1) However, there is no proven method for neutralizing LMWH. There are no human studies that convincingly demonstrate or refute a beneficial effect of protamine sulfate on bleeding associated with the use of LMWH (Massonnet-Castel et al, 1986; Andrassy, 1993).

1) It has been suggested that the degree of sulphonation of individual LMWH products, and their molecular size, are the primary reasons that these products are not completely neutralized by protamine (Crowther et al, 2002). Product-specific recommendations may be necessary for protamine to neutralize a particular drug.

a) Hypotension has been reported in the literature following intravenous protamine administration (Prod Info protamine sulfate injection, 2006; Welsby et al, 2005; Blaise, 1998; Horrow, 1985b; Holland et al, 1984; Shapira et al, 1982; Shapira et al, 1982; Cobb & Fung, 1982a; Jackson, 1970).
b) Hypotension is generally mild and of short duration; however, reports of prolonged hypotension accompanied by bradycardia, cyanosis, syncope, stupor, loss of consciousness, or momentary cardiac standstill have been described (Weiler et al, 1985). Hypotension following protamine has been attributed to peripheral vasodilation, depression of myocardial contractility, or both (Sharath et al, 1985; Goldman et al, 1969).
c) MECHANISM - Several investigators have suggested that protamine, heparin, or the heparin/protamine complex can affect the complement system (Takada & Takada, 1980; Rent et al, 1975; Siegel et al, 1974; Weiler et al, 1978). The complex of protamine and heparin may activate the classic pathway of the complement system in a similar manner to immune complexes (Rent et al, 1975).
d) Hypotensive reactions with protamine may result from direct, non-cytotoxic, nonimmune effects on mast cells (Schnitzler et al, 1981).
e) Based upon in vitro data, others have speculated that protamine in high concentrations is directly toxic to myocardial tissue in humans, whether given alone or following complex formation with heparin (Hendry et al, 1987).
f) In a retrospective study of hemodialysis patients, high anti-protamine IgG antibody titers and use of M-insulin identified a group with the highest occurrence of protamine associated hypotension (Tsai et al, 2009).
g) It is thought that the adverse hemodynamic effects of intravenous protamine can be minimized by giving the drug slowly (Horrow, 1985c; Michaels & Barash, 1983). However, cases of severe hypotension are still known to occur with the appropriate administration of the correct dose.
h) PEDIATRIC

a) Intravenous administration of protamine can cause bradycardia along with a sudden decline in blood pressure (Prod Info protamine sulfate injection, 2006; Konstadt, 1987a; Horrow, 1985c; Horrow, 1985a; Weiler et al, 1985).

a) In a study with anesthetized rats, protamine administration (dose range: 1 to 32 mg/kg) produced aberrant electrical activity. Dysrhythmias were observed at all doses and were associated with brief reductions in blood pressure. The ectopic beats were characterized as premature ventricular complexes (Pugsley et al, 2002).

a) RIGHT VENTRICULAR FAILURE was associated with protamine administration, presumably as a result of pulmonary vasoconstriction (Conahan et al, 1981; Lowenstein et al, 1983; Michaels & Barash, 1983). Alternatively, other investigators have reported no consistent detrimental effects on right ventricular performance with protamine in patients undergoing coronary artery bypass grafting (Hines & Barash, 1986). The mechanism of sporadic alterations in right ventricular function with protamine remain unclear.
b) CORONARY ARTERY SPASM - A case of severe coronary artery spasm occurred in a 65-year-old man with administration of protamine after cardiopulmonary bypass for mitral valve plasty and Maze's operation. After administration of protamine, severe systemic hypotension occurred suddenly with electrocardiographic ST-segment elevation and wide QRS intervals. Typical anaphylactic manifestations such as bronchospasm and rash were not present. Ultimately, the use of an intra-aortic balloon pump was needed to assist pulmonary circulation (Lee et al, 2005).

a) Potentially severe and irreversible circulatory collapse associated with myocardial failure and reduced cardiac output has developed with therapeutic use (Prod Info protamine sulfate injection, 2006; Frater et al, 1984; Holland et al, 1984; Vontz et al, 1982; Vierthaler & Becker, 1983; Weiler et al, 1985).
b) CASE REPORT - Life threatening cardiopulmonary failure following protamine reversal of heparin after cardiopulmonary bypass occurred in a 6 week-old girl. Critical pulmonary hypertension developed and severe hemorrhagic pulmonary edema result in severe hypoxia (Boigner et al, 2001).

a) CASE REPORT - Hypertension was also described with protamine administration in a 76-year-old woman with chronic renal failure undergoing hemodialysis (Andersen & Johnson, 1981). It was speculated that the excess protamine given to the patient to neutralize heparin effects released either histamine or serotonin, resulting in the rapid changes in blood pressure, heart rate, and breathing patterns.

a) Although hypotension and bradycardia are more likely to occur following overdose, hypertension has been observed (Prod Info protamine sulfate injection, 2006).

a) Cardiac arrest has been observed following protamine administration during vascular surgery and regional anesthesia (Chung & Miles, 1984; Menk, 1986). Both patients were diabetic and had been receiving NPH insulin, which suggests that severe reactions are more frequent in patients who are previously exposed to protamine.

a) According to a retrospective chart review, 13.2% of patients (7 of 53) undergoing cardiopulmonary bypass (CPB) who experienced an adverse event within 10 minutes after protamine administration died during the same hospital admission. The odds ratio (OR) for the occurrence of an adverse event 10 minutes after protamine administration and subsequent death was 5.50; after adjustment for confounding variables, the OR was 6.98 (p=0.017). In contrast to that 13.2% mortality rate, a mortality rate of 2.7% (6 of 223) was found for a comparison group who also had CPB and protamine, but did not experience an adverse event shortly after receiving protamine. All subjects received protamine via peripheral venous infusion for 5 minutes to reverse the anticoagulant effects of heparin. Study investigators identified 4 types of adverse events which occurred within 30 minutes of protamine administration and lasted longer than the 5-minute period of protamine infusion:
b) These events were considered 'adverse protamine events' in the absence of other measurable causes of hemodynamic compromise. For adverse protamine events classified as severe, the mortality rate was 23.5% compared with 8.3% among those with adverse protamine events not considered severe (severe events and mortality, p for trend=0.001). The authors estimated that protamine-related events could account for approximately 7% of all the deaths after CPB (Kimmel et al, 2002).
c) The incidence of protamine reactions in patients undergoing catheter ablation for atrial fibrillation is 1.2%. Although the incidence in this setting is low reactions tend to be dramatic and often with profound hypotension (Chilukuri et al, 2009).

a) ANAPHYLACTOID OR ANAPHYLACTIC REACTION: Dyspnea has been reported with protamine use and is likely attributable to an anaphylactoid or anaphylactic reaction. Anaphylactic reactions require prior exposure and sensitization to initiate IgE mediated mast cell degranulation and histamine release. An anaphylactoid reaction does not require prior sensitization and is triggered instead by non-IgE mechanisms which directly cause the release of these same mediators (Prod Info protamine sulfate injection, 2006). Wheezing and bronchospasm and increased airway resistance have also been observed (Weiler et al, 1985).

a) SUMMARY
b) CASE SERIES
c) CASE REPORTS

a) Acute lung injury and anasarca has been reported, developing approximately 30 minutes after protamine administration in several patients, none or whom had a history of protamine allergy (Horrow, 1985).

a) Lassitude has been reported with therapeutic use (Prod Info protamine sulfate injection, 2006).

a) Nausea and vomiting has been reported with therapeutic use (Prod Info protamine sulfate injection, 2006).

a) Protamine itself exerts mild anticoagulant effects (Perkash, 1980a; Horrow, 1985c). With very high doses, protamine has been demonstrated to cause reductions in fibrinogen concentrations (Weiler et al, 1985); however, this is not considered relevant as high doses are seldom employed clinically. Only minimal and transient effects have occurred on the coagulation system following protamine overdoses of up to 800 mg (Ellison et al, 1971a). Thus, it is doubtful that doses normally used in cardiopulmonary bypass procedures will produce excessive anticoagulation.

a) Bleeding may occur following overdose due to the potential anticoagulation effects of protamine. However, bleeding after protamine administration is more likely to be secondary to rebound anticoagulation, which may occur 30 minutes to 18 hours following the reversal of heparin with protamine administration (Prod Info protamine sulfate injection, 2006).

a) Heparin rebound has been reported with protamine in some patients following extracorporeal bypass procedures. Heparin rebound is a resurgence of anticoagulant (antithrombin) activity in a heparinized patient following adequate neutralizing doses of protamine (Shanberge et al, 1987a). This phenomenon has occurred within 30 minutes to 18 hours after cardiac surgery. Additional doses of protamine may be indicated in these patients based upon coagulation studies (heparin titration tests with protamine, plasma thrombin time) (Prod Info Protamine sulfate,, 1996.). The incidence of heparin rebound can be greatly reduced if a moderate excess of protamine (1.5:1, protamine to heparin) is administered following bypass procedures (Shanberge et al, 1987a). Rebound has also been reported with protamine in patients undergoing hemodialysis (Blaufox et al, 1966). The incidence of heparin rebound varies considerably; some studies suggest that it is never observed while others indicate an incidence of greater than 50% (Shanberge et al, 1987a).
b) The mechanism of heparin rebound remains unclear. Some investigators suggest that an increase in heparin concentration (free heparin) may occur as heparin returns from extravascular spaces or is liberated from intravascular surfaces (Shanberge et al, 1987a; Gollub, 1967). Another theory is that a naturally-occurring plasma protaminase may break apart the heparin/protamine complex, freeing the previously complexed heparin to reactivate antithrombin III (Fabian & Aronson, 1980; Shanberge et al, 1987a). Heparin rebound appears to be infrequent when an excess of protamine is administered after bypass procedures, whereas the incidence is greater when patients receive the minimal amount of protamine required to neutralize the heparin as determined by titration methods (Shanberge et al, 1987a; Kaul et al, 1979; Lambert et al, 1979). The use of excess amounts of protamine in this setting has been advocated by some investigators (Hanowell et al, 1983a; Shanberge et al, 1987a).
c) The neutralization of heparin activation of antithrombin III in plasma represents an equilibrium reaction that remains stable only in the presence of an excess of protamine (Shanberge et al, 1987a). It is speculated that a protamine-splitting plasma enzyme (protaminase) causes breakdown of the "excess" free protamine, resulting in instability of the complex and liberation of heparin, which reestablishes antithrombin activity (heparin rebound). It is felt that rebound can be produced by increased heparin levels or increased amounts of antithrombin III (transfusion of fresh frozen plasma). To minimize the possibility of heparin rebound, a moderate excess of protamine should be administered to neutralize the heparin (at least 1.5:1, protamine:heparin) assuming 1 mg of heparin is equivalent to 100 units. A reduction in the use of fresh frozen plasma after bypass procedures may also reduce the incidence of heparin rebound, but clinical studies are required to confirm this theory.
d) POSSIBLE PREVENTION OF BLEEDING

a) Mild and reversible leukopenia has been rarely observed following protamine administration (Horrow, 1985b; Weiler et al, 1985; Al-Mondhiry et al, 1985).

a) Mild and reversible thrombocytopenia has been described during protamine administration (Weiler et al, 1985; Horrow, 1985b; Horrow, 1985a). The mechanism of thrombocytopenia is unclear, but may involve activation of the complement system via the classic pathway or a direct toxic effect of the heparin/protamine complex on blood cells (Al-Mondhiry et al, 1985).

a) Skin flushing, urticaria, and angioedema have been reported with protamine administration in association with hypersensitivity reactions (Prod Info protamine sulfate injection, 2006; Weiler et al, 1985; Sanchez et al, 1982; Doolan et al, 1981). These symptoms are generally mild and are often accompanied by hypotension (Weiler et al, 1985). These symptoms may be mediated via anaphylactic or anaphylactoid reactions. They are clinically similar, however the underlying mechanisms differ. Anaphylactic reactions require prior exposure and sensitization to initiate IgE mediated mast cell degranulation and histamine release. An anaphylactoid reaction dose not require prior sensitization and is triggered instead by non-IgE mechanisms which directly cause the release of these same mediators.

a) These symptoms may be mediated via anaphylactic or anaphylactoid reactions. They are clinically similar, however the underlying mechanisms differ. Anaphylactic reactions require prior exposure and sensitization to initiate IgE mediated mast cell degranulation and histamine release. An anaphylactoid reaction dose not require prior sensitization and is triggered instead by non-IgE mechanisms which directly cause the release of these same mediators.
b) Reactions have been described following intravenous protamine administration, and may include relatively mild symptoms of flushing and feelings of warmth along with dyspnea. Severe reactions have included respiratory distress including bronchospasm, flushing, circulatory collapse and capillary leak (Prod Info protamine sulfate injection, 2006; Horrow, 1985b). Most anaphylactic reactions have occurred in patients who were previously exposed to protamine. However, infrequent reports of anaphylactic reactions with protamine have occurred in patients with a history of fish allergy, patients who developed a delayed capillary leak after cardiopulmonary bypass, and patients with catastrophic pulmonary vasoconstriction after cardiopulmonary bypass (Horrow, 1985b).
c) The exact mechanism has not been determined, but proposed theories include complement activation, histamine release, thromboxane induced vasoconstriction, nitric oxide production and antibody production (Prod Info protamine sulfate injection, 2006; Knape et al, 1981; Weiler et al, 1985; Porsche & Brenner, 1999; Carr & Silverman, 1999).
d) Nonimmune anaphylactoid mechanisms and complement-mediated reactions have also been implicated in serious protamine reactions (Weiler et al, 1985). The release of C3a and C5a and the subsequent activation of cyclo-oxygenase pathway of arachidonic acid metabolism resulting in thromboxane and prostaglandin release are thought to mediate the anaphylactic and anaphylactoid reactions caused by protamine (Hobbhahn et al, 1991).
e) VASECTOMIZED MEN: Anti-protamine IgG has been observed in approximately one-third of vasectomized men, which may place these patients theoretically at risk for developing adverse reactions to protamine (Prod Info protamine sulfate injection, 2006; Weiler et al, 1985a; Weiler et al, 1990). Patients with previous protamine exposure (including from NPH insulin) may also be at increased risk.
f) FISH ALLERGY: Protamine is commercially produced from salmon sperm or related species. Patients with fish allergy may be at greater risk of protamine reactions (Collins & O'Donnell, 2008). (Prod Info protamine sulfate injection, 2006). Infrequent reports of reactions with protamine have occurred in patients with a history of fish allergy and include delayed capillary leak after cardiopulmonary bypass, and catastrophic pulmonary vasoconstriction after cardiopulmonary bypass (Horrow, 1985c).
g) DIABETICS and prior insulin use, patients with previous protamine exposure (including use of NPH insulin) may also be at increased risk. In such cases of previous exposure, reactions could be anaphylactic (Nybo & Madsen, 2008).
h) CASE REPORT - A fatal anaphylactic reaction to protamine sulphate occurred in a diabetic patient undergoing femoropopliteal bypass surgery. Sensitization from prior use of NPH insulin was though to have been a risk factor in this case (Hakala & Suojaranta-Ylinen, 2000).

