- Bacterial Infections 101 Pictures Slideshow
- Take the Tummy Trouble Quiz
- Hepatitis C Slideshow Pictures
- What's the Difference Between Keflex and Penicillin?
- What are Keflex and Penicillin?
- What Are the Side Effects of Keflex vs. Penecillin?
- What Is the Dosage for Keflex vs. Penicillin?
- What Drugs Interact with Keflex and Penicillin?
- Are Keflex and Penicillin Safe to Use While Pregnant or Breastfeeding?
What's the Difference Between Keflex and Penicillin?
- Keflex (cephalexin) and penicillin are antibiotics used to treat bacterial infections.
- Keflex and penicillin are in different drug classes. Keflex is a cephalosporin antibiotic, and penicillin is a penicillin-type antibiotic.
- Brand names for penicillin include Bicillin, Bicillin CR, and Bicillin LA.
- Side effects of Keflex and penicillin that are similar include diarrhea, nausea, abdominal pain, vomiting, dizziness, and skin rash.
- Side effects of Keflex that are different from penicillin include headaches, fever, abnormal liver tests, and vaginitis.
- Side effects of penicillin that are different from Keflex include heartburn, insomnia, itching, confusion, easy bruising, bleeding, and allergic reactions.
What are Keflex and Penicillin?
Keflex (cephalexin) belongs to a class of antibiotics called cephalosporins. They are similar to penicillin in action and side effects. They stop or slow the growth of bacterial cells by preventing bacteria from forming the cell wall that surrounds each cell. The cell wall protects bacteria from the external environment and keeps the contents of the cell together, and without a cell wall, bacteria are not able to survive. Bacteria that are susceptible to cephalexin include Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, E. coli and several others.
Penicillins are antibiotics used to treat bacterial infections that are derived from the antibiotic penicillin. Penicillin antibiotics are used to treat many types of infections caused by susceptible bacteria. They are used to treat infections of the middle ear, sinuses, stomach and intestines bladder, and kidney. They also are used for treating pneumonia, blood infections (sepsis), uncomplicated gonorrhea, meningitis, endocarditis, and other serious infections. Penicillin itself is active against streptococci (including Streptococcus pneumoniae), Listeria, Neisseria gonorrhoeae, Clostridium, Peptococcus, and Peptostreptococcus.
Quick GuideSymptoms of Mono: Infectious Mononucleosis Treatment
What Are the Side Effects of Keflex vs. Penecillin?
The most common side effects of cephalexin are:
- abdominal pain,
- skin rash,
- abnormal liver tests, and
Individuals who are allergic to penicillin may also be allergic to cephalexin. Serious but rare reactions include seizures, severe allergic reactions (anaphylaxis), and low platelet or red blood cell count.
Cephalexin, like almost all antibiotics, may cause mild or severe cases of pseudomembranous colitis, a mild to severe inflammation of the colon. Antibiotics, including cephalexin alter the types of bacteria in the colon and permit overgrowth of a bacterium called Clostridium difficile. Studies indicate that toxins produced by Clostridium difficile are a primary cause of pseudomembranous colitis.
Side effects of penicillin antibiotics include
- abdominal pain,
- easy bruising,
- rash, and
- allergic reactions.
Individuals who are allergic to the cephalosporin class of antibiotics, which are related to the penicillins, for example, cefaclor (Ceclor), cephalexin (Keflex), and cefprozil (Cefzil), may or may not be allergic to penicillins.
Serious but rare reactions include
- kidney problems,
- oral fungal infections,
- severe allergic reactions (anaphylaxis), and
- low blood platelet levels (thrombocytopenia) or red blood cell count.
Like other antibiotics, penicillin antibiotics can alter the normal bacteria in the colon and encourage overgrowth of some bacteria such as Clostridium difficile, which causes inflammation of the colon (C. difficile colitis or pseudomembranous colitis).
Signs and symptoms of C. difficile colitis include
What Is the Dosage for Keflex vs. Penicillin?
- The dose of cephalexin for adults is 1 to 4 grams in divided doses.
- The usual adult dose is 250 mg every 6 hours.
- Some infections may be treated with 500 mg every 12 hours.
- Children are treated with 25-100 mg/kg/day in divided doses.
- The dosing interval may be every 6 or 12 hours depending on the type and seriousness of the infection.
Penicillin dosage is based on the disease type and severity. Penicillin antibiotics are available as
- powder for oral suspension, and
- powder for injection.
