Drug
A pharmaceutical, which may result in allergy symptoms in sensitised individuals.

Allergen Exposure

Geographical distribution
Protamines are proteins that, in nature, are bound to nuclear material in fish sperm heads. Protamines are strongly alkaline polycationic proteins of around 4.5 kDa in size, containing multiple positively charged arginine residues (1).

Commercially available Protamine is prepared from sperm (milt) or matured testes of salmon or related species of fish, which has been defatted, precipitated with alcohol and sodium chloride, and then depyrogenated (2).

During the 1930’s, 2 clinical uses for Protamine were discovered: to neutralise the anticoagulant effect of heparin, and to slow the absorption of insulin, thereby reducing the frequency of insulin injections required to achieve euglycemia.

During surgery requiring cardiopulmonary bypass and most perfusion procedures, including vascular surgery, cardiac catherterisation, dialysis and phoresis, unfractionated heparin is utilised to prevent blood clotting. Neutralisation of heparin post-procedure is performed with an intravenous infusion of Protamine. Heparin is a polyanionic mucopolysaccharide that induces anti-coagulation by activating antithrombin III. The polycationic Protamine combines ionically with the polyanionic heparin to form a stable complex that has no anticoagulant activity. One milligram of Protamine neutralises approximately 90 USP U of heparin activity derived from lung tissue or about 115 USP U of heparin activity derived from intestinal mucosa. Heparin disappears rapidly from the circulation, and therefore the dose of Protamine required will also decrease rapidly with the time elapsed following IV injection of heparin (2).

Protamine sulfate is also used complexed to insulin to delay absorption. The complex is called neutral Protamine Hagedorn (NPH) insulin or isophane insulin (e.g., Mixtard® from Novo Nordisk). NPH insulin contains 0.3-0.5 mg Protamine/100 U of insulin; there is also Protamine-zinc insulin (PZI), containing 1-1.7 mg Protamine/100 U of insulin (2).

Protamine solutions contain paraben compounds as antimicrobial agents (3).

Allergens

Onc m Protamine, isolated from Rainbow trout (Salmo gairdneri).

Potential Cross-reactivity

As Protamine is produced from the sperm or matured testes of Salmon or related species of fish, a group theoretically at risk for IgE mediated reactions to protamine are individuals allergic to fish that may have serum antibodies directed to Protamine. Furthermore, commercial Protamine preparations may hypothetically be contaminated with other fish antigens that fish-allergic patients might react to. To date, studies supporting the increased risk of Protamine reactions in fish-allergic patients are lacking and limited to case reports (2). For instance, in a study of 2 subjects who had experienced anaphylaxis to Salmon, serum from these patients demonstrated high binding to Salmon that was not inhibited by preincubation of sera with 500 or 1000 micrograms of Protamine. However, serum from a patient who experienced anaphylaxis from Protamine was demonstrated to be indistinguishable from sera from controls in ELISA tests for IgE to Salmon, and anti-Protamine IgE could not be demonstrated. The authors concluded that 1) serum IgE antibodies to Salmon is not inhibited by Protamine, and 2) serum from a patient experiencing a severe reaction to Protamine did not contain IgE antibodies to Salmon or Protamine. The authors concluded from this study that the notion that there is cross-reactivity between IgE to Salmon and Protamine sulfate was not supported, or at least not in the cases evaluated (4).

Clinical Experience

IgE-mediated reactions
With its increased use have come increased reports of adverse Protamine reactions. Protamine may elicit both immune and non-immune adverse reactions through multiple mechanisms dependent on its ionic charge and antigenicity (2, 5-8).

Intravenous administration of Protamine may be associated with severe anaphylactic and anaphylactoid reactions (9).

Reactions to Protamine vary from mild ones, such as erythema, urticaria (2) and transient mild elevations in pulmonary artery pressure (10) to more severe reactions, which include pulmonary oedema with the loss of capillary membrane integrity (11-13) bronchospasm (14) decrease in systemic vascular resistance, systemic hypotension without changes in pulmonary artery pressure (15) myocardial depression (16) vasodilation with decreased systemic and pulmonary vascular resistance (17) and, although uncommon, cardiovascular collapse and death (1-2, 18-26).  Anaphylactoid reactions and anaphylaxis mediated by IgE or IgG antibodies (8, 27) occasionally resulting in death, have also been described (4, 18, 28-30).

