Does cefadroxil have a 1-Methyl-1H-tetrazol-5-yl (1-MTT) side chain in its chemical structure?

Chemical Structure of Cefadroxil: No NMTT Side Chain

Cefadroxil does not have a 1-Methyl-1H-tetrazol-5-yl (1-MTT) side chain in its chemical structure. 1

Chemical Structure Details

Cefadroxil is a semisynthetic cephalosporin antibiotic with the chemical formula C₁₆H₁₇N₃O₅S•H₂O and a molecular weight of 381.40. 1 Its chemical structure consists of:

1. A beta-lactam ring (common to all cephalosporins)
2. A dihydrothiazine ring
3. An R1 side chain consisting of an amino(4-hydroxyphenyl)acetyl group
4. An R2 side chain that is a methyl group

The FDA drug label clearly identifies cefadroxil's chemical designation as "5-Thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid, 7-[[amino(4-hydroxyphenyl)acetyl]amino]-3-methyl-8-oxo-, monohydrate, [6R-[6(α),7β(R*)]]" 1, which does not include an NMTT/1-MTT tetrazole ring structure.

Side Chain Significance

The R1 side chain of cefadroxil is particularly important for its clinical properties:

• Cefadroxil shares its R1 side chain (amino(4-hydroxyphenyl)acetyl) with amoxicillin 2, 3
• This shared R1 side chain is responsible for potential cross-reactivity between cefadroxil and amoxicillin in patients with penicillin allergies 2, 3
• According to allergy guidelines, cross-reactivity between amoxicillin and cefadroxil is approximately 35% due to this shared side chain 3

Clinical Implications of Side Chain Structure

The absence of an NMTT side chain and the presence of the specific R1 side chain has important clinical implications:

• Cefadroxil is classified as an "aminocephalosporin" due to its side chain structure 2
• Cross-reactivity with penicillins varies from 16.45% (95% CI: 11.07-23.75) for aminocephalosporins like cefadroxil to 2.11% (95% CI: 0.98-4.46) for cephalosporins with different side chains 2
• Cefadroxil's side chain structure contributes to its pharmacokinetic properties, including longer serum half-life and sustained tissue concentrations compared to similar cephalosporins 4

Comparison with Other Cephalosporins

Cefadroxil's side chain structure differs from cephalosporins that do contain NMTT side chains:

• Cefazolin has a unique side chain structure with very low cross-reactivity with penicillins 2
• Ceftibuten also has unique side chains that make cross-reactions with penicillins exceedingly rare 2
• Cefadroxil is grouped with cephalexin, cefprozil, and cefaclor as sharing similar R1 side chains 2

The chemical structure of cefadroxil, with its specific side chains, allows it to be administered once or twice daily (unlike some other cephalosporins requiring more frequent dosing), which can improve patient compliance in outpatient settings. 4