Tinidazole--microbiology, pharmacology and efficacy in anaerobic infections

Functionalized Nitroimidazole Scaffold Construction and Their Pharmaceutical Applications: A 1950–2021 Comprehensive Overview

Nitroimidazole represents one of the most essential and unique scaffolds in drug discovery since its discovery in the 1950s. It was K. Maeda in Japan who reported in 1953 the first nitroimidazole as a natural product from Nocardia mesenterica with antibacterial activity, which was later identified as Azomycin 1 (2-nitroimidazole) and remained in focus until now. This natural antibiotic was the starting point for synthesizing numerous analogs and regio-isomers, leading to several life-saving drugs and clinical candidates against a number of diseases, including infections (bacterial, viral, parasitic) and cancers, as well as imaging agents in medicine/diagnosis. In the present decade, the nitroimidazole scaffold has again been given two life-saving drugs (Delamanid and Pretomanid) used to treat MDR (multi-drug resistant) tuberculosis. Keeping in view the highly successful track-record of the nitroimidazole scaffold in providing breakthrough therapeutic drugs, this comprehensive review focuses explicitly on presenting the activity profile and synthetic chemistry of functionalized nitroimidazole (2-, 4- and 5-nitroimidazoles as well as the fused nitroimidazoles) based drugs and leads published from 1950 to 2021. The present review also presents the miscellaneous examples in each class. In addition, the mutagenic profile of nitroimidazole-based drugs and leads and derivatives is also discussed.

In Situ Reactivity of Electrochemically Generated Nitro Radical Anion on Tinidazole and Its Monomeric and Dimeric CuII Complexes on Model Biological Targets with Relative Manifestation of Preventing Bacterial Biofilm Formation

Formation of nitro radical anion (-NO₂ ^•-) and other reduction products of 5-nitroimidazoles, although important for antimicrobial activity, makes the drugs neurotoxic. Hence, an appropriate generation and their role in the free radical pathway needs proper realization. This was attempted by studying the action of tinidazole and its Cu^II complexes on model targets (nucleic acid bases and calf thymus DNA). Results obtained were correlated with studies on biological species where prevention of biofilm formation on Staphylococcus aureus and Pseudomonas aeruginosa was followed. Tinidazole and its Cu^II complexes subjected to electrochemical reduction in aqueous solution, under de-aerated conditions, interact with model nucleic acid bases and calf thymus DNA. These model targets were followed to realize what happens when such compounds undergo enzymatic reduction within cells of microorganisms that they eventually kill. Studies reveal that Cu^II complexes were better in modifying nucleic acid bases and calf thymus DNA than tinidazole; damage caused to nucleic acid bases was correlated with that caused to DNA, indicating that compounds affect DNA rich in thymine and adenine. Minimum bactericidal concentrations on sessile S. aureus and P. aeruginosa for the monomeric Cu^II complex were 12.5 and 20.25 μM respectively, while those for the dimeric complex were 40.0 and 45.0 μM, respectively. Biofilm formation by P. aeruginosa and S. aureus and viability count of sessile cells were also determined. Cu^II complexes of tinidazole brought about substantial reduction in carbohydrate and protein content in S. aureus and P. aeruginosa. Downregulation of quorum sensing signaling mechanism viz. reduced production of pyocyanin and elastase during biofilm formation was also detected. Cu^II complexes showed much higher tendency to prevent biofilm formation than tinidazole, almost comparable to amoxicillin, an established drug in this regard.

