First-generation cephalosporins are narrow-spectrum, mainly gram-positive coverage, some gram-negative like E. coli, Klebsiella, Proteus mirabilis.

Oral First Generation Cephalosporin:

Antibiotics of first generation cephalosporin are orally classified into 

1. Cefadroxil
2. Cephalexin (Keflex)
3. Cephradine

Intravenous and Intramuscular First Generation Cephalosporins:

Antibiotics of first generation cephalosporin are intravenously and Intramuscularly classified into

1. Cefazolin (Ancef) — most commonly used, especially for surgical prophylaxis
2. Cephalothin (largely discontinued in many countries)
3. Cephapirin (largely discontinued)
4. Cephradine (also available parenterally)
5. Cephaloridine

Uses Of First-Generation Cephalosporins

1. Skin and Soft Tissue Infections that are caused by Staphylococcus aureus MSSA only, and Streptococcus species.
2. Cefazolin is a choice drug of surgeons used in surgical prophylaxis before surgeries, like cardiac, orthopedic etc to prevent post-op wound infections.
3. It acts as an alternative drug to penicillin to treat infections called Streptococcal pharyngitis in patients who can’t tolerate it and shows response to it (non-anaphylactic reactions).
4. Uncomplicated UTIs (Urinary Tract Infections) caused by susceptible organisms including bacterias like E.coli, Klebsiella, Proteus mirabilis.
5. Bone and Joint Infections like Osteomyelitis and septic arthritis caused by susceptible staph/strep are also treated with cephalosporins. 
6. Ear inflammation diseases like Otitis Media, Respiratory Tract Infections are treated with Cephalosporins. 
7. Endocarditis Prophylaxis (dental/surgical procedures) is also treated with 1st generation of cephalosporins when patients are at risk.

Key limitation: 

There is no reliable coverage against MRSA, enterococci, Beside this  E. coli, Klebsiella (Gram Positive Bacterias). 1st Generation cephalosporins are not used for meningitis.

Mechanism Of Action Of First-Generation Cephalosporins 

1. Inhibition of Cell Wall (Murein) Development: 

Cephalosporins are bactericidal so they kill bacterias instead of just inhibiting their growth. They belong to the beta-lactam class of Cephalosporin antibiotics, structurally resembling penicillins.

1. Penicillin-Binding Proteins (PBPs). 

Cephalosporins bind and inhibit penicillin binding proteins (PBPs) located on the bacterial cell membrane which weakens the cell membrane and results in rupturing of cell due to high internal pressure.

1. Transpeptidases Enzymes:

Transpeptidases are enzymes responsible for the final cross-linking step of peptidoglycan synthesis, the main structural component of the bacterial cell wall. The beta-lactam ring of the cephalosporin is structurally a copy of the D-alanyl-D-alanine portion of the peptidoglycan precursor. This allows the drug to bind irreversibly to the active site of Transpeptidase enzyme. This blocks the cross-linkings of peptidoglycan chains called transpeptidation that gives the cell wall its strength, turgidity and rigidity.

1. Bacterial Cell Wall Lysis: 

Without proper binding and cross linking of proteins with the cell wall, the cell wall becomes weak structurally and unstable functionally. Autolysins (Autolytic enzymes) continue breaking down cell wall components. The bacterial cell becomes unable to sustain its structure and withstand osmotic pressure. This leads to cell lysis (Rupturing of Cell) and finally cell death occurs.

1. High Affinity:

First Generation Cephalosporin have high affinity for PBPs of gram-positive bacterias like Staphylococcus, Streptococcus except MRSA and enterococci.

1st Generation cephalosporins have low and weak affinity for PBPs of most gram-negative bacteria due to:

• Difficulty in penetrating the outer membrane of bacteria called Murein.
• They are susceptible to beta-lactamases produced by many gram-negative bacterias.
• Some first generation cephalosporin drugs have modest activity against a few gram negative bacterias like E. coli, Klebsiella pneumoniae, and Proteus mirabilis.
• 1st Generation Cephalosporins reduced permeability in gram-negative bacteria with outer membrane barriers.

1. Resistive Working: 

They don’t work against everything because Beta-lactamase (A bacterial enzyme that hydrolyze  and break the beta-lactam ring of Bacteria), inactivates the cephalosporins drug

Precautions for First-Generation Cephalosporins

1. Choice Antibiotic: 

Cephalosporin is the second best choice to use in diffent diseases that have not responded or been treated by penicillins.

1. Allergy/Hypersensitivity: 

Humans or animals that are facing allergy by the use of penicillins. In severe penicillin allergy anaphylaxis, Stevens-Johnson syndrome and angioedema, avoid in these cases.

