Reference Guide for Antibiotics

Highlights

• Antibiotics interfere with the reproduction and function of bacteria, shortening infection times and making them less severe.
• Antibiotics are for use on bacterial infections. They won’t help with viral infections like colds, or fungal infections such as athlete’s foot.
• There are multiple classes of antibiotics used for different infections, depending on resistance, severity, and condition.
• BidRX can help you get the best prices for the antibiotics you need.

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Antibiotics have saved countless lives, and remain one of the most common classes of medication prescribed around the world. However, as resistant strains emerge and new classes of antibiotics are developed, guidelines for which you take and for which infection change over time. Regardless of which antibiotic you need, BidRX can help you find the best price.

Antibiotics — Overview

Antibiotics are substances that interfere with the life cycle of bacteria, limiting their spread and destroying them. While we use the word “antibiotic” as shorthand for all substances that kill microbes, not all microbes are affected by them. Athlete’s foot, for example, is a common fungal infection, while a flu is caused by a virus. 

Adding to the confusion is that fungi, bacteria, and viruses often compete within the body, and antibiotics can sometimes trigger a “superinfection,” where as bacteria are killed off, a fungal or viral infection moves in. This is often mistaken for an antibiotic-resistant infection, and many antibiotics can be paired with antifungals or antivirals to help prevent this.

In general, antibiotics are considered either “broad spectrum,” used for a number of different and usually less serious ailments, or “narrow spectrum,” only used for very specific infections. This may change over time based on new research and the possible development of bacteria resistant to a specific class. Regardless of the class of antibiotic, it’s crucial to complete any course — even if you feel better — to help limit the growth of resistant bacteria.

The classes of antibiotics include:

• Penicillins
• Tetracyclines
• Cephalosporins
• Quinolones
• Lincomycins
• Macrolides
• Sulfonamides

Several classes of antibiotics are reserved for use in a hospital setting or under direct supervision by a doctor, and are generally used only in those settings. They include:

• Glycopeptides
• Aminoglycosides
• Carbapenems

Penicillins

The original antibiotics, penicillins work by compromising the cell walls of infectious bacteria, keeping them from dividing and ultimately killing them. Several penicillins are still in use today, generally either semi-synthetic or fully synthetic compounds. 

Penicillins draw from natural defense mechanisms found in nature, usually imitating them. Most often, they’re used for serious and rare infections that haven’t developed resistance to this class of drugs. 

Commonly prescribed penicillins include:

• Amoxicillin 
• Ampicillin 
• Benzylpenicillin or benzetacil
• Dicloxacillin 
• Flucloxacillin 
• Phenoxymethylpenicillin (penicillin V) 
• Piperacillin 

Contraindications — Penicillins

Penicillins are contraindicated if you have an allergy to them. Otherwise, they’re generally seen as safe, including during pregnancy and nursing.

Side Effects — Penicillins

The common side effects of penicillins are:

• Hives
• Diarrhea
• Nausea 
• Rash
• Allergic hypersensitivity

In rarer cases, a penicillin-resistant infection can spread while a non-resistant one dies out.

Interactions — Penicillins

Penicillins should not be taken with tetracyclines for some infections. Be sure your doctor knows if you’re already taking any other antibiotic. 

Tetracyclines

Tetracyclines prevent bacteria from creating proteins, a process called protein synthesis, disrupting the life cycle and killing the cell. Tetracyclines were first discovered in 1948, and they treat a wide range of bacterial infections, including acne and some sexually transmitted infections.

Commonly used tetracyclines include:

• Tetracycline
• Chlortetracycline
• Oxytetracycline
• Demeclocycline
• Minocycline
• Doxycycline
• Tigecycline
• Eravacycline
• Sarecycline
• Omadacycline

Contraindications — Tetracyclines

Tetracyclines should not be used when pregnant and should only be taken by children under eight with a doctor’s supervision. Due to how they interfere with protein synthesis, it may cause problems with tooth development and increase skin sensitivity. People undergoing chemotherapy should verify that tetracyclines won’t interact with their chemotherapy medications before taking them.

Side Effects — Tetracyclines

The most common side effect is heightened skin sensitivity under sun exposure. Use sun protection if you’ll be outside while using tetracyclines.

Less commonly, you may experience:

• Pain in the abdomen
• Headache
• Appetite loss
• Nausea and vomiting
• Changes to eyesight
• Skin discoloration, usually in the form of yellowing.

