Antimicrobial agents are a class of drugs that eliminate potentially harmful organisms in the body. They are used to treat infections caused by bacteria, fungi, viruses, and protozoa.

In this article, we will provide an overview of antimicrobial agents, including their mechanism of action, use, and indications.

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What are Antimicrobial Agents?

Antimicrobial agents are a class of drugs that kill or inhibit the growth of microorganisms, such as bacteria, viruses, fungi, and parasites.

They are often administered to treat infections in patients who have a weakened immune system.

Antimicrobial agents work by targeting the cell walls of bacteria, which are composed of peptidoglycans. When the cell walls are damaged, the bacteria are unable to maintain their shape and integrity, which leads to cell death.

Types of Antimicrobial Agents

Antimicrobial drugs are typically classified according to the type of microorganism they target. Some of the most common examples include:

  • Antibiotics
  • Antifungal agents
  • Antipneumocystis agents
  • Pentamidine
  • Tobramycin
  • Aztreonam (Cayston)
  • Ribavirin (Virazole)
  • Zanamivir (Relenza)

Each of these antimicrobial agents is administered to specifically target a certain type of infection.


Antibiotics are the most commonly prescribed type of antimicrobial agent. They are used to treat infections caused by bacteria, such as pneumonia.

Bacterial infections often lead to signs and symptoms, such as fever, chills, diaphoresis, dark sputum, and an increased white blood cell count.

Therefore, if a patient presents with these symptoms, it is an indication that an antibiotic may be administered.

Two common types of antibiotics include:

  1. Penicillin
  2. Gentamicin

Penicillin is used to treat gram-positive bacteria, such as streptococcus and staphylococcus. Gentamicin is used to treat gram-negative bacteria, such as E. coli and Pseudomonas.

Antifungal Agents

Antifungal agents are a class of drugs that are used to treat fungal infections. They work by inhibiting the growth of fungi or killing them outright.

Antipneumocystis Agents

Antipneumocystis agents are a class of drugs that are used to treat infections caused by the Pneumocystis jirovecii fungus.

This type of infection often occurs in patients who have a weakened immune system, such as those with HIV/AIDS or cancer.


Pentamidine (NebuPent) is an anti-infective agent that is often administered to treat pneumonia caused by the Pneumocystis carinii fungus.


Tobramycin (TOBI) is an antibiotic that is used to treat infections caused by gram-negative bacteria, such as Pseudomonas aeruginosa.

It’s an aerosolized drug that is often administered to patients with cystic fibrosis.


Aztreonam (Cayston) is an antibiotic that is similar to tobramycin, and is also used to treat infections caused by gram-negative bacteria. Therefore, it is also helpful in patients with cystic fibrosis.


Ribavirin (Virazole) is an antiviral agent that is used to treat respiratory syncytial virus (RSV) infections. It is often administered to infants and young children who are hospitalized with RSV.


Zanamivir (Relenza) is an antiviral drug that is used to treat influenza. It is a neuraminidase inhibitor, which blocks the enzyme that is responsible for the release of virions from infected cells.

Zanamivir is administered through an inhaler to patients who have been diagnosed with the flu.

What are Inhaled Anti-Infective Agents?

An inhaled anti-infective agent is a general term that describes a drug that works to fight the spread of an infectious organism. This class of medication includes antiviral, antifungal, and antituberculosis agents.

Inhaled anti-infective agents are delivered in the form of an aerosol, which is a fine mist that can be inhaled into the lungs.

Antimicrobial Agents Practice Questions:

1. What are antimicrobial agents?
They are chemicals that eliminate living microorganisms that are toxic (pathogenic) to the patient.

2. What is the ELISA (Enzyme-linked immunosorbent assay) Test?
It shows what bacteria is resistant to antibiotics.

3. What is the most common reaction to Penicillin?

4. What is the meaning of MRSA?
Methicillin-resistant Staphylococcus aureus.

5. What does Pharmacodynamics mean?
It is how the drug affects the body.

6. What is an agent that kills bacteria or inhibits bacterial growth and/or replication?
Antibacterial agent.

7. What is the preferred agent that kills bacteria at serum levels that are safe for the patient?
Bactericidal agents.

8. What is an agent that inhibits the growth and replication of bacteria at serum levels that are safe for the patient?
Bacteriostatic agents.

9. What can happen if a bacteriostatic agent and the immune system does not kill the bacteria, the doses are skipped, too low or stopped completely, before the immune system has killed all the bacteria?
Resistant bacteria emerge or enough variable organisms may remain to start a 2nd cycle of infection.

