Antibiotics: What You Need to Know

Antibiotics treat bacterial infections, not viruses. That simple rule avoids a lot of trouble: taking antibiotics for colds or flu won’t help and can cause harm. If a doctor suspects bacteria, they’ll pick a drug based on the illness, severity, allergies, and local resistance patterns.

There are several common antibiotic classes—penicillins (like amoxicillin), macrolides (clarithromycin/Biaxin), sulfa combinations (sulfamethoxazole-trimethoprim/Bactrim), tetracyclines, and fluoroquinolones. Each class works differently and has different side effects. For example, clarithromycin can upset the stomach or interact with other meds; fluoroquinolones can affect tendons and nerves.

How antibiotics work and when to use them

Antibiotics either kill bacteria or stop them from growing. Doctors decide whether to treat right away or wait for tests. For mild infections, sometimes watching symptoms for 48–72 hours is fine. For severe infections, fast treatment matters. Always follow your provider’s instructions: finish the full course unless they tell you otherwise. Stopping early can let surviving bacteria become resistant.

If you don’t respond to a first antibiotic, the next step might be switching to a different class. Our guide on safe alternatives to amoxicillin explains common replacements and why a switch can be needed. For specific drugs like Bactrim or Biaxin, dosing, side effects, and interactions vary—so check the individual guides or ask your clinician.

Staying safe: resistance, side effects, and buying meds

Antibiotic resistance happens when bacteria adapt and no longer respond. Using antibiotics only when needed and not sharing pills helps slow resistance. Watch for allergic reactions—rash, breathing trouble, swelling—and get care immediately if they appear. Common side effects include nausea, diarrhea, and yeast infections; many are manageable but worth discussing with your provider.

Buying antibiotics online requires caution. Use licensed pharmacies and avoid sites that sell prescription meds without a prescription. Our articles review online pharmacy options and warning signs of shady sites. If cost is a problem, ask your prescriber about cheaper generic options or patient assistance programs.

Keep records of past infections and allergies so future prescribers make safer choices. If you’re unsure whether an antibiotic is needed, ask your clinician about tests like cultures or rapid antigen tests. Simple hygiene—handwashing, vaccines, and wound care—also reduces need for antibiotics by preventing infections in the first place.

Children, older adults, and people with kidney or liver problems need dose adjustments. Always tell your prescriber about current medicines, herbs, and supplements—some antibiotics pair badly with blood thinners, heart meds, or antacids. Store antibiotics in a cool dry place unless the label says refrigerate; never use leftovers from past illnesses. If side effects are severe—high fever, persistent vomiting, jaundice, or severe diarrhea with blood—seek medical attention. You can often ease mild stomach upset by taking medicine with food, but some drugs require an empty stomach—check instructions. Some patients benefit from a short course of probiotics after antibiotics to reduce diarrhea risk; discuss timing and strains with your clinician. Keeping a list of prior antibiotic failures helps clinicians choose effective second-line drugs faster. Bring questions to appointments.