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Medicine at the End of The World - Chapter 5 - Antibiotics

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Antibiotics are one of the most talked about subjects in austere and survival medicine. This is an area where there is widespread misinformation and ignorance. There are multiple different antibiotics and they work best depending on the bacteria causing the infection and the location of the infection. What follows is an overview designed to give you a better understanding of what works for what.

Antibiotics only work in bacterial infections and some parasitic infections. They don’t work in treating viral infections which accounts for the vast majority of coughs, colds, flu’s, earache, sinus, and chest infections which people suffer from every winter. While there are some specific antiviral medications most viruses do not have a specific drug to treat infections caused by them.

There is no one antibiotic that works in every situation and giving the wrong antibiotic can be worse (long-term) than not giving one at all. Each organism has one or two antibiotics that are specific for that organism and that is the antibiotic which should be used.

The Bacteria:
A basic understanding of how bugs (read bacteria) cause infections is required to appropriately use antibiotics. There are hundreds of millions of different species of bacteria; most do not cause illness in man.

There are four main classes of bacteria

- Gram-positive (+ ve)
- Gram-negative (- ve)
- Anaerobes
- Others

Gram-positive bacteria stain blue and gram-negative bacteria stain pink when subjected to a gram staining test. They are further subdivided by their shape (cocci = round, bacilli = oval) and if they form aggregates or not. This is described in much more detail in chapter 8. Anaerobic bacteria are ones which require no oxygen to grow.

Gram-Positive Bacteria (Gram +ve)

* Staphylococcus: Commonest pathogen is S. aureus; Gram-positive cocci in clumps. Causes boils, abscesses, impetigo, wound infections, bone infections, pneumonia (uncommonly), food poisoning, and septicaemia. Generally very sensitive to Flucloxacillin as first choice drug, and Augmentin, and the cephalosporins. A strainwhich is resistant to the above known as MRSA is currently treated with vancomycin.

* Streptococcus: Gram-positive cocci in pairs or chains. Most are not pathogenic in man except Strep pneumoniae and the Strep pyogenes. Strep pneumoniae causes pneumonia, ear infections, sinusitis, meningitis, septic arthritis, and bone infections. Strep pyogenes causes sore throats, impetigo, scarlet fever, cellulitis, septicaemia, and necrotising fasciitis. Streps are usually very sensitive to penicillins, cephalosporins, and the quinolones.

Gram-Negative Bacteria (Gram -ve)

* Neisseria meningitidis: Gram-negative cocci in pairs. Common cause of bacterial meningitis, may also cause pneumonia and septicaemia. Can be rapidly fatal. Sensitive to penicillins, cephalosporins, quinolones, Co-trimoxazole, and tetracyclines.

* Neisseria gonorrhoeae: Gram-negative cocci in pairs. Causes gonorrhoea. Sensitive to high dose amoxicillin (single dose), Augmentin, and also cephalosporins, and quinolones.

* Moxella catarrhalis: Gram-negative cocci in pairs. Common cause of ear and sinus infections, also chronic bronchitis exacerbations. Sensitive to Augmentin, cephalosporins, quinolones, Co-trimoxazole, and tetracyclines.

* Haemophilus influenzae: Gram-negative cocci-bacilli. Can cause meningitis (esp. in children under 5), epiglottitis, cellulitis, and a sub group causes chest infections. Sensitive as M.catarrhalis

* Escherichia coli: Gram-negative bacilli. Normally found in the bowel. Causes urinary infections, severe gastroenteritis, peritonitis (from bowel injury), and septicaemia. The antibiotic of choice has traditionally been a quinolone or cephalosporin. However E.Coli is becoming increasingly resistant to both (although in many areas they work fine – that is why it is important to understand local resistant patterns which can be obtained from the microbiology labs at your local hospital). We recommend Co-trimoxazole as a first choice – especially for urinary tract infections.

* Proteus species (sp).: Gram-negative bacilli. Lives in the bowel. Causes Urinary tract infections (UTI’s), peritonitis (from bowel injuries), and wound infections. Drug of choice is the quinolones.


* Bacteroides sp.: Gram-negative bacilli. Normal bowel flora. Commonly causes infections following injury to the bowel, or wound contamination, causes abscess formation. Treated first choice with metronidazole or second with chloramphenicol or Augmentin. Chloramphenicol is moderately high risk with high doses (>4gm/day) causing bone marrow suppression which rarely can be fatal – but it is cheap, readily available, and complications are rare. Metronidazole and cefotaxime IV combination
is good for Bacteroides fragilis. Zosyn or imipenem is a good single agent therapy.

* Clostridium sp.: Gram-positive species produce spores and toxins:

I. C. perfringens/C. septicum – common cause of gangrene; treat with penicillins or metronidazole
II. C. tetani – tetanus damage is from toxins, not the bacteria themselves.
III. C. botulinum – botulism)
IV. C. difficille – causes diarrhoea following antibiotic dosages; treat with metronidazole


* Chlamydia sp: Includes C. pneumonia; responsible for a type of atypicalpneumonia and C. trachomatis; responsible for the sexually transmitted disease Chlamydia. It is best treated with tetracyclines or as second choice a macrolide.

* Mycoplasma pneumoniae: A cause of atypical pneumonia. Treated best with a macrolide, second choice of tetracycline.


Penicillins – These act by preventing replicating bacteria from producing a cell wall. A number of bacteria produce an enzyme which inactivates the penicillins ( Blactamase).

A number of varieties:

* Benzylpenicillin (Penicillin G Benzathine): Injectable preparation. Antibiotic of choice against severe Strep pneumoniae and Neisseria sp infections such as chest infections, meningitis, and cellulitis.

* Phenoxymethyl penicillin (Penicillin V): Oral preparation of above. Usually used only for the treatment of sore throats (strep throats); in other infections largely replaced by amoxicillin which is better absorbed.

* Flucloxacillin: Oral and IV drug of choice for Staph infection such as cellulitis, boils, abscess, and bone infections. Also usually effective against Strep but not first choice.

* Amoxicillin: (newer version of ampicillin): Oral and IV. Effective against most gram-positive and negative bugs. Limited use secondary to B-lactamase resistance in many bugs. Beta-lactamase production is a method by which the bacteria try and protect themselves against an antibiotic – it is a bacterial enzyme which breaks down the main active ingredient of penicillin antibiotics. This is overcome with the addition of clavulanic acid (e.g. Augmentin). Overcoming this resistance makes this combination my ideal survival antibiotic, with good gram-positive, negative, and anaerobic cover. This drug we feel is the best broad-spectrum antibiotic commonly available. Other antibiotics may be better for specific infections but this is the best all purpose one.

Cephalosporins – Same method of action as penicillins. Developed in three generations. There is now a fourth but not yet widely available. The third generation e.g., efotaxime (Claforan, IV only) and ceftriaxone (Rocephin, IV/IM only) have the most broad spectrum effect. They are effective against most gram-positives, negatives, and some variable anaerobic cover. The second generation e.g., cefuroxime (Zinacef, oral and IV) and Cefaclor (Ceclor, oral only) also have good general coverage, but are not as effective against some gram-negative bacilli. This loss of gram-negative coverage expands to most gram-negative cocci and bacilli in the first-generation cephalosporins e.g., cephalexin (Keflex, oral only) and cephazolin (Kefzol, IV only). The third generation is ideal for use in those with very severe generalised infection,meningitis, or intra-abdominal sepsis (e.g., penetrating abdominal wound or appendicitis), with metronidazole added in, and the second-generation offers a good broad-spectrum antibiotic for general use in skin, wound, urinary, and chest infections.

Quinolones – Act by inhibiting DNA replication in the nucleus of the replicating bacteria. This is a new generation of antibiotics. Most common is ciprofloxacin. They offer very broad spectrum cover except for anaerobes. Excellent survival antibiotic and our second choice due to the fact that amoxycillin + clavulanic acid gives better cover of anaerobes. Effective for most types of infections except intraabdominal sepsis and gangrene.

Gatifloxacin (Tequin) is recommended by the TCCC for gunshot or fragment wounds. It is very broad spectrum and has once daily dosing. It is relatively expensive at about$10 USD a tablet

Macrolides – Act by inhibiting protein synthesis in the replicating bacteria. Includes erythromycin, and the newer Roxithromycin, and clarithromycin. Often used for people with a penicillin allergy, however it does have a reduced spectrum (esp. with gram-negatives) but is an alternative to tetracycline in Chlamydia. First choice in atypical pneumonias, e.g. with Mycoplasma pneumonia. Co-trimoxazole (SMX-TMP) – Acts by interfering with folate metabolism in the replicating bacteria. Previously a very broad-spectrum antibiotic now has a much more variable response rate due to resistance. Still useful for urinary and mild chest infections.

Tetracyclines – Acts by blocking protein synthesis. Broad-spectrum coverage – gram-positive, gram-negative, anaerobes; rickettsiae (syphilis, typhus), Chlamydia, and Mycoplasma. A commonly used treatment for common biological warfare agents – Anthrax, Tularaemia, Plague, Brucellosis, Melioidosis, Psittacosis, Q fever, Typhus. Good oral absorption. Can be given parentally – but commercial preparations now uncommon. Can cause bone and teeth growth problems when given to children. As discussed elsewhere used to be manufactured with a compound which became toxic
as it broke down – this no longer occurs.

Metronidazole (Flagyl) – Acts by directly damaging the structure of the DNA of the bacteria/protozoa. Drug of choice for anaerobic infection. Should be used with another broad-spectrum antibiotic for any one with possible faecal contamination of a wound or intra-abdominal sepsis (such as severe appendicitis). Also the drug of choice for parasitic infections such as Giardia.

In the same family as Metronidazole is tinidazole (Fasigyn). The treatment course is usually shorter with generally less side effects and is cheaper. It is also more effective against Giardia.

Others – There are many other antibiotics available. We have only discussed the common ones above.

For further information you should consult any major antibiotic guide (see Reference Books chapter). Which bacteria are sensitive to which antibiotics varies to a degree depending on local resistance patterns among the bacteria – local hospitals will normally be able to tell you what the local patterns are for common bacteria

Pregnancy and Breastfeeding:
In pregnancy penicillins and cephalosporins are safe to use. Many others are not (or only during certain parts of the pregnancy). You should always check if any drug you are using is safe, before using in pregnancy and breast-feeding. The PDR will tell you. If you want a specific reference try “Drugs in Pregnancy”, Ed D.F. Hawkins.

Next Chapter Post:  Sterilization and Disinfection

Written and Edited by The Remote, Austere, Wilderness and Third World Medicine
Discussion Board Moderators
April 2005

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