10. What is an agent that is effective against a wide variety of microbial species?
Broad spectrum.

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11. What is an agent that is effective against only a single or very limited number of microbial species?
Narrow spectrum.

12. Where does the choice of microbial agent depend on?
It depends on the agent that is most selectively active against M.O and has the least potential to cause toxic effects.

13. What should be noted when choosing an antimicrobial agent in an emergency?
Start with a broad-spectrum agent, and when culture and sensitivity results are available, then switch to narrow-spectrum agent.

14. What is the major reason why bacteria acquires drug resistance?
Overuse and misuse of antibacterial agents are the major reason.

15. What drug class is among the most narrow-spectrum agents and can cause hypersensitivity, neurotoxicity, and hemolysis?

16. What bactericidal drug class inhibits the synthesis of the bacterial cell wall, contains the B-lactam ring, and is used for the treatment of gram-positive bacterial infections?

17. What are the goals of antimicrobial therapy?
They are administered to an infected person and the drug can destroy the infectious agent without harming the host’s cells.

18. What is the proper use of antibiotics?
Take exactly as prescribed (do not skip doses or discontinue before completing therapy). Follow instructions regarding foods/beverages, as acidity can affect efficacy.

19. What is bacteria?
It causes more infectious diseases than any other parasite, and bacterial infections cause substantially more morbidity and mortality. Anti-bacterial drugs are among the most important pharmacological agents we possess. Anti-bacterial agents belong to the chemotherapeutic drugs classification (selective toxicity to invading parasites). Anti-bacterial agents and antibiotics destroy or inhibit the growth and multiplication of microorganisms.

20. What is associated with gram-positive cocci bacteria?
Staphylococcus, streptococcus, streptococcus pneumoniae, and enterococcus.

21. What is associated with gram-positive bacilli?
Clostridia, corynebacterium, listeria, lactobacillus, and actinomyces.

22. What is associated with staphylococcus associated infections?
Skin, soft tissue, bone or joint infections, endocarditis, and food poisoning.

23. What is associated with streptococcus associated infections?
Skin infection, pharyngitis, endocarditis, and toxic shock syndrome.

24. What is associated with streptococcus pneumoniae infections?
Pneumonia, otitis, sinusitis, and meningitis.

25. What is associated with enterococcus infections?
UTI, GI tract infection, and catheter-related infection.

26. What is associated with clostridia infections?
Tetanus, antibiotic-associated diarrhea, gangrene, and botulism.

27. What is associated with corynebacterium infections?
Catheter-related infection and diphtheria.

28. What are the properties of antibiotics concerning the antimicrobial spectrum?
Those antibiotics that have activity against many different bacteria are called broad-spectrum agents, usually prescribed first. Selective activity against a few organisms is called narrow-spectrum agents after an organism is identified. ID is performed via culture in the agar plate.

29. What are the properties of antibiotics concerning drug-resistant bacteria?
Organisms frequently make biochemical or genetic changes to adapt to their environment, bacteria can multiply in as little as 20 minutes after several hours, some bacteria could have genetic mutations making them more resistant to the drug. Repeated courses kill off susceptible organisms but leave more resistant strains unaffected. The main cause of antimicrobial resistance is overuse or inappropriate use of antibiotics and can be viewed as a bacterial survival mechanism.

30. What are the specific bacterial infections and their treatment for MRSA?
Staphylococcus aureus often found on the skin of many people but does not cause a problem among healthy individuals. The biggest threat is to the older-adult population and hospital-bound; and it is increasingly common among the athletic populations. Unresponsive to first-line antibiotics for staph infections.

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31. What are the therapeutic concerns of using antibiotics?
The most common are allergic reactions and GI problems (nausea, vomiting, diarrhea, abdominal discomfort). These can be minimized by taking the medication with food but it varies by drug. Others include ototoxicity and nephrotoxicity with prolonged use. Sulfonamides, tetracyclines, and fluoroquinolones all increase patient’s sensitivity to UV light. All antibiotics can cause c. difficile enteritis. Those taking metronidazole, vancomycin, linezolid or quinupristin/dalfopristin means that the patient has a resistant type of infection.

32. Which type of antimicrobial agent should be administered for a bacterial infection?

33. What are signs of a bacterial infection?
Fever and chills, green or yellow sputum, and an increased white blood cell count.

34. How can you identify the specific type of organism?
Perform a Culture and Sensitivity or Gram Stain test.

35. Which antimicrobial medication would be recommended to treat MRSA?

36. How is Aztreonam administered?
Each patient should be pretreated with bronchodilator before each dosing. Any prescribed mucolytic should also be given before Cayston and should be refrigerated.

