Cephalexin interactions to avoid

We are all likely to cross paths with cephalexin at some point. As an antibiotic commonly used for skin infections, strep throat, ear infections (otitis media), and urinary tract infections, its brand-name counterpart, Keflex, became a household name over the years. Now, generic cephalexin continues with broad use by being a first-generation cephalosporin with excellent antimicrobial activity against gram-positive bacterial infections like staph and strep. Like other antibiotics, Cephalexin does not treat viral infections like the common cold or Covid-19. Cephalexin is available in capsules, tablets, and in a liquid form oral suspension. Cephalexin is typically taken two, three, or four times daily. If a missed dose occurs, take the next dose when remembered (unless it’s close to dosing time, then skip the remembered dose) to continue with the regular dosing schedule.

The popularity of this antibiotic makes it imperative that everyone understands its negative attributes, too. Adverse side effects are essential to remember, but recognizing the potential for drug interactions with other prescription medications, nonprescription drugs, and food is crucial, too. These interactions could jeopardize cephalexin’s effectiveness or heighten the risk of serious side effects.

RELATED: Cephalexin dosage, forms, and strengths

Key takeaways:

• Cephalexin interacts with warfarin, a common oral anticoagulant, leading to a risk of bleeding.
• Metformin, one of the most frequently used medications for Type 2 diabetes mellitus, may be more likely to cause dangerous lactic acidosis when taken with cephalexin.
• Taking either the diuretic Lasix (furosemide) or an aminoglycoside antibiotic, such as gentamicin, with cephalexin could negatively affect kidney function.
• Blood levels of cephalexin can be higher if taken with probenecid, a gout prevention pill, which could lead to more side effects.
• If prescribed cephalexin while taking any drug that interacts with the antibiotic, discuss this concern with the healthcare provider to see if any changes need to be made to a medication regimen or if blood test monitoring is recommended.

Cephalexin-drug interactions

The most significant drug interactions linked to cephalexin span various therapeutic categories. A pill for diabetes, a diuretic, a blood thinner, an antibiotic, and a gout drug are all on this motley list. None of these interactions require complete avoidance of cephalexin, but they do call for awareness and more monitoring. These are not the only drug-drug interactions pertaining to cephalexin; they are the most significant.

Warfarin

Warfarin, or the brand-name version of Jantoven, is one tough drug to take. It interacts with many different medications and foods, causing its effectiveness to vary widely. Antibiotics are a major drug class that can wreak havoc on warfarin’s anticoagulant effects, and cephalexin is no different. 

Bacteria in our gut produce vitamin K, which we gladly absorb into our bloodstream and use to produce proteins that help our blood clot. Warfarin blocks vitamin K-related synthesis of these clotting factor proteins, leading to the resolution or prevention of blood clots and an elevated risk of bleeding. With the use of cephalexin or other antibiotics, some beneficial bacteria in our gut are unfortunately killed. Less intestinal bacteria means less vitamin K for us and, in the setting of warfarin, blood that can be too thin, making us more apt to hemorrhage. Blood work can be done to monitor for this issue while taking cephalexin.

Metformin

Metformin is typically the first drug to be prescribed when Type 2 diabetes mellitus is diagnosed. The biguanide pill helps by making our body tissues more sensitive to natural insulin and reducing internal glucose production. This latter effect is likely why metformin has a rarely-occurring but serious potential side effect of lactic acidosis, a life-threatening condition.

When taken with cephalexin, metformin concentrations are increased. Higher drug levels may increase the chance of adverse effects, including lactic acidosis. Lab chemistry testing can be performed to watch for this condition. Of note, some references list the cardiac antiarrhythmic drug dofetilide as another example of a drug whose level can be dangerously boosted by cephalexin.

Lasix

Holding the title of most commonly known and used diuretic, Lasix, and its generic version, furosemide, helps to reduce body fluid levels. Lasix is a loop diuretic. It is used for edema related to heart, liver, or kidney disease. Naturally, as a diuretic, Lasix asks the kidneys to do more work; sometimes, kidney function declines. The risk of renal function deterioration may be higher when Lasix and cephalexin are taken together, so kidney function blood work may be ordered for monitoring.

Aminoglycosides

Taken concurrently, an aminoglycoside antibiotic and a cephalosporin can increase the risk of kidney complications compared to either alone. Aminoglycosides are notorious for this side effect and require regular monitoring anyway. If taken with cephalexin, the lab tests may need to be more frequent.