The Synergistic Effect of Mud Crab Antimicrobial Peptides Sphistin and Sph12-38 With Antibiotics Azithromycin and Rifampicin Enhances Bactericidal Activity Against Pseudomonas Aeruginosa

Overuse or abuse of antibiotics has undoubtedly accelerated the increasing prevalence of global antibiotic resistance crisis, and thus, people have been trying to explore approaches to decrease dosage of antibiotics or find new antibacterial agents for many years. Antimicrobial peptides (AMPs) are the ideal candidates that could kill pathogens and multidrug-resistant bacteria either alone or in combination with conventional antibiotics. In the study, the antimicrobial efficacy of mud crab Scylla paramamosain AMPs Sphistin and Sph₁₂₋₃₈ in combination with eight selected antibiotics was evaluated using a clinical pathogen, Pseudomonas aeruginosa. It was interesting to note that the in vitro combination of rifampicin and azithromycin with Sphistin and Sph₁₂₋₃₈ showed significant synergistic activity against P. aeruginosa. Moreover, an in vivo study was carried out using a mouse model challenged with P. aeruginosa, and the result showed that the combination of Sph₁₂₋₃₈ with either rifampicin or azithromycin could significantly promote the healing of wounds and had the healing time shortened to 4–5 days compared with 7–8 days in control. The underlying mechanism might be due to the binding of Sphistin and Sph₁₂₋₃₈ with P. aeruginosa lipopolysaccharides (LPS) and subsequent promotion of the intracellular uptake of rifampicin and azithromycin. Taken together, the significant synergistic antibacterial effect on P. aeruginosa in vitro and in vivo conferred by the combination of low dose of Sphistin and Sph₁₂₋₃₈ with low dose of rifampicin and azithromycin would be beneficial for the control of antibiotic resistance and effective treatment of P. aeruginosa-infected diseases in the future.

Controlled delivery of the antiprotozoal agent (tinidazole) from intravaginal polymer matrices for treatment of the sexually transmitted infection, trichomoniasis

Microporous polymeric matrices prepared from poly(ɛ-caprolactone) [PCL] were evaluated for controlled vaginal delivery of the antiprotozoal agent (tinidazole) in the treatment of the sexually transmitted infection, trichomoniasis. The matrices were produced by rapidly cooling co-solutions of PCL and tinidazole in acetone to -80 °C to induce crystallisation and hardening of the polymer. Tinidazole incorporation in the matrices increased from 1.4 to 3.9% (w/w), when the drug concentration in the starting PCL solution was raised from 10 to 20% (w/w), giving rise to drug loading efficiencies up to 20%. Rapid 'burst release' of 30% of the tinidazole content was recorded over 24 h when the PCL matrices were immersed in simulated vaginal fluid. Gradual drug release occurred over the next 6 days resulting in delivery of around 50% of the tinidazole load by day 7 with the released drug retaining antiprotozoal activity at levels almost 50% that of the 'non-formulated' drug in solution form. Basic modelling predicted that the concentration of tinidazole released into vaginal fluid in vivo from a PCL matrix in the form of an intravaginal ring would exceed the minimum inhibitory concentration against Trichomonas vaginalis. These findings recommend further investigation of PCL matrices as intravaginal devices for controlled delivery of antiprotozoal agents in the treatment and prevention of sexually transmitted infections.

Tinidazole for bacterial vaginosis

Tinidazole has been used for bacterial vaginosis (BV) outside the USA for almost four decades. Tinidazole has recently been resurrected and FDA approved for trichomoniasis and BV in the USA and is being restudied as an alternative to metronidazole for BV. In vitro antimicrobial activity and pharmacokinetics studies indicate that when compared directly with metronidazole, tinidazole has minor but possibly relevant antimicrobial as well as pharmacokinetic advantages. Clinical comparisons have been infrequent, although the limited head-to-head studies indicate minimal therapeutic advantage with tinidazole. Perhaps the more relevant differences relate to the enhanced tolerance and reduced toxicity of tinidazole. Currently, studies are still ongoing directly comparing the clinical efficacy of metronidazole and tinidazole. These studies should establish the role of tinidazole in the treatment of BV; however, cure rates are unlikely to be significantly different.

