Hesperian Health Guides
Antibiotics Fight Infection
Antibiotics are medicines that fight infection from bacteria. They do not help against viral infections like chicken pox, rubella, flu, or the common cold. Not all antibiotics will fight all infections from bacteria. Antibiotics that share the same chemical make-up are said to be from the same family. It is important to know about the families of antibiotics for 2 reasons:
- Antibiotics from the same family can often treat the same problems. This means you can use a different medicine from the same family.
- If you are allergic to an antibiotic of one family, you will also be allergic to the other members of the same family of antibiotics. This means you will have to take a medicine from another family instead.
Antibiotics must be given for their full “course.” Stopping before you have finished all the days of treatment can make the infection stronger.
Medicines in the penicillin family are some of the most useful antibiotics. Penicillins fight certain infections, including many that produce pus.
Penicillin is measured in milligrams (mg) or units (U). For penicillin G, 250 mg = 400,000 U.
For most people, penicillin is one of the safest medicines. Using more than the recommended dose wastes money but is not likely to harm the person.
Resistance to penicillin
Certain infections have become “resistant” to penicillin. This means that in the past penicillin would have been able to cure someone with these infections, but now penicillin does not work. If the infection does not respond to ordinary penicillin, another antibiotic may be tried or a different form of penicillin may work. For example, pneumonia is sometimes resistant to penicillin. Try cotrimoxazole or erythromycin.
Some people are allergic to penicillin. Mild allergic reactions cause a rash. Often this comes several hours or days after taking penicillin and may last for days. Stop taking the penicillin immediately. Antihistamines help calm the itching. Stomach upset and diarrhea from taking penicillin are not signs of an allergic reaction and, while uncomfortable, are not a reason to stop taking it.
Rarely, penicillin can cause a severe allergy called allergic shock. Within a few minutes or hours after taking penicillin, the person becomes flushed, gets a swollen throat and lips, has trouble breathing, feels faint, and goes into a state of shock. This is very dangerous. Epinephrine (adrenalin) must be injected at once. Always have epinephrine ready when you inject penicillin.
Someone who has once had an allergic reaction to penicillin should not be given any kind of penicillin – ampicillin, amoxicillin, or others – ever again, either by mouth or by injection. This is because the next time the reaction could be worse and might kill him. People allergic to penicillin can use erythromycin or another antibiotic instead.
Penicillin usually works well when given by mouth. Injected forms of penicillin can be dangerous. They are more likely to cause severe allergic reactions and other problems, and should be used with caution. Use injectable penicillin only for severe or dangerous infections.
Ampicillin and Amoxicillin: broad-spectrum antibiotics
Ampicillin and amoxicillin are broad-spectrum penicillins, which means they kill more kinds of bacteria than other medicines in the penicillin family. The two are often interchangeable. When you see a recommendation for ampicillin in this book, you will often be able to use amoxicillin in its place, in the correct dose.
Ampicillin and amoxicillin are very safe and are especially useful for babies and small children. They are both useful in treating pneumonia or ear infections. Ampicillin is also useful in treating meningitis and other severe infections in newborns.
Both these medicines, but especially ampicillin, tend to cause nausea and diarrhea. Avoid giving them to children who already have diarrhea if you can give another antibiotic instead.
The other common side effect is rash. Raised, itchy bumps that come and go in a few hours are probably a sign of penicillin allergy. Stop giving the medicine right away and do not give the child a penicillin medicine again. Future allergic reactions may be more severe and even life-threatening. For some problems erythromycin can be used instead. A flat rash that looks like measles, and usually starts a week after starting the medicine and takes days to go away, is not necessarily an allergy. But it is impossible to know for sure if the rash is from allergy or not, so it is usually better to stop the medicine.
Resistance to these medicines is growing more common. Depending on where you live, they may not work any more against staphylococcus, shigella, or other infections.
Ampicillin and amoxicillin work well when taken by mouth. Ampicillin can also be given by injection, but should be injected only for severe illnesses such as meningitis, or when the child is vomiting or cannot swallow.