What Drugs Interact with Keflex and Penicillin?
Penicillin antibiotics have few important drug interactions.
- Probenecid (Benemid) causes an increase in the amount of penicillins in the body by preventing excretion of penicillin by the kidneys.
- Combining ampicillin with allopurinol (Zyloprim) can increase the incidence of drug-related skin rash.
- Penicillin antibiotics may reduce the effect of BCG live vaccine and typhoid live vaccine.
Are Keflex and Penicillin Safe to Use While Pregnant or Breastfeeding?
Penicillin antibiotics are considered safe to use during pregnancy. Although small amounts of penicillins pass into breast milk they are considered safe to use while breastfeeding.
Keflex (cephalexin) and penicillin are antibiotics used to treat a variety of bacterial infections. Keflex and penicillin are in different drug classes. Keflex is a cephalosporin antibiotic, and penicillin is a penicillin-type antibiotic.
Multimedia: Slideshows, Images & Quizzes
Picture of Bacterial Conjunctivitis (Pink Eye)
Pink eye, or conjunctivitis, is redness and inflammation of the membranes (conjuctiva) covering the whites of the eyes and the...
Bacterial Infections 101: Types, Symptoms, and Treatments
Learn more about bacteria and the most common bacterial infections. Get more information on bacterial skin infections, which...
Germs: Everyday Items with the Most Bacteria
Explore the germiest places you may encounter daily. Bacteria is everywhere. Learn tips to avoid germs and bacteria in public...
Related Disease Conditions
Staph Infection (Staphylococcus Aureus)
Staphylococcus or staph is a group of bacteria that can cause a multitude of diseases. Staph infections can cause illness...
Second Source article from Government...
Group A Streptococcal Infections
Second Source article from Government...
PANDAS (Pediatric Autoimmune Neuropsychiatric Disorders Associated With Streptococcal Infections)
PANDAS is in part caused by an autoimmune response to a strep infection. Symptoms mimic those of OCD, ADHD, and include motor and...
Sepsis (blood poisoning) is a potentially deadly infection with signs and symptoms that include elevated heart rate, low or high...
Ear Infection (Otitis Media)
Middle ear infection or inflammation (otitis media) is inflammation of the middle ear. There are two forms of this type of ear...
Group B Strep
Group B strep are bacteria called Streptococcus agalactiae that may sometimes cause infections both in a pregnant woman and her...
Gonorrhea In Women
Gonorrhea is a bacterial infection transmitted during sexual contact. In women, symptoms include a yellow vaginal discharge,...
Strep Throat (Treatment, Causes, Home Remedies)
Strep throat is a bacterial infection of the throat. Signs and symptoms of strep throat include headache, nausea,...
Is Strep Throat Contagious?
Strep throat is caused by group A streptococcus bacterium. Symptoms of strep throat are: sore throat, white patches or...
Encephalitis is a brain inflammation that causes sudden fever, vomiting, headache, light sensitivity, stiff neck and back,...
Is a Staph Infection Contagious?
A staph infection is caused by the bacteria Staphylococcus aureus. Staph can cause boils, food poisoning, cellulitis, toxic shock...
Group A streptococcal infections are caused by group A streptococcus, a bacteria that causes a variety of health problems,...
Is Sepsis Contagious?
Sepsis is a potentially life-threatening infection that may be caused by: bacteria, fungi, viruses, or parasites. Sepsis...
Influenza (flu) is a respiratory illness caused by a virus. Flu symptoms include fever, cough, sore throat, runny nose, headache,...
Endocarditis, a serious infection of one of the four heart valves is caused by growth of bacteria on one of the heart valves;...
Treatment & Diagnosis
- Is It Dangerous to Use Antibiotics Excessively or Inappropriately?
- Do Antibiotics Interfere With Birth Control Pills?
- What Are the Side Effects of Taking Antibiotics Long-Term?
- Do Antibiotics Treat Crohn's Disease?
