Cephalexin, also known by the brand name Keflex, is a first-generation cephalosporin antibiotic used to treat a wide range of bacterial infections [1.9.5]. It works by inhibiting the growth of bacterial cell walls [1.9.4]. Common uses include treating respiratory tract infections, urinary tract infections (UTIs), skin infections, and ear infections [1.9.2]. While generally effective and safe for most people, certain substances can interact with cephalexin, leading to negative outcomes [1.9.2]. It is vital to inform your healthcare provider of all medications, supplements, and health conditions before starting treatment [1.2.1, 1.7.1].
Major Drug Interactions to Be Aware Of
Certain prescription medications have significant interactions with cephalexin. These interactions can either increase the risk of side effects from cephalexin or the other drug, or they can reduce the effectiveness of the antibiotic [1.2.3]. Always consult with a doctor or pharmacist before combining medications [1.2.1].
Metformin
Metformin is a common medication used to manage blood sugar levels in people with type 2 diabetes [1.4.2]. Taking cephalexin with metformin can increase the concentration of metformin in the blood [1.4.3, 1.4.5]. This buildup raises the risk of metformin-related side effects, including nausea, diarrhea, and a dangerous drop in blood sugar (hypoglycemia) [1.4.2]. In some cases, it may also increase the risk of a serious condition called lactic acidosis [1.2.5]. If you take metformin, your doctor may need to adjust your dose or recommend more frequent blood sugar monitoring while you are on cephalexin [1.4.2, 1.4.3].
Probenecid
Probenecid, a medication used to treat gout, can significantly increase the blood levels of cephalexin [1.6.1]. It does this by slowing down the removal of the antibiotic from the body via the kidneys [1.6.5]. This interaction can be intentional; sometimes doctors prescribe both together to make the antibiotic more effective against certain infections [1.6.5]. However, elevated levels of cephalexin can also increase the risk and severity of its side effects, such as nausea, diarrhea, and kidney problems [1.6.1].
Warfarin and Other Blood Thinners
Warfarin (Jantoven) is a blood thinner used to prevent blood clots [1.2.4]. Cephalexin, like many antibiotics, can interfere with the bacteria in the gut that produce vitamin K, a crucial component for blood clotting [1.2.5]. This can enhance the effect of warfarin, increasing the risk of unusual bleeding or bruising [1.2.4, 1.2.5]. If you take warfarin, your doctor will likely monitor your blood more closely during your course of cephalexin [1.2.4].
Live Vaccines
Cephalexin can have serious interactions with certain live vaccines, rendering them less effective. These include the live vaccines for cholera and typhoid [1.2.1]. It's important to discuss your vaccination schedule with your healthcare provider if you are taking cephalexin.
Loop Diuretics
Loop diuretics, such as furosemide (Lasix), are used to treat fluid retention [1.2.3]. Both cephalexin and loop diuretics can carry a risk of kidney-related side effects when taken alone [1.2.3, 1.2.5]. Taking them together can further increase the risk of kidney damage [1.2.4].
Comparison of Key Cephalexin Interactions
| Interacting Substance | Drug Class/Type | Potential Consequence of Mixing | Management Strategy |
|---|---|---|---|
| Metformin | Antidiabetic | Can increase metformin levels, raising the risk of side effects like low blood sugar [1.4.2] | Monitor blood sugar closely; doctor may adjust metformin dose [1.4.2]. |
| Probenecid | Uricosuric (for Gout) | Increases cephalexin levels in the blood, raising the risk of cephalexin side effects [1.6.1] | Dose adjustment may be necessary; used therapeutically in some cases [1.6.4, 1.6.5]. |
| Warfarin | Anticoagulant (Blood Thinner) | Can increase the risk of bleeding [1.2.4, 1.2.5] | Doctor may order more frequent blood tests to monitor clotting time [1.2.4]. |
| Zinc Supplements | Mineral Supplement | Can reduce the absorption of cephalexin, making it less effective [1.5.2, 1.5.4] | Take zinc supplements at least 3 hours before or after the cephalexin dose [1.5.1, 1.5.4]. |
| Alcohol | Beverage | No direct interaction, but can worsen overlapping side effects like nausea and stomach upset [1.3.2] | It is generally recommended to avoid or limit alcohol to allow the body to recover [1.3.1, 1.3.3]. |
| Loop Diuretics (e.g., Furosemide) | Diuretic | Can increase the risk of kidney-related side effects [1.2.3] | Discuss with your doctor, especially if you have pre-existing kidney conditions [1.2.3]. |
Interactions with Supplements and Alcohol
Zinc and Iron Supplements
Supplements containing minerals like zinc or iron can interfere with the absorption of cephalexin, making the antibiotic less effective [1.2.4, 1.5.2]. This also applies to multivitamins that contain these minerals [1.5.2]. To prevent this, it's recommended to take any products containing zinc or iron at least three hours apart from your cephalexin dose [1.5.1, 1.5.4].
Alcohol
While the FDA label does not report a direct interaction between cephalexin and alcohol, mixing them is generally discouraged [1.3.1]. Both alcohol and cephalexin can cause similar side effects, such as nausea, indigestion, vomiting, and dizziness [1.3.2, 1.3.5]. Combining them can worsen these effects [1.3.1]. Furthermore, alcohol consumption can weaken the immune system, potentially making it harder for your body to fight the infection you're being treated for [1.3.1, 1.3.6].
Conclusion
To ensure both safety and treatment success, it's critical to know what cannot be mixed with cephalexin. The most significant interactions involve the diabetes medication metformin, the gout medication probenecid, blood thinners like warfarin, and certain mineral supplements such as zinc [1.2.3, 1.2.5]. While alcohol doesn't directly interact with the drug's mechanism, it can amplify side effects and hinder recovery [1.3.1]. Always provide your healthcare provider with a complete list of your current medications and supplements to avoid potentially harmful interactions. Do not start, stop, or change the dosage of any medicine without first checking with your doctor [1.2.1].
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional before making any decisions about your health or treatment.
For more official information, you can visit the FDA's drug label information for Keflex (cephalexin).