Children younger than eight may develop yellow or brown teeth due to tetracycline use.

Interactions — Tetracyclines

Tetracyclines shouldn’t be taken with dairy products or foods high in calcium, as calcium can negate their effects. Many common antacids and heartburn medications can also inactivate tetracyclines and shouldn’t be taken with drugs in this class. 

Cephalosporins

Cephalosporins are similar to penicillins, with a similar action. However, they’re derived from a different organism, so they’re safe for people who are allergic to penicillin. Cephalosporins weaken and destroy the cell wall, preventing bacteria from dividing and ultimately killing them. As of this writing, they’re most often used for skin infections and to prevent infections after surgery.

Cephalosporins are divided into “generations” as new ones are discovered. Some generations are more effective against certain types of infections than others. 

Commonly used cephalosporins include:

First-generation cephalosporins:

• Cefadroxil
• Cefazolin
• Cephalexin

Second-generation cephalosporins: 

• Cefotetan
• Cefoxitin
• Cefprozil
• Cefuroxime

Third-generation cephalosporins: 

• Cefdinir
• Cefditoren
• Cefixime
• Cefotaxime
• Cefpodoxime
• Ceftazidime
• Ceftriaxone

Fourth-generation cephalosporin:

• Cefepime 

Fifth-generation cephalosporin:

• Ceftaroline 

Contraindications — Cephalosporins

If you have kidney or liver disease, you should take cephalosporins with caution. Kidney disease, in particular, is associated with a higher risk of seizures with cephalosporins. Third-generation drugs in this class can also enter the cerebrospinal fluid, although it remains unclear what impact they may have.

Before taking this medication, get an allergy test to confirm you don’t have a cephalosporin allergy. There is some risk of a cross-allergic reaction for people with a penicillin allergy, especially for earlier generations. The risk has lessened with later generations of the class.

Side Effects — Cephalosporins

The most common side effects of cephalosporins include:

• Diarrhea
• Nausea
• Rash
• Imbalances in electrolytes

Less commonly, you may experience:

• Vomiting
• Headache
• Dizziness
• Fever

There is a small risk of superinfection or impact on the immune system. If you have an immune disorder, discuss these risks with your doctor before use.

Interactions — Cephalosporins

If you’re taking anticoagulants or blood thinners, cephalosporins may not be a good option for you. They’ve been associated with reduced clotting ability and may increase safety risks from injury. Consuming alcohol while taking cephalosporins may trigger an adverse and potentially fatal reaction.

Quinolones

A broad-spectrum antibiotic, quinolones are currently among the most commonly used antibiotics in the world. They prevent bacterial DNA from duplicating and can more easily enter the cell than other antibiotics, so they’re often used for serious infections, particularly around the urinary tract. 

The quinolones currently in use include:

• Ciprofloxacin (Cipro, Proquin XR)
• Delafloxacin (Baxdela)
• Gemifloxacin (Factive)
• Levofloxacin (Levaquin)
• Moxifloxacin (Avelox)
• Ofloxacin (Floxin)

Contraindications – Quinolones

Children are only given quinolones under very strict and serious circumstances, as animal studies have found possible effects on the bones and muscles of juveniles. If you have a musculoskeletal concern, discuss the risks with your doctor before taking them, as they may increase the risk of tendonitis and similar ailments.

If you have diabetes, quinolones may cause low blood sugar, and you may need to monitor your blood sugar more often.

Side Effects – Quinolones

The most common side effects of quinolones as a class include:

• Diarrhea
• Nausea and vomiting
• Rash

They also may impact the results of liver function tests and electrocardiograms (ECGs). 

More rarely, quinolones may cause:  

• Anxiety
• Insomnia
• Nerve pain/loss of feeling
• Light sensitivity

Interactions – Quinolones

Iron, magnesium, aluminum, calcium, and zinc can all interfere with the absorption of quinolones, and supplements or over-the-counter medicines like antacids with these elements should be avoided during a course.

People taking benzodiazepines may experience withdrawal symptoms, as quinolones bond to the same sites as these drugs. Quinolones also interact with liver enzymes to varying degrees, so any drug cleared by these enzymes should be closely managed while on a course of quinolones.

