Pharmacology of Metronidazole and Antibacterials

Metronidazole (Flagyl)

• Functions as a bactericidal agent, effective against specific pathogens.
• Used for protozoal infections and infections from obligate anaerobes, including C. difficile and intra-abdominal infections.
• Also targets Helicobacter pylori, implicated in peptic ulcers.
• Potential adverse effects include neurotoxicity, nephrotoxicity, allergic reactions, and superinfections.
• Infusion site reactions may occur; careful monitoring for allergic and CNS side effects is essential.
• Alcohol consumption leads to disulfiram reaction, causing severe nausea and vomiting.

Additional Antibacterial Drugs

• Rifampin

  • Broad-spectrum antibacterial primarily used for tuberculosis (TB) treatment.
  • Sometimes utilized in conjunction with other drugs for certain meningitis cases, not as monotherapy.

• Rifaximin

  • Oral non-absorbable rifampin variant for treating traveler’s diarrhea.
  • Common side effects include nausea, flatulence, and urgency in defecation.

• Bacitracin

  • Mostly used topically for bacterial infections; systemic use may cause significant toxicity.

• Polymyxin B

  • Applied topically for ear, eye, and skin infections, often in combination with other agents.
  • Not recommended for systemic infections due to the risk of toxicity.

Systemic Mycoses

• Challenging treatment; often resistant to therapy.
• Long-term treatment may involve potentially toxic drugs.

Major Groups of Antifungal Agents

• Systemic Mycoses Infections

  • Opportunistic: Candidiasis, aspergillosis, cryptococcosis, mucormycosis occur in immunocompromised hosts.
  • Non-opportunistic: Sporotrichosis, blastomycosis, histoplasmosis, coccidioidomycosis can affect any host.

• Superficial Mycoses Infections

  • Includes candidiasis and dermatophyte infections; some drugs treat both types.

Amphotericin B

• Recognized as a broad-spectrum antifungal, also active against certain protozoa.
• Known for high toxicity; causes infusion reactions and renal damage in all patients.
• Exclusively administered intravenously; oral administration is not possible.
• Considered the drug of choice for most systemic mycoses, with prior systemic fungal infections often being fatal.

Azoles (“-azole”)

• Broad-spectrum antifungal agents include ketoconazole, fluconazole, and itraconazole.
• Serve as an alternative to amphotericin B for most systemic mycoses with lower toxicity.
• Can be administered orally but may inhibit P450 enzymes, raising levels of various other medications.

Antiviral Therapy

• Treatment for viral infections remains limited due to the challenge of suppressing viral replication without harming host cells.
• Antivirals are designed to target biochemical processes unique to viral reproduction.

Acyclovir (Zovirax)

• Active specifically against herpesvirus family members.
• First-choice treatment for infections such as herpes simplex genitalis, mucocutaneous herpes simplex, varicella-zoster, and cytomegalovirus (CMV).

Valacyclovir (Valtrex)

• Acts as a prodrug form of acyclovir.
• Prescribed for herpes zoster, herpes simplex genitalis, and herpes labialis.
• In immunocompromised patients, it may cause thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS).