Review Nanoparticles as drug delivery systems Agnieszka Z. Wilczewska 1 , Katarzyna Niemirowicz 2 , Karolina H. Markiewicz 1 , Halina Car 2 Institute of Chemistry, University of Bialystok, al. J. Pilsudskiego 11/4, PL 15-433 Bia³ystok, Poland Department of Experimental Pharmacology, Medical University of Bialystok, Szpitalna 37, PL 15-295 Bia³ystok, Poland Correspondence: Halina Car, e-mail: hcar@umb.edu.pl (concerning medical applications); Agnieszka Z. Wilczewska, e-mail: agawilcz@uwb.edu.pl (concerning chemistry of nanoparticles) Abstract: Controlled drug delivery systems (DDS) have several advantages compared to the traditional forms of drugs. A drug is transported to the place of action, hence, its influence on vital tissues and undesirable side effects can be minimized. Accumulation of therapeutic compounds in the target site increases and, consequently, the required doses of drugs are lower. This modern form of therapy is espe- cially important when there is a discrepancy between the dose or the concentration of a drug and its therapeutic results or toxic ef- fects. Cell-specific targeting can be accomplished by attaching drugs to specially designed carriers. Various nanostructures, including liposomes, polymers, dendrimers, silicon or carbon materials, and magnetic nanoparticles, have been tested as carriers in drug delivery systems. In this review, the aforementioned nanocarriers and their connections with drugs are analyzed. Special atten- tion is paid to the functionalization of magnetic nanoparticles as carriers in DDS. Then, the advantages and disadvantages of using magnetic nanoparticles as DDS are discussed. Key words: drug delivery system, nanocarriers, nanoparticles, magnetic nanoparticles, targeting therapy Introduction Delivering therapeutic compound to the target site is a major problem in treatment of many diseases. A conventional application of drugs is characterized by limited effectiveness, poor biodistribution, and lack of selectivity [111]. These limitations and draw- backs can be overcome by controlling drug delivery. In controlled drug delivery systems (DDS) the drug is transported to the place of action, thus, its influence on vital tissues and undesirable side effects can be minimized. In addition, DDS protects the drug from rapid degradation or clearance and enhances drug concentration in target tissues, therefore, lower doses of drug are required [111]. This modern form of ther- apy is especially important when there is a discrep- ancy between a dose or concentration of a drug and its therapeutic results or toxic effects. Cell-specific targeting can be achieved by attach- ing drugs to individually designed carriers. Recent de- velopments in nanotechnology have shown that nano- particles (structures smaller than 100 nm in at least one dimension) have a great potential as drug carriers. Due to their small sizes, the nanostructures exhibit unique physicochemical and biological properties (e.g., an enhanced reactive area as well as an ability to cross cell and tissue barriers) that make them a favor- able material for biomedical applications. 1020