Antibiotic directory

Clinicians use amoxicillin for susceptible infections such as confirmed strep throat, some ear and sinus infections, some pneumonias, and as part of combination therapy for H. pylori. Dental infections sometimes include it as an adjunct to a procedure, not as a substitute for the dentist. It does nothing for a cold, flu, COVID-19, or uncomplicated bronchitis.

Course length, not a dose. Confirmed strep throat is often treated for about 10 days with a penicillin-class drug. Other infections are often shorter. The prescriber chooses the strength and the number of days. Follow that label. Do not borrow a leftover bottle because the name matches.

Warnings. A prior serious reaction to penicillin or amoxicillin — hives, wheezing, swelling, fainting — is a reason not to take it. Tell the clinician about any earlier rash, including one during mononucleosis; that rash is not always a lifelong allergy, and you should not retest it at home. People taking methotrexate need the combination checked, because penicillins can raise methotrexate levels. Most antibiotics, including amoxicillin, do not meaningfully reduce the effect of combined birth-control pills. Vomiting or severe diarrhea can. Rifampin is the antibiotic class that reliably interacts with hormonal contraception. Ask the pharmacist if you are unsure.

Not the right story for a virus, for a person with anaphylaxis to penicillin, or for a kidney infection that has not been assessed.

Full amoxicillin page, including Augmentin and label examples.

This combination is used when the likely bacteria make beta-lactamase: some bite wounds, some sinus and ear infections that need an antibiotic, and some skin and respiratory infections. It is still a penicillin. A serious allergy to amoxicillin or penicillin rules it out.

Course length, not a dose. Adult courses for the infections above are often measured in a few days to about 10 days. Longer is not better by default. The prescription states the duration.

Warnings. Diarrhea is more common than with amoxicillin alone. Take it with food if the label says so. Clavulanate has been linked to liver injury, including cholestatic jaundice, especially with longer use and in older adults. Stop and call a clinician for yellow skin or eyes, dark urine, or severe upper-abdominal pain. Do not use a friend’s leftover Augmentin for a chest cold.

How Augmentin differs from amoxicillin.

Azithromycin is used for some susceptible respiratory infections, some sexually transmitted infections, and selected other diagnoses a clinician names. It is a poor default for acute bronchitis, which is usually viral, and it is not the usual first-line drug for bacterial sinusitis. Macrolide resistance is common in some respiratory bacteria. CDC is explicit that antibiotics do not help most chest colds.

Warnings. FDA has warned that azithromycin can cause abnormal and sometimes fatal heart rhythms. Risk is higher with a known long QT interval, low potassium or magnesium, a slow heart rate, heart failure, and other drugs that prolong QT, including some antiarrhythmics, some antipsychotics, and methadone. Tell the clinician about fainting or a family history of sudden unexplained death. Separate the dose from aluminum or magnesium antacids if the label says to. Liver injury is uncommon but real: yellowing of the skin needs a call.

Not a substitute for a penicillin in someone whose only issue is “I would rather have a Z-Pak.” If you have a true penicillin allergy, the alternative is chosen from your reaction history, not from what is in the cupboard.

Full azithromycin page.

Early Lyme disease, when doxycycline is appropriate for that person, is often treated on the order of 10 to 14 days. Acne courses are a dermatology plan, not an urgent-care impulse. Rocky Mountain spotted fever and similar severe tickborne infections are emergencies; treatment should not wait on a mail-order package. Do not start leftover doxycycline after a tick bite. Prevention rules depend on the tick, the region, and how long it was attached.

Warnings. It can cause severe sunburn. Cover skin and use the sunscreen your pharmacist recommends; skip tanning beds. Swallow each dose with a full glass of water and stay upright for at least 30 minutes. Lying down after a dose can ulcerate the esophagus. Separate the dose by several hours from iron, antacids, calcium, and dairy-heavy meals, which bind the drug. It is generally avoided in pregnancy and in children under 8 because of tooth and bone effects, with important exceptions for serious infections such as Rocky Mountain spotted fever, where a clinician weighs the risk. Rare intracranial hypertension shows up as headache and vision changes. Stop and seek care if that happens. Do not decide the exception yourself.

