Particular antibiotics

Some antibiotics are particularly important in district hospital surgery, either because they are life-saving, or because they are good value for money.

Benzyl penicillin is cheap and safe. For organisms that might possibly be sensitive, it is the antibiotic of choice. There is little point in giving very high doses. If penicillin fails to cure a patient, this will probably be because the [gb]- lactamase of penicillin resistant bacteria is destroying it, not because you are not giving enough. In an adult a megaunit six- hourly is the standard dose for a severe infection, such as spreading hand sepsis, or cellulitis round an infected wound. However, if drugs are scarce, one megaunit given to four people is likely to do more good than four megaunits given to one person. In infants, and in patients with cardiac or renal disease, the sodium or potassium in the penicillin can cause undesirable side effects, so be aware of this.

Metronidazole is effective against anaerobes, and as these are often the most important invaders, it has been a major advance. It is bactericidal to most of them, particularly Bacterioides fragilis, and is the drug of choice in the treatment of non-clostridial anaerobic infections and amoebiasis. Resistance to it is unknown, and it has few side effects. It has been expensive, but it is now much cheaper. Give it, blindly if necessary, to all patients who are severely ill with an infection that might be caused by anaerobes, and particularly to patients with intra-abdominal sepsis. Intravenous metronidazole is expensive, but you can achieve adequate blood levels by giving it as suppositories, or as oral tablets rectally. Like this, it is only a tenth the price. Intravenous metronidazole with an aminoglycoside, such as gentamicin, avoids the risk of pseudomembranous colitis (rare). The expensive alternatives, lincomycin and clindamycin, both have this danger. Metronidazole is one of the drugs that no surgeon should be without.

Chloramphenicol is almost outmoded in the industrial world, where expense is less of a constraint. But it is cheap, and has a broad spectrum of activity against aerobic Gram- negative bacilli and Gram-positive cocci. Also, if you don't have metronidazole for anaerobic infections, chloramphenicol is next best. It has good in vitro activity against anaerobes from most parts of the world. It also enters the eye (24.3). Its life-saving properties outweigh the small risk of aplastic anaemia. Chloramphenicol with metronidazole is an excellent combination for established or expected peritonitis (6.2).

Cephalosporins (cephradine). If chloramphenicol is freely available in your community, so that it is much used outside hospital, resistant organisms will be common. If so, instead of using chloramphenicol, use whichever cephalosporin you can get most cheaply, such as cephradine. This is active by mouth, but you may need to give it intravenously. Use cephradine and metronidazole as a substitute for chloramphenicol and metronidazole. For infections with intestinal organisms cephradine and metronidazole is a substitute for gentamicin and metronidazole. Remember that 10% of penicillin-sensitive patients are also sensitive to cephalosporins.

Gentamicin is a very valuable broad spectrum aminoglycoside antibiotic for organisms which are likely to be resistant to other antibiotics. It has been expensive, but is now out of patent and is much cheaper. At the time of writing (June 1988) ECHO cost a day's treatment at $0.13 compared with $2.3 for cephradine. For the ''blind' treatment of a serious infection, especially one due to intestinal bacteria, give gentamicin with metronidazole, perhaps with penicillin.

Trimethoprim alone is preferable to cotrimoxazole (''Bactrim', ''Septrin'), which is a combination of trimethoprim and sulphamethoxazole. The latter is rather toxic and not very effective. If you don't have trimethoprim, use cotrimoxazole.

Tetracycline. Oxytetracycline (''Terramycin') is likely to be the cheapest tetracycline.