1. Dose/interval adjustment: 

Proper Dosage adjustment is essential and the need of the day. Cefazolin and cephalexin require dose/interval adjustment based on creatinine clearance.

1. Gastrointestinal Effects:

There is a risk of Clostridioides difficile-associated diarrhea (antibiotic-associated colitis). Use the narrowest effective spectrum to minimize risk and to make a safe use.

1. Pregnancy and Lactation: 

Cephalosporins and penicillins are the only antibiotics that are pregnancy safe. But take care of the medicines that are here with cephalosporins in composition. Maybe there is something else that can affect pregnancy. So Be careful and use only when clearly needed.

1. Bleeding Risk: 

There is a bleeding risk which is rare, but high doses may affect vitamin K-dependent clotting factors monitored in patients on anticoagulants. Use “Transamin injection” in such a situation to stop bleeding other than bleeding of direct veins.

1. Neurotoxicity:

if you do adjust the dose so very high doses (especially in renal impairment) can cause seizures or encephalopathy.

1. Drugs Interactions: 

Cephalosporin levels increase Probenecid where it can be used therapeutically.

1. Local Reactions: 

IM injections can be painful in both humans and animals. While IV administration may cause phlebitis.

1. Superinfection: 

If you use drugs prolonged then it may lead to overgrowth of resistant organisms either fungi or bacteria.

Examples of First-Generation Cephalosporins

1. Cephalexin (Keflex)
2. Cefadroxil (Duricef)
3. Cephradine (Velosef)
4. Cefazolin (Ancef, Kefzol)
5. Cephalothin (Keflin)
6. Cephapirin (Cefadyl) 
7. Cephradine (Velosef) 

       Cefazolin (parenteral) and Cephalexin (oral) are the two most commonly used in current practice.

Classification of Cephalosporins:

First Generation Cephalosporins

1. Cefadroxil
2. Cefadroxil (Duricef)
3. Cefazolin (Ancef, Kefzol)
4. Cephalothin (Keflin) 
5. Cephapirin (Cefadyl)
6. Cephalexin (Keflex)
7. Cephradine (Example: Vericef Susp, Velosef)
8. Cephalexin (Example: Ceporex, Keflex)

Second Generation Cephalosporins

1. Cefamandole
2. Cefoxitin
3. Cefuroxime
4. Cefotiam
5. Cefotetan
6. Cefmetazole
7. Cefonicid

Third Generation Cephalosporins

1. Ceftizoxime
2. Cefmenoxime
3. Cefoperazone
4. Ceftazidime
5. Latamoxef
6. Flomoxef
7. Cefodizime
8. Cefotaxime Sodium(Example: Ceforine, Excef)
9. Ceftriaxone Sodium (Example: Zeftrox, Oxidil)
10. Ceftiofur Hydrochloride (Example: Cefur RTU, Excenel RTU)

Fourth Generation Cephalosporins

1. Cefepime
2. Cefpirome
3. Cequinome (Example: Cefanome, Cefanil)

Fifth Generation Cephalosporins

1. Ceftobiprole
2. Ceftaroline Fosamil

Key Clinical Notes for Veterinary Use:

1. Cephalexin is the vet workhorse for canine pyoderma (bacterial skin infection) which often dosed at higher levels for dogs than for humans
2. Cefazolin is standard for surgical prophylaxis in veterinary surgery (dogs, cats, horses)
3. Cephapirin intramammary products are specifically formulated for dairy cattle mastitis treatment and are a FSHZ (food safety/withhold time) consideration important instamps withdrawal times for milk/dairy production, exposed animals
4. Dry cow therapy with cephapirin is a use to prevent new mastitis infections during the non-non-lactating period
5. Withdrawal times matter significantly in food-producing animals (dairy cattle). Always check current label/regulatory withdrawal periods before use.

Frequently Asked Questions

Is cefazolin a first generation cephalosporin?

Yes, Cefazolin is a 1st generation Cephalosporin like Ancef, most commonly used especially for surgical prophylaxis.

Is Ancef a first generation cephalosporin? 

Yes, Ancef of Cefazolin class is a 1st generation Cephalosporin, most commonly used especially for surgical prophylaxis.

Is cephalexin a first generation cephalosporin?  

Yes, Cephalexin like Keflex is a 1st generation Cephalosporin.

Is keflex a first generation cephalosporin? 

Yes, Keflex of Cephalexin class is a 1st generation Cephalosporin.

What are 1st generation cephalosporins? 

1st generation cephalosporins are narrow-spectrum, mainly gram-positive coverage, some gram-negative like E. coli, Klebsiella, Proteus mirabilis.

Is ceftriaxone 1st generation cephalosporin? 

No Cefriaxone is not a 1st generation cephalosporin. It belongs to 3rd generation of cephalosporins.