37. What is the Aztreonam mode of action?
In vitro activity against gram-negative aerobic bacteria and binds to penicillin-binding proteins of pathogens, such as Pseudomonas aeruginosa.

38. What are the Aztreonam side effects?
Injectable aztreonam has caused severe allergic reactions and nebulized: bronchospasm and decrease patient’s FEV1.

39. How to prevent the Aztreonam environmental effects?
Use expiratory filters with one-way valves and thumb control.

40. What are the Zanamivir side effects?
Bronchospasm, deteriorating of lung function, undertreated of bacterial infection and allergic reactions.

41. What are the clinical indications from pentamidine?
Prevention of pneumocystis pneumonia (PCP) in HIV infected patients.

42. What is Ribavirin given for?

43. What is Tobramycin given for?
Pseudomonas aeruginosa in cystic fibrosis patients.

44. What is another name for Aztreonam and what is it given for?
Cayston; and it is given for Pseudomonas aeruginosa in cystic fibrosis.

45. What is the Pentamidine mode of action?
Unknown but may block RNA and DNA synthesis.

46. What are the RSV resulting diseases?
It can cause bronchiolitis and pneumonia, mainly in children. Outbreaks occur in the late fall through the early spring.

47. What is the Ribavirin mode of action?
It is unknown.

48. What is the Zanamivir mode of action?
Binds to enzyme neuraminidase thus blocking the enzymes action.

49. What is the Aztreonam mode of action?
Inhibits bacterial cell wall synthesis and ultimately death of the cell.

50. What are the Pentamidine aerosol side effects?
SOB, cough, bad taste, bronchospasms and wheezing, pneumonothoraces, eye and skin, irritation and hypoglycemia.

51. What are the Relenza limitations?
DPI for children age 5 and above and adults.

52. What is the Respirgard II Neb used for?
For Pentamidine.

53. What is the SPAG used for?
For Ribavirin (Virazole).

54. What are the indications for Pentamidine?
Prevention of Pneumocystis pneumonia (PCP) in HIV patients.

55. What is the Pentamidine brand name?

56. What is the description of the Pentamidine aerosol administration?
It is for Prophylactic Therapy and for Local targeted lung delivery. Fewer or less severe side effects compared with systemic administration.

57. What is the Pentamidine dose?
300 mg given by inhalation once every 4 weeks, dry powder, 300 mg/vial, reconstituted with 6 mL of sterile water and not saline (can cause precipitation).

58. What is the description of the Pentamidine administration?
Powered by a flow rate of 5-7 L/min from 50-psi gas source, escaped particles may be filtered to limit exposure of healthcare workers, nebulizer performance and mass median diameter (MMD) of 1-2 μm.

59. What is the Pentamidine nebulizer name?
Respirgard II (manual system with thumb port).

60. What are the side effects of Pentamidine?
Hypoglycemia (up to 62% of patients) with cumulative cytotoxic effect on pancreatic beta cells; impaired renal function and azotemia; cough and bronchial irritation; shortness of breath; bronchospasm and wheezing; and, spontaneous pneumothoraces.

61. What are the environmental precautions of Pentamidine?
Use nebulizer system with one-way valves and expiratory filter; stop nebulization if patient takes mouthpiece out of mouth (thumb control on power gas tubing gives more control); use nebulizers producing an MMD of 1-2 μm to increase alveolar targeting and decrease large airway deposition and cough production; and, do not let patient out of room.

62. What is the description of the Aerosol Therapy for Pentamidine?
Oral trimethoprim-sulfamethoxazole (TMP-SMX) preferred for prophylaxis of PCP, as long as adverse side effects from TMP-SMX were absent or acceptable.

63. What are the Ribavirin indications (aerosolized)?
Treatment of hospitalized infants with severe lower respiratory tract infection caused by respiratory syncytial virus (RSV) and active against influenza viruses and herpes simplex virus.

64. What is Respiratory Syncytial Virus (RSV)?
It can take over only on children not in adults. Cells change their shape when RSV sticks to cell and this produces very sticky mucous. Can cause bronchiolitis and pneumonia, formation of large, multinucleated cells, or syncytium and inflammation of small airways.

65. What is the mechanism of action of Ribavirin?
Virostatic not virocidal; inhibits both DNA and RNA (retrovirus) viruses; highly toxic; and, not completely understood. Probably based on its structural resemblance to nucleosides used to construct the DNA chain.

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66. What is the Ribavirin dose?
20-mg/mL solution; 12 to 18 hour/day; minimum of 3 days; not more than 7 days; supplied as 6g of powder in 100-mL vial; and, concentration of 6 g/300 mL.