Full doxycycline page.

These antibiotics still have uses: some kidney infections, some complicated urinary infections, some abdominal infections, and situations where safer drugs cannot be used. FDA has directed clinicians to avoid them for uncomplicated sinusitis, uncomplicated bronchitis, and uncomplicated UTI when other options exist. If one is prescribed, you should hear why the safer drugs do not fit.

Boxed warning, in plain language. Tendinitis and tendon rupture can occur at any age, within hours of the first dose or months later. The Achilles tendon is the classic site. Risk is higher over age 60, with corticosteroid medicines, and after kidney, heart, or lung transplant. Peripheral neuropathy — burning, numbness, weakness — can become permanent. Central-nervous-system effects include confusion, agitation, and seizures. Myasthenia gravis can worsen. Blood sugar can swing high or low, especially in people on diabetes drugs.

Aorta. Epidemiologic studies found a higher rate of aortic aneurysm and dissection in the two months after fluoroquinolone use, particularly in older adults. People with a known aneurysm, high blood pressure, atherosclerotic disease, or conditions such as Marfan or Ehlers-Danlos syndrome should not receive these drugs unless there is no alternative. Sudden, severe, constant chest, back, or abdominal pain is an emergency: call 911.

What to do about symptoms. Stop the drug and get care at the first sign of tendon pain, swelling, or a pop, or of numbness, weakness, or confusion. Do not “walk it off.” For other side effects, call the prescriber before the next dose rather than swapping in a leftover antibiotic. Ciprofloxacin is contraindicated with tizanidine. Both drugs interact with warfarin, antacids, iron, and calcium. Levofloxacin also prolongs the QT interval. Caffeine can feel stronger on ciprofloxacin.

Full ciprofloxacin page.

This is a standard drug for uncomplicated cystitis, a bladder infection, in non-pregnant women when the prescriber confirms that picture. It concentrates in the urine. It does not reliably treat a kidney infection (pyelonephritis). Fever, flank pain, or vomiting is the wrong setting for a leftover bottle of it.

Course length, not a dose. Common published courses for uncomplicated cystitis are short, on the order of five days for the usual twice-daily product. Your label is the authority. A five-day bladder plan is not a plan for any other organ.

Warnings. Take it with food. Urine often turns dark yellow or brown; that color change is expected. It is avoided when kidney function is significantly reduced, because the drug may not reach the urine and side effects become more likely. The prescriber checks kidney function. It is avoided at the very end of pregnancy because of a risk of hemolytic anemia in the newborn. Long courses, measured in weeks to months, have caused lung and liver toxicity and nerve injury. Call for a new cough, shortness of breath, numbness, or yellow skin. A short treatment course is a different exposure, but those symptoms still deserve a call.

Full nitrofurantoin page.

Clinicians use it for some bladder infections when local resistance is low, for some skin infections where MRSA is a concern, and for prevention or treatment of specific opportunistic infections. Resistance varies by city. A three-day course that is sometimes used for uncomplicated cystitis is not a course for a skin infection or a kidney infection. The diagnosis decides the duration.

Warnings. Do not take it after a serious reaction to sulfa antibiotics. Rarely it causes Stevens-Johnson syndrome or toxic epidermal necrolysis: a painful rash, mouth sores, or peeling skin is an emergency, and you should not take the next dose. It raises the effect of warfarin; the INR can climb and bleeding can follow. It can raise potassium, especially with ACE inhibitors, ARBs, spironolactone, kidney disease, or older age. It is avoided in the first trimester when possible and near term because of effects on folate and on newborn bilirubin. People with G6PD deficiency can hemolyze. Drink enough fluid unless you are on a fluid restriction, and ask the pharmacist before adding potassium supplements.