As with other antibiotics, how long to give them can vary for many reasons. But the general rule is continue the medicine until all signs of infection (including fever) have been gone for at least 24 hours. For people with HIV, give the medicine for the full number of days listed. Likewise there is a range for how much to give. In general, give the lower amount of the range for a thinner person or for less severe infection, and the higher amount for a fatter person or more severe infection.AMOXICILLIN (ORAL)
For most infections in children
dose by age:
Under 3 months: give 125 mg, 2 times a day for 7 to 10 days.
3 months to 3 years: give 250 mg, 2 times a day for 7 to 10 days.
4 to 7 years: give 375 mg, 2 times a day for 7 to 10 days.
8 to 12 years: give 500 mg, 2 times a day for 7 to 10 days.
Over 12 years: give 500 to 875 mg, 2 times a day for 7 to 10 days.
Continue giving amoxicillin until all signs of infection have been gone for at least 24 hours.
dose by age:
Under 1 year: give 100 mg, 4 times a day for 7 days.
1 to 3 years: give 125 mg, 4 times a day for 7 days.
4 to 7 years: give 250 mg, 4 times a day for 7 days.
8 to 12 years: give 375 mg, 4 times a day for 7 days.
Over 12 years: give 500 mg, 4 times a day for 7 days.
Continue giving ampicillin until all signs of infection have been gone for at least 24 hours.AMPICILLIN (INJECTION)
Ampicillin can also be given by injection, but should be injected only for severe illnesses, or when someone is vomiting or cannot swallow.
dose by age:
Under 1 year: inject 100 mg, 4 times a day for 7 days.
1 to 5 years: inject 300 mg, 4 times a day for 7 days.
6 to 12 years: inject 625 mg, 4 times a day for 7 days.
Over 12 years: inject 875 mg, 4 times a day for 7 days.
If you suspect meningitis or severe pneumonia, inject the combination of ampicillin and gentamicin below. See the warnings about gentamicin.
See Medicines, Tests, and Treatments (in development) for how to inject. Dilute a 500 mg vial of ampicillin with 2.1 ml sterile water. This makes a concentration of 500 mg per 2.5 ml. Use an undiluted 2 ml vial of gentamicin at 40 mg per ml.
GENTAMICIN Inject 7.5 mg per kg, once a day for at least 5 days.
0.5 to 1 ml gentamicin 1 time a day, for at least 5 days.
4 to 12 months, weighing 6 to 9.9 kg: inject 2 ml ampicillin 4 times a day, AND
1.1 to 1.8 ml gentamicin 1 time a day, for at least 5 days.
1 to 3 years, weighing 10 to 13.9 kg: inject 3 ml ampicillin 4 times a day, AND
1.9 to 2.7 ml gentamicin 1 time a day, for at least 5 days.
4 to 5 years, weighing 14 to 19 kg: inject 5 ml ampicillin 4 times a day, AND
2.8 to 3.5 ml gentamicin 1 time a day, for at least 5 days.
Give the lower amount of gentamicin for children who weigh at the lower end of the range, and the higher amount for the children who weigh at the higher end.
If you are fairly certain the infection is meningitis, increase the ampicillin to as much as 200 mg per kg, 4 times a day.
Penicillin by mouth, penicillin V, penicillin VK
Penicillin by mouth (rather than by injection) can be used for mild and moderately severe infections, including:
- sore throat with sudden, high fever (strep throat)
- ear infection
- rheumatic fever
Even if you started with injected penicillin for a severe infection, you can usually switch to penicillin by mouth once the person starts to improve. If improvement does not begin within 2 or 3 days, consider switching to another antibiotic and get medical advice.
To help the body make better use of the medicine, take penicillin on an empty stomach, at least 1 hour before or 2 hours after meals.
Under 1 year: give 62.5 mg, 4 times a day for 10 days.
1 to 5 years: give 125 mg, 4 times a day for 10 days.
6 to 12 years: give 125 to 250 mg, 4 times a day for 10 days.
Over 12 years: give 250 to 500 mg, 4 times a day for 10 days.
For more serious infections, double the doses above.
Adults: give 500 mg, 2 times a day for 10 days.
Injectable penicillin, penicillin G
Injectable penicillin should be used for certain severe infections, including:
- severe pneumonia
- badly infected wounds
- when a bone pokes through the skin
Injectable penicillin comes in different forms. The main difference is how long the medicine lasts in the body: short-acting, intermediate-acting, or long-acting.
