Comparative pharmacokinetics of metronidazole and tinidazole and their tissue penetration

Infection Protocols for Implants

Infection can be a devastating complication of surgically inserted prosthetic implants and intramedullary rods, plates and pins. About 2 million implants were inserted in the United States in 2004, and, despite appropriate perioperative antibiotics, approximately 5% of internal fixation devices became infected. Infection rates in fractures that pierce the skin can be as high as 22.7%. Complications of infection include excessive antibiotic use, implant removal, reoperation, and potential amputation. Infections caused by colonized prosthetic implants are often difficult to predict, diagnose, and treat, because they form biofilms. This article explores the approach to infected implants.

Systemic antibiotic therapy for chronic osteomyelitis in adults

The standard recommendation for treating chronic osteomyelitis is 6 weeks of parenteral antibiotic therapy. However, oral antibiotics are available that achieve adequate levels in bone, and there are now more published studies of oral than parenteral antibiotic therapy for patients with chronic osteomyelitis. Oral and parenteral therapies achieve similar cure rates; however, oral therapy avoids risks associated with intravenous catheters and is generally less expensive, making it a reasonable choice for osteomyelitis caused by susceptible organisms. Addition of adjunctive rifampin to other antibiotics may improve cure rates. The optimal duration of therapy for chronic osteomyelitis remains uncertain. There is no evidence that antibiotic therapy for >4-6 weeks improves outcomes compared with shorter regimens. In view of concerns about encouraging antibiotic resistance to unnecessarily prolonged treatment, defining the optimal route and duration of antibiotic therapy and the role of surgical debridement in treating chronic osteomyelitis are important, unmet needs.

Guidelines for the treatment of bacterial vaginosis: focus on tinidazole

Bacterial vaginosis (BV) is a complex vaginal infection most commonly associated with women of child-bearing age. Risk factors for BV are numerous. There are currently multiple clinical and laboratory tests for diagnosis of BV, including the most commonly used diagnostic methods: Amsel’s criteria or Nugent’s Gram stain scale. The mainstay of BV therapy is metronidazole, but tinidazole as well as a few other agents have also been used successfully. Tinidazole is the second nitroimidazole antiprotozoal agent and a structural derivative of metronidazole. With a favorable pharmacokinetic profile and reduced side effects, tinidazole is an alternative agent for BV treatment. There are minimal head-to-head comparative data to establish tinidazole’s superiority to metronidazole or other therapeutic agents. Available data suggest tinidazole has a role in special populations particularly for refractory or relapsing BV.

Presentation of a structurally diverse and commercially available drug data set for correlation and benchmarking studies

A multivariate analysis of drugs on the Swedish market was the basis for the selection of a small, physicochemically diverse set of 24 drug compounds. Factors such as structural diversity, commercial availability, price, and a suitable analytical technique for quantification were considered in the selection. Lipophilicity, pKa, solubility, and permeability across human Caco-2 cell monolayers were measured for the compiled data set. The results show that, by use of a physicochemically diverse data set, experimental responses over a wide range were obtained. The paper also shows how experimental difficulties due to the diversity of the data set can be overcome. We anticipate that this data set can serve as a benchmark set for validation of new experimental techniques or in silico models. It can also be used as a diverse starting data set for the development of new computational models.

Pharmacokinetics and pharmacodynamics of intravenous levofloxacin at 750 milligrams and various doses of metronidazole in healthy adult subjects

