Antibiotic Comparison: A Simple Guide to Choosing the Right Drug
Picking an antibiotic can feel confusing. This quick guide explains how common antibiotics differ, which infections they treat, and what safety flags to watch for. Read this before you call the pharmacy or talk to your prescriber.
How antibiotics differ
Antibiotics vary by class and spectrum. Penicillins (like amoxicillin) target many gram-positive and some gram-negative bugs. Cephalosporins (like cephalexin/Keflex) are similar but often used when penicillin can't be used or for certain skin and ear infections. Tetracyclines (doxycycline) work well for respiratory infections and tick-borne illnesses. Macrolides (azithromycin) cover respiratory bugs and are used when penicillin is not an option. Fluoroquinolones (ciprofloxacin, levofloxacin) cover many urinary and gastrointestinal infections but carry higher risk of tendon and nerve problems. Each class has different side effects, dosing, and drug interactions.
Broad-spectrum antibiotics hit many bacteria and can be useful for unclear infections, but they also raise the risk of side effects and resistance. Narrow-spectrum drugs target fewer bacteria and are safer when you know the cause. When available, lab tests or culture results help pick a narrow-spectrum option.
Quick picks by common infections
Strep throat: Penicillin or amoxicillin remains first choice for most people unless allergic. Skin infections: Cephalexin often works for simple cellulitis or infected cuts; MRSA concerns may push treatment toward doxycycline or trimethoprim-sulfamethoxazole. Urinary tract infections: Nitrofurantoin or trimethoprim-sulfamethoxazole are common first-line choices; fluoroquinolones are usually saved for resistant cases. Community-acquired pneumonia: A macrolide or doxycycline is common for healthy adults; combination therapy or different choices apply for older adults or those with comorbidities.
Pregnancy and kids need special care. Some antibiotics like doxycycline and fluoroquinolones are avoided in pregnancy and young children. Tell your provider if you are pregnant, breastfeeding, or have young kids at home.
Allergies and interactions matter. If you have a penicillin allergy, many providers will test or choose a safe alternative such as a macrolide or doxycycline depending on the infection. Check interactions: antibiotics can change how birth control, blood thinners, and other drugs work. Ask your pharmacist about major interactions when you pick up a prescription.
Side effects to watch for: nausea, diarrhea, yeast infections, photosensitivity, and in rare cases severe allergic reactions. If you notice difficulty breathing, swelling, or a fast-spreading rash, seek emergency care. Long antibiotic courses raise the chance of C. difficile, which causes severe diarrhea; report persistent symptoms to your doctor.
Quick action steps: take the right dose at the right time, finish the course unless your doctor says otherwise, and avoid using leftover antibiotics. If symptoms don’t improve in 48–72 hours, call your provider. Resistance patterns change, so local guidance and culture results matter more than general rules.
Pet care note: antibiotics for animals differ. Never give human antibiotics to pets without a vet. Metronidazole is commonly used in dogs for GI infections; dosing and diet matters. If your pet seems worse after starting an antibiotic, call the vet. Keep human and pet meds separate and store them securely. Your pharmacist can help with questions. Anytime. Seriously.
