superficial, non-replicating layer of nuclei from the gastric mucosa and stimulation of thymidine uptake seems to be unique for gastric carcinogens. It is upon the unique nature of this stimulation of thymidine uptake that the potential value of the Burlinson et all observations depend as an indicator of the induction of DNA damage. Proof of the induction of DNA repair synthesis produced by DNA damage could be provided by convincing evidence that the the
TABLE !)—OPT!CAL DENSITY VALUES ON FIFTEEN ANT!-HCV-POSmVE SAM PlES WITH AN D WITHOUT UREA WASH
*Patient also had
hepatoma
infections is low and increases with maturation of the immune
response’ shows the reduction in OD after urea treatment. 8/9 anti-HCV-positive patients with cryptogenic cirrhosis had predominantly high-avidity antibodies (less than 50% reduction in presence of urea) whereas only 1 of 6 antibody-positive patients with other chronic liver disease had high-avidity antibody. All the livers from patients with cryptogenic cirrhosis were cirrhotic but in 1 patient there was more piecemeal and spotty parenchymal necrosis than was seen in the other 8--and this patient was the 1 with predominantly low-avidity antibody, suggesting continuing disease activity or more recent infection. In chronic liver disease non-specific low-avidity antibodies may sometimes be present and cross-react with the recombinant HCV antigen used in the assay. We recommend, in the absence of a confirmatory or specific neutralisation test, that all samples from patients with chronic liver disease which are anti-HCV positive should be retested in the presence of 8 mol/1 urea. This method is only valid for chronic infection; specific low-avidity antibody may be present for some months after acute infection or during active infection. This assay, with and without a urea wash, in conjunction with histological examination may help to distinguish recent from remote HCV infections. Table
II
Clinical Microbiology and Public Health Laboratory, Cambridge CB2 2QW, Department of Surgery, University of Cambridge; and Histopathology Laboratory, Addenbrooke’s Hospital
GRAY T. G. WREGHITT P. J. FRIEND D. G. D. WIGHT V. SUNDARESAN R. Y. CALNE
J. J.
G, Choo Q-L, Alter HJ, et al. An assay for circulating antibodies to a major etiologic virus of human non-A, non-B hepatitis. Science 1989; 244: 362-64. 2. Inouye S, Hasegawa A, Matsuno S, Katwo S. Changes in antibody avidity after virus infections: detection by an immunosorbent assay in which a mild proteindenaturing agent is employed. JClin Microbiol 1984; 20: 525-29. 3. Eisen HN, Siskind GW. Variations in affinities of antibodies during the immune response. Biochemistry 1964; 3: 996-1008. 4. Webster RG. The immune response to influenza virus III changes in the avidity and specificity of early IgM and IgG antibodies. Immunology 1968; 14: 39-52. 1. Kuo
Cyclosporin toxicity SIR,-Dr Lucey and colleagues (Jan 6, pl1) report a liver transplant patient with cyclosporin (Cy) toxicity (nephrotoxicity and neurotoxicity) with therapeutic blood concentrations, and attribute the toxicity to a metabolite which may be related to a deficiency of P450 III A enzyme. Cy is effective treatment for psoriasis.12 However, because of the side-effects of nephrotoxicity and hypertension thought to be related to dose and blood concentration
severe cases that have not responded to other Methotrexate (MTX), widely used in psoriasis, may cause hepatotoxicity, which is related to the cumulative dose. Cy is metabolised in the liver and excreted in the bile. If liver function is abnormal after MTX treatment, high blood concentrations of Cy may result even at low doses because of impaired excretion in the bile. We have seen cyclosporin toxicity (nephrotoxicity and hypertension) in psoriasis, but have measured parent drug concentrations with a monoclonal antibody assay and parent drug and metabolites with a polyclonal antibody assay. We investigated 8 female and 5 male patients with chronic plaque psoriasis treated with Cy and compared the 7 patients who had previously received MTX (group I: mean age 55 years, range 27-77) with the 6 who had not (group II: mean age 40 years, range 32-45). The average duration of Cy treatment was 2-5 years, mean dose 3 mg/kg daily (range 1-5). The average cumulative dose of MTX was 3270 mg (range 1200-3700). In group 1,5 patients had raised alkaline phosphatase and aspartate aminotransferase before starting Cy which persisted throughout the study. In group II, 2 patients had an initial transient abnormality in liver function tests. Parent drug and metabolites were measured by a polyclonal antibody (’Sandium-kit polyclonal’) in the first half of the study; the therapeutic range for transplantation was 400-800 ng/ml, above which toxicity may be expected. 5 patients in group I had blood concentrations above the therapeutic range on more than one occasion whereas none in group II had such concentrations. In group I the mean Cy blood concentration was 626 ng/ml and in group IIit was 296 ng/ml (p < 0-01). In the latter half of the study we used a monoclonal antibody assay that measures parent drug alone (’Sandimmun-R kit specific ab’). The therapeutic range for transplantation patients is 200-400 ng/ml. In only 1 patient was the concentration above the therapeutic range, and this patient was in group I. Hypertension (systolic over 160 mm Hg, diastolic over 95 mm Hg) developed in 7 patients, 6 of whom were in group I. Serum creatinine was consistently increased by over 30% of the initial concentration in 4 patients, all of whom were in group I. Although the patients in group I were significantly older than those in group II, this difference does not explain the abnormal liver function tests in the MTX-treated group. The high blood concentrations shown by the polyclonal antibody assay in patients who had received MTX suggest that this group can metabolise Cy but that excretion via the bile is impaired leading to accumulation in the blood. These results indicate that Cy metabolites are synergistic to the side-effects of the parent drug and that patients with impaired liver function from MTX treatment may be at risk of Cy toxicity. Thus it may be advisable to consider Cy as the first line oral drug for psoriasis in preference to MTX in systemic treatment.
