Bactrim vs Keflex

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Bactrim and Keflex are two major antibiotics that are commonly prescribed to patients suffering from bacterial infections. They each target different types of bacteria, yet both are effective in treating various kinds of infections. Bactrim is a combination medication consisting of sulfamethoxazole and trimethoprim, which work together to inhibit the growth of certain bacteria by interfering with their ability to produce folic acid; it's particularly helpful for urinary tract infections or ear infections. On the other hand, Keflex belongs to the class of drugs known as cephalosporin antibiotics. It works by stopping the growth of bacteria through disrupting cell wall synthesis, making it an ideal first-line treatment for skin and soft tissue infections.

What is Bactrim?

Trimethoprim/sulfamethoxazole (the generic name for Bactrim) was one of the initial antibiotic combinations developed to tackle a broader range of bacterial infections. This combination came into medical practice in 1973 and has been extensively used ever since. Bactrim inhibits two consecutive steps in the biosynthesis of nucleic acids and proteins essential to many bacteria, effectively halting their growth or killing them outright. It is typically prescribed for urinary tract infections, bronchitis, and certain types of diarrhea.

On the contrary, cephalexin (Keflex's generic name) belongs to a class of antibiotics known as cephalosporins that were first introduced in 1964. Keflex works by disrupting the formation of bacterial cell walls leading to leakage and eventual death of bacteria. It is primarily prescribed for skin infections, ear infections, urinary tract infections among others.

Both drugs have unique mechanisms; while Bactrim affects metabolic processes inside bacteria, Keflex disrupts structural components on their outer layer with varying side effect profiles due to these differences.

What conditions is Bactrim approved to treat?

Bactrim is approved for the treatment of various infections such as:

  • Urinary tract infections (UTIs)
  • Middle ear infections (acute otitis media) in children
  • Chronic bronchitis exacerbation
  • Shigellosis, a type of intestinal infection caused by Shigella bacteria
  • Pneumocystis pneumonia (a fungal infection in the lungs), typically in patients with weakened immune systems.

How does Bactrim help with these illnesses?

Bactrim is an antibiotic that helps manage bacterial infections by inhibiting the synthesis of folic acid in bacteria, which is essential for their growth and multiplication. It does this by combining two antibiotics: sulfamethoxazole, which inhibits the enzyme involved in the first step of folic acid production, and trimethoprim, which blocks a later step. The synergy between these two drugs makes Bactrim highly effective against many types of bacteria.

On the other hand, Keflex works differently to combat bacterial infections. It belongs to a class of antibiotics known as cephalosporins. These work by interfering with the formation of bacterial cell walls - a structure crucial for their survival. When Keflex disrupts this process, it causes the bacteria's cell wall to rupture and eventually leads to its death.

Both antibiotics are used for treating various types of bacterial infections but their selection largely depends on type and location of infection as well as individual patient factors.

What is Keflex?

Keflex, also known as cephalexin, is a first-generation cephalosporin antibiotic that works by interfering with the formation of the bacteria's cell wall so that it ruptures resulting in the death of the bacteria. It was first approved by the FDA in 1971. As Keflex is not a sulfamethoxazole/trimethoprim (SMZ-TMP) combination like Bactrim, it does not inhibit folic acid synthesis in bacteria which can lead to their growth cessation. Its lack of action on bacterial folate synthesis means its side-effect profile is different from SMZ-TMP antibiotics such as Bactrim; particularly it does not cause sun sensitivity and hyperkalemia (elevated blood potassium levels). The effects on bacterial cell walls make Keflex beneficial for treating infections caused by gram-positive cocci and some gram-negative bacilli organisms that are resistant to penicillin-based antibiotics.

What conditions is Keflex approved to treat?

Keflex, also known as cephalexin, has been approved by the FDA for treating a variety of bacterial infections. These include:

  • Skin and skin structure infections
  • Bone Infections
  • Genitourinary (urinary tract) infections
  • Respiratory tract (throat, airways or lungs) infections

How does Keflex help with these illnesses?

Keflex, also known as cephalexin, is an antibiotic that works by disrupting the formation of bacterial cell walls. This action leads to a cessation in bacterial growth and replication which ultimately helps the body's immune system eliminate the infection. Much like Bactrim, Keflex is used for treating various types of infections caused by bacteria such as ear infections, skin infections, urinary tract infections and respiratory tract infections.

However unlike Bactrim which belongs to a class of drugs called sulfonamides or sulfa drugs and may cause allergic reactions in some people who are sensitive to sulfa medications; Keflex falls into a category of antibiotics known as cephalosporins. Its activity tends not to be affected significantly by most forms of antibiotic resistance which makes it potentially more effective when certain strains do not respond well to other typical antibiotics.

How effective are both Bactrim and Keflex?

Both trimethoprim/sulfamethoxazole (Bactrim) and cephalexin (Keflex) are established antibiotics used for treating bacterial infections, and were approved by the FDA within a decade of each other. Since they belong to different classes of antibiotics and act on different types of bacteria, they may be prescribed under varying circumstances.

The effectiveness of Bactrim mainly against gram-negative bacteria like E. coli, H. influenzae, etc., has been well-studied in clinical trials over several decades; it exhibits good efficacy in managing urinary tract infections as well as respiratory tract infections caused by susceptible strains. It also offers an additional benefit with its activity against Pneumocystis jirovecii pneumonia often seen in immunocompromised patients.

In contrast, Keflex is commonly effective against gram-positive bacteria such as S. aureus & streptococcus species including skin & soft tissue infections along with respiratory tract ones due to susceptible strains.

A 2004 meta-analysis report published about Bactrim demonstrated that it's still a first-line treatment for uncomplicated urinary tract infection due to its high potency and low resistance profile compared to many other drugs currently available despite being more than four decades old at the time.

As per a 2016 review article about Keflex identified that it remains one of the most frequently prescribed oral cephalosporins globally due to its strong safety profile coupled with wide-ranging antimicrobial coverage involving both community-acquired and hospital-acquired pathogens even after more than five decades since its initial approval.

It’s crucial however always consult healthcare professionals before choosing any antibiotic therapy considering their side effect profiles along with local sensitivity patterns which could vary significantly leading towards choice between these two or some completely different antibiotic altogether based on individual case scenarios.

abstract image of a researcher studying a bottle of drug.

At what dose is Bactrim typically prescribed?

Dosages of Bactrim range from 160/800 mg (one double-strength tablet) every 12 hours, but studies have indicated that one single-strength tablet twice daily is sufficient for treating urinary tract infections in most people. Children and adolescents may be started on a dosage calculated by body weight. In either population, the dosage can be adjusted after a few days if there is no response. The maximum dosage should not exceed two double-strength tablets every 12 hours.

On the other hand, Keflex dosages typically range from 250–1000 mg taken orally every 6 hours for adults depending upon the type and severity of infection. Pediatric doses are usually administered at levels of 25-50 mg/kg in divided doses for children over one year old to treat most common infections. Dosage adjustments would depend on clinical response as well as renal function.

At what dose is Keflex typically prescribed?

Keflex treatment is typically initiated at a dosage of 250–500 mg every 6 hours or 500 mg every 12 hours, depending on the nature and severity of the infection. Dosage can then be increased to up to 4 g/day, divided into several doses. The exact frequency and number will depend on your doctor's instructions. For severe infections, it may be necessary to increase the dose even further; however, this should only be done under medical supervision after careful consideration of both benefits and potential risks.

What are the most common side effects for Bactrim?

Common side effects of Bactrim include:

  • Nausea
  • Vomiting
  • Loss of appetite
  • Abdominal pain or discomfort
  • Dizziness
  • Tiredness, fatigue
  • Insomnia (trouble sleeping)
  • Rash and itching
  • Increased sensitivity to sunlight

Potential adverse reactions to Keflex may encompass:

  • Diarrhea
  • Nausea, vomiting
  • Dyspepsia (burning sensation in the stomach)
  • Hives or welts, skin rash
  • Headache
  • Dizziness
  • Agitation and confusion in some cases.

Always consult with your healthcare provider for potential side effects based on your medical history.

abstract image of a patient experiencing side effect

Are there any potential serious side effects for Bactrim?

While both Bactrim and Keflex are antibiotics used to treat bacterial infections, they do have different side effect profiles. Serious side effects from Bactrim may include:

  • Allergic reactions such as rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, or trouble breathing
  • Signs of a serious liver disease including persistent nausea/vomiting, severe stomach/abdominal pain, yellowing eyes/skin, dark urine
  • Unusual tiredness or weakness
  • Severe diarrhea due to Clostridium difficile bacteria which may develop after antibiotic treatment

On the other hand, potential serious side effects from Keflex might be:

  • Signs of an allergic reaction: hives; difficult breathing; swelling in your face or throat
  • Severe skin reaction--fever, sore throat
  • Burning eyes, skin pain followed by a red or purple skin rash that spreads especially in the face and upper body causing blistering and peeling.

In case you experience any above mentioned symptoms while on either drug it's important to contact your medical provider immediately.

What are the most common side effects for Keflex?

Keflex, a commonly prescribed antibiotic, can cause an array of side effects which might include:

  • Digestive issues such as nausea, vomiting, diarrhea and abdominal pain
  • Headache or dizziness
  • Dry mouth or sore throat
  • Rash or itchiness
  • Fatigue and general malaise
  • Joint or muscle pains Please remember that while these are potential side effects, not everyone experiences them. It's important to discuss any concerns with your healthcare provider before starting new medication.

Are there any potential serious side effects for Keflex?

While Keflex is generally a well-tolerated drug, in rare cases it can cause severe side effects. If you experience any of the following symptoms while taking Keflex, seek medical help immediately:

  • Signs of an allergic reaction such as difficulty breathing, hives, swelling in your face or throat
  • Severe skin reactions featuring symptoms like fever, sore throat, burning eyes and skin pain accompanied by a red or purple rash that spreads and causes blistering and peeling
  • Unusual behavior changes or confusion
  • Troublesome side effects on your digestive system including severe stomach pain and diarrhea which may be bloody
  • Little or no urination along with feelings of fatigue
  • Yellowish tint to the skin or eyes indicating potential liver problems

Please note that this list is not exhaustive; if you're experiencing other significant health issues after starting Keflex treatment do consult with your healthcare provider promptly.

Contraindications for Bactrim and Keflex?

Both Bactrim and Keflex, like most antibiotics, may cause side effects such as nausea, vomiting, or diarrhea. If you notice these symptoms worsening or any other adverse reactions while taking either of these medications, please seek immediate medical assistance.

Neither Bactrim nor Keflex should be taken if you are currently on methotrexate therapy; both can increase the risk of methotrexate-induced toxic reactions. Always tell your physician which medications you are taking to avoid harmful interactions.

Bactrim specifically requires caution in patients with a history of drug-induced immune thrombocytopenia (low platelet count). It is advisable to perform frequent blood counts during the first few months of therapy for patients receiving high-dose trimethoprim.

Keflex should not be administered to anyone with known allergies to cephalosporin group antibiotics due to potential serious allergic reactions.

Remember that proper use of antibiotics involves completing the full course prescribed by your doctor even if your condition seems better before finishing all medication.

How much do Bactrim and Keflex cost?

For the brand name versions of these antibiotics:

  • The price of 20 tablets of Bactrim DS (800 mg/160 mg) averages around $120, which works out to $6 per day if taken twice daily as commonly prescribed.
  • In comparison, the price for 28 capsules of Keflex (500 mg) is roughly $220, working out to approximately $7.85 per day when taken four times a day.

So on a per-day treatment basis, if you are in need of an antibiotic and considering these two options, brand-name Bactrim may be less expensive than Keflex. However, cost shouldn't be your sole consideration in deciding which drug is right for you - efficacy and side effects should also play a part.

In terms of generic equivalents:

  • Trimethoprim/sulfamethoxazole (generic for Bactrim) can significantly lower costs with prices starting from about $0.25-$1.00 per tablet depending on dose and quantity purchased.
  • With Cephalexin (generic version of Keflex), the cost can range between $0.50-$2.00 per capsule again based on dosage strength and pack size chosen.

Please note that actual prices can vary greatly by pharmacy location and insurance coverage or discounts available at point-of-sale.

Popularity of Bactrim and Keflex

Sulfamethoxazole/Trimethoprim, in generic form as well as brand names such as Bactrim, was estimated to have been prescribed to about 20 million people in the US in 2020. This accounted for just over 21% of antibiotic prescriptions for urinary tract infections (UTIs) in the US. However, it appears to be the most common “broad-spectrum” antibiotic used for UTIs and has been generally increasing in prevalence since 2013.

Cephalexin, including brand versions such as Keflex, was prescribed to approximately 18 million people in the USA during 2020. In the US, cephalexin accounts for around 19% of cephalosporin prescriptions and just under 6% of overall antibiotic prescriptions specifically meant for skin infections. The prevalence of cephalexin use has remained relatively steady over the last decade.


Both Bactrim (sulfamethoxazole and trimethoprim) and Keflex (cephalexin) are antibiotics with a long history of use in treating bacterial infections. They have been validated by numerous clinical studies as being more effective than placebo treatments. While both drugs can be used to treat similar types of infections, they work differently due to their unique mechanisms of action. Bactrim is a combination drug that inhibits the synthesis of folic acid in bacteria, while Keflex is a cephalosporin antibiotic that interferes with bacterial cell wall synthesis.

Bactrim may be considered as a first-line treatment option for certain urinary tract and respiratory infections, whereas Keflex is often prescribed for skin or soft tissue infections caused by susceptible organisms. In some cases, these medications could potentially be combined under careful consideration from your healthcare provider.

Both antibiotics are available in generic form which presents significant cost savings especially for patients who must pay out-of-pocket. Both Bactrim and Keflex require an adjustment period during which time effects may not yet be noticeable right away.

The side effect profile between the two drugs varies slightly: common side effects such as nausea, vomiting, rash or diarrhea are generally well-tolerated but somewhat more frequent with Bactrim compared to Keflex due to its combination nature. For either medication, it’s crucial patients monitor their symptoms closely when beginning treatment because allergic reactions can occur; medical help should immediately be sought if there's difficulty breathing or swelling occurs.