67. What is the Ribavirin nebulizer?
SPAG (Large volume, pneumatically powered nebulizer); approximately 1.3 μm, MMD; and, solutions in the SPAG reservoir should be replaced after 24 hours.

68. What are the pulmonary side effects of Ribavirin?
Deterioration of pulmonary function and worsening of asthma or chronic obstructive disease; pneumothorax, apnea, and bacterial pneumonia.

69. What are the cardiovascular side effects of Ribavirin?
Cardiovascular instability, including hypotension, cardiac arrest, and digitalis toxicity.

70. What are the hematological side effects of Ribavirin?
Effects on blood cells have been reported with oral or parenteral administration.

71. What are the dermatological/topical side effects of Ribavirin?
Rash, eyelid erythema, and conjunctivitis.

72. What are the equipment-related side effects of Ribavirin?
Occlusion and impairment of expiratory valves and sensors with ventilator use and endotracheal tube blockage from drug precipitate.

73. What is the environmental contamination concern with aerosolized ribavirin?
Potential for mutagenic and carcinogenic effects; effect on fertility is uncertain caused testicular lesions in rats; and, effect on pregnancy is of particular concern and use as last line of defense.

74. What are the Palivizumab indications?
Prevention of serious lower respiratory tract disease caused by RSV in children and infants at high risk. Safety and efficacy established for infants with BPD, premature infants (<35 weeks), and children with congenital heart disease.

75. What are the indications for Tobramycin?
Management of chronic Pseudomonas aeruginosa infection in cystic fibrosis.

76. What is the indication for Virostatic?
Stopping a virus from replicating.

77. What is the indication for Virucidal?
Killing a virus.

78. What is the Aztreonam brand name?

79. What is the Zanamivir brand name?

80. What is the Tobramycin brand name?
TOBI and Bethkis.

81. What is an Anti-infective agent?
They are substances that act against or destroy infections including: bacteria, viruses, Protozoa, and parasites.

82. What alternate therapy is most likely prescribed for a patient with pneumocystis pneumonia, who is unable to tolerate trimethoprim-sulfamethoxazole therapy?
Aerosolized pentamidine.

83. What drug will a respiratory therapist use as an alternative to intravenous therapy in a patient with cystic fibrosis to manage a chronic Pseudomonas aeruginosa infection?

84. What aerosolized anti-infective agents are used in the airway management of a patient with cystic fibrosis who has had the Pseudomonas aeruginosa infection?
Inhaled tobramycin (TOBI) and inhaled aztreonam (Cayston).

85. What agent is used in the treatment and prophylaxis of H1N1 influenza A?
Zanamivir (Relenza).

86. What are the possible side effects observed in a patient under parenteral pentamidine therapy?
Leukopenia, hypoglycemia, and abscess formation.

87. What is an antiprotozoal aerosolized anti-infective agent?
Pentamidine isethionate (NebuPent).

88. What medication is beneficial for a patient diagnosed with bronchiolitis caused by respiratory syncytial virus (RSV)?
Ribavirin (Virazole).

89. What drug prevents bronchoconstriction in a patient with pneumocystis pneumonia (PCP) and is under aerosolized pentamidine therapy?

90. A physician prescribes nebulized tobramycin to a patient. For what conditions does a respiratory therapist check the patient’s medical history before administration?
Renal impairment, vestibular problems, and neuromuscular dysfunction.

91. What aerosolized medication would be used to treat a patient with acquired immunodeficiency syndrome (AIDS) who has opportunistic pneumonia caused by pneumocystis jiroveci?
Pentamidine isethionate (NebuPent).

92. What aerosolized medication should a respiratory therapist prescribe while treating an 8-year-old child with acute, community-acquired, atypical pneumonia caused by influenza A?
Zanamivir (Relenza).

93. What systemic side effects are most likely to have occurred in a patient who was switched from parenteral pentamidine (Pentacarinat) therapy to aerosolized pentamidine (NebuPent) to prevent systemic side effects?
Leukopenia, hypotension, and hepatic dysfunction.

94. What possible pulmonary side effects are observed in a patient on aerosolized ribavirin therapy?
Apnea, pneumothorax, and bacterial pneumonia.

95. What are the systemic reactions that are observed in a patient under aerosolized pentamidine therapy?
Dysglycemia, conjunctivitis, and renal insufficiency.

96. What is an indication for Aztreonam?
To improve pulmonary symptoms in cystic fibrosis patients with pseudomonas aeruginosa.

97. What is Tobramycin?
It is the drug we typically give to cystic fibrosis patients. Its brand name is TOBI and Bethkis. The dose is 300 mg/ 5ml ampule. Its clinical use is to treat Pseudomonas aeruginosa in Cystic fibrosis.