- Appendicitis Treatment with Antibiotics
- Antibiotics 101
- Antibiotics 101 - Audio Podcast
Medications & Supplements
- cephalexin - oral, Keflex
- cephalexin (Keflex)
- Penicillin (Antibiotics)
- Cipro, XR (ciprofloxacin) vs. Keflex (cephalexin)
- penicillin V potassium (Beepen-VK, Penicillin VK, V-Cillin-K)
- penicillin G benzathine (Bicillin L-A)
- penicillin V, (Veetids and Pen-Vee-K have been discontinued)
- penicillin g benzathine/penicillin g procaine - injection, Bicillin C-R
- Cefdinir vs. cefixime (Suprax) 3rd Generation Antibiotics
- penicillin v potassium - oral liquid, Pen-Vee K, Veetids
Infectious Disease Resources
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
FDA Prescribing Information
Top Keflex vs Penicillin Related Articles
Pink Eye PicturePink eye, or conjunctivitis, is redness and inflammation of the membranes (conjuctiva) covering the whites of the eyes and the membranes on the inner part of the eyelids. See a picture of Pink Eye and learn more about the health topic.
Bacterial Infections 101Learn more about bacteria and the most common bacterial infections. Get more information on bacterial skin infections, which bacteria cause food poisoning, sexually transmitted bacteria, and more.
Hidden Places Where Germs LurkExplore the germiest places you may encounter daily. Bacteria is everywhere. Learn tips to avoid germs and bacteria in public places.
Middle ear infection or inflammation (otitis media) is inflammation of the middle ear. There are two forms of this type of ear infection, acute and chronic. Acute otitis media is generally short in duration, and chronic otitis media generally lasts several weeks. Seventy-five percent of children in the U.S. suffer from otitis media at some point.
Signs and symptoms in babies, toddlers, and children may:
- Be irritable and pull and tug at their ears
- Be fussy
- Have problems feeding or sleeping
- Complain about pain and fullness in the ear
- Have a fever
- A buildup of pus in the ear
- Have signs and symptoms of an upper respiratory infection
Treatment depends upon the type (chronic or acute).
Encephalitis and MeningitisEncephalitis is a brain inflammation that causes sudden fever, vomiting, headache, light sensitivity, stiff neck and back, drowsiness, and irritability. Meningitis is an infection that causes inflammation of the meninges that surround the brain and spinal cord. Symptoms of meningitis include high fever, headache, nausea, vomiting, and stiff neck.
Gonorrhea In Women
Gonorrhea is a bacterial infection transmitted during sexual contact. In women, symptoms include a yellow vaginal discharge, burning or frequent urination, and redness, swelling, burning and itching of the vaginal area. Gonorrhea can be treated with injectable (penicillin) or oral medications.
Group B StrepGroup B strep are bacteria called Streptococcus agalactiae that may sometimes cause infections both in a pregnant woman and her newborn. Symptoms include fever, seizures, heart rate abnormalities, breathing problems, and fussiness. Intravenous antibiotics are used to treat group B strep infections.
Is a Staph Infection ContagiousA staph infection is caused by the bacteria Staphylococcus aureus. Staph can cause boils, food poisoning, cellulitis, toxic shock syndrome, MRSA, and various other illnesses and infections. Most staph infections are transmitted from person to person.
Is Strep Throat ContagiousStrep throat is caused by group A streptococcus bacterium. Symptoms of strep throat are:
- sore throat,
- white patches or spots on the tonsils,
- headache, and
- nausea and vomiting.
PANDASPANDAS is in part caused by an autoimmune response to a strep infection. Symptoms mimic those of OCD, ADHD, and include motor and verbal tics. Treatment involves medication and cognitive behavioral therapy.
SepsisSepsis (blood poisoning) is a potentially deadly infection with signs and symptoms that include elevated heart rate, low or high temperature, rapid breathing and/or a white blood cell count that is too high or too low and has more than 10% band cells. Most cases of sepsis are caused by bacterial infections, and some cases are caused by fungal infections. Treatment requires hospitalization, IV antibiotics, and therapy to treat any organ dysfunction.
Staphylococcus or staph is a group of bacteria that can cause a multitude of diseases. Staph infections can cause illness directly by infection or indirectly by the toxins they produce. Symptoms and signs of a staph infection include redness, swelling, pain, and drainage of pus. Minor skin infections are treated with an antibiotic ointment, while more serious infections are treated with intravenous antibiotics.
Strep Throat (GAS)
Strep throat is a bacterial infection of the throat. Signs and symptoms of strep throat include headache, nausea, vomiting, sore throat, and fever.
Strep throat symptoms in infants and children are different than in adults. Strep throat is contagious and is generally passed from person-to-person. Treatment for strep throat symptoms include home remedies and OTC medication; however, the only cure for strep throat are antibiotics.