Iron (III) complexes of ciprofloxacin, amoxicillin, and cloxacillin were synthesized and their aqueous solubility profiles, relative stabilities, and antimicrobial properties were evaluated. The complexes showed improved aqueous solubility when compared to the corresponding ligands. Relative thermal and acid stabilities were determined spectrophotometrically and the results showed that the complexes have enhanced thermal and acid stabilities when compared to the pure ligands. Antimicrobial studies showed that the complexes have decreased activities against most of the tested microorganisms. Ciprofloxacin complex, however, showed almost the same activity as the corresponding ligand. Job’s method of continuous variation suggested 1？:？2 metals to ligand stoichiometry for ciprofloxacin complex but 1？:？1 for cloxacillin complex. 1. Introduction Many drugs possess modified pharmacological, toxicological, and physicochemical properties when administered in the form of metal complexes [1]. Physicochemical properties of drugs are very pertinent to dosage forms and drug delivery and complex formation affects these properties, sometimes to advantage and sometimes adversely. Among the properties that may be altered upon complex formation are solubility, energy absorption, stability, partitioning behaviour, and chemical reactivity [2–4]. For many systems, it has been shown that the complex provides faster dissolution and greater bioavailability than the physical mixture. The processing characteristics (physical state, stability, flow ability, etc.) of the complexes may also be better than those of the free drugs [5]. In some cases, complexation has been found to improve biological activity [6–11]. Quinolones are complexing agents for a variety of metal ions including alkaline earth and transition metal ions. Reports indicate that the coordination of quinolones to metal ions such as Cu (II), Mg (II), and Ca (II) appears to be important for the activity of the quinolone antibiotics [11–13]. Coordination compounds may also release valuable trace elements needed for maintenance of life when they are administered as drugs. The structure-activity relationship of drugs could be predicted by complexation. If a particular biological activity of a drug is lost or diminished on complexation with metal ions, it would be reasonable to suggest that one or more of the groups bonded to the metal is necessary for the activity. Drug complexation experiments can also help medicinal chemists to predict some dosage form incompatibilities, explain the mode of action of some drugs, and
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