Ventricular excitability may generate re-entry ventricular arrhythmia.Most myocardial cells with an associated increased propensity to arrhythmia development have an associated loss of membrane potential. That is, the maximum diastolic potential is less negative and therefore exists closer to the threshold potential. Cellular depolarisation can be due to a raised external concentration of potassium ions K+, a decreased intracellular concentration of sodium ions Na+, increased permeability to Na+, or a decreased permeability to K+. The ionic basic automaticity is the net gain of an intracellular positive charge during diastole in the presence of a voltage-dependent channel activated by potentials negative to –50 to –60 mV.Myocardial cells are exposed to different environments. Normal cells may be exposed to hyperkalaemia; abnormal cells may be perfused by normal environment. For example, with a healed myocardial infarction, abnormal cells can be exposed to an abnormal environment such as with a myocardial infarction with myocardial ischaemia. In conditions such as myocardial ischaemia, possible mechanism of arrhythmia generation include the resulting decreased internal K+ concentration, the increased external K+ concentration, norepinephrine release and acidosis. When myocardial cell are exposed to hyperkalemia, the maximum diastolic potential is depolarized as a result of the alteration of Ik1 potassium current, whose intensity and direction is strictly dependent on intracellular and extracellular potassium concentrations. With Ik1 suppressed, an hyperpolarizing effect is lost and therefore there can be activation of funny current even in myocardial cells (which is normally suppressed by the hyperpolarizing effect of coexisting potassium currents).
Besifloxacin (INN/USAN) is a fourth-generation fluoroquinolone antibiotic. The marketed compound is besifloxacin hydrochloride. It was developed by SSP Co. Ltd., Japan, and designated SS734. SSP licensed U.S. and European rights to SS734 for ophthalmic use to InSite Vision Incorporated (OTC Pink: INSV) in 2000. InSite Vision developed an eye drop formulation (ISV-403) and conducted preliminary clinical trials before selling the product and all rights to Bausch & Lomb in 2003.The eye drop was approved by the United States Food and Drug Administration (FDA) on May 29, 2009, and marketed under the trade name Besivance. Pharmacodynamics
Besifloxacin is a fluoroquinolone that has a broad spectrum in vitro activity against a wide range of Gram-positive and Gram-negative ocular pathogens: e.g., Corynebacterium pseudodiphtheriticum, Moraxella lacunata, Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus hominis, Streptococcus mitis, Streptococcus oralis, Streptococcus pneumoniae and Streptococcus salivarius. Besifloxacin has been found to inhibit production of pro-inflammatory cytokines in vitro. The mechanism of action of besifloxacin involves inhibition of two enzymes which are essential for the synthesis and replication of bacterial DNA: the bacterial DNA gyrase and topoisomerase IV. Clinical trials indicated that Besifloxacin was 91% effective at eliminating the causative bacteria after five days, compared to 60% in the placebo group. This did not, however necessarily correlate with condition resolution, as bacterial presence is only a part of conjunctivitis. Medical use
Besifloxacin is indicated in the treatment of bacterial conjunctivitis caused by sensitive bacteria, as well as in the prevention of infectious complications in patients undergoing laser therapy for the treatment of cataracts.