it is
only used in
treatments.
London W2 1NY, UK
A. V. POWLES B. S. BAKER LIONEL FRY
Department of Immunology, Landsitalinn, Reykjavik, Iceland
H. VALDIMARSSON
Dermatology Department, St Mary’s Hospital,
CEM, Powles AV, McFadden J, Baker BS, Valdimarsson H, Fry L. Long cyclosporin for psoriasis. Br J Dermatol 1989; 120: 253-60 2. Van Joost TH, Box JD, Heule F, et al. Low dose cyclosporin A in severe psoriasis a double-blind study. Br J Dermatol 1988; 188: 183-90. 1. Griffiths term
Clostridium difficile
carriage after infection
SIR,-Asymptomatic stool carriage of Clostridium difficile in healthy patients has been described with rates varying from between 2 and 52% in newborn babies,1 2-8% in chronically ill elderly patientsand 20-30% in adults receiving antibiotics.3 However, the stool carriage rate of this organism following an episode of C difficile-associated diarrhoea is still unclear. We report an investigation of patients who had C difficile-associated diarrhoea during an outbreak, and excretion of the organism and/or its cytotoxin three to six weeks after the onset of diarrhoea. Between Sept 23 and Oct 27, 1989, 13 patients aged 23-70 years (mean 53) at the Queen Elizabeth Hospital, Birmingham, were
611
diagnosed as having C difficile-associated diarrhoea on the basis of clinical history, positive culture, and specific cytotoxin. 3 of these patients had pseudomembranous colitis, confirmed by histology. All 13 patients had received at least one antibiotic during the week preceding the onset of diarrhoea. 3 subsequently died, 2 of whom had pseudomembranous colitis. The remaining 10 patients were all treated with 250-500 mg vancomycin orally four times daily for seven days, and broad-spectrum antibiotics were stopped where possible. A follow-up stool specimen was obtained from each patient three to six weeks after the first cytotoxin-positive specimen. When the follow-up specimen was obtained no patient had diarrhoea. 5 of the 10 patients were excreting C difficile cytotoxin and 3 were excreting the organism when the follow-up specimens were obtained. The role of C difficile as a nosocomial pathogen has been demonstrated.’ Since a proportion of patients who have had C difficile-associated diarrhoea continue to excrete the organism and/or its cytotoxin despite apparent adequate treatment and resolution of symptoms, they are still a possible source of infection. We therefore recommend that symptom-free patients with recent C difficile-associated diarrhoea should be assumed to be potentially infective, and if the patients remain in hospital or are re-admitted shortly after discharge, appropriate precautions should be maintained until a negative result is obtained on stool microbiology. This procedure should particularly apply in areas where there are immunocompromised patients. Department of Clinical Microbiology, Queen Elizabeth Hospital, Queen Elizabeth Medical Centre, Birmingham B15 2TH, UK
M. I. ISSACK T. S. J. ELLIOTT
1. Larson ME, Barclay FE, Honour P, Hill ID. Epidemiology of Clostridium difficile in infants. J Infect Dis 1982; 146: 727-33. 2. Cefai C, Elliott TSJ, Woodhouse KW. Gastrointestinal carriage rate of Clostridium difficile m elderly, chronic care hospital patients. J Hosp Infect 1988; 11: 335-39. 3. Viscidi R, Willey S, Bartlett JG. Isolation rates and toxigenic potential of Clostridum difficile isolates from various patient populations. Gastroenterology 1981; 81: 5-9. 4. McFarland LV, Milligan ME, Kirole RYY, Stamm WE. Nosocomial acquisition of Clostridium difficile infection. N Engl J Med 1989; 320: 204-10. 5. Testore GP, Pantosti A, Cerquetti M, et al. Evidence for cross-infection in an outbreak of Clostridium difficile associated diarrhoea in a surgical unit, J Med Microbiol 1988; 26: 125-28. 6. Nolan NPM, Kelly CP, Humphreys JFH, et al. An epidemic of pseudomembranous colitis: importance of person to person spread. Gut 1987; 28: 1467-73.
