Precipitation of Sugammadex With Nicardipine And Labetalol

Background There is a paucity of clinical data about whether sugammadex forms precipitates with other medications. This laboratory experimental study was performed to determine the drugs that produce precipitate with sugammadex. Methods Samples of 1 mL of sugammadex were prepared in transparent cylinders, to which 1 mL of test drugs (rocuronium, neostigmine, glycopyrrolate, atropine, nitroglycerin, dobutamine, dopamine, epinephrine, vasopressin, norepinephrine, phenylephrine, ephedrine, esmolol, nicardipine, labetalol) was then added. The precipitation reaction was observed by eyes and light microscope. The pH of each drugs before and after mixing with sugammadex was measured.


Introduction
Precipitation reactions in which two ions in aqueous solution bond together to form an insoluble solid occur frequently between drugs. Alkalinised local anesthetics (e.g. ropivacaine, bupivacaine) and corticosteroid, thiopental sodium and aminosteroidal neuromuscular blocking agents (e.g. rocuronium, vecuronium) are known to form precipitates via acid-base reactions, which can lead to unexpected medical events, such as occlusion of intravenous (IV) tubing or embolism [1][2][3]. A great deal of care is required when applying anesthesia, because various drugs are often injected together within a short time.
Sugammadex antagonises aminosteroidal muscle relaxants by encapsulation. It allows rapid and complete reversal and can even be used for deep and profound neuromuscular blockade. Compared with neostigmine, sugammadex minimises residual neuromuscular blockade and does not have cholinergic side effects, such as bradycardia, nausea and vomiting [4]. Therefore, sugammadex is increasingly being used in anesthesia.
However, there is a paucity of clinical data about whether sugammadex forms precipitates with other medications widely used in clinical practice. Only a few short reports of crystal formation of sugammadex with amiodarone, dobutamine, protamine and labetalol have been published to date [5][6][7]. This in vitro study was performed to determine the drugs commonly administered with sugammadex that produce such precipitation reactions.

Methods
Sugammadex and a number of drugs commonly used in anesthesia, i.e. rocuronium, neostigmine, glycopyrrolate, atropine, nitroglycerine, dobutamine, dopamine, epinephrine, vasopressin, norepinephrine, phenylephrine, ephedrine, esmolol, labetalol and nicardipine, were prepared. All drugs were tested at the concentrations used in the clinical setting. Table 1 provides information on the manufacturer and undiluted and diluted concentrations of the drugs. Nitroglycerin, vasopressin and norepinephrine were diluted with 5% dextrose water, while epinephrine, phenylephrine and ephedrine were diluted with 0.9% normal saline. The pH of each drug was measured using a pH meter (inoLab® pH 7110, xylem Analytics Germany GmbH, Weilheim, Germany). Samples of 1 mL of sugammadex were prepared in transparent cylinders, to which 1 mL of test drug was then added. Each mixture was observed by eye and light microscopy (BX-43; Olympus, Tokyo, Japan), and images were acquired. The existence and appearance of the particles of each mixture were evaluated by light microscopy. After observation, the pH of mixtures was determined using the pH meter.  Table 2 lists the pH of the drugs before and after mixing. The most marked reaction was observed with nicardipine, where white crystals formed on the top of the mixture and remained undissolved. The second strongest reaction was seen with labetalol, where the mixture appeared turbid to the naked eye but the precipitate dissolved after several minutes. There was no visible precipitate in the other mixtures. Figure 1 shows the control and sugammadex/nicardipine and sugammadex/labetalol mixtures. Figure 2 shows the results of microscopic analysis of the mixtures. Circular aggregates measuring 5-10 µm in diameter were observed in the mixture of nicardipine and sugammadex contained oating circular aggregates 2-6 µm in diameter. No visible precipitate was observed in the other mixtures.

Discussion
The results showed that sugammadex reacts with nicardipine and labetalol under in vitro, producing precipitates that could be observed by both the naked eye and light microscopy.
A previous study also reported the formation of white precipitates when sugammadex was mixed with labetalol and, to a lesser degree with epinephrine, vasopressin and hydralazine [7]. Another experiment, in which 57 drugs used in anaesthesia were mixed with sugammadex, indicated that precipitation occurred with amiodarone (50 mg/ml), dobutamine (12.5 mg/ml), and protamine (1000 IU/ml); however, nicardipine and labetalol were not included in this previous study [5]. In contrast, we observed no precipitation in the mixtures of sugammadex with epinephrine, vasopressin or dobutamine. These discrepancy between the studies were probably due to differences in the drug concentrations and manufacturers.
Sugammadex, which is modi ed gamma-cyclodextrin, has a hydrophobic internal cavity and eight hydrophilic side chains. These structural properties make the complexes of lipophilic molecules and sugammadex water-soluble [8,9]. Sugammadex and rocuronium form a rigid complex by two mechanisms. Firstly, hydrophobic interactions trap steroidal neuromuscular blocking agents in the cavity. Secondly, electrostatic binding occurs between the negatively charged carboxyl side chain of sugammadex and the positively charged quaternary nitrogen of rocuronium [10,11]. In addition to aminosteroidal neuromuscular blocking agents, caution is required when using some other medications because they react with sugammadex. For example, the hormonal steroidal contraceptive, etonogestrel, is captured at a rate of 34% by 4 mg/kg sugammadex due to hydrophobic interactions [12]. Interactions due to the side chains of sugammadex have also been reported. For example, negatively charged sugammadex has been reported to react with positively charged protamine to form precipitate [6]. This mechanism may explain our experimental results, i.e. the positively charged amino groups of nicardipine and labetalol were assumed to react with the negatively charged sugammadex. These ndings have clinical implications for anaesthesiologists. Firstly, nicardipine, labetalol and sugammadex can be administered within a short time in emergence situations. Insu cient uid ushing between administrations of these drugs could lead to precipitate formation, resulting in occlusion within the IV tubing. Secondly, changes in the e cacy of sugammadex are also possible, suggesting that residual neuromuscular blockade can occur despite administration of the appropriate dose. Thirdly, the precipitate may form emboli that obstruct blood vessels, resulting in organ damage. Red blood cells have a diameter of 7 µm, so particles larger than this size can clog capillaries. In animal experiments, it has been reported that particles larger than 30 µm caused pulmonary embolism and cerebral infarction [13,14].
This study had several limitations. Firstly, not all drug classes were included in the investigation. Additional experiments on the interactions of sugammadex with sedatives, narcotic drugs, analgesics, anti-emetics and uids are required. Secondly, the drugs in this study were selected based on the author's clinical setting. Drugs made by other manufacturers may show different reactions due to differences in additives or concentrations. Thirdly, it is not yet clear how various substances and enzymes in the plasma affect precipitation. The temperature and pH of plasma are also different from the experimental environment in the present study. Further studies regarding the effects of these reactions on the e cacy of sugammadex are required.

Conclusions
In conclusion, sugammadex formed precipitate when mixed with nicardipine or labetalol in vitro. Su cient uid ushing is required between injections of each drug to prevent these reactions.

Abbreviations IV: intravenous
Declarations Ethics approval and consent to participate Ethic approval and patient consent was waived due to the retrospective design.

Consent for publication
Not applicable Availability of data and materials The datasets generated and analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests