Antibiotic, prophylactic agent

The most common causes of traveler s diarrhea are infections due to coliform bacteria and viruses. Most such infections are self-limiting, and fluid and electrolyte replacement is usually adequate treatment. Antibiotics (eg, doxycycline. trimethoprim-sulfamethoxazole) are useful prophylactic agents against such organisms but are ineffective in gastrointestinal infections due to viruses and only minimally effective against intestinal protozoans. 

Recently, the U.S. Food and Drug Administration (U.S. FDA) has approved the release of rifaximin, a rifamycin antibiotic, for the treatment of travelers diarrhea (TD) caused by enterotoxigenic Escherichia coli. Although the drug is not intended for the treatment of TD, there are indications that the drug may be effective as a prophylactic agent. 

Because an infection slows the healing of a corneal abrasion, prophylactic antibiotics are often used. Studies on the efficacy of this are mixed. Discontinue the use of contact lenses until the abrasion is healed and the antibiotic course complete. In contact lens wearers, choose an antibiotic that covers Pseudomonas aeruginosa, like gentamicin ointment or solution or a fluoroquinolone.3 Antibiotic resistance is an increasing problem. Resistance occurs primarily with older antibiotics, but has been reported for fluoroquinolones as well. Two newer fluoroquinolones, gatifloxacin and moxifloxacin, do not yet have reports of resistance. These agents are more expensive.6... 

Animal and human studies support the use of antibiotics for the prevention of infectious morbidity and mortality in severe ANP. The most effective antimicrobial agents are the fluoroquinolones, imipenem-cilastatin, and metronidazole, which achieve adequate penetration into pancreatic juice and necrotic tissue and inhibit the growth of enteric bacteria. Although a recent meta-analysis [185] suggested that prophylactic antibiotic administration reduces sepsis and mortality and this approach has been recommended by recent guidelines and consensus state-... 

For livestock producers to approach the care we have exercised in in avoiding antibiotic exposure would require a complete ban of all antibiotics and other antibacterial agents. Periodic exposure to prophylactic or therapeutic levels of antibacterials would result in high levels of resistance and, in a production environment, that resistance would be very slow in declining. 

Treatment cf these disease states may be based on vaccination or drugs. In some cases, e.g. swine dysentery, no vaccines are available, so antibiotic treatment is essential. Antibiotic administration may be prophylactic or therapeutic with pigs, in particular, agents to control dysentery are routinely added to feedstuff or drinking water. The route of administration may also be highly important. For instance, in ruminants the preferred mode is injection, e.g. parenterally. The oral route, which introduces antibiotics directly into the rumen, may upset the delicate balance of rumen bacteria which are necessary to ferment carbohydrates to fatty acids — an essential component of the energy supply of ruminants. 

Certain clinical situations (Figure 28.8) require the use of antibiotics for the prevention rather than the treatment of infections. Since the indiscriminate use of antimicrobial agents can result in bacterial resistance and superinfection, prophylactic use is restricted to clinical situations in which benefits outweigh the potential risks. The duration of prophylaxis is dictated by the duration of the risk of infection. 

Some practitioners prefer not to recommend the use of therapeutic soft contact lenses during episodes of bullae eruption. When a patient presents with corneal epithelial defects due to ruptured bullae, a prophylactic antibiotic ointment such as 0.3% tobramycin or 0.3% ciprofloxacin four times a day can be administered, along with a cycloplegic agent (e.g., 5% homatropine two times a day). 

During acute episodes a broad-spectrum topical prophylactic antibiotic ointment, such as 0.3% tobramycin or 0.5% moxifloxacin, protects the cornea from secondary infection while it heals. The use of a therapeutic contact lens and topical NSAIDs, such as diclofenac sodium 0.1% solution or ketorolac 0.5% solution, provide symptomatic relief. The therapeutic soft contact lens also protects the regenerating epithelium and temporarily provides epithelial stability. A cycloplegic agent, such as 5% homatropine, should be instilled to decrease ciliary spasm and pain. Oral analgesics can be prescribed as needed (see Chapter 7). The eye should be examined in 24 hours and the therapy continued until the epithelial defect is healed. 

If there is an anterior chamber reaction or if debridement has been performed, a cycloplegic agent such as 5% homatropine or 0.25% scopolamine should be used two to three times a day. Topical steroids should be tapered or discontinued in any patient using them, because they are contraindicated in the presence of active HSV corneal epithelial disease. Antibiotics have no benefit in the treatment of herpes simplex epithelial disease but can be used prophylactically if the epithelial defect is greater than 6 mm in size. 

Unlike dendritic keratitis, indolent ulcers are typically very difficult to treat. Instillation of a prophylactic antibiotic, such as polymyxin B-bacitracin ointment two to four times a day, and a cycloplegic agent, such as 5% homatropine two to three times a day, is indicated. Therapeutic soft contact lens use with appropriate antibiotic therapy can also be considered as alternatives. These patients must be monitored carefully to ensure that no secondary infection develops. If the ulcer deepens, a new infiltrate forms, or if there is an increase in the anterior chamber reaction while the patient is being treated, cultures should be performed to rule out bacterial or fungal infection. Cyanoacrylate glue, conjunctival flap surgery, or tarsorrhaphy may be required if healing does not occur. 

Clearly, inhibition of enzymatic degradation is fundamental to the medical management of corneal ulceration. The ocular surface is openly accessible to topical proteinase inhibitor therapy, administered by direct instillation or via a sub-palpebral lavage system. Inhibitor therapy is of most value in acute frank ulceration where it is used in conjunction with antimicrobial agents, but it may also be useful in promoting healing of refractory ulcers and chronic superficial erosions. Antiproteinases may be used prophylactically along with antibiotics in superficial injury where ulceration threatens. 

It has also been suggested that antibiotics be administered prophylactically to individuals who think they might have been exposed to the infectious agent. However, there is one serious drawback to this approach it would likely expose a large number of individuals to antibiotics unnecessarily. This, in turn, could contribute to the development of antibiotic resistant organisms and thus compromise the health of others who depend on these same drugs. On balance, it appears that the risks of routine use of antibiotics outweigh the benefits. 

Management approaches have therefore emphasized the need for prevention through the addition of good sterile technique at the time of insertion. Manufacturers have also responded by using materials and creating surface characteristics of implanted materials inclement to microbial attachment. Likewise the use of prophylactic antibiotics at the time of insertion of deep-seated devices such as joint and heart valve prostheses has further reduced the risk of infection. Once a medical device becomes infected, management is difficult. Treatment with agents such as flucloxacillin, vancomycin and most recently linezolid is often unsuccessful and the only course of action is to remove the device. 

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