[M. Gohel, T. Patel and Sh. Bariya, Studies in preparation and evaluation of pH-independent sustained-release matrix tablets of verapamil HCl using directly compressible Eudragits, Pharm. Dev. Technol.8 (2003) 323-333; DOI: 10.1081/PDT-120024686.10.1081/PDT-120024686]Search in Google Scholar
[K. Gabr, Effect of organic acids on release patterns of weakly basic drugs from innert sustained release matrix tablets, Eur. J. Pharm. Biopharm.38 (1992) 199-202.]Search in Google Scholar
[M. Dimitrov and N. Lambov, Study of verapamil hydrochloride release from compressed hydrophilic Polyox-Wsr tablets, Int. J. Pharm.189 (1999) 105-111; DOI: 10.1016/S0378-5173(99) 00242-2.]Search in Google Scholar
[A. Tatavarti, K. Menta, L. Augsburger and S. Hoag, Influence of methacrylic and acrylic acid polymers on the release performance of weakly basic drugs from sustained release hydrophilic matrices, J. Pharm. Sci.93 (2004) 2319-2331; DOI: 10.1002/jps.20129.10.1002/jps.20129]Search in Google Scholar
[A. Streubel, J. Siepmann, A. Dashevsky and R. Bodmeier, pH-independent release of a weakly basic drug from water-insoluble and -soluble matrix tablets, J. Control. Rel.67 (2000) 101-110; DOI: 10.1016/S0168-3659(00)00200-5.10.1016/S0168-3659(00)00200-5]Search in Google Scholar
[P. Timmins, A. M. Delargy and J. R. Howard, Optimization and characterization of a pH-independent extended-release hydrophilic matrix tablet, Pharm. Dev. Technol.2 (1997) 25-31.10.3109/10837459709022606]Search in Google Scholar
[R. J. MacRae and J. S. Smith, Controlled-release Pharmaceutical Formulations Containing Low Molecular Weight Polyethylene Oxide and Hydroxypropylmethyl Cellulose, WO Pat. 97/18814, 29 May 1997; ref. Chem. Abstr.127 (1997) 55911u; DOI: 10.1016/0032-3861(94)90913-X.10.1016/0032-3861(94)90913-X]Search in Google Scholar
[K. Nam, J. Watanabe and K. Ishihara, pH-modulated release of insulin entrapped in a spontaneously formed hydrogel system composed of two water-soluble phospholipid polymers, J. Biomater. Sci., Polym. Ed.13 (2002) 1259-1269; DOI: 10.1163/156856202320892993.10.1163/156856202320892993]Search in Google Scholar
[M. Blanco, J. Rego and M. Huglin, Drug release with simultaneous dimensional changes from a new copolymeric hydrogel, Polymer35 (1994) 3487-3491; DOI: 10.1016/0032-3861(94)90913-X.10.1016/0032-3861(94)90913-X]Search in Google Scholar
[G. Georgiev, E. Kamenska, E. Vassileva, I. Kamenova, V. Georgieva, S. Iliev and I. Ivanov, Properties and biomedical application of polyzwitterions, Ann. Univ. Sofia, Chem.98-99 (2005) 305-325; ref. Chem. Abst.147 (2007) 196825.]Search in Google Scholar
[I. Ivanov, I. Kamenova, V. Georgieva, E. Kamenska and G. Georgiev, Mixed surfactant-polyzwitterion self-assemblies in aqueous solutions, Colloid Surf. A. Physicochem. Eng. Asp.282-283 (2006) 129-133; DOI: 10.1016/j.colsurfa.2006.02.038.10.1016/j.colsurfa.2006.02.038]Search in Google Scholar
[Ch. Smilkov, I. Kamenova, E. Kamenska, Ch. Betchev and G. Georgiev, Synthesis, Morphology and Structural Characterization of Polysulfobetaine Copolymers as Potential Materials for Medical Applications, in PPS-21: Proceedings of the 21st Annual Meeting of the Polymer Processing Society, Leipzig, June 19-23, 2005, Halle/S. 2005, p. 148.]Search in Google Scholar
[G. Georgiev, A. Tzoneva, L. Lyutov, S. Iliev, I. Kamenova, V. Georgieva, E. Kamenska and A. Bund, Electrostimulated shift of the precipitation temperature of aqueous polyzwitterionic solutions, Macromol. Symp.210 (2004) 393-401; DOI: 10.1002/masy.200450644.10.1002/masy.200450644]Search in Google Scholar