Tinidazole in the treatment of bacterial vaginosis

Bacterial vaginosis (BV) is the commonest cause of vaginal discharge in women of childbearing age. Oral metronidazole has long been established as an effective therapy in the treatment of BV. However, adverse effects due to metronidazole are frequent and this may lead to problems with adherence to a 7-day course of treatment and subsequently result in treatment failure. Oral tinidazole has been used to treat bacterial vaginosis for over 25 years but in a number of different dosage regimens. Placebo controlled trials have consistently shown increases in cure rate with tinidazole. Longer courses of treatment (eg, 1 g daily for 5 days) appear to be more effective than a 2 g oral single dose. Comparative studies suggest that oral tinidazole is equivalent to oral metronidazole, intravaginal clindamycin cream, and intravaginal metronidazole tablets, in efficacy in treating BV. However, tinidazole has a more favorable side effect profile than oral metronidazole notably with better gastrointestinal tolerability and less metallic taste. Bacterial vaginosis is associated with high rates of recurrence and appropriate management of such recurrences can prove difficult. Recurrent BV has been linked with persistence of Gardnerella vaginalis after treatment; however the clinical implications of the possible greater activity of tinidazole against G. vaginalis are not yet clear. Repeated courses of oral metronidazole may be poorly tolerated and an alternative but equally effective treatment that is better tolerated may be preferable. In comparison to oral metronidazole, cost is clearly an issue as oral metronidazole is considerably cheaper and available in generic form. However where avoidance of oral metronidazole is necessary because of side effects, oral tinidazole is a cost-effective alternative.

Tinidazole for the treatment of vaginal infections

Tinidazole has been used for vaginal infection worldwide but not in the US for > 40 years. Recently, tinidazole has been re-introduced and approved by the FDA for trichomoniasis and restudied as an alternative to metronidazole for bacterial vaginosis. In vitro antimicrobial activity and pharmacokinetics studies indicate that tinidazole has minor but possibly relevant antimicrobial as well as pharmacokinetic advantages when compared directly with metronidazole. Clinical comparison has been infrequent although the limited head-to-head studies indicate minimal therapeutic advantage with tinidazole. Perhaps the more relevant differences relate to the enhanced tolerance and reduced toxicity of tinidazole. Ongoing, as yet incomplete, studies directly comparing the clinical efficacy of metronidazole and tinidazole for bacterial vaginosis should clarify the status of tinidazole; however, cure rates are unlikely to be significantly different. Although uncommon, high-level trichomonal metronidazole resistance can be reliably cured by using tinidazole, which is an invaluable advantage.

Tinidazole: a nitroimidazole antiprotozoal agent

BACKGROUND

Tinidazole, a structural analogue of metrondazole, is an antiprotozoal agent that has been widely used in Europe and developing countries for >2 decades with established efficacy and acceptable tolerability. It was recently approved by the US Food and Drug Administration for the treatment of trichomoniasis, giardiasis, amebiasis, and amebic liver abscess.

OBJECTIVE

This article reviews the pharmacologic and pharmacokinetic properties and clinical usefulness of tinidazole.

METHODS

Relevant information was identified through a search of MEDLINE (1966-August 2005), Iowa Drug Information Service (1966-August 2005), and International Pharmaceutical Abstracts (1970-August 2005) using the terms tinidazole, Fasigyn, and nitroimidazole.

RESULTS

In vitro, tinidazole exhibits activity against pathogenic protozoa (eg, Tricbomonas vaginalis, Entamoeba bistolytica, Giardia duodenalis), a wide range of clinically significant anaerobic bacteria (eg, Bacteroides fragilis, Clostridium difficile), and the microaerophilic bacterium Helicobacter pylori. In susceptible protozoal and bacterial cells, tinidazole is reduced to cytotoxic intermediates that covalently bind to DNA, causing irreversible damage. In human adults, tinidazole had a bioavailability of 100% and a V(d) of 50.7 L, was minimally bound to plasma protein (12%), had a plasma elimination t((1/2)) of 12.3 hours, and was eliminated primarily by hepatic metabolism (approximately 63%). Dose adjustment does not appear to be necessary on the basis of race, sex, or renal function. No data were found on the disposition of tinidazole in patients with hepatic insufficiency; therefore, use of tinidazole in patients with severe hepatic impairment (Child-Pugh class C) is not recommended. Clinical cure rates in patients with trichomoniasis, giardiasis, amebiasis, and amebic liver abscess were generally >90%. In comparative trials, tinidazole was as effective as metronidazole in the treatment of trichomoniasis and was significantly more effective than metronidazole in the treatment of giardiasis (P < 0.05) and amebiasis (P < 0.05). The most commonly reported (>1%) adverse effects included bitter taste, nausea, abdominal discomfort, anorexia, vomiting, and fatigue. The recommended dosage of tinidazole is a single dose of 2 g for trichomoniasis and giardiasis, and 2 g/d for 3 to 5 days for amebiasis.

CONCLUSIONS

Tinidazole appears to be a promising agent for the treatment of trichomoniasis, giardiasis, amebiasis, and amebic liver abscess. Clinical studies are needed to evaluate the use of tinidazole against anaerobic bacteria and H pylori.

Chronic Lyme borreliosis at the root of multiple sclerosis – is a cure with antibiotics attainable?

Apart from its devastating impact on individuals and their families, multiple sclerosis (MS) creates a huge economic burden for society by mainly afflicting young adults in their most productive years. Although effective strategies for symptom management and disease modifying therapies have evolved, there exists no curative treatment yet. Worldwide, MS prevalence parallels the distribution of the Lyme disease pathogen Borrelia (B.) burgdorferi, and in America and Europe, the birth excesses of those individuals who later in life develop MS exactly mirror the seasonal distributions of Borrelia transmitting Ixodes ticks. In addition to known acute infections, no other disease exhibits equally marked epidemiological clusters by season and locality, nurturing the hope that prevention might ultimately be attainable. As minocycline, tinidazole and hydroxychloroquine are reportedly capable of destroying both the spirochaetal and cystic L-form of B. burgdorferi found in MS brains, there emerges also new hope for those already afflicted. The immunomodulating anti-inflammatory potential of minocycline and hydroxychloroquine may furthermore reduce the Jarisch Herxheimer reaction triggered by decaying Borrelia at treatment initiation. Even in those cases unrelated to B. burgdorferi, minocycline is known for its beneficial effect on several factors considered to be detrimental in MS. Patients receiving a combination of these pharmaceuticals are thus expected to be cured or to have a longer period of remission compared to untreated controls. Although the goal of this rational, cost-effective and potentially curative treatment seems simple enough, the importance of a scientifically sound approach cannot be overemphasised. A randomised, prospective, double blinded trial is necessary in patients from B. burgdorferi endemic areas with established MS and/or Borrelia L-forms in their cerebrospinal fluid, and to yield reasonable significance within due time, the groups must be large enough and preferably taken together in a multi-centre study.

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.

Impact of antimicrobial agents on the gastrointestinal microflora and the risk of infections

The most common and significant cause of disturbances in the normal gastrointestinal microflora is the administration of antimicrobial agents. The microflora can be influenced by antimicrobial agents because of incomplete absorption of any orally administered antimicrobial agent, secretion of an antimicrobial agent by the salivary glands and in the bile, or secretion from the intestinal mucosa. In most cases the influence is not beneficial to the patient because suppression of the indigenous microorganisms often permits potential pathogens to overgrow and cause septic conditions, diarrhea, or colitis. Antimicrobial agents that influence the normal microflora also promote the emergence of antimicrobial-resistant strains. The authors' experience on the impact of different beta-lactams, erythromycin, clindamycin, tetracycline, and nitroimidazoles on the gastrointestinal microflora and the risk of infections when these agents are used is reviewed.