The exact mechanisms by which Protamine produces these adverse reactions are not completely understood and may involve the generation of anaphylatoxins and prostanoids either from Protamine-heparin complexes or complement-fixing anti-Protamine IgG antibodies, from inhibition of plasma Carboxypeptidase N, from crosslinking of cell-surface anti-Protamine IgE on mast cells and basophils with subsequent mediator release, or from potentiation of IgE-mediated release of histamine through a polycationin-recognition site (1-2).

Other mechanisms
It has been suggested that the majority of anaphylactic/anaphylactoid reactions are associated with complement activation and the release of anaphylatoxins C3a and C5a. These activate the cyclo-oxygenase pathway of the arachidonic acid metabolism in yet unidentified cells, probably within the lung. As a result, thromboxane and prostaglandins are released. Thromboxane is the pivotal mediator responsible for the pulmonary vasoconstriction and, presumably, also for the bronchospasm during Protamine reactions (3).

The incidence of adverse reactions to Protamine sulfate range from 0.06% to 27% and vary from mild urticaria to anaphylactic shock and death (31).

Cardiac surgery
The incidence of adverse reactions to Protamine has been reported as varying from 0.06% to 10.7% (32). An early study reported a high prevalence, of about 27%, for major adverse events during cardiac investigation when heparin coagulation was reversed by intravenous Protamine injection (22). Other studies reported an incidence of anaphylaxis between 0.6% (1 of 160) to 2% (1 in 50). A prospective study was done of cardiac surgical patients with prior vasectomies and fish allergies, and of a cohort of 3,245 consecutive cardiac surgical patients requiring cardiopulmonary bypass over a 2-year period.  In this cohort, the study investigated Protamine-containing insulin use and clinical evidence of adverse reactions after Protamine administration for heparin reversal after cardiopulmonary bypass. Clinical reactions to Protamine did not occur in the 6 patients with fish allergies or the 16 patients with prior vasectomies. There was 1 reaction (0.6%) among 160 patients with neutral Protamine Hagedorn insulin-dependent diabetes. The incidence of clinical reactions in the other patients was 2/3085 (0.06%) (33).

A recent study reported that the prevalence of anaphylactoid reactions was estimated to be 109 (7.4%) among 1,504 cardiosurgical patients, and that Protamine was a cause in 12.1% (34). An epidemiological survey was done of anaphylactoid reactions occurring during anaesthesia obtained in France. The study involved 1,750 patients tested in 27 diagnostic centres from January 1992 to June 1994. Reactions of IgE-dependent anaphylaxis were diagnosed in 1,000 patients (57.8%); drugs given during anaesthesia but not primarily for anaesthesia, such as aprotinine and Protamine, were blamed for 2.2% (35).

Anaphylaxis may be the sole event (36), but may also be combined with other pathophysiological mechanisms and symptoms. Three of 9 patients experienced adverse reactions to Protamine sulphate: 1 of these patients suffered a fatal IgE-mediated anaphylactic episode, and 2 developed audible wheezing (37). A study reported on 4 patients who developed severe adverse reactions: immediate anaphylaxis, or delayed onset with profound vascular damage presenting as noncardiogenic pulmonary oedema, or total vascular collapse with prolonged hypotension and anasarca (12).

Although adverse reactions to Protamine were initially reported to be infrequent and usually mild, in 1985 the first fatal case of type I anaphylaxis resulting from Protamine was observed. This patient had previously been sensitised to Protamine during cardiac catheterisation and had high levels of Protamine-specific immunoglobulin-E in the serum (38).

Subsequently, many anaphylactic and anaphylactoid reactions have been reported for a number of surgical procedures that required heparin reversal with Protamine (39-46), including fatal anaphylactoid shock in a 19-year-old female (47), fatal anaphylactic reaction after femoropopliteal by-pass surgery (48), and anaphylactoid reactions with acute facial oedema and marked increase of tryptase (49).

Insulin therapy
Clinically significant immunological reactions to exogenous insulin are classified as local or generalised. Most insulin allergies involve local reactions, which usually improve or resolve spontaneously. Generalised allergic reactions to insulin range in severity from simple urticaria to life-threatening anaphylaxis. Symptoms may include the immediate onset of diffuse pruritic urticaria and angioedema with progression to hypotension, as well as a local reaction. Most of the allergic reactions to exogenous insulin are antibody-mediated reactions to antigens such as zinc, Protamine, non-insulin proteins, and aggregates of insulin molecules, as well as animal antigens (50-51).

