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Conjugation of penicillin G (<b>PenH</b>) with silver(I) ions forms a new CoMeD (conjugate of metal with a drug) with formula [Ag(pen)(CH₃OH)]₂ (<b>PenAg</b>). <b>PenAg</b> was characterized by a plethora of physical and spectroscopic techniques, which include in the solid state m.p.; elemental analysis; X-ray fluorescence (XRF) spectroscopy; scanning electron microscopy (SEM); energy-dispersive X-ray spectroscopy (EDX); FT-IR; and in solution: attenuated total reflection spectroscopy (FT-IR-ATR), UV&#8722;Vis, ¹H NMR, and atomic absorption (AA). The structure of <b>PenAg</b> was determined by NMR spectroscopy. Silver(I) ions coordinate to the carboxylic group of <b>PenH</b>, while secondary intra-molecular interactions are developed through (i) the nitrogen atom of the amide group in MeOD-d₄ or (ii) the sulfur atom in the thietane ring in deuterated dimethyl sulfoxide DMSO-<i>d₆</i>. The antibacterial activities of <b>PenAg</b> and the sodium salt of penicillin (<b>PenNa</b>) (the formulation which is clinically used) against Gram positive (<i>Staphylococcus epidermidis</i> (<i>S. epidermidis</i>) and <i>Staphylococcus aureus</i> (<i>S. aureus</i>)) and Gram negative (<i>Pseudomonas aeruginosa</i> (<i>P. aeuroginosa PAO1</i>)) bacteria were evaluated by the means of minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and inhibition zone (IZ). <b>PenAg</b> inhibits the growth of the Gram negative bacterial strain <i>P. aeuroginosa</i> with a MIC value of 23.00 &#177; 2.29 &#956;M, in contrast to <b>PenNa</b>, which shows no such activity (&gt;2 mM). The corresponding antimicrobial activities of <b>PenAg</b> against the Gram positive bacteria <i>S. epidermidis</i> and <i>S. aureus</i> are even better than those of <b>PenNa</b>. Moreover, <b>PenAg</b> exhibits no in vivo toxicity against <i>Artemia salina</i> at concentration up to 300 &#956;&#924;. The wide therapeutic window and the low toxicity, make <b>PenAg</b> a possible candidate for the development of a new antibiotic.