Keflex vs Amoxicillin

Listen to the article instead of reading through it.


For patients suffering from bacterial infections, certain antibiotics that inhibit the growth of bacteria or kill them directly can help in managing symptoms and fighting off the infection. Keflex and Amoxicillin are two such drugs that are commonly prescribed for various types of bacterial infections. Both belong to different classes of antibiotics but work towards a common goal: eradicating harmful bacteria.

Keflex is a type of antibiotic known as a cephalosporin, which works by disrupting the formation of the bacteria's cell wall leading to its rupture. On the other hand, Amoxicillin falls under the class of penicillins and operates slightly differently - it hinders a critical step in cell wall synthesis unique to bacteria, causing them to die off due to instability. Despite their differences in operation ways, both Keflex and Amoxicillin serve as effective tools against many similar kinds of bacterial infections.

What is Keflex?

Cephalexin (the generic name for Keflex) is a first-generation cephalosporin antibiotic, which was a significant leap forward from the original class of antibiotics known as penicillins. Cephalexin was initially approved by the FDA in 1971. It acts by disrupting bacterial cell wall synthesis, effectively "trapping" bacteria and leading to their death more rapidly than usual. This medication is routinely prescribed for the treatment of various types of bacterial infections, including those affecting skin, bone, respiratory tract and urinary tract among others. Keflex specifically targets certain types of bacteria with little effect on our normal body flora or other organisms within us; this selective action results in it having fewer side effects than some other antibiotics that have broader spectrum activity.

Amoxicillin on the other hand belongs to the penicillin class of antibiotics and works against many different bacteria through inhibition of cell wall synthesis as well but has slightly different coverage compared to Keflex.

What conditions is Keflex approved to treat?

Keflex is approved for the treatment of various bacterial infections, including:

  • Respiratory tract infections
  • Otitis media, also known as an ear infection
  • Skin and skin structure infections
  • Bone infections
  • Genitourinary (GU) tract infections.

Amoxicillin is similarly used to treat a variety of bacterial illnesses:

  • Ear, nose, and throat infections
  • Urinary tract Infections
  • Uncomplicated gonorrhea
  • Helicobacter pylori infection (in combination with other drugs)

How does Keflex help with these illnesses?

Keflex is an antibiotic that works by disrupting the formation of bacterial cell walls, which in turn causes the bacteria to die. This mechanism allows Keflex to effectively treat a variety of bacterial infections, particularly those caused by Gram-positive bacteria such as Staphylococcus and Streptococcus species.

On the other hand, Amoxicillin also functions as an antibiotic but it targets a broader range of bacteria including both Gram-positive and Gram-negative types. Like Keflex, Amoxicillin impedes bacterial cell wall synthesis leading to cell death. However, because Amoxicillin affects more diverse types of bacteria than Keflex does, it's often chosen for infections when the exact type of bacterium is unknown or when a broad-spectrum antibiotic is required.

Both antibiotics are very effective at treating their respective target organisms and have been used extensively for many years. The choice between one or another will largely depend on the specific infection being treated and any potential allergies or intolerances a patient might have.

What is Amoxicillin?

Amoxicillin is a widely used antibiotic, classified as a penicillin-like drug. It works by inhibiting the synthesis of bacterial cell walls, thereby killing bacteria and preventing their growth. Amoxicillin was first approved by the FDA in 1972 and it's deemed one of the safest antibiotics to use during pregnancy and breastfeeding.

It's available in various forms such capsules, tablets, oral suspension (liquid), pediatric drops or chewable tablets making it versatile for different patient needs. As an antibiotic from the penicillin family, its side-effect profile is usually mild but may include common antibiotic-related side effects like diarrhea, nausea and skin rash.

Considered broad spectrum, amoxicillin is effective against many Gram-positive and Gram-negative bacteria which makes it a popular choice for treating conditions such as middle ear infections, strep throat, pneumonia among others. However unlike Keflex (a cephalosporin type antibiotic), amoxicillin can be less effective against certain types of Staphylococcus bacteria.

What conditions is Amoxicillin approved to treat?

Amoxicillin is a penicillin antibiotic that has been given FDA approval for treating the following conditions:

  • Various bacterial infections, such as pneumonia and bronchitis
  • Infections of the ear, nose, throat, skin, or urinary tract
  • It's also used in combination with other medicines to treat stomach ulcers caused by H. pylori bacteria.

How does Amoxicillin help with these illnesses?

Amoxicillin is a potent antibiotic that plays an integral role in the treatment of various bacterial infections, functioning by inhibiting the formation of bacterial cell walls. This mechanism disrupts the growth and multiplication of bacteria, thereby aiding in combating infection. Similar to Keflex, Amoxicillin belongs to a group known as beta-lactam antibiotics but has a broader spectrum of activity against both gram-positive and gram-negative bacteria. It's often chosen as first-line therapy for common types of infections like middle ear infections or strep throat due to its efficacy and generally well-tolerated nature. Where patients are allergic or do not respond adequately to penicillins such as Amoxicillin, alternatives like cephalosporins (such as Keflex) may be considered.