98. What is Pentamidine isethionate?
Brand name: NebuPent; dosage: 300 mg of powder in 6 ml of sterile water; 300 mg once every 4 weeks; and, clinical use: PCP prophylaxis.

99. What is Ribavirin?
Brand name: Virazole; dosage: 6 mg of powder in 300 ml of sterile water (20-mg/mL solution) given 12-18 hr. /day for 3-7 days by SPAG-2 neb; and, clinical use: RSV. It is used with RSV (respiratory syncytial viral) infections in children and infants at risk for severe or complicated disease, influenza, and the herpes simplex virus.

100. What is Aztreonam?
Brand name: Cayston; dosage: 75 mg/1mL; adults and children over 7 years: 75mg TID, 28 days on 28 days off; and, clinical use: Pseudomonas aeruginosa in Cystic Fibrosis.

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101. What is Zanamivir?
Brand name: Relenza; DPI: 5mg/inhalation; adults and children over 5: 2 inhalations (one 5-mg blister per inhalation) BID less than 12 hours apart for 5 days; and, clinical use: Influenza. It is an Antiviral agent approved for use in the treatment of uncomplicated influenza illness in adults and children older than 7 years during early onset (within the first 2 days) of infection.

102. What is Aerosolized Pentamidine used for?
Prevention of PCP (Pneumocystis pneumonia is a fungus) in high risk human immunodeficiency virus (HIV) infected patients.

103. What is the Pentamidine brand name?

104. What is a Pentamidine nebulizer?
Respirgard II (no medication can escape because of the expiratory filter, thumb port, one way valves).

105. What is the Pentamidine Dose in dry powder?
300mg in 6 mL of sterile water every 4 weeks.

106. What is the description of the Pentamidine administration?
It should not be exposed to the medication. It is given with the Respirgard II nebulizer at a flow rate of 5-7L/min from 50 psi gas source.

107. What are the Pentamidine side effects?
Parenteral: Hypoglacemia, impaired renal function; aerosol: Cough, bronchospasm, shortness of breath, bronchial irritation, and wheezing, spontaneous pneumothoraces; and, should be used with B-adrenergic bronchodilator before inhaling aerosolized pentamidine.

108. What is the Ribavirin brand name?

109. What is the Ribavirin nebulizer?
The SPAG II (1.3 micro meter MMD, large volume).

110. What is the normal Ribavirin Dose?
20mg/ml 12-18 hours per day; minimum 3 days; and, maximum 7 days.

111. What is the Respiratory Syncytial Virus (RSV)?
It is a virus that can cause bronchiolitis and pneumonia. It is seasonal in nature and the peak occurs during winter months. RSV sticks to cells changing their shape and this produces very sticky mucus.

112. Can you administer Ribavirin to infants?
Manufacturers warn against the administration of the drug to infants on mechanical ventilation.

113. What are the side effects of Ribavirin?
Pulmonary: worsening of asthma or COPD; cardiovascular: hypotension, cardiac arrest; hematologic: blood cells; dermatologic/topical: rash, conjunctivitis; and, equipment-related: impairment of expiratory valves and sensors.

114. What is the Palivizumab brand name?

115. What are the side effects of Palivizumab?
Anaphylaxis, fever, upper respiratory infection, otitis media, rhinitis, rash, and coughing/wheezing.

Final Thoughts

Antimicrobial agents are a class of drugs that are used to treat infections and kill harmful microorganisms in the body. There are several different types of antimicrobial agents, each of which is designed to target a specific type of microorganism.

Respiratory therapists often administer inhaled antimicrobial agents to patients who are hospitalized with an infection. These drugs are delivered in the form of an aerosol, which is a fine mist small enough to be inhaled into the lungs.

Be sure to check out our guide on the different types of lung infections that these drugs are used to treat. Thanks for reading!

Medical Disclaimer: This content is for educational and informational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Please consult with a physician with any questions that you may have regarding a medical condition. Never disregard professional medical advice or delay seeking it because of something you read in this article. We strive for 100% accuracy, but errors may occur, and medications, protocols, and treatment methods may change over time.


The following are the sources that were used while doing research for this article:

  • Rau’s Respiratory Care Pharmacology. 10th ed., Mosby, 2019.
  • Egan’s Fundamentals of Respiratory Care. 12th ed., Mosby, 2020.
  • “Antimicrobial Drugs.” PubMed Central (PMC), 2003,

Medical Disclaimer: The information provided by Respiratory Therapy Zone is for educational and informational purposes only. It should not be used as a substitute for professional medical advice, diagnosis, or treatment. Please consult with a physician with any questions that you may have regarding a medical condition.