The purpose of this investigation was to evaluate the steady-state pharmacokinetics, pharmacodynamics, and safety of intravenous levofloxacin at 750 mg administered once daily combined with three different dosages of intravenous metronidazole (500 mg every 8 h [q8h], 1,000 mg q24h, and 1,500 mg q24h). Eighteen healthy adult subjects received all three combinations in a randomized, crossover fashion. Serial blood and urine samples were collected on the third day of each study period. The 24-h areas under the inhibitory (AUIC(0-24)) and bactericidal (AUBC(0-24)) curves of these three combination regimens were determined against clinical isolates of Bacteroides fragilis, Bacteroides thetaiotaomicron, Peptostreptococcus asaccharolyticus, and Escherichia coli. The mean concentrations of levofloxacin were not different between study periods and were similar to those previously published. The mean (+/- standard deviation) areas under the metronidazole plasma concentration-time curve (AUC(0-24)) for 1,500-mg q24h (338 +/- 105 mg.h/liter) and 500-mg q8h (356 +/- 68 mg.h/liter) regimens were not different (P > 0.05), but both were significantly higher than the 1,000-mg q24h AUC(0-24) (P < 0.05, 227 +/- 57 mg.h/liter). Mean (+/- standard deviation) total body clearance and renal clearance values were similar among the 500-mg q8h, 1,000-mg q24, and 1,500-mg q24h regimens (62 +/- 7, 67 +/- 13, and 67 +/- 14 and 11 +/- 3, 12 +/- 2, and 12 +/- 5 ml/min/1.73 m2, respectively). Levofloxacin at 750 mg q24h plus metronidazole at 500 mg q8h or 1,500 mg q24h resulted in similar AUIC(0-24) and AUBC(0-24) values with one exception: the AUIC(0-24) for the 1,500-mg q24h regimen against B. thetaiotamicron was significantly higher (P < 0.05) than those of the other regimens. Overall, the combination of levofloxacin at 750 mg once daily and metronidazole at 500 mg q8h or 1,500 mg q24h appeared to have greater AUIC(0-24) and AUBC(0-24) values than did the 1,000-mg q24h regimen. All combination regimens of levofloxacin and metronidazole were well tolerated, and no serious drug-related adverse effects were reported. The pharmacokinetic, safety, and pharmacodynamic data from our study suggest that a once-daily regimen of intravenous levofloxacin at 750 mg and metronidazole at 1,500 mg warrants further clinical investigation.

Comparative effects of omeprazole, amoxycillin plus metronidazole versus omeprazole, clarithromycin plus metronidazole on the oral, gastric and intestinal microflora in Helicobacter pylori-infected patients

Fourteen patients with Helicobacter pylori infection were treated with 20 mg omeprazole, 1 g amoxycillin and 400 mg metronidazole bd for 7 days (OAM), and 16 patients were treated with 20 mg omeprazole, 250 mg clarithromycin and 400 mg metronidazole bd for 7 days (OCM). Saliva, gastric biopsies and faecal samples were collected before, during (day 7) and 4 weeks after treatment in order to analyse alterations of the normal microflora and to determine antimicrobial susceptibility. Both treatment regimens resulted in marked quantitative and qualitative alterations. A selection of resistant streptococcal strains were noticed in both treatment groups, most apparent in the OCM group where a shift from susceptible to resistant strains was recorded. In the OAM group, six patients had overgrowth of resistant enterobacteriaceae during treatment compared with none in the OCM group, in the gastric microflora. The MICs for Enterococcus spp. and Enterobacteriaceae in faeces increased significantly during treatment in both groups. Nine patients in the OAM group became intestinally colonized by yeasts during treatment. The total anaerobic microflora was strongly suppressed in both treatment groups, although most pronounced in the OCM group, where the frequency of clarithromycin-resistant bacteroides strains increased from 2 to 76% during treatment, and remained at 59% 4 weeks post-treatment. Even if the treatment outcome was better in the OCM group (100%) than in the OAM group (71%), the amoxycillin-based treatment might be preferable from an ecological point of view, since the qualitative alterations in terms of emergence and persistence of resistant strains seemed to be most pronounced in the clarithromycin-treated group.

