Flora gastrointestinal

It has recently been shown (14) that nitrate from food can be detected in the feces of germfree animals but not in the feces of conventional animals. This result and the results of Witter et al. (18-20) suggest that nitrate is available in the lower gastrointestinal tract and is metabolized by the microbial flora. The intestine may thus be a site for the endogenous formation of N-nitroso compounds. 

Additionally, with chronic hypoxia, normal hemoglobin and hematocrit values may represent relative anemia.12 Increased red blood cell production is a physiologic response to hypoxia however, this response may be blunted in CF and may result in symptoms of anemia despite normal lab values. Abnormal bleeding may also be observed as a result of vitamin K malabsorption or antibiotic-associated depletion of gastrointestinal flora and vitamin K synthesis. 

Colonization and metabolic activity of gastrointestinal bacterial flora do not approach adult values until 2-4 years of age [19]. This has resulted in increased bioavailability of digoxin in infants and young children. 

Drasar BS, Shiner M, Mcloed GM Studies on the intestinal flora. The bacterial flora of the gastrointestinal tract in healthy and achlorhydric persons. Gastroenterology 1969 56 71— 79. 

Hill M Normal and pathological microbial flora of the upper gastrointestinal tract. Scand J Gastroenterol Suppl 1985 111 1-6. 

Toskes PP, Donaldson RM Enteric bacterial flora and bacterial overgrowth syndrome in Sleisenger MH, Fordtran JS (eds) Gastrointestinal Disease. Philadelphia, Saunders, 1993, pp 1106-1125. 

The answer is b. (Katzung, p J129.) Ampicillin decreases the entero-hepatic circulation of estrogen, thereby reducing its efficacy It is thought that this occurs because of an alteration in the gastrointestinal flora. Other oral antibiotics may produce a similar effect... 

An acute intravenous study can provide accurate rates of metabolism without interference from intestinal flora, plus rates of renal and biliary elimination, if urine and bile are collected. This route also avoids the variability in delivered dose associated with oral absorption and ensures that the maximum amount of radiolabel is excreted in the urine or bile for purposes of detection. Once IV data and parameters are available, they can be used with plasma concentrations from limited oral studies to compute intestinal absorption via the ratio of Areas Under the (plasma and/or urine) Curves or via simulations of absorption with gastrointestinal absorption models. 

Example 2 Chloramphenicol and Tetracycline—Sparingly soluble broad-spectrum antibiotics like chloramphenicol and tetracycline found to damage the gastrointestinal epithelium besides changing the normal micro-flora in the Gl-tract that are required for normal good health. 

The gastrointestinal flora may modify foreign compounds and either render them toxic to their host or assist in detoxication. An example of the former is cycasin, a compound in food made from cycad nuts that by itself is not toxic to rats. Hydrolysis by the rat s microflora generates metabolites, one of which is toxic. Germ-free rats suffer no toxic effects from ingested cycasin. 

Differences in clinical effectiveness are partly due to differences in absorption, distribution and excretion of the individual drugs. In general tetracyclines are absorbed irregularly from the gastrointestinal tract and part of the dose remains in the gut and is excreted in the faeces. However this part is able to modify the intestinal flora. Absorption of the more lipophilic tetracyclines, doxycycline and minocycline is higher and can reach 90-100%. The absorption is located in the upper small intestine and is better in the absence of food. Absorption is impaired by chelation with divalent cations. In blood 40-80% of tetracyclines is protein bound. Minocycline reaches very high concentrations in tears and saliva. Tetracyclines are excreted unchanged, in both the urine by passive filtration and in the feces. Tetracyclines are concentrated in the bile via an active... 

A combination of neomycin and nonabsorbable erythromycin base given orally prior to colorectal surgery can markedly reduce the incidence of postoperative wound infection. Orally administered neomycin is sometimes used to suppress the facultative flora of the gut in patients with hepatic encephalopathy. It is unclear how this improves coma, but one theory is that it reduces systemic absorption of the bacterial metabo-htes that allegedly cause hepatic encephalopathy. Although more than 95% of an oral dose of neomycin is excreted unchanged in the stool of normal subjects, the bioavaUabUity of neomycin may be much higher in patients with an abnormal gastrointestinal mucosa. 

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. 

Several antibiotics have been used to treat intestinal protozoal infections. Erythromycin and tetracycline do not have a direct effect on the protozoa they act by altering intestinal bacterial flora and preventing secondary infection. Tetracycline also reduces the normal gastrointestinal bacterial flora on which the amebas depend for growth. 

A. Southgate. The effects of two di- SO084 etary fiber supplements on gastrointestinal transit, stool weight and frequency, and bacterial flora, and fecal bile acids in normal subjects. Me- SO085 tabolism 1977 26(2) 117-128. 

Drugs of the neomycin group are poorly absorbed from the gastrointestinal tract. After oral administration, the intestinal flora is suppressed or modified, and the drug is excreted in the feces. Excretion of any absorbed drug is mainly through glomerular filtration into the urine. 

Drug Interactions Acyclovir Antacids with magnesium and aluminum hydroxides Cholestyramine Drugs that alter gastrointestinal flora may interact with mycophenolate mofetil by disrupting enterohepatic recirculation Probenecid... 

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