The choice of antibiotics

Antibiotics are chosen individually according to the causative infectious agent.

The main antibiotics against staphylococci in modern times are currently semi-synthetic penicilinase-resistant penicillins (dicloxacillin, oxacillin, methycillin). If the infection is resistant to the aforementioned agents or the patient is allergic to penicillins, lincomycin, fuzidin, gentamicin combined with cephalosporins can alternatively be used. These antibiotics are also effective against purulent-infection causingBacteroides.

In purulent surgical diseases caused by mixed infections, a combination of semi-synthetic penicillins and aminoglycosides is highly effective. Chloramphenicol is indicated for infections caused by non-sporiferous anaerobic strains.

In Proteus-caused infections, a combination of carbenicillin and aminoglycosides may be effective. When purulent infections are caused by non-sporiferous anaerobic strains or a mixture of aerobic and anaerobic strains, treatment is effected with macrolides (erythromycin), lincomycin, chloramphenicol are indicated. The latter is the most effective when combined with aminoglycosides. In non-sporiferous anaerobic strains and Bacteroides, chemical antiseptic metronidazole (Trichopol) may be effective.

Antibiotics vary in the mode of action on infection. Aminoglycosides and polymixin act, for example, at the stage of proliferation, while at other stages of microbial life cycle these may appear ineffective. This precludes their use for chronic infections.

Antimicrobial susceptibility to antibiotics The choice of antibiotics should be based on the susceptibility of microorganisms to them. Investigation of microbial cultures obtainer from wounds, sputum, blood, exudates should be performed each 3-5 days to duly change the antibiotics and thus to prevent development of microbial resistance to the antibiotic administered. When it is not possible to isolate the microorganisms to check their susceptibility, broad-spectrum antibiotics are at first prescribed, and after the susceptibility has been elucidated, the therapy can be changed accordingly.

Combination of antibacterial agents Combination of antibiotics is necessary in cases of microbial associations. In choosing antibiotics the way those drug interact should be considered, as the interaction can be synergistic, antagonistic or indifferent, i.e. do not affect each other's activity. The best choice is the combination of drugs with synergistic effect. In such a case the microorganisms have to be susceptible to each antibiotic combined.

Combination of antibiotics with different spectrum of action is more sound. Antibiotics with similar mode of action should not be combined because of the sum of their side effects (toxic effect). Nephrotoxic and ototoxic effect of aminoglycosides, for example, are enhanced when they are prescribed simultaneously or subsequently. An exception is the penicillins.

Sulphonamides, derivatives of nitrofuran, chinoxydin may serve an example of chemotherapeutic agents mostly often combined with antibiotics. Combined with antibiotics, derivatives of nitrofuran (e.g. furagin, furazolidon) prevent drug resistance of microorganisms.

Side effects are enhanced when such combinations of antibiotics as aminoglycosides + polymixin, chloramphenicol + ristomycin, chloramphenicol + sulphonamides + nitrofuran are administered. When aminoglycosides are given to the patient under general endotracheal anaesthesia, a serious complication (apnoea) can occur after awakening because of reactivation of curare.

Dosing

Antibacterial (bactericidal or bacteriostatic) effect of the agents only occurs if particular concentrations at the focus of infection or in blood for a particular period are being maintained. The minimum inhibitory concentration is the least amount of drug necessary to inhibit visible growth after 24 hours (lower amounts of the drug do not cause antibacterial effect and the microorganisms quickly acquire resistance to the antibiotics). If, on the other hand, the concentrations of the drug are too high, in addition to its antibacterial effect it can cause a number of adverse effects. With this in mind, starting doses, intervals and ways of administration should always conform with the instructions of the drug. Assessment of the patient's condition To duly detect complications of antibiotic therapy it is necessary to observe the patient closely. Complete blood count and urinalysis are to be ordered each 4-5 days. The early signs of complications may include leukopenia, eosinophilia, anaemia, and proteinuria, appearance of urinary casts. Skin rash is a sign of allergic reaction. On the contrary, such changes as a fall in white blood cell count and positive changes in the blood smear, a reduction in ESR, body temperature are all signs indicative of successful antibiotic therapy. The latter should always be accompanied with vitamin supplementation, correction of protein deficiency or electrolyte imbalance. Antibiotic therapy may by no means substitute for surgery in purulent infection. The duration of antibiotic therapy The duration of antibiotic therapy depends on the rate of inhibition of inflammation and normalisation of body temperature. The course of treatment in acute infection is about 5-7 days. If the treatment needs to be prolonged, the antibiotic should be changed. Earlier stopping the antibiotic therapy may cause relapse, while unduly prolonging the treatment can lead to complications (e.g. intestinal dysbiosis, toxic effects).