Lincosamides

Similar to penicillins, lincosamides work by preventing bacterial replication. Most commonly, clindamycin is used for a wide range of infections, including dental infections, joint infections, and ear infections. The first lincosamide, lincomycin, is only used on resistant bacteria and for people who have penicillin allergies due to its often strong toxicity and side effects.

Contraindications – Lincosamides

Due to its impacts on the gut biome, if you have a gastrointestinal concern, you should use lincosamides with caution as they may increase the risk of enterocolitis, and it may make your symptoms more uncomfortable.

If you’re allergic to yellow food dye or aspirin, lincosamides are not recommended. If you’re using a topical version, inform your doctor if you have eczema or skin allergies.

Side effects – Lincosamides

Taken internally, side effects of lincosamides include:

• Abdominal pain
• Diarrhea
• Nausea and vomiting

When used on the skin, the most common side effects are:

• Rash
• Dermatitis
• Dryness
• Itching
• Burning
• Scaling
• Peeling

Interactions – Lincosamides

Lincosamides should not be combined with other antibiotics, particularly macrolides, chloramphenicol, or erythromycin.

Macrolides

Originally found in soil, macrolides block protein synthesis and are primarily used to fight gram-positive infections as well as some respiratory and soft tissue infections. It’s also effective against some infections that other antibiotics can treat, such as mycobacteria. Some macrolides are not antibiotics and are used as immunosuppressants.

Common antibiotic macrolides include: 

• Azithromycin (Zithromax or a “Z-pack”)
• Clarithromycin (Biaxin)
• Erythromycin

Contraindications – Macrolides

If you have liver disease, most macrolides are not recommended, although azithromycin is generally safe. Macrolides generally leave the body through the liver and can build up in the body. For this reason, infants shouldn’t take macrolides.

Some macrolides may cause a lengthening of the QT interval, the time between when the heart’s ventricles contract and relax. People with abnormal heart rhythms should only use macrolides under a doctor’s supervision.

Side Effects – Macrolides

The most common side effect of macrolides are gastrointestinal symptoms, as they disrupt gut flora. Headaches and nausea are sometimes also reported. You may also sunburn more easily and should use high-SPF sun protection when taking macrolides.

Interactions – Macrolides

Aluminum and magnesium may interfere with metabolizing macrolides, so avoid any supplements or over-the-counter medications that contain them. You should also avoid any drugs that affect the QT interval.

Sulfonamides

Sometimes called “sulfa” drugs, sulfonamides were first discovered in 1906 and began to be widely used in the 1930s. They are bacteriostatic, preventing reproduction but not otherwise harming the bacteria. They stop the synthesis of folic acid in bacteria, and similar to macrolides, several nonantibiotic sulfonamides are used for other purposes. 

Sulfonamides are most commonly used to treat acne or urinary tract infections, but interest is growing in using them against bacteria resistant to other classes.

Currently, the most common sulfonamides still in use for antibiotic purposes are:

• Sulfacetamide (Klaron, Ovace)
• Sulfadiazine
• Sulfamethoxazole (Bactrim)
• Sulfisoxazole (Truxazole)

Contraindications – Sulfonamides

An estimated 3% of the population may be allergic to antibiotic sulfonamides, especially when given in large doses, so take an allergy test before using them. If you have HIV, your risk may be elevated. 

Currently, research indicates that non-antibiotic sulfonamides are less likely to trigger an allergic reaction, so previous use of this class of drugs for an unrelated purpose should not replace a formal allergy test.

If you have kidney disease or a blood disorder, sulfonamides should only be used in the absence of a better alternative. 

Side Effects – Sulfonamides

As a class, sulfonamides have the following common side effects:

• Gastrointestinal upset, including diarrhea and vomiting.
• Candidiasis (thrush)
• Dizziness
• Fatigue
• Folic acid deficiency
• Headaches
• Itch and rash

If you become dehydrated while taking sulfonamides, crystals may form in the kidneys.

Interactions – Sulfonamides

Sulfonamides should not be used with blood thinners, except in the absence of other options.

BidRX can help you get the best price for antibiotics

When you need antibiotics, BidRX can help you get the best price. After a simple sign-up, create a bid, and pharmacies across the country will tender offers to fill your prescription.

From there, compare prices and choose your pharmacy. Choose a local pharmacy or have your antibiotics mailed to you. Mail-order, specialty, and general pharmacies all offer bids on BidRX. Visit our antibiotics page to learn more.