How effective are both Keflex and Amoxicillin?

Both cephalexin (Keflex) and amoxicillin are established antibiotics with a long history of effectiveness in treating bacterial infections. They were approved by the FDA just a few years apart, with amoxicillin receiving approval in 1972 and cephalexin in 1971. Their spectrum of activity covers similar types of bacteria, but they belong to different antibiotic classes and work via different mechanisms.

In terms of efficacy, both drugs have been directly compared in several clinical studies; for example, an open-label randomized controlled trial from 2007 found no significant difference between them when used for treating skin and soft tissue infections. Both medications also generally exhibit good safety profiles. However, like all medications, they can cause side effects: most commonly gastrointestinal symptoms such as nausea or diarrhea.

A review study from 2018 highlighted that amoxicillin is frequently prescribed for respiratory tract infections due to its broad-spectrum activity against many common pathogens including Streptococcus pneumoniae and Haemophilus influenzae. Amoxicillin is also often favored over other antibiotics because it has good oral absorption properties resulting in high plasma concentrations, which allows for less frequent dosing schedules than some other options.

Cephalexin is commonly used as a first-line treatment option for uncomplicated urinary tract infections caused by E.coli or Proteus mirabilis due to its robust effectiveness against these organisms. Although effective on its own , it's important to note that there isn't extensive data confirming its standalone use as superior compared to combination therapy involving other antibiotics - particularly amongst more severe cases or those caused by resistant pathogens.

The choice between cephalexin and amoxicillin will depend largely on the type of infection being treated as well as individual patient factors such as allergy history since approximately 10% individuals allergic to penicillins may cross-react with cephalosporins like Keflex.

abstract image of a researcher studying a bottle of drug.

At what dose is Keflex typically prescribed?

Oral dosages of Keflex range from 250-1000 mg every 6 hours, but for most bacterial infections, a dosage of 500 mg every 12 hours is typically sufficient. Children may start with doses ranging from 25 to 50 mg/kg/day in divided doses. If there's no response after a few days, your doctor might consider increasing the dose or changing the medication. The maximum dosage that should not be exceeded is generally considered to be about 4000mg/day. For Amoxicillin, oral dosages typically range between 250-875mg every eight hours or even up to twice daily depending on the severity and type of infection. In children, it tends to vary based on weight but usually starts at around 20-45mg/kg/day in divided doses.

At what dose is Amoxicillin typically prescribed?

Amoxicillin treatment typically begins at a dosage of 250-500 mg every 8 hours or 500-875 mg every 12 hours, depending on the severity and nature of the infection. For more severe infections, such as chronic cases of pneumonia or sinusitis, doses may increase to up to 1000 mg three times a day. This higher dose is usually taken in divided doses throughout the day, spaced approximately eight hours apart. If after two weeks there's no response to treatment at these dosages, your doctor might consider increasing the daily amount or switching antibiotics altogether.

What are the most common side effects for Keflex?

Common side effects of Keflex (cephalexin) can include:

  • Diarrhea
  • Dizziness
  • Tiredness or fatigue
  • Headache
  • Stomach upset, including nausea and vomiting
  • Joint pain
  • Vaginal itching or discharge

Whereas the common side effects of Amoxicillin may include:

  • Nausea and vomiting
  • Diarrhea
  • Stomach pain,
  • Rash, hives, and itchiness
  • Leukopenia (low white blood cell count)
  • Thrombocytopenic purpura (low platelet count that leads to excessive bruising)

Remember to consult with your healthcare provider if you experience any unusual symptoms while taking these medications.

abstract image of a patient experiencing side effect

Are there any potential serious side effects for Keflex?

While both Keflex (Cephalexin) and Amoxicillin are antibiotics used to treat bacterial infections, they do have potential side effects that patients should be aware of. With either drug, you may experience:

  • Allergic reactions ranging from a rash or hives to more severe symptoms such as difficulty breathing, swelling in your face or throat
  • Gastrointestinal problems such as stomach pain, nausea, vomiting or diarrhea
  • Unusual bleeding or bruising
  • Yellowing of the skin or eyes (jaundice)

More specifically with Keflex:

  • Genital and rectal itching
  • Vaginal discharge

With Amoxicillin:

  • Dark urine
  • Fever
  • Persistent sore throat

If you experience any of the above side effects while taking either medication, it's important that you seek medical attention immediately.

What are the most common side effects for Amoxicillin?

Potential side effects of taking Amoxicillin may include:

  • Nausea, vomiting, stomach pain or discomfort
  • Diarrhea
  • Headache
  • Mild skin rash or itching
  • Oral thrush or a new yeast infection (white patches inside your mouth or throat)

These side effects are usually mild and often resolve on their own. However, if they persist or worsen over time, it's imperative to contact your healthcare provider for advice. Remember that serious allergic reactions to amoxicillin are rare but can manifest as severe dizziness, trouble breathing, swelling of the face/lips/tongue/throat - these symptoms require immediate medical attention.