Pharmacokinetics and pharmacodynamics of the nitroimidazole antimicrobials

Metronidazole, the prototype nitroimidazole antimicrobial, was originally introduced to treat Trichomonas vaginalis, but is now used for the treatment of anaerobic and protozoal infections. The nitroimidazoles are bactericidal through toxic metabolites which cause DNA strand breakage. Resistance, both clinical and microbiological, has been described only rarely. Metronidazole given orally is absorbed almost completely, with bioavailability > 90% for tablets; absorption is unaffected by infection. Rectal and intravaginal absorption are 67 to 82%, and 20 to 56%, of the dose, respectively. Metronidazole is distributed widely and has low protein binding (< 20%). The volume of distribution at steady state in adults is 0.51 to 1.1 L/kg. Metronidazole reaches 60 to 100% of plasma concentrations in most tissues studied, including the central nervous system, but does not reach high concentrations in placental tissue. Metronidazole is extensively metabolised by the liver to 5 metabolites. The hydroxy metabolite has biological activity of 30 to 65% and a longer elimination half-life than the parent compound. The majority of metronidazole and its metabolites are excreted in urine and faeces, with less than 12% excreted unchanged in urine. The pharmacokinetics of metronidazole are unaffected by acute or chronic renal failure, haemodialysis, continuous ambulatory peritoneal dialysis, age, pregnancy or enteric disease. Renal dysfunction reduces the elimination of metronidazole metabolites; however, no toxicity has been documented and dosage alterations are unnecessary. Liver disease leads to a decreased clearance of metronidazole and dosage reduction is recommended. Recent pharmacodynamic studies of metronidazole have demonstrated activity for 12 to 24 hours after administration of metronidazole 1 g. The post-antibiotic effect of metronidazole extends beyond 3 hours after the concentration falls below the minimum inhibitory concentration (MIC). The concentration-dependent bactericidal activity, prolonged half-life and sustained activity in plasma support the clinical evaluation of higher doses of metronidazole given less frequently. Metronidazole-containing regimens for Helicobacter pylori in combination with proton pump inhibitors demonstrate higher success rates than antimicrobial regimens alone. The pharmacokinetics of metronidazole in gastric fluid appear contradictory to these results, since omeprazole reduces peak drug concentration and area under the concentration-time curve for metronidazole and its hydroxy metabolite; however, concentrations remain above the MIC. Other members of this class include tinidazole, ornidazole and secnidazole. They are also well absorbed and distributed after oral administration. Their only distinguishing features are prolonged half-lives compared with metronidazole. The choice of nitroimidazole may be influenced by the longer administration intervals possible with other members of this class; however, metronidazole remains the predominant antimicrobial for anaerobic and protozoal infections.

Randomized controlled comparison of nitroimidazoles for the eradication of Helicobacter pylori and relief of ulcer-associated and non-ulcer dyspepsia

BACKGROUND

A combination of omeprazole, clarithromycin and either metronidazole or tinidazole is commonly used for Helicobacter pylori eradication. Metronidazole is considerably cheaper than tinidazole but the two have not previously been compared in a randomized trial.

METHODS

One hundred and twenty dyspeptic H. pylori-positive patients with endoscopically defined peptic ulcer [DU (n = 65), GU (n = 12)] or non-ulcer dyspepsia (NUD, n = 43) were randomized to receive a 1-week course of twice daily omeprazole 20 mg, clarithromycin 250 mg and either metronidazole 400 mg (OCM) or tinidazole 500 mg (OCT) in a double-blind fashion. Eradication of H. pylori, safety and side-effects of treatment, dyspeptic symptom score and consumption of antisecretory drugs were assessed at 6 weeks and 1 year after treatment.

RESULTS

H. pylori eradication was successfully achieved in 57/60 (95%, ITT analysis) of patients receiving OCT and 58/60 (97%, ITT analysis) receiving OCM. Both regimens had similar side-effect profiles, which accounted for only one patient withdrawal. All patients remained uninfected (as assessed by 14C-urea breath test) at 1-year follow-up, but major symptom improvements and decreased antisecretory drug use were only seen in patients with DU (P<0.0001).

CONCLUSIONS

Treatment with OCM is as effective as the more expensive OCT at eradicating H. pylori. H. pylori eradication results in long-term relief of dyspeptic symptoms and reduced antisecretory consumption only in patients with DU, and not in those with NUD.

Bacterial mutagens in the urine of patients under tinidazole treatment

Tinidazole is an antiparasitic drug belonging to the 5-nitroimidazole family. It is prescribed against protozoal infestations and is widely used in Mexico as well as other underdeveloped countries where infectious diseases are the first cause of children mortality. The drug is a direct mutagen in Salmonella typhimurium TA100 strain and the presence of S9 mixture did not modify its mutagenic effect. At low doses no mutagenicity was detected with strains TA100NR, TA98 or UTH8414 (Uvr+ derivative of TA100). Urine from four patients under tinidazole treatment exhibited a mutagenic activity on strain TA100, greater than the expected from the tinidazole concentrations determined by high-performance liquid chromatography (HPLC). Components from the urine samples were separated on thin-layer chromatography (TLC) plates, and their mutagenic effects tested by direct application of the Salmonella assay onto sections of the developed chromatoplate. The Rf of one component (0.62) corresponded to the one obtained for a tinidazole standard and showed the expected mutagenicity, while a second component with an Rf=0.39, exhibited a mutagenic potency slightly greater than the observed for tinidazole; however, as in the case of the drug itself, reduction of the nitro group was necessary for a mutagenic activity.

