💊Pharmacology for Nurses Unit 7 – Anti–infective Drugs

What Are Anti-infective Drugs?

• Medications used to treat or prevent infections caused by various microorganisms (bacteria, viruses, fungi, and parasites)
• Work by either killing the infectious agents (bactericidal) or inhibiting their growth and reproduction (bacteriostatic)
• Classified based on their mechanism of action, spectrum of activity, and the type of microorganism they target
• Can be administered orally, intravenously, intramuscularly, or topically depending on the type of infection and drug properties
• Play a crucial role in managing infectious diseases and reducing morbidity and mortality associated with infections
• Proper use of anti-infective drugs helps prevent the development and spread of antibiotic-resistant strains of microorganisms
• Selecting the appropriate anti-infective drug depends on factors such as the causative agent, site of infection, patient's age, and comorbidities

Types of Anti-infective Drugs

• Antibiotics target bacterial infections and are further classified into subgroups based on their chemical structure and mechanism of action
  • Beta-lactams (penicillins, cephalosporins, carbapenems, and monobactams) inhibit bacterial cell wall synthesis
  • Aminoglycosides (gentamicin, tobramycin) disrupt bacterial protein synthesis
  • Tetracyclines (doxycycline, minocycline) inhibit bacterial protein synthesis
  • Macrolides (erythromycin, azithromycin) inhibit bacterial protein synthesis
  • Fluoroquinolones (ciprofloxacin, levofloxacin) inhibit bacterial DNA replication
• Antiviral drugs target viral infections by inhibiting viral replication or entry into host cells
  • Nucleoside analogs (acyclovir, famciclovir) inhibit viral DNA synthesis
  • Protease inhibitors (ritonavir, saquinavir) block viral protein synthesis
  • Neuraminidase inhibitors (oseltamivir, zanamivir) prevent the release of viral particles from infected cells
• Antifungal drugs treat fungal infections by disrupting fungal cell membranes or inhibiting fungal growth
  • Azoles (fluconazole, itraconazole) inhibit fungal cell membrane synthesis
  • Polyenes (amphotericin B, nystatin) bind to ergosterol in the fungal cell membrane, causing cell lysis
  • Echinocandins (caspofungin, micafungin) inhibit the synthesis of fungal cell wall components
• Antiparasitic drugs target parasitic infections by interfering with parasite metabolism or reproduction
  • Antiprotozoal agents (metronidazole, tinidazole) disrupt parasite DNA synthesis
  • Anthelmintics (albendazole, mebendazole) inhibit parasite glucose uptake or microtubule formation

How Anti-infective Drugs Work

• Interfere with essential processes or structures specific to the target microorganism while minimizing harm to human cells
• Inhibit bacterial cell wall synthesis by preventing the formation of peptidoglycan, a key component of the bacterial cell wall
• Disrupt bacterial protein synthesis by binding to bacterial ribosomes and interfering with the translation of mRNA into proteins
• Block bacterial DNA replication or transcription by inhibiting enzymes involved in these processes (DNA gyrase, topoisomerase IV)
• Alter fungal cell membrane permeability by binding to ergosterol, a lipid unique to fungal cell membranes, causing cell lysis
• Inhibit viral replication by incorporating into viral DNA or RNA, leading to chain termination and halting viral genome replication
• Prevent viral entry into host cells by blocking viral surface proteins that facilitate attachment and fusion with host cell membranes
• Disrupt parasite metabolism by inhibiting the synthesis of essential compounds (folic acid, pyrimidines) or interfering with energy production

Common Uses and Indications

• Treat bacterial infections of various body systems (respiratory, urinary, gastrointestinal, skin, and soft tissue infections)
  • Pneumonia, bronchitis, and other respiratory tract infections
  • Urinary tract infections (cystitis, pyelonephritis)
  • Skin and soft tissue infections (cellulitis, impetigo, wound infections)
  • Gastrointestinal infections (Helicobacter pylori, Salmonella, Shigella)
• Manage viral infections, including herpes simplex virus (HSV), varicella-zoster virus (VZV), influenza, and HIV
• Treat fungal infections of the skin (dermatophytosis), nails (onychomycosis), and mucous membranes (oral candidiasis, vaginal candidiasis)
• Address parasitic infections such as malaria, toxoplasmosis, and helminthic infestations (roundworms, tapeworms)
• Prevent infections in high-risk situations (surgical prophylaxis, immunocompromised patients, exposure to infectious agents)
• Eradicate colonization of multidrug-resistant organisms (MRSA decolonization) to reduce the risk of infection and transmission

