Gastrointestinal tract antibiotics

Lactic Acid B cteri. The lactic acid bacteria are ubiquitous in nature from plant surfaces to gastrointestinal tracts of many animals. These gram-positive facultative anaerobes convert carbohydrates (qv) to lactic acid and are used extensively in the food industry, for example, for the production of yogurt, cheese, sour dough bread, etc. The sour aromatic flavor imparted upon fermentation appears to be a desirable food trait. In addition, certain species produce a variety of antibiotics. 

As with all drugs, the specific side effects of the quinolones must be considered when they are chosen for treatment of bacterial infections [5]. Reactions of the gastrointestinal tract and the central neivous system are the most often observed adverse effects during therapy with quinolones. It should be underlined, however, that compared with many other antimicrobials, diarrhea is less frequently observed during quinolone treatment. Antibiotic-associated colitis has been observed rarely during quinolone therapy. Similarly, hypersensitivity reactions, as observed during therapy with penicillins and other (3-lactams, is less frequently caused by quinolones. Some other risks of quinolone therapy have been defined and must be considered if a drug from this class is chosen for treatment of bacterial infections. 

The antibiotic is administered orally as the palmitate, which is tasteless this is hydrolysed to chloramphenicol in the gastrointestinal tract. The highly water-soluble chloramphenicol sodium succinate is used in the parenteral formulation, and thus acts as a pro-drug. 

Antibiotics with activity against urease-producing bacteria, such as neomycin [42], paromomycin [44] or metronidazole [45], also reduce the production of intestinal ammonia and have proved to be of value. Vancomycin has also been used in patients with lactulose-resistant chronic encephalopathy [46]. The efficacy of neomycin is similar to that of lactulose [42]. However, a small percentage of this drug is absorbed from the gastrointestinal tract and may cause ototoxic and nephrotoxic effects, especially with continuous use over several months [47]. This drug should be used with particular caution by patients with renal insufficiency. The efficacy of metronidazole for... 

The hemolytic anemia caused in pregnant rabbits by diflunisal was severe enough to explain the concomitant axial skeletal malformations (Clark et ah, 1984). Acetazolamide-induced fetal malformations in mice are apparently related to maternal hypercapnia (Weaver and Scott, 1984a, b) and hypokalemia (Ellison and Maren, 1972). The increased resorption rate induced in rabbits by the antibiotic norfloxacin depends on exposure of the maternal gastrointestinal tract (Clark et ah,... 

Chloramphenicol, isolated in 1947, is a broad spectiarm antibiotic. It is rapidly absorbed from the gastrointestinal tract and hence can be given orally in case of typhoid, dysentery, acute fever, certain form of urinary infections, meningitis and pneumonia. Vancomycin and ofloxacin are the other important broad spectr-um antibiotics. The antibiotic dysidazirine is supposed to be toxic towards certain strains of cancer cells. 

Topical formulations of nystatin and of amphotericin B are useful in the management of Candida albicans infections of the skin. Both antibiotics are ineffective against dermatophytes. The use of nystatin is limited to topical treatment of cutaneous and mucosal Candida infections because of its narrow spectrum and its negligible absorption from the gastrointestinal tract. Hypersensitivity reactions are rare. It is not known whether topical nystatin can cause fetal harm when used by a pregnant woman. Amphotericin B has broader antifungal activity but its topical use is restricted to Candida. Topical use of amphotericin B has shown minimal absorption through the skin and is well tolerated. Limited human surveillance data do not indicate any harm to mother or fetus, but relative safety is still unknown. 

The spectrum of gastrointestinal tract infections (GTI) cover a wide spectrum from asymptomatic Helicobacter pylori gastritis to self-limiting viral gastroenteritis to food poisoning to bacterial enterocolitis to antibiotic-associated Clostridium difficile colitis to typhoid fever with sepsis and multi-organ failure. 

These antibiotics are partially absorbed from the stomach and upper gastrointestinal tract. Food impairs absorption of all tetracyclines except doxycycline and minocycline. Absorption of doxycycline and minocy-cbne is improved with food. Since the tetracyclines form insoluble chelates with calcium (such as are found in many antacids), magnesium, and other metal ions, their simultaneous administration with milk (calcium), magnesium hydroxide, aluminum hydroxide, or iron will interfere with absorption. Because some of the tetracyclines are not completely absorbed, any drug remaining in the intestine may inhibit sensitive intestinal microorganisms and alter the normal intestinal flora. 

Bacitracin is primarily a topical antibiotic. Previously, it was administered intramuscularly, but the toxicity associated with its parenteral administration has precluded systemic use. The bacitracins are not absorbed from the gastrointestinal tract following oral administration. 

Polymyxin B and colistin are not well absorbed from the gastrointestinal tract. An intramuscular injection of the polymyxins results in high drug concentrations in the liver and kidneys, but the antibiotic does not enter the cerebrospinal fluid (CSF), even in the presence of inflammation. 

Interference with transport characteristics can serve many purposes. The introduction of a hydrophilic disposable moiety can restrict a drug to the gastrointestinal tract and prevent its absorption. Such a type of drug is represented by the intestinal disinfectant succinyl-sulfathiazole (3.27). On the other hand, lipophilic groups can ensure peroral activity, as in the case of the penicillin derivative pivampicillin (3.28), which enters the circulation and then slowly releases the antibiotic in its free acid form, producing high blood levels of the latter. 

Drugs that are not absorbed from the gastrointestinal tract of the baby, such as warfarin, are safe for the mother to take. The administration of antibiotics to a breast-feeding mother usually poses no concern for the newborn infant. However, metronidazole, which has mutagenic properties, reaches concentrations in milk that equal or exceed maternal plasma levels. Caution is also advised with sulphonamides, nitrofurantoin, or naladixic acid since these can cause haemolysis in infants with glucose-6-phosphate dehydrogenase deficiency. 

In most species, chloramphenicol is rapidly and almost completely absorbed from the gastrointestinal tract. This route of administration provides antibiotic levels in blood comparable witli or higher than die intramuscular or the subcutaneous routes. The only known exception is in ruminants in which the drug is destroyed by the rumen microflora. 

This antibiotic is used as an economical oral treatment for gram-positive infections in farm animals at a dosage of 8 mg/kg bw because it has the property of being stable in the gastric acid, allowing it to be bioavailable by the oral route. It is well absorbed from the gastrointestinal tract and metabolized in the liver. Unchanged compound and metabolites are excreted in urine. Small amounts are also found in bile. 

Both pirlimycin and its sulfoxide metabolite were partially converted to ribonucleotide adducts by gastrointestinal tract microflora and excreted in feces. Such adducts have been well documented as products of antibiotic inactivation by bacteria for a variety of substances including lincomycin and clindamycin (117-119). 

Amphotericin B, a polyene antibiotic, is the most suitable remedy, despite the nephrotoxicity that may occur, for treating systemic mycoses such as coccidio-mycoses, histoplasmosis, and blastomycosis in animals. It is not effective against dermatophytes and has no activity against bacteria. It is only available in form of a colloidal dispersion for intravenous injection since its poor absorption from the gastrointestinal tract obviates oral administration. 

Balantidiasis Lower gastrointestinal tract Iodoquinol [tetracycline antibiotics are also effective] Metronidazole... 

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