SiR,—As one of those responsible for the decision that no clinical trials be done with loxtidine (and as a consultant to Glaxo now, in retirement) I would like to comment on correspondence in your issue of Feb 17. The results reported by Mr Burlinson and colleagues may be difficult to interpret but it is very unlikely that they can be accounted for simply by a rise in gastrin levels, as suggested by Professor Ekman and his colleagues. No increases in tritiated thymidine incorporation were seen with loxtidine, which, in the doses used, would have produced a degree of hypergastrinaemia equivalent to that seen with omeprazole; and a negative result was also reported for pentagastrin. Comprehensive genotoxicity tests with loxtidine have been consistently negative’ while those for omeprazole have provoked comment2 because a mouse micronucleus test at 625 and 6250 times the human dose gave a borderline result, as did an in-vivo bone marrow chromosome aberration test. Do such results indicate some possible genotoxicity? These animal tests may well have resulted in the formation of the sulphenamide, which is formed at low pH. The in-vitro tests were negative but they would not have included the sulphenamide, the active moiety, which binds covalently to the parietal cell canaliculus. However, the decision not to proceed with loxtidine was based not on genotoxicity but on the finding of malignant gastric carcinoids in mice and rats. Elsewhere3Ihave discussed the significance of these fmdings to the clinical situation. There are reasons why powerful antisecretory agents with persistent effects on parietal cells may be associated with subsequent gastric malignancy. The findings of Burlinson et al do nothing to assuage such doubts and they introduce the additional possibility of direct effects on DNA. Your accompanying editorial mentions that "eight weeks’ limited duration treatment with omeprazole is suggested for general prescribing purposes". Why eight weeks and why general prescribing? Surely prudence dictates that compounds with prolonged and persistent effects should be reserved for conditions unresponsive to established therapy. Hoddesdon, Hertfordshire, UK
DESMOND POYNTER
1. Gatehouse D, Wedd 2
DJ, Paes D, et al. Investigations into the genotoxic potential of loxtidine, a long-acting H2 receptor antagonist. Mutagenesis 1988; 3: 57-68. Transcription of Proceedings of the Gastrointestinal Drugs Advisory Committee (34th meeting, March 15, 1989). Washington, DC: Food and Drug Administration.
3.
Omeprazole and genotoxicity SiR,—Your editorial (Feb 17, p 386) presents a sensible, balanced, and cautious analysis of the possible genotoxic effects of omeprazole in an in-vitro system apparently capable of detecting unscheduled DNA synthesis (UDS) and reported by Mr Burlinson and colleagues (same issue, p 419). The necessity for further experiments to confirm the observations available so far and to further validate the technique is rightly stressed. However, two points deserve comment. The omeprazole controversy bears no resemblance to the alleged association between cimetidine and cancer which was put about soon after the introduction of that agent. That association was plainly nonsense. The work on intragastric nitrosation done subsequently has been concerned with the long-term safety of acid-lowering drugs. The present concern with effects of omeprazole has arisen as a consequence of data produced by laboratory experiments-which is very different from the speculation over cimetidine. Secondly, it is debatable whether Glaxo’s freeze on studies comparing omeprazole with ranitidine should be called premature. If the genotoxicity results do not stand up to re-examination, perhaps Glaxo could be seen as having been overcautious, but it is not a bad thing to be overcautious about drug safety. If, on the other hand, the data are confirmed the action may come to be seen as the right one. The UD S data have to be lived with until they can be fully assessed in the light of further information. Department of Gastroenterology and Nutrition, Central Middlesex Hospital, London NW10 7NS, UK
J. J. MISIEWICZ
Poynter D Some possible pathological 1990; 31: 243-44
consequences of peptic ulcer
therapy.
Gut
SIR,-Mr Burlinson and his colleagues report that omeprazole 30 mg/kg increased the incorporation of tritiated thymidine into the DNA of the gastric mucosa of treated rats. They interpret their observations as indicating that omeprazole and/or a metabolite has
potential to induce DNA damage, leading to unscheduled or repair synthesis in the gastric mucosa. In the absence of positive results from a range of conventional mutagenicity studies the observations of Burlinson et al are unique in demonstrating a potential genotoxic activity with this gastric acid inhibiting drug. Astra, the manufacturers of omeprazole, conclude that the technique used by Burlinson et all is unsound and that the observations are not clinically relevant. This demonstration of the stimulation of tritiated thymidine uptake by omeprazole requires further analysis and clarification. The test used is based upon the quantification of thymidine incorporation by scintillation counting and can be criticised because of the inability of the method to distinguish between nuclei undergoing replicative or repair DNA synthesis. The tissue extraction procedures1 may harvest a superficial, non-replicating layer of nuclei from the gastric mucosa and stimulation of thymidine uptake seems to be unique for gastric carcinogens. It is upon the unique nature of this stimulation of thymidine uptake that the potential value of the Burlinson et all observations depend as an indicator of the induction of DNA damage. Proof of the induction of DNA repair synthesis produced by DNA damage could be provided by convincing evidence that the the