[G. Georgiev, I. Kamenova, V. Georgieva, E. Kamenska, R. Hempelmann and H. Natter, Poly(dimethylaminoethylmethacryloylpropanesulfonate) suitable polymer additive for pulsed electrodeposition of nanocrystalline nickel, J. Appl. Polym. Sci.102 (2006) 2967-2970; DOI: 10.1002/ app.24574.10.1002/app.24574]Search in Google Scholar
[G. Georgiev, E. Kamenska, E. Vassileva, I. Kamenova, V. Georgieva, S. Iliev and I. Ivanov, Self-assembly, antipolyelectrolyte effect and nonbiofouling properties of polyzwitterions, Biomacro-molecules7 (2006) 1329-1334; DOI: 10.1021/bm050938q.10.1021/bm050938q]Search in Google Scholar
[E. Kamenska, E. Vassileva, I. Kamenova, A. Tzoneva, V. Georgieva, S. Iliev and G. Georgiev, A new approach to the description and control of the unique biocompatibility of polyzwitterions, Bulg. Chem. Commun.38 (2006) 49-54.]Search in Google Scholar
[J. Bredas, R. Chance and R. Silbey, Head-head interactions in zwitterionic associating polymers, Macromolecules21 (1988) 1633-1639; DOI: 10.1021/ma00184a019.10.1021/ma00184a019]Search in Google Scholar
[S. Tsonchev, A. Troisi, G. Schatz and M. Ratner, All-atom numerical studies of self-assembly of zwitterionic peptide amphiphiles, J. Phys. Chem. B.108 (2004) 15278-15284; DOI: 10.1021/jp04788.0e.]Search in Google Scholar
[M. Huglin and J. Rego, Influence of a salt on the properties of hydrogels of 2-hydroxyethyl methacrylate with a sulfobetaine comonomer, Macromolecules26 (1993) 3118-3126; DOI: 10.1021/ ma00064a020.10.1021/ma00064a020]Search in Google Scholar
[A. Lowe and C. McCormick, Synthesis and solution properties of zwitterionic polymers, Chem. Rev.102 (2002) 4177-4190; DOI: 10.1021/cr020371t.10.1021/cr020371t]Search in Google Scholar
[A. Elkheshen, Interaction of verapamil hydrochloride with carbopol 934P and its effect on the release rate of the drug and the water uptake of the polymer matrix, Pharm. Dev. Ind. Pharm.27 (2001) 925-934; DOI: 10.1081/DDC-100107673.10.1081/DDC-100107673]Search in Google Scholar
[E. Kamenska, B. Kostova, I. Ivanov, D. Rachev and G. Georgiev, Emulsifier-free emulsion copolymerization of vinyl acetate-3-dimethyl(methacryloyloxyethyl)-ammonium propane sulfonate and swelling behavior of their copolymer matrices, Macromol. React. (2007) 553-562; DOI: 10.1002/mren.200700013.10.1002/mren.200700013]Search in Google Scholar
[United States Pharmacopoeia 28 - National Formulary 23, USP Convention, Rockville 2005, pp. 2412-2414.]Search in Google Scholar
[H. Vogelpoel, J. Welnik, G. Amidon, H. Junginger, K. Midha, H. Möller, M. Oling, V. Shah and D. Barends, Biowaiver monographs for immediate release solid oral dosage forms based on biopharmaceutics classification system (BCS) literature data: Verapamil hydrochloride, Propanolol Hydrochloride, and Atenolol, J. Pharm. Sci.93 (2004) 1945-1956; DOI: 10.1002/jps.20131.10.1002/jps.20131]Search in Google Scholar
[Drug Information - American Hospital Formulary Service (DI-AHFS) (Ed. G. K. McEvoy), American Society of Health-System Pharmacists, Bethesda (MD) 1995, pp. 1148-1152.]Search in Google Scholar
[W. Lee and C. Chen, Poly(2-hydroxyethyl methacrylate-co-sulfobetaine) hydrogels. II. Synthesis and swelling behaviors of the [2-hydroxyethyl methacrylate-co-3-dimethyl(methacryloyloxyethyl) ammonium propane sulfonate] hydrogels, J. Appl. Polym. Sci.69 (1998) 2021-2034; DOI: 10.1002/(SICI)1097-4628(19980906)69:10<2021::AID-APP14>3.0.CO;2-4.10.1002/(SICI)1097-4628(19980906)69:10<2021::AID-APP14>3.0.CO;2-4]Search in Google Scholar
[A. Kasim, M. Whitehouse, C. Ramachandran, M. Bermejo, H. Lennernäs, S. Hussain, H. Junginger, S. Stavachansky, K. Midha, V. Shah and G. Amidon, Molecular properties of WHO essential drugs and provisional biopharmaceutical classification, Mol. Pharm.1 (2004) 85-96; DOI: 10.1021/mp034006h.10.1021/mp034006h]Search in Google Scholar