We report, to the best of our knowledge, the first Raman sensor for antibiotics spiked in human plasma using silicon nitride waveguides functionalized with a mesoporous silica top-cladding. Leveraging waveguiding signal enhancement, chemical enrichment, and molecular sieving, we demonstrate detection of 1 mg/l ceftazidime in plasma within 2 min. Ceftazidime quantification is achieved in plasma over 0, 20, 40, and 60 mg/l, demonstrating its potential for clinical use. Requiring minimal sample preparation, this method has great potential for point-of-need monitoring for optimal antibiotic therapy.