Antibiotics vs. Antivirals

• More antibiotics than antivirals are made to assist what good bacteria is left.
• Viral infections have no specific drug targets; treatment relies on the body's natural defenses and preventative measures.
• There are four main categories for treating viral infections

Viral Infection Treatment Categories

• Cell wall inhibitors (60-70%) are antibiotics
• Cell membrane inhibitors are antibiotics, antifungals, and antiparasitics
• Protein synthesis inhibitors constitute 40-50% of treatments
• Nucleic acid inhibitors are antimicrobials and antivirals, but have significant side effects.
• Taking only some antibiotics can lead to antibiotic resistance, especially during viral infections.

Origins of Antibiotic Drugs

• Antibiotics are derived from common metabolic products of aerobic spore-forming bacteria and fungi
• Streptomyces and Bacillus bacteria
• Penicillium and Cephalosporium molds

Drug and Microbe Interactions

• Antimicrobial drugs should be selectively toxic to kill or inhibit microbial cells without harming host tissues
• Bacteria possess a cell wall, but challenges arise when microbes share similarities with host cells
• People are given cell wall inhibitors
• Protein synthesis inhibitors are a secondary option due to the presence of more ribosomes in humans.

Antimicrobial Drug Spectrum

• Narrow-spectrum antibiotics are better for targeted treatment, such as gut infections which minimizes nausea and vomiting
• Broad-spectrum antibiotics are typically administered first when the infection is unknown

Drugs Affecting Bacterial Cell Walls

• Penicillins work best against gram-positive bacteria but are associated with more allergies
• Cephalosporins work best against gram-negative bacteria and are associated with fewer allergies

Drugs Disrupting Cell Membrane Function

• These drugs are highly toxic because they can damage cells
• Antibacterials and antifungals are commonly used as cell membrane inhibitors
• Polymyxins are effective against gram-negative bacteria and function as antibacterials

Drugs and Nucleic Acid Synthesis

• These drugs target the genetic material of microbes, which includes blocking synthesis, inhibiting replication, and stopping transcription
• Chloroquine binds and cross-links the double helix, while quinolones inhibit DNA helicases

Drugs Blocking Protein Synthesis

• These drugs attack bacterial ribosomes
• They target the body's own mitochondrial ribosomes.
• Side effects include tiredness
• Aminoglycosides (streptomycin, gentamicin) insert on the 30s subunit and cause misreading of mRNA
• Tetracyclines block protein synthesis by binding to ribosomes
• Chloramphenicol blocks peptide bond formation

Beta-Lactam Cell Wall Inhibitors

• This is a chemical structure found in antibiotics
• Penicillium chrysogenum are a major source
• With three parts: A thiazolidine ring, a Beta-lactam ring (effectiveness is reduced if bacteria break down the B-ring) and an R group

Beta-Lactam Antibiotics

• A variable side chain (R group) dictates microbial activity through carbons and hydrogens
• Carbapenems and Monobactams
• Cephalosporins are preferred over penicillins

Non-Beta-Lactam Cell Wall Inhibitors

• They are hard to administer and very toxic due to a narrow spectrum
• Vancomycin is used as a last resort for MRSA, and SA can mutate to develop VRMSA (Vancomycin-resistant MRSA)
• Isoniazid (INH) is used as a combination drug for tuberculosis (TB) infections

Treating Parasites with Chemotherapy

• Antimalarial drugs include quinine, chloroquine, primaquine, and mefloquine
• Antiprotozoan drugs include metronidazole, sulfonamides, and tetracyclines
• Anti-helminthic drugs work by immobilizing, disintegrating, or inhibiting the metabolism of worm infections
• Types include mebendazole, thiabendazole, pyrantel, and piperazine
• The biggest challenge is removing completely grown worms inside the host

Treating Viral Infections

• Block penetration into host cell
• Block transcription or translation of viral genetic material with nucleotide analogs
  • AZT is a thymine analog used for HIV that blocks viral DNA.
• Prevent maturation of viral particles

Drugs for Treating Influenza

• Amantadine and rimantidine are limited to influenza A and prevent the fusion of the virus with cell membranes.
• Relenza and Tamiflu block neuraminidase in influenza A and B
• It's key to take the drug early on, as it blocks antiviral particles.

Drugs for Treating HIV and AIDS

• Azidothymidine (AZT) is a thymine analog that acts as a reverse transcription enzyme
• Some antivirals are nucleotide analogs, resembling nucleotides
• AZT blocks viral DNA as an antiviral.