Immune compounds

For active immunization anatoxins are used. Staphylococcal anatoxins are given subcutaneosly in doses of 0, 1 ml at the scapular area, and repeated each 2-3 days, with an increase in the dose by 0, 1 ml each time up to a maximum of 1 ml. In emergency, 0, 5 ml can be given preoperatively.

Tetanus antitoxin is used for both scheduled and emergent prophylaxis against tetanus. Injection of the drug in emergency is combined with prophylactic doses of antitetanus serum.

For passive immunization preparations containing antibodies to causative agents of other surgical infections are used.

Antistaphylococcal hyperimmune plasma is native (liquid or frozen) plasma of donors' blood immunized by adsorbed staphylococcal anatoxins. The titre of antistaphylococcal plasma should be at least 6 IU. The plasma is administered intravenously in the dose of 4-6 ml/kg, in serious infections caused by staphylococci (e.g. sepsis, purulent peritonitis, osteomyelitis). It is given once or can be repeated depending on the condition of the patient. In clinical practice anti-Pseudomonas hyperimmune plasma is also used.

Antistaphylococcal gamma globulin is prepared from donors' blood immunized by adsorbed staphylococcal anatoxin. 1 ml of the compound contains 20-50 units of antistaphylococcal immunoglobulin. It is kept in sterile ampoules. One therapeutic dose contains 100 IU of immunoglobulin. Antistaphylococcal gamma globulin is used for treatment and prophylaxis of diseases caused by staphylococci. It is given intramuscularly.

Antitetanus gamma globulin is prepared from donors' blood immunized by adsorbed tetanus anatoxins. It is available in sterile 1 ml ampoules, which is equivalent to 150 IU of antitetanus immunoglobulin. It is used for treatment and prophylaxis of tetanus (see «Tetanus»). The drug is given intramuscularly; immunity is maintained for a month.

Antitetanus serum is immune serum produced from the blood of animals (horse) immunized by tetanus anatoxins. One ampoule of serum contains 1, 500-3, 000 IU, prophylactic dose of the serum is 3, 000 IU. The initial prophylactic dose protects against tetanus for 5 days. Therapeutic doses of the serum are tenfold higher than prophylactic ones. The serum should always be given cautiously because of the risk of anaphylactic reactions.

Antigangrene serum is immune serum of animals (horse) that contains antibodies to the four main causative agents of gas (anaerobic) gangrene - Cl. perfringes, Cl. oedematiens, Cl. septicum, Cl. histolyticum. It is used both for prophylaxis and treatment. The drug should be given cautiously, intramuscularly for prophylaxis and intravenously for treatment (see «Specific wound infection»).

Immune stimulators are the agents that improve non-specific immune defense of the body include prodigiozan, lyzozyme and levamisole.

Prodigiozan is bacterial polysaccharide which stimulates leukopoiesis, increases the number of B lymphocytes and stimulates phagocytosis. It is indicated for patients whose leukopoiesis and phagocytosis are inhibited due to a deficit in lymphocytes and monocytes and the immunogramme shows a decrease in the number of B lymphocytes. The drug is given 50 mcg i/m 4 times a day with an interval of 3-4 days.

Levamisole (decaris) stimulates production of T lymphocytes, phagocytosis and enhances synthesis of antibodies. It is indicated for patients who are deficient in T lymphocytes which, in turn, inhibits phagocytosis. The daily dose of 150 mg is given 6 times.

Lyzozyme is a natural non-specific humoral immune factor with bactericidal effect. The drug enhances non-specific immune response hence increases the efficacy of antibiotics.

For prophylaxis and treatment of wound infections and complications, staphylococcal, streptococcal, Proteus and anaerobic bacteriophages are used. Bacteriophages are given in their original forms or in combination with each other. Solutions of bacteriophages can be used to soak the dressing gauze, which is applied to the wound, or to infiltrate the tissue around the wound. In extensive wounds with crushed tissue, a preparation of anaerobic and cocci phages are used for the prophylaxis of anaerobic and pyogenic infections of the wound.

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