PENICILLINS AND CEPHALOSPORINS

Penicillins are a group of antibiotics used to kill bacteria or prevent infections. They are probably the least toxic of all the antibiotics. The penicillins are some of the most commonly prescribed antibiotics and are often the drugs of choice for people who are not allergic to them.

Cephalosporins are relatives of the penicillins and have a similar, if slightly expanded, range of action. They have a good safety record,[1] but certain problems can occur with their use. Diarrhea is the most common adverse effect, and it may become so bad that treatment must be stopped.

Following is a list of the penicillins and cephalosporins that are discussed on this web site (generic and BRAND names). It does not identify the ones that are given mainly as injections or intravenously, most of which are used primarily in the hospital.

Penicillins (Oral)

• amoxicillin (AMOXIL)
• amoxicillin and clavulanate (AUGMENTIN)
• ampicillin (OMNIPEN)
• cloxacillin
• dicloxacillin (DYCILL, DYNAPEN)
• penicillin G
• penicillin (VK)

Cephalosporins (Oral)

• cefaclor (CECLOR)
• cefadroxil (DURICEF)
• cefditoren (SPECTRACEF)
• cefixime (SUPRAX)
• cefpodoxime (VANTIN)
• cefprozil (CEFZIL)
• cefuroxime axetil (CEFTIN)
• cephalexin (KEFLEX)
• cephradine (VELOSEF)
• loracarbef (LORABID)

Types of Allergic Reactions

Allergic reactions are the most common adverse effects observed with penicillins. Between 5 and 10% of the general public are allergic to them. If you are allergic to penicillins, you should carry a card or wear an ID bracelet stating that you are allergic. Make sure to tell your doctor if you think you have an allergy to penicillins so that the information will be recorded.

There are three kinds of allergic reactions to penicillins: immediate, accelerated, and delayed.

Immediate reactions, also known as anaphylaxis, usually happen within 20 minutes of receiving the drug. Symptoms range from skin rash and itching to swelling, difficulty breathing, and even death. Immediate anaphylactic reactions are very rare, occurring in less than 1% of the people who are allergic to penicillins.[2]

Accelerated reactions usually happen between 20 minutes and two days after taking penicillins. Itching, rash, and fever are some of the symptoms.

Delayed reactions usually happen at least two days to one month after taking penicillins. Symptoms can include fever, feeling sick or uncomfortable, skin rash, muscle or joint pain, or pain in the abdomen.

Similar allergies can occur in people who take cephalosporins, since the drugs are related to penicillins. If you experience any of the above symptoms, call your doctor immediately. Although penicillin and cephalosporin allergies are more common in people who have had such a reaction previously, they also can occur in people who have repeatedly taken penicillins without prior incident.

Some people who are allergic to a penicillin may also be allergic to a cephalosporin; this occurs about 5% of the time. Cephalosporins should not be used for people who have had immediate reactions to penicillins. People who have had delayed reactions, such as a rash, should discuss with their doctors whether they should take a cephalosporin.

In older adults, caution must be used with high intravenous or intramuscular doses of penicillins and cephalosporins to prevent damage to the nervous system resulting in seizures, drowsiness, and confusion.12 The dose of most penicillins and cephalosporins must be reduced when the kidneys do not function normally in order to prevent other complications. For example, a normal dose of 20 million units of penicillin G potassium injection in someone with kidney problems could potentially lead to a severe or even fatal increase of potassium (hyperkalemia). Older adults and people with decreased kidney function are more likely to have damage to the kidney when a cephalosporin and an aminoglycoside antibiotic (gentamicin, tobramycin, and neomycin, for example) are used at the same time.

Almost any antibiotic can cause antibiotic-associated colitis (inflammation of the colon). Clindamycin, lincomycin, and ampicillin are thought to cause this disease most frequently. Other penicillins and cephalosporins are implicated less often, but this reaction is still common. Risk of this disease seems to increase with the age of the user.

Dosage Forms, Effects, and Uses

Oral forms of cefaclor, a cephalosporin, and most penicillins should be taken on an empty stomach (one hour before or two hours after meals) with a full glass (eight ounces) of water. Most other cephalosporins and amoxicillin can be taken on a full stomach. Try to take your doses at evenly spaced times during the day and night so that the amount of drug in your body will stay constant. Store liquid forms in the refrigerator, but do not allow them to freeze. Capsules may be opened to facilitate swallowing. Oral penicillins and cephalosporins may cause nausea, vomiting, or diarrhea.

Injectable forms of penicillins and cephalosporins can cause pain and swelling at the site of injection. Diabetics may not absorb these drugs well when they are given in the muscle. Tell your doctor if you are on a salt-restricted (sodium-restricted) diet, because injected penicillins and cephalosporins contain sodium. People who have congestive heart failure may have a hard time getting rid of extra sodium.[3]

People who are elderly, have poor nutrition, or are alcoholic may have a greater risk of developing bleeding problems (blood takes longer to clot, for example) that are associated with some of the cephalosporins.[4] Vitamin K supplements, as pills or injections, may prevent this complication.

Cephalosporins are often used to prevent infections caused by surgery. In most operations where an artificial part is used, such as open heart surgery, and in gynecologic and gastrointestinal surgery, the use of cephalosporins before surgery is generally justified.[5] For many operations, an older cephalosporin, such as cephalexin (KEFLEX), is preferred. An exception to this is pelvic and gastrointestinal surgery, for which cefoxitin (MEFOXIN) may be a better choice.[6]

Loracarbef is another expensive alternative for treatment of respiratory, urinary tract, and skin infections. For acute pharyngitis, penicillin remains the drug of choice. For skin or soft-tissue infections, there is no reason to use loracarbef rather than dicloxacillin, cephalexin, or cephradine.[7] Cefprozil may be used as an alternative to cefaclor and cefuroxime axetil for treatment of otitis media or bronchitis. The same can be said for cefprozil as for loracarbef. For acute pharyngitis and skin infections, there is no reason to use cefprozil rather than dicloxacillin, cephalexin, or cephradine.[7] However, in treating strep pharyngitis (strep throat), there is some evidence that second-generation oral cephalosporins such as cefpodoxime can be used for a shorter period of time.

Cephalosporins are widely overused in the United States. They are not the first-choice drugs to treat most infections. Usually when a cephalosporin is chosen to treat an infection, an equally effective and less expensive antibiotic is available. The newer cephalosporins are relatively expensive, but some of them have become the drugs of choice for some serious infections.[8]