Penetration of tinidazole into skin blister fluid following its oral administration

Plasma and skin blister fluid concentrations of tinidazole following a single oral dose of 2 g drug, and after multiple doses of 0.25 g every 12 h, were determined. Skin blisters were produced by direct application of 0.25% cantharidin ointment to the skin. The maximum concentration in plasma of about 36 mg.l-1 was observed after about 2 h, whereas in skin blister fluid the peak occurred after about 6 h and was 30 mg.l-1. The half-life in plasma was slightly shorter than in blister fluid at 17 and 19 h, respectively, but the difference was not significant. The penetration of tinidazole into cantharidin-induced skin blister fluid, defined according to Wise as the ratio of the AUCs in blister fluid and plasma was 1.00. During routine treatment with tinidazole (0.25 g every 12 h), the concentrations in plasma and blister fluid collected before and 3 h after the morning dose exceeded the minimal inhibitory concentrations for susceptible pathogens. The results provide a pharmacokinetic basis for the proven efficacy of tinidazole in the treatment of protozoal and anaerobic infections.

Clinical pharmacokinetics of metronidazole and other nitroimidazole anti-infectives

Metronidazole was first introduced for the treatment of trichomoniasis. Its therapeutic use has subsequently been expanded to include amoebiasis, giardiasis and, more recently, anaerobic infections. Most of the early pharmacokinetic studies employed nonspecific assays such as microbiological and chemical assays. These assays were not able to differentiate the parent drug from the metabolites or other interfering substances. Pharmacokinetic data obtained through the use of specific chromatographic techniques provide the basis for this review of recent pharmacokinetic findings concerning metronidazole and other nitroimidazole antibiotics. When given intravenously or orally at usual recommended doses, metronidazole attains concentrations well above the minimum inhibitory concentrations for most susceptible micro-organisms. The drug has an oral bioavailability approaching 100%. Rectal and vaginal administration results in a smaller amount of drug absorption and lower serum concentrations. Metronidazole has limited plasma protein binding but can attain very favourable tissue distribution, including into the central nervous system. The drug is extensively metabolised by the liver to form 2 primary oxidative metabolites: the hydroxy and acetic acid metabolites. The kidney is responsible for the elimination of only a small amount of the parent drug; however, normal excretion of the 2 metabolites is dependent on the integrity of kidney function. The metabolism of metronidazole was found to vary among patient groups. Preterm and term infants have lower total body clearance (CL) and prolonged elimination half-lives. However, children older than 4 years old were observed to have pharmacokinetic parameters similar to those in adults. Reduced CL was also observed in children who are malnourished. Elderly patients have reduced renal excretion of both the parent drug and hydroxy metabolite. Pharmacokinetic parameters in pregnant patients were not significantly different from those in nonpregnant women; however, the drug is distributed into breastmilk and the infant will be exposed to the drug through the nursing mother. Patients undergoing gastrointestinal surgery or having enteric diseases and those who are hospitalised or critically ill also have altered pharmacokinetics. Metabolism of the drug is reduced in patients with liver dysfunction, giving delayed production of metabolites. In contrast, renal failure has little effect on the elimination of the parent drug, but affects the excretion of the metabolites more significantly. Haemodialysis was found to remove a substantial amount of the metronidazole while the effect of peritoneal dialysis was more limited. Energy and protein deficient diets as well as occupational exposure to gasoline did not alter metronidazole pharmacokinetics. However, the effect of alcohol consumption on metronidazole CL requires further study.(ABSTRACT TRUNCATED AT 400 WORDS)

Design and trial of a metronidazole loading dose regimen for patients undergoing emergency surgery

A dosing regimen for administration of metronidazole to patients undergoing emergency surgery was designed using pharmacokinetic data. Computer estimates of the pharmacokinetic parameters from normal volunteers were used to determine a loading dose protocol that would achieve plasma metronidazole levels above 6.2 micrograms/mL, that is, above the minimum inhibitory concentration (MIC) of most pathogenic anaerobic bacteria, at the time of surgery. The protocol aimed to identify the minimum intravenous metronidazole dose in combination with a rectal suppository regimen. This was calculated to be a 1 g (two 500 mg) metronidazole rectal suppository dose administered when the decision to operate was made, followed by a 200 mg intravenous dose at the induction of anaesthesia if the time to surgery was within 1-8 h. This protocol was tested in 10 patients undergoing emergency abdominal/pelvic surgery. All patients in the trial were found to have levels well above the MIC at the time of surgery (mean = 17.06 micrograms/mL, s.d. = 4.76). It is concluded that appropriate use of metronidazole suppositories can minimize intravenous dosage requirements for metronidazole under conditions of emergency loading as well as elective surgery.