Administration and Dosing

• Route of administration depends on the type of infection, drug properties, and patient factors
  • Oral administration is preferred for mild to moderate infections and when the drug has good bioavailability
  • Intravenous administration is used for severe infections, when oral intake is not possible, or when high tissue concentrations are required
  • Intramuscular injections are used for certain drugs with poor oral bioavailability or when intravenous access is not available
  • Topical application is used for localized skin, eye, or ear infections
• Dosing regimens are based on the drug's pharmacokinetic properties, the severity of the infection, and patient characteristics (age, weight, renal function)
  • Loading doses may be given to rapidly achieve therapeutic concentrations
  • Maintenance doses are administered at regular intervals to maintain steady-state concentrations
  • Dose adjustments may be necessary for patients with renal or hepatic impairment, obesity, or other factors affecting drug metabolism and elimination
• Duration of therapy depends on the type and severity of the infection, the patient's response to treatment, and the risk of relapse or resistance development
  • Shorter courses may be sufficient for uncomplicated infections (e.g., 3-7 days for cystitis)
  • Longer courses are required for deep-seated, chronic, or recurrent infections (e.g., 4-6 weeks for osteomyelitis)
• Therapeutic drug monitoring may be necessary for drugs with narrow therapeutic indices (aminoglycosides, vancomycin) to ensure efficacy and minimize toxicity

Side Effects and Adverse Reactions

• Gastrointestinal disturbances (nausea, vomiting, diarrhea, abdominal pain) are common with many oral antibiotics due to alterations in gut microbiota
• Allergic reactions can range from mild (rash, itching) to severe (anaphylaxis) and may be more common with certain drug classes (beta-lactams, sulfonamides)
• Nephrotoxicity can occur with drugs excreted primarily by the kidneys (aminoglycosides, vancomycin) or those that form insoluble crystals in the renal tubules (acyclovir, sulfadiazine)
• Hepatotoxicity is a potential risk with some anti-infective agents (isoniazid, rifampin, ketoconazole) and may manifest as elevated liver enzymes or frank hepatitis
• Neurotoxicity, including ototoxicity, can occur with certain drugs (aminoglycosides, linezolid) and may be irreversible
• Hematologic abnormalities, such as anemia, neutropenia, or thrombocytopenia, can be associated with various anti-infective drugs (trimethoprim-sulfamethoxazole, linezolid)
• Clostridium difficile-associated diarrhea is a potentially serious complication of antibiotic therapy that results from the disruption of normal gut flora and overgrowth of toxigenic C. difficile strains
• QT prolongation and cardiac arrhythmias are rare but serious adverse effects associated with some anti-infective agents (macrolides, fluoroquinolones)

Drug Interactions and Precautions

• Concomitant use of antibiotics with oral contraceptives may reduce the effectiveness of contraception due to alterations in gut flora and increased drug metabolism
• Antacids, iron supplements, and multivitamins can chelate certain antibiotics (tetracyclines, fluoroquinolones), reducing their absorption and efficacy
• Warfarin's anticoagulant effect may be potentiated or inhibited by various anti-infective drugs, necessitating close monitoring of INR and dose adjustments
• Nephrotoxic and ototoxic drugs (loop diuretics, NSAIDs) should be used cautiously with aminoglycosides due to the increased risk of kidney damage and hearing loss
• Hepatotoxic drugs (acetaminophen, statins) should be used with caution in patients receiving potentially hepatotoxic anti-infective agents
• Drug-induced QT prolongation can be exacerbated by the concomitant use of other QT-prolonging medications (antiarrhythmics, antipsychotics, tricyclic antidepressants)
• Pregnancy and lactation: certain anti-infective drugs may be contraindicated or require careful risk-benefit assessment and monitoring due to potential fetal or neonatal harm
• Renal and hepatic impairment may necessitate dose adjustments or avoidance of certain anti-infective agents to prevent accumulation and toxicity

Nursing Considerations and Patient Education

• Assess patient allergies and previous adverse reactions to anti-infective drugs before administration
• Obtain baseline laboratory tests (CBC, renal function, liver enzymes) and monitor periodically during treatment as indicated
• Administer medications at the prescribed time, dose, and duration, ensuring proper storage and handling of the drugs
• Monitor for signs and symptoms of infection resolution (decreased fever, improved wound appearance, reduced pain) and report any lack of improvement or worsening to the healthcare provider
• Observe for adverse drug reactions and promptly report any serious or unexpected side effects to the medical team
• Educate patients on the importance of completing the full course of therapy even if symptoms improve to prevent relapse and reduce the risk of resistance development
• Instruct patients to take medications as directed, with or without food as appropriate, and to avoid skipping or doubling doses
• Teach patients about common side effects and when to seek medical attention for severe or persistent adverse reactions
• Advise patients to inform their healthcare providers about all medications, supplements, and herbal products they are taking to avoid potential drug interactions
• Emphasize the importance of proper hygiene, handwashing, and infection control measures to prevent the spread of infectious agents
• Provide written instructions and educational materials to reinforce verbal teaching and ensure patient understanding of their anti-infective drug therapy