PROCAINE PENICILLIN (intermediate-acting)
Inject only in the muscle (IM), not in the vein (IV).
2 months to 3 years: inject 150,000 units, 1 time a day for 10 to 15 days.
4 to 7 years: inject 300,000 units, 1 time a day for 10 to 15 days.
8 to 12 years: inject 600,000 units, 1 time a day for 10 to 15 days.
Over 12 years: inject 600,000 to 4,800,000 units, 1 time a day for 10 to 15 days.
Do not use for babies under 2 months unless no other penicillin or ampicillin is available. If this is your only choice, inject 50,000 units, 1 time a day for 10 to 15 days.
For very severe infections in any age, double the above dose.
The dose for procaine penicillin combined with a short-acting penicillin is the same as the dose for procaine penicillin alone.
BENZATHINE BENZYLPENICILLIN, PENICILLIN G, BENZATHINE PENICILLIN (long-acting)
Inject only in the muscle (IM ), not in the vein (IV).
Adults and children over 30 kg, or over 8 years: inject 1.2 million units. For mild infections, 1 injection may be enough.
For strep throat, give 1 injection of the dose above.
For someone who has had rheumatic fever, inject the dose above 1 time every 4 weeks. Continue this treatment for 5 to 10 years to prevent rheumatic heart disease.
For syphilis in newborns, inject 1 dose of 50,000 units per kg.
Erythromycin works against many of the same infections as medicines in the penicillin family but is a little more expensive. In many parts of the world, erythromycin now works better than penicillins for some cases of pneumonia. It can also be used for diphtheria and pertussis.
For people who are allergic to penicillins, erythromycin is a good replacement. For many infections, it can also be used instead of tetracycline.
Erythromycin often causes nausea and diarrhea, especially in children. Do not use for more than 2 weeks as it may cause jaundice.
Newborns: give 65 mg, 2 times a day for 7 to 10 days.
Under 2 years: give 125 mg, 3 times a day for 7 to 10 days.
2 to 8 years: give 250 mg, 3 times a day for 7 to 10 days.
Over 8 years: give 250 to 500 mg, 4 times a day for 7 to 10 days.
For severe infections, double the doses above.
Cotrimoxazole, sulfamethoxazole with trimethoprim, TMP-SMX
This combination of 2 antibiotics is inexpensive and fights a broad-spectrum of infections such as bladder infections (urinary tract infections), typhoid, and ear infections. It is an important medicine for people with HIV and can prevent the many infections that occur as a result of HIV infection.
Avoid giving cotrimoxazole to babies less than 6 weeks old. Allergy to this medicine is common. Signs of allergic reaction are fever, difficulty breathing, or rash. Stop giving cotrimoxazole if the child develops a rash or if you think there may be an allergy.
Cotrimoxazole comes in different strengths of each of the 2 medicines it contains. So it may say 200/40 (meaning 200 mg sulfamethoxazole and 40 mg trimethoprim) or 400/80 or 800/160. Dose is sometimes described only in terms of the amount of trimethoprim.For most infections
6 to 12 years: give sulfamethoxazole 400 mg + trimethoprim 80 mg, 2 times a day.
Over 12 years: give sulfamethoxazole 800 mg + trimethoprim 160 mg, 2 times a day.
6 months to 5 years: give sulfamethoxazole 200 mg + trimethoprim 40 mg, 1 time a day, every day.
6 to 14 years: give sulfamethoxazole 400 mg + trimethoprim 80 mg, 1 time a day, every day.
Over 14 years: give sulfamethoxazole 800 mg + trimethoprim 160 mg (two 400/80 tablets, or one “double strength” tablet), 1 time a day, every day.
Gentamicin is a very strong antibiotic of the aminoglycoside family. It can only be given by injection or IV (in the vein). This drug can damage the kidneys and hearing, and therefore should only be used in emergencies.
For pneumonia or meningitis in babies and children, give a combination of gentamicin and ampicillin.
Gentamicin must be given in the exactly correct dose. Giving too much can cause kidney damage or permanent deafness. Give the right dose for the child’s weight – do not base the dose on the child’s age. And do not give gentamicin for more than 10 days.