Year : 1998 | Volume
: 4 | Issue : 3 | Page : 156--158
Susceptibility of helicobacter pylori to metronidazole and its bioactive derivatives
Robert McCay Bannatyne
Department of Pathology, King Fahad National Guard Hospital, P.O. Box 22490, Riyadh 11426, Saudi Arabia
Robert McCay Bannatyne
Department of Pathology, King Fahad National Guard Hospital, P.O. Box 22490, Riyadh 11426
The hydroxy derivative of metronidazole can exhibit equal or greater activity to the parent drug against several bacteria. The susceptibility status of 22 H. pylori strains to these breakdown compounds was determined in order to determine their possible role in the therapy of H. pylori associated peptic ulcer disease. The susceptibility was determined using the agar dilution method and substantial activity (MIC90 = 0.33 .tg/ml) for the hydroxy metabolite of metronidazole versus H. pylori was observed. The findings define a role for the hydroxy derivative of metronidazole in peptic ulcer disease and support the limited data on the possibility of cooperative interactions between the parent compound, its main derivatives and related companion drugs in this condition.
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Bannatyne RM. Susceptibility of helicobacter pylori to metronidazole and its bioactive derivatives.Saudi J Gastroenterol 1998;4:156-158
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Bannatyne RM. Susceptibility of helicobacter pylori to metronidazole and its bioactive derivatives. Saudi J Gastroenterol [serial online] 1998 [cited 2018 Apr 22 ];4:156-158
Available from: http://www.saudijgastro.com/text.asp?1998/4/3/156/33910
Helicobacter pylori is etiologically linked to both peptic ulcer disease and gastric carcinoma. Susceptible strains respond clinically to metronidazole and companion drugs and the cure rates are high. Unfortunately the incidence of metronidazole resistance (87%) in Saudi Arabia strains is prohibitive,. Metronidazole is partly broken down in the liver. Because some of its metabolites can exhibit superior activity to the parent drug the present study was undertaken to determine the susceptibility of H. pylori to metronidazole and its bioactive derivatives.
Twenty-two susceptible strains of H. pylori were selected for testing. They were recovered from glycerol-citrate membrane filters stored at -70°C by subculture twice on Columbia blood agar containing 7% defibrinated horse blood in closed anaerobic jars (7% oxygen, 7% carbon dioxide, 26% nitrogen and 60% hydrogen) for five days at 37°C.
Metronidazole, its acid metabolite (2-methyl-5nitro-imidazolyl-acetic acid) and its hydroxy metabolite (1-[2-hydroxy-ethyl]-2-hydroxymethyl5-nitro-imidazole) were supplied by Rhone-Poulouc Pharma Inc., Montreal, Quebec, Canada. Each was dissolved in N, N-dimethyl formamide and diluted in distilled water to produce a stock solution with a concentration of lmg/ml. From this, testing solutions were prepared in two-fold serial dilutions to cover the range 0.125 to 256 mg/l and incorporated into Diagnostic Sensitivity agar (Oxoid Ltd.) supplemented with 5% lysed horse blood.
The agar dilution method of susceptibility testing using a multiple replicator apparatus was utilized. Suspensions were made from blood agar cultures incubated at 37°C for five days in 2 ml of Penassay broth (Difco Antibiotic Medium number 3) and adjusting the turbidity to a Mac Farland Number 2 standard. This was equivalent to approximately 2.0 x 107 colony-forming-units (cfu) /m1 as determined by viable count. Appropriate dilution were delivered onto DST agar containing 5% lysed horse blood and antimicrobial agent by means of a Steers replicator to give a final inoculum of approximately 1 to 5 x 10[4organisms/ml. Plates were incubated in anaerobic jars for five days at 37°C. Control strains (B. fragilis ATCC 22582 and B. thetaiotamicron ATCC 29741) were included for reference in each run. Susceptibility was defined as the absence of growth at the point of inoculation. Minimum concentrations which inhibited 50% and 90% of the strains (MIC 50 's and MIC 90 's) were calculated by the Reed and Muench method
The MIC 50 's and MIC 90 's in mg/mel for metronidazole, the hydroxy derivative and the acid metabolite were 0.29/1.79, 0.22/0.33 and 1.15/2.95 respectively. The MIC's of the control strains were in the expected ranges 0.25, 0.5, 8 and 0.5, 16.0 mg/l respectively for B. fragilis and B. thetaiotamicron.
The level of activity of the hydroxy metabolite of metronidazole against H. pylori was substantial. In fact it was even greater than that of the parent compound. This is not an unusual observation and the increased potency of the hydroxy derivative over metronidazole has been remarked previously with other bacteria, such as Gardnerella vaginalis. Attainable serum levels of the hydroxy breakdown product at 6.2-6.6 μg/ml are well in excess of the MIC 50 (0.33 μg/ml) for the drug against H. pylori.
The acid derivative demonstrated inferior activity. Other investigators, working with Bacteroides fragilis, have also noted the negligible activity of this compound,. These observations together with the unfavorable pharmacokinetic properties of the acid metabolite - [it attains low to negligible levels in the blood and appears mainly in the urine] make it unlikely that it contributes significantly to the overall antimicrobial effects of metronidazole and its derivatives.
Additional studies suggest a further manner in which the hydroxy derivative may play a role in the therapy of H. pylori infection. Limited data suggests that the hydroxy compound and the parent drug may act synergistically against H. pylori and other bacteria such as B. fragilis and A. actinomycetemcomitants,. Again a number of precedents for this type of interaction between parent drug and metabolite exist for other antimicrobial agents such as cefotaxime and its desacetyl derivative and clarithromycin and its 14-hydroxy metabolite. Furthermore cooperative effects between metronidazole and/or its hydroxy derivative, antibiotics such as ampicillin and tetracycline, and companion drugs such as bismuth have been identified,. It seems likely that the clinical response in H. pylori infection treated with metronidazole is not determined solely by the organism's susceptibility to metronidazole but may involve complex interactions between the antibiotic, its breakdown products and partner drugs.
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