12.3 Antibiotic Medications

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Now that we have reviewed antimicrobial basics, we will take a closer look at specific antimicrobial classes. Each of the following sections of this chapter is based on a class or subclass of anti-infective medications. This page will focus on antibiotics and the different classes of antibiotics available. Although some classes are similar, there are still important differences between antibiotics and considerations for when and why they are prescribed.

Penicillins

Penicillin was the first antibiotic discovered, and its detection was a bit of an accident (Fig. 12.4). In 1928, Alexander Fleming, a professor of bacteriology at St. Mary’s Hospital in London, England, discovered penicillin growing in a petri dish in his lab. The penicillin was the result of “mould juice” that had grown there inadvertently. Fleming noted that this “mould juice” inhibited the growth of Staphylococcus bacteria that was previously growing in the petri dish, thereby discovering the first antibiotic (Parker et al., 2016).

 

Penicillins are prescribed to treat a variety of infectious processes such as streptococcal infections, pneumococcal infections, and staphylococcal infections. They can also be used to treat various forms of gram-positive and gram-negative bacteria, and they all share the common molecular structure of a beta-lactam ring. Penicillins may be administered orally, intravenously, or intramuscularly. They are bactericidal and kill bacteria by interfering with the synthesis of proteins needed in their cellular walls (Parker et al., 2016). When the bacterial cell wall is impaired, the cell rapidly breaks down and is destroyed. Penicillin antibiotics are considered broad-spectrum antibiotics because they can be used to treat a wide variety of bacterial infections.

Examples of penicillin antibiotics (WebMD, 2023):

• amoxicillin (Amoxil)
• ampicillin (Principen)
• penicillin V (Penicillin VK, Veetids)
• piperacillin (Pipracil)

Cephalosporins

Carbapenems

Carbapenems are a beta-lactam “cousin” to penicillins and cephalosporins. Cross-sensitivity may occur in patients allergic to penicillin or cephalosporins. Carbapenems are useful for treating life-threatening, multidrug-resistant infections owing to their broad spectrum of activity (Parker et al., 2016). These antibiotics are effective in treating gram-positive and gram-negative infections and are especially useful for treating complex hospital-acquired infections or for patients who are immunocompromised. Carbapenems are typically bactericidal and work by inhibiting the synthesis of the bacterial cell wall.

Monobactams

Like penicillins, cephalosporins, and carbapenems, monobactams also have a beta-lactam ring structure. They are narrow-spectrum antibacterial medications that are used primarily to treat gram-negative bacteria such as Pseudomonas aeruginosa. Monobactams are bactericidal and work to inhibit bacterial cell wall synthesis (Parker et al., 2016).

Sulfonamides

Sulfonamides are one of the oldest broad-spectrum antimicrobial agents that work by competitively inhibiting the bacterial metabolic enzymes needed for bacterial function. Sulfonamides are used to treat urinary tract infections, otitis media, meningitis, acute exacerbations of chronic bronchitis, and travellers’ diarrhea. This mechanism of action provides bacteriostatic inhibition of growth against a wide spectrum of gram-positive and gram-negative pathogens.

Examples of sulfonamide antibiotics (WebMD, 2023):

• sulfadiazine (Silvadene)
• sulfisoxazole (Gantrisin Pediatric)
  • Often combined with generic trimethoprim (TMP) to become SMZ/TMP (Bactrim, Septra)

Fluoroquinolones

Fluoroquinolones are synthetic antibacterial medications that work by inhibiting bacterial DNA replication. They are bactericidal owing to the action they take against the DNA of the bacterial cell wall. Many fluoroquinolones are broad spectrum and are effective against a wide variety of both gram-positive and gram-negative bacteria.

Fluoroquinolones have been associated with disabling and potentially irreversible serious adverse reactions, including the following:

• Tendinitis and tendon rupture
• Peripheral neuropathy
• Central nervous system effects
• Exacerbation of muscle weakness in patients with myasthenia gravis

Patients who experience any of these serious adverse reactions should discontinue the medication immediately and avoid the use of fluoroquinolones.

