Specific populations
Pregnancy
Ceftriaxone is pregnancy category B. It has not been observed to cause birth defects in animal studies, but a lack of well-controlled studies done in pregnant women exists. Breastfeeding
Low concentrations of ceftriaxone are excreted in breast milk that are "not expected to cause adverse effects in breastfed infants." The manufacturer recommends that caution be exercised when administering ceftriaxone to women who breastfeed. Newborns
Hyperbilirubinemic neonates are contraindicated for the use of ceftriaxone. It can compete with bilirubin and displace it from binding to albumin, increasing the risk of bilirubin encephalopathy. Elderly
According to the package insert, clinical studies did not 
show differences in efficacy and safety of ceftriaxone in geriatrics compared to younger patients but "greater sensitivity of some older individuals cannot be ruled out." Adverse effects
Although generally well tolerated, the most common adverse reactions associated with ceftriaxone are changes in white blood cell counts, local reactions at site of administration, rash, and diarrhea.Incidence of adverse effects greater than 1%:

Eosinophilia (6%)
Thrombocytosis (5.1%)
Elevations in liver enzymes (3.1–3.3%)
Diarrhea (2.7%)
Leukopenia (2.1%)
Elevation in BUN (1.2%)
Local reactions: pain, tenderness, irritation (1%)
Rash (1.7%)Some less frequently reported adverse events (incidence < 1%) include phlebitis, itchiness, fever, chills, nausea, vomiting, elevations of bilirubin, elevations in creatinine, headache and dizziness.Ceftriaxone may precipitate in bile, causing biliary sludge, biliary pseudolithiasis, and gallstones, especially in children. Hypoprothrombinaemia and bleeding are specific side effects. Haemolysis is reported. It has also been reported to cause post kidney failure in children. Like other antibiotics, ceftriaxone use can result in Clostridium difficile-associated diarrhea ranging from mild diarrhea to fatal colitis.
Contraindications
Ceftriaxone should not be used in those with an allergy to ceftriaxone or any component of the formulation. Although there is negligible cross-reactivity between penicillins and third-generation cephalosporins, caution should still be used when using ceftriaxone in penicillin-sensitive patients. Caution should be used in people who have had previous severe penicillin allergies. It should not be used in hyperbilirubinemic neonates, particularly those who are premature because ceftriaxone is reported to displace bilirubin from albumin binding sites, potentially causing bilirubin encephalopathy. Concomitant use with intravenous calcium-containing solutions/products in neonates (≤28 days) is contraindicated  even if administered through different infusion lines due to rare fatal cases of calcium-ceftriaxone precipitations in neonatal lungs and kidneys. Mechanism of action
Ceftriaxone is a third-generation antibiotic from the cephalosporin family of antibiotics. It is within the β-lactam family of antibiotics. Ceftriaxone selectively and irreversibly inhibits bacterial cell wall synthesis by binding to transpeptidases, also called transamidases, which are penicillin-binding proteins (PBPs) that catalyze the cross-linking of the peptidoglycan polymers forming the bacterial cell wall. The peptidoglycan cell wall is made up of pentapeptide units attached to a polysaccharide backbone with alternating units of N-acetylglucosamine and N-acetylmuramic acid. PBPs act on a terminal D-alanyl-D-alanine moiety on a pentapeptide unit and catalyze the formation of a peptide bond between the penultimate D-alanine and a glycine unit on an adjacent peptidoglycan strand, releasing the terminal D-alanine unit in the process. The structure of ceftriaxone mimics the D-alanyl-D-alanine moiety, and the PBP attacks the beta-lactam ring in ceftriaxone as if it were its normal D-alanyl-D-alanine substrate.