In the present study, we demonstrate that the N
-chloramines NCT, NVC-422, and NVC-612 have anticoagulant activity and retain their broad-spectrum antimicrobial activities in the presence of up to 75% human blood. These two critical properties make NCT, NVC-422, and NVC-612 potential CVC lock solutions for the prevention of CVC-related bloodstream infections and catheter blockage. Since tolerability has been shown for 1% (55 mM) aqueous NCT solution in several clinical trials and at different body sites, for instance, the skin, outer ear canal, and the eye (9
), and also for 1.5% (61 mM) NVC-422 gel on the skin (11
), a concentration of about 1% NCT, NVC-422, and NVC-612 in aqueous or buffered solution is estimated to be preferable for the development of these compounds as catheter lock solutions. This is confirmed by all presently available data or considerations on safety (see below). Addition of heparin is conceivable, but the benefit remains to be investigated.
The anticoagulant activity was dose dependent, and the activity of a concentration of 55 mM NCT, which is generally applied therapeutically (9
), by far exceeded the test limits in the pilot tests. To gain numeric results, which enabled investigation of the combined effect with heparin and a reasonable comparison with previous literature on active chlorine compounds, we applied lower concentrations for the more comprehensive experiments. NCT (1.38 mM), NVC-422 (1.02 mM), and NVC-612 (1.38 mM) still had anticoagulant activity in all main coagulation tests in human blood (). These results confirm those of a previous study, in which it was found that NaOCl, chloramine T, and NCT (prepared from hypochlorous acid and taurine and not from the sodium salt, as in our study) at concentrations of 2 to 3 mM oxidize and inactivate plasminogen activator inhibitor-1, fibrinogen, factor V, factor VIII, and factor X and inhibit platelet aggregation at 1 mM (22
). The latter effect has recently been confirmed for NCT, N
-dichlorotaurine, and N
). Moreover, the inhibition of primary and secondary aggregation of thrombocytes and of the release of the contents of their dense granules by chloramines has been demonstrated (15
). Because of these results, human granulocytes have been considered to participate in physiologic thrombolysis (21
). The absence of any influence on the D-dimer test fits with the observed anticoagulant effect and absence of formation of fibrin. Thus, no cleavage products of fibrin occur. The significance of our study compared to the previous studies is that NCT in its clinically applied form (prepared from the crystalline sodium salt [8
]) and its novel analogs NVC-422 and NVC-612 were tested in a setting of experiments designed for their use as catheter lock solutions.
Besides a limited additive anticoagulant effect, there was no interaction with heparin, which is widely used to avoid clotting of central venous catheters. Since it is presently unknown whether or not chloramines can replace heparin for that purpose, it is conceivable that a combination of both compounds could provide an antimicrobial and an anticoagulant effect. Heparin consists of sulfonated glycosaminoglycans (glucosamine and glucuronic acid) and contains amidic groups, which do not react with NCT, suggesting compatibility between heparin and NCT (8
Efficacy criteria are that the lock solution has to be antimicrobial even in the presence of blood on the tip of the catheter or trace amounts leaked back into the catheter (20
). Active chlorine compounds are known to be consumed by organic substances, mainly by sulfhydryl, thio, and aromatic compounds (6
). Despite this, NVC-422, NVC-612, and NCT at a concentration of 55 mM, which appears to be very suitable for most clinical applications (9
), continued to kill bacteria even in 50 to 75% blood. Only 100% blood largely prevented bacterial killing. Differences between the three tested chloramines are small and are probably irrelevant for practical use. Since catheters leading to blood vessels are irrigated with saline after use and the instillation of a lock solution further dilutes possible blood residues, only low concentrations of organic matter remain to consume any of the chloramines. Therefore, it is likely that they will have sufficient antimicrobial efficacy as lock solutions in vivo
. This is confirmed by the finding that NCT had microbicidal activity down to 13.8 to 5.5 mM in 10% blood. On the other hand, these results () clearly show that 55 mM should be preferred regarding efficacy. Its tolerability seems probable, as discussed in the following.
Regarding the safety of catheter lock solutions, no systemic toxic side effects should occur in case of leakage into the bloodstream (3
). Other chloramines, namely, N
-dichlorotaurine and N
-chlorophenylalanine, had antithrombotic activity and obviously were well tolerated when applied intravenously into mice at concentrations of 3.4 to 6.8 mg/kg of body weight (0.25 to 0.37 mM) and 13.6 mg/kg (1 mM), respectively (15
). Their lethal doses causing death of 50% of mice were 48 and 105 mg/kg, respectively (15
). Another active chlorine compound consisting of a chlorodioxide, tetrachlorodecaoxide (WF10) (7
), is already in use as an intravenous infusion in humans for immune stimulation and treatment of postradiation chronic inflammatory cystitis and proctitis (25
). A comprehensive battery of good laboratory practice safety pharmacology and toxicology studies has been conducted to support the use of NVC-422 in a number of clinical indications under several investigational new drug dossiers (4
). Concentrations up to 80 mg/kg were tested intravenously in animals. Even in the case that 10 ml of a 1% NVC-422 or 1% NCT solution (containing 100 mg of drug) was accidentally applied intravenously in humans, this would amount to 1.5 mg/kg for a 70-kg person, which is more than 50 times below the 50% lethal dose of NVC-422 and more than 30 times below that of N
-dichlorotaurine in mice (4
). All these data and considerations may predict a high degree of safety of small amounts of NCT, NVC-422, and NVC-612 entering the circulation.
The results of this study confirm that millimolar concentrations of NCT, NVC-612, and NVC-422 have broad-spectrum microbicidal activity in blood and anticoagulant properties, which suggest their further investigation as catheter lock solutions.