All patients on fluoroquinolone therapy should be instructed to avoid direct and indirect sunlight because of the photosensitivity that can be experienced while on these medications. Patients should take measures to ensure that dosages are spaced evenly throughout the day and that fluid balance is maintained. It is important to maintain a fluid intake of 1,500 mL to 2,000 mL per day while taking the medication.

Examples of fluoroquinolone antibiotics (WebMD, 2023):

• ciprofloxacin (Cipro)
• levofloxacin (Levaquin)

Macrolides

Macrolides are complex antibacterial broad-spectrum medications that are effective against both gram-positive and gram-negative bacteria. Macrolides inhibit RNA protein synthesis and suppress bacterial reproduction. They are bacteriostatic because they do not actually kill bacteria but inhibit additional growth, allowing the body’s immune system to kill the offending bacteria (Parker et al., 2016).

Macrolides are often used to treat respiratory infections, otitis media, pelvic inflammatory infections, and chlamydia. They can have a significant impact on liver function and should be used cautiously in patients with liver disease or impairment. Gastrointestinal upset is common, and patients should be advised to take the medication with food. Patients should also be advised to avoid excessive sunlight and to wear protective clothing and use sunscreen when outside.

• azithromycin (Zithromax)
• clarithromycin (Biaxin)
• erythromycin (E-Mycin)

Aminoglycosides

Aminoglycosides are potent broad-spectrum antibiotics that are useful for treating severe infections. They are bactericidal and inhibit protein synthesis in the cell wall, which results in bacterial death.

Many aminoglycosides are poorly absorbed in the gastrointestinal tract; therefore, the majority are given intravenously or intramuscularly. All aminoglycoside antibiotic medications have the potential to cause toxic effects to the auditory nerve (ototoxicity) or to the kidneys (nephrotoxicity). They should be administered cautiously, and patients receiving aminoglycoside antibiotics must be carefully monitored with hearing tests (audiograms) and blood tests (BUN and creatinine) for kidney function.

Examples of aminoglycoside antibiotics (WebMD, 2023):

• gentamicin (Cidomycin)
• neomycin (Neosporin)
• tobramycin (TOBI, Tobrex)

Tetracyclines

Tetracyclines are broad-spectrum antibiotics that are bacteriostatic, inhibiting bacterial growth. They stop the growth of bacteria by preventing protein synthesis in the cell wall. Tetracycline medications are useful for treating many gram-positive and gram-negative infectious processes, yet their use is limited because of the significant side effects experienced by many patients.

The side effects of tetracycline medications include photosensitivity, discolouration of developing teeth, and renal and liver impairment. Patients should be instructed to avoid direct sunlight exposure and wear sunscreen to prevent skin reactions. Also, patients who are on oral contraceptives should be educated that tetracyclines may impede the effectiveness of oral contraceptives and an alternative measure of birth control should be used while on the antibiotic.

Examples of tetracycline antibiotics (WebMD, 2023):

• demeclocycline (Declomycin)
• doxycycline (Vibramycin, Vibra-Tabs)
• minocycline (Dynacin, Minocin)
• tetracycline (Sumycin)

Combination Antibiotics

Combination antibiotic medications are also available. These include combinations of anti-infectives and antibiotics that work together within bacteria and affect the areas within the organisms needed to build cellular proteins. These medications are often used against methicillin-resistant Staphylococcus aureus (MRSA) bacterial infections of the skin.

Some of the antibiotics that are often combined include the following (WebMD, 2023):

• sulfamethoxazole/trimethoprim (Bactrim Septra)
• clindamycin (Cleocin)
• vancomycin (Vancocin)

Table 12.1. Common Antibiotic Medications

(WebMD, 2023)

References

Parker, N., Schneegurt, M., Thi Tu, A.-H., Lister, P., & Forster, B. M. (2016). Microbiology. OpenStax. https://openstax.org/details/books/microbiology?Book%20details, licensed under CC BY 4.0

WebMD. (2023). Drugs and medications A–Z. https://www.webmd.com/drugs/2/index 

Image Credit 

Penicillin treatment (45905411884) by Owen Massey McKnight, CC BY-SA 2.0