Are there any potential serious side effects for Amoxicillin?

While Amoxicillin is a commonly prescribed antibiotic with a generally good safety profile, some individuals may experience severe side effects which include:

  • Signs of an allergic reaction such as difficulty breathing, hives, swelling in your face or throat
  • Skin reactions including red/purple skin rashes that can blister and peel off accompanied by fever, swollen glands
  • Liver problems: jaundice (yellowing of the skin or eyes), dark-coloured urine or pale stools and upper stomach pain
  • Kidney problems: urination issues like less frequent urinating than usual or not at all, blood in urine and swelling around feet/ankles. -Severe stomach cramps accompanied by watery/diarrhea which could be bloody

These symptoms are rare but if any appear it's important to discontinue Amoxicillin immediately and consult with your healthcare provider.

Contraindications for Keflex and Amoxicillin?

Both Keflex and Amoxicillin, as with most other antibiotics, can sometimes cause side effects such as diarrhea or allergic reactions in some patients. If you notice severe diarrhea (especially if it contains blood or mucus), skin rash, difficulty breathing, swelling of your lips, face, tongue or throat – these may be signs of an allergic reaction to the antibiotic - please seek immediate medical attention.

Neither Keflex nor Amoxicillin should be taken if you are allergic to penicillins or cephalosporins. Always inform your doctor about any allergies and which medications you are currently taking; potentially harmful interactions can occur with certain medicines like probenecid and live bacterial vaccines. It's also necessary to tell your physician about any kidney disease before starting treatment with these drugs.

Remember that antibiotics work best when the amount of medicine in your body is kept at a constant level. Thus take this drug at evenly spaced intervals and continue using it until the full prescribed amount is finished even if symptoms disappear after a few days since stopping the medication too early may allow bacteria to continue growing resulting in a return of the infection.

How much do Keflex and Amoxicillin cost?

For the brand name versions of these antibiotics:

  • The price for 20 capsules of Keflex (500 mg) averages around $300, which works out to approximately $15/day based on a typical dose.
  • Meanwhile, the cost for 30 capsules of Amoxil, a brand-name variety of amoxicillin (500 mg), is about $400, or roughly $13.33/day.

Therefore, if you are taking equivalent dosages in the higher end for both medications, then brand-name Amoxil tends to be slightly less expensive per day. However, remember that cost should not be your primary consideration when choosing between these two drugs; it's more important to consider their effectiveness and possible side effects.

As with most medications though, costs are significantly lower for generic versions:

  • Generic cephalexin (Keflex) can range from as low as $.50 per capsule up to about $1.50 depending on where you purchase them and in what quantity.
  • Similarly priced is generic amoxicillin starting from about $.40 per capsule up to around $2.00 each.

These prices may vary widely depending on your geographical location and whether or not you have insurance coverage.

Popularity of Keflex and Amoxicillin

Cephalexin, known by its brand name Keflex among others, is a first-generation cephalosporin antibiotic. In 2020, it was prescribed to about 6 million people in the US, accounting for around 15% of all cephalosporin prescriptions. Cephalexin has been steadily used over several decades as an effective treatment against gram-positive bacterial infections and some forms of gram-negative bacterial infections.

Amoxicillin is another commonly prescribed antibiotic with its usage extending beyond cephalexins'. Approximately 40 million people in the USA were prescribed amoxicillin in 2020. It accounts for just under half of all penicillin prescriptions and around a quarter of overall antibiotic prescriptions. Though dating back even further than cephalexin's introduction to medicine (1962 compared to cephalexin's mid-70s), amoxicillin remains popular due to its broad-spectrum antibacterial activity and safety profile.


Both Keflex (cephalexin) and amoxicillin are long-standing antibiotics used to combat bacterial infections. They have strong records of efficacy, backed by numerous clinical trials indicating their superiority over placebo treatments. The two drugs can be combined in some instances, although this should always occur under the guidance of a healthcare professional due to potential drug interactions.

The primary difference between these two medications lies in their mechanisms of action and the types of bacteria they target. Keflex is a cephalosporin antibiotic that disrupts the formation of the bacterial cell wall leading to its rupture, while amoxicillin is a penicillin-type antibiotic that also prevents bacteria from forming protective cell walls.

Keflex may be selected for certain skin or respiratory tract infections caused by specific strains of Staphylococcus or Streptococcus species, whereas amoxicillin might be chosen as first-line treatment for middle ear infections or sinusitis among others.

Both drugs come in generic forms offering significant cost savings particularly for patients who must pay out-of-pocket expenses. Patients on either medication should expect an adjustment period during which effects might not immediately be noticeable as it takes time for antibiotics to eradicate infection-causing bacteria.

Side effect profiles are similar between these two medications with both typically well-tolerated but capable of causing side effects like diarrhea, nausea and rash among others. As with all antibiotics, patients taking either Keflex or Amoxicillin should complete their full course even if symptoms resolve sooner unless advised otherwise by a doctor.