a) A positive immune response has been observed following skin testing with protamine in some individuals (Horrow, 1985b).
b) CASE REPORT - A 63-year-old diabetic man was receiving protaphane insulin and after two months he developed itchy erythematous plaques at the injection sites. Intradermal testing with protaphane insulin was positive with the formation of 12 mm erythematous plaques. Clinical evidence and cutaneous testing were consistent with delayed-type hypersensitivity to protamine. The patient was successfully changed to another insulin therapy with no further reactions (Raap et al, 2005).

a) The following doses are suggested for severe bleeding or large overdoses of selected LMWH(s):
b) DALTEPARIN: Slowly administer protamine 1 mg IV for every 100 anti-Xa international units of dalteparin given. A second infusion of protamine 0.5 mg per 100 anti-Xa international units of dalteparin may be given if aPTT measured 2 to 4 hours after the first infusion remains prolonged (Prod Info FRAGMIN(R) subcutaneous injection, 2014).
c) ENOXAPARIN: If enoxaparin was injected within the past 8 hours, the initial recommended dose of protamine 1% IV should equal the enoxaparin dose on a mg to mg basis (eg, protamine 1 mg to neutralize enoxaparin 1 mg). Protamine 0.5 mg IV per 1 mg of enoxaparin may be given if more than 8 hours have elapsed or a second dose of protamine is required. A second protamine 0.5 mg per 1 mg of enoxaparin may be given if aPTT measured 2 to 4 hours after the first infusion remains prolonged. Protamine may not be necessary if 12 or more hours have elapsed since the last enoxaparin dose (Prod Info Lovenox(R) subcutaneous injection, intravenous injection, 2013).
d) NADROPARIN CALCIUM: The initial recommended dose of protamine IV should equal the dose of nadroparin on a mg to mg basis. A second protamine 0.5 mg per 1 mg of nadroparin may be given if aPTT measured 2 to 4 hours after the first infusion remains prolonged (Prod Info FRAXIPARINE(R) FORTE injection solution, 2011; Prod Info FRAXIPARINE(R) injection solution, 2011).
e) TINZAPARIN: In clinical trials, overdoses of greater than 200 international units of tinzaparin produced bleeding complications in 16% of patients. For severe effects, slowly administer protamine 1 mg IV for every 100 anti-Xa international units of tinzaparin given. A second infusion of protamine 0.5 mg per 100 anti-Xa international units of tinzaparin may be given if aPTT measured 2 to 4 hours after the first infusion remains prolonged (Prod Info Innohep(R) subcutaneous injection, 2010).

a) LESS THAN 30 MIN: 1 mg per 100 units heparin received (Monagle et al, 2008).
b) 30 to 60 MIN: 0.5 to 0.75 mg per 100 units heparin received (Monagle et al, 2008).
c) 60 to 120 MIN: 0.375 to 0.5 mg per 100 units heparin received (Monagle et al, 2008).
d) GREATER THAN 120 MIN: 0.25 to 0.375 mg per 100 units heparin received (Monagle et al, 2008).
e) MAXIMUM DOSE: 50 mg
f) Patients who are allergic to fish, or have previously been exposed to protamine or protamine-containing insulin therapy may be at risk of developing hypersensitivity reactions to protamine sulfate (Monagle et al, 2004).