Probenecid

Probenecid is a rarely used drug to help prevent gout by eliminating uric acid through the urine. Conversely, it decreases the urinary elimination of cephalosporin antibiotics like cephalexin. As a result, cephalexin levels rise, which can be both good and bad. High antibiotic levels may be bad news for bacteria, but they also can mean more side effects of cephalexin, such as vaginal discharge from a yeast infection.

Cephalexin-food interactions

Food can slow the absorption of cephalexin like it can for other drugs. However, cephalexin is still absorbed effectively, meaning cephalexin can be taken with or without food.

Other cephalexin interactions

While worth mentioning, the following interactions with cephalexin are not as substantial as the aforementioned drug-drug interactions. One still may benefit from knowing how alcohol, caffeine, probiotics, and certain medical conditions combine with the antibiotic. 

Cephalexin and alcohol

Product labeling does not advise alcohol avoidance with cephalexin. Prudence may still make it wise to avoid alcohol when taking the drug. They both can cause stomach side effects, including vomiting and diarrhea. Mixing them could put one in jeopardy of additive intestinal ill effects.

Cephalexin and caffeine

Likewise, caffeine can be associated with gastrointestinal distress. Coupling cephalexin and caffeine could make diarrhea and stomach pain more likely.

Cephalexin and probiotics or oral live vaccines

This one makes perfect sense. Probiotics contain “good” bacteria to help populate the intestines. As mentioned, an antibiotic like cephalexin eliminates some helpful germs, making the probiotic less effective. 

Oral live vaccines contain weakened bacteria, such as typhoid and cholera. These bacteria stimulate our immunity, but if given concurrently with an antibiotic, the bacteria from the vaccine could be eradicated before they have done their job.

Cephalexin and penicillin allergy

Cephalosporin and penicillin-family antibiotics are cousins in that they both have a beta-lactam ring to their chemical structure and impair the ability of bacteria to build their cell walls. Suppose one is allergic to penicillin, amoxicillin, or other members of the penicillin family. In that case, there is a risk that one could have a serious allergic reaction with hives, trouble breathing, or severe skin reactions such as a skin rash. A literature review quantified the risk of that cross-reacting hypersensitivity as only being about 1%.

Cephalexin and antibiotic-associated colitis

Typified by diarrhea, abdominal pain, and fever, pseudomembranous colitis is a serious medical condition caused by clostridium difficile bacteria (C.diff). Lesser severities of the infection, without pseudomembranes, are termed antibiotic-associated colitis. C. diff usually gets a foothold in our gut when an antibiotic has killed off our “good” bacterial helpers. Cephalexin is no exception. Cephalexin or other antibiotics can lead to C. diff infection and colitis; taking cephalexin can worsen if C. diff is an active infection.

Cephalexin and kidney disease

Impaired renal function is critical to recognize because it can impact the dosing of many medications. If blood tests show that the kidneys are not operating normally, drug dosing must often be adjusted. The dose of cephalexin should be reduced in some cases of kidney dysfunction.

How to minimize cephalexin interactions

Interactions between medications and cephalexin may be unavoidable, but their risk can be reduced. First, let the healthcare professional know what medications are already being prescribed. This can be facilitated by reviewing the list of prescription drugs, over-the-counter medications, and any supplements being taken with the prescribing professional. An important interaction could be missed if they are unaware of some meds. Take an updated med list to every appointment and ensure it is reviewed compared to the office’s medical record.

Once an interaction between cephalexin and one of the routine meds is identified, get medical advice from the treating provider. Their recommendation may be to take a different antibiotic or, more likely, monitor for interaction-related effects via blood tests. They may want cephalexin stopped if lab work results are awry. If the antibiotic choice, be it cephalexin or another, seems too expensive, show the pharmacist a SingleCare discount card for some savings.

When to talk to a healthcare provider about cephalexin interactions

When a new prescription is mentioned, one of the first questions should be whether it will interact with other medications. Getting into that habit can save a person from bad outcomes. If cephalexin is prescribed, ask the provider if it interacts with anything else being taken. Don’t hesitate to ask the pharmacist too. This type of dialogue is critical for staying safe. While we have not covered every potential cephalexin interaction, we have provided important examples and, hopefully, ample reason to ask about drug interactions with each prescription given.