Acute and delay-mediated hypersensitivity to Protamine usually occur as a complication of neutral Protamine Hagedorn insulin (NPH-insulin) therapy (52-55).

A study reported that 122 of 319 NPH-treated diabetic patients had IgG antibodies to Protamine, compared with 8% (3/39) of lente insulin-treated diabetics and 2.5% (5/202) control subjects (56). A prospective study of 21 patients, followed for 12 months from the initiation of NPH insulin for diabetes, found that 6/21 (29%) of the NPH insulin-treated patients developed IgG antibodies to Protamine (57). A recent study estimated that Protamine sensitisation had been reported in approximately 50% of NPH (Neutral Protamine Hagedorn) insulin-treated subjects (58).

Significantly, diabetic patients who have not received NPH-insulin may nevertheless have specific IgE antibodies to Protamine. This is illustrated in a report of a 63-year-old nonatopic female with type II diabetes and severe local and systemic immediate-type allergic reactions to injections of different recombinant human insulin products, who was found by serum- and skin-specific IgE tests to show immediate-type sensitisation not only to human insulin but also to porcine and bovine insulin, as well as IgE-mediated sensitisation to Protamine (58). Similarly, in a study evaluating allergy to recombinant human (rDNA) insulin preparations, of 22 cases, 9 (41%) were due to non-insulin allergic causes: poor injection technique (n = 5), skin disease (n = 3) and other systemic allergy (n = 1). Three patients were found to be allergic to Protamine (59).

Skin-specific IgE tests are not always helpful in determining whether sensitisation has occurred to Protamine and/or insulin (1). Eleven patients with insulin allergy and 53 patients receiving insulin but without an insulin allergy were evaluated. Of the 11 patients, 3 had anaphylaxis and 8 displayed localised reactions. All 11 were found to have skin-specific IgE. Five of the 11 also were positive on intradermal tests for skin-specific IgE antibodies to Protamine sulfate, and 4 to insulin. Two patients who were not tested with Protamine sulfate were positive for NPH insulin. A patient with anaphylaxis was shown to have skin-specific IgE to a concentration as low as 0.03 ng/ml (60).

An insulin-treated diabetic patient was described who experienced 3 severe anaphylactic reactions over a 2-month period after self-administering NPH human recombinant DNA insulin. He had local and systemic symptoms, including dyspnoea and hypotension. Sensitisation to both human insulin and to Protamine was demonstrated by the determination of both skin- and serum-specific IgE. The authors suggest that Protamine sensitisation also should be evaluated in any patient with a history of reactions to subcutaneous Protamine-containing insulins, even if insulin sensitisation is present (61).

Thus, allergy to Protamine may exist together with allergy to other components of insulin. A 19-year-old woman with insulin-dependent diabetes and regular and NPH insulin hypersensitivity developed urticaria and angioedema. She was found to have high Protamine-specific as well as insulin-specific IgE levels (62). Similarly, generalised allergy due to zinc and Protamine in an insulin preparation was reported (63).

Anaphylaxis to Protamine may unexpectedly occur in patients who have been using NPH insulin for some time. A 36-year-old woman, without a history of local insulin reactions or interruption of insulin therapy, experienced anaphylaxis within 15 minutes of her usual morning dose of NPH human insulin. A 62-year-old man with a history of generalised reactions to NPH human insulin and of anaphylaxis to intravenously administered Protamine had generalised urticaria after injection of NPH human insulin. Skin test results in both these patients were negative to regular and lente insulin preparations but positive to NPH insulin and to Protamine at concentrations tested. In vitro assays demonstrated that both patients had markedly elevated serum levels of IgE and IgG antibodies to Protamine, but not to regular human insulin, and that their IgE antibodies to Protamine recognised Protamine antigenic determinants in NPH human insulin (64).

As stated above, allergy to NPH insulin may occur following initial sensitisation during cardiac surgery. This is illustrated by a report of a patient who experienced anaphylaxis after intravenous administration of Protamine sulfate during arterial bypass surgery and was shown to have skin- and serum-specific IgE to Protamine-containing (NPH) insulin and Protamine sulfate USP. Lente insulin and controls were negative (51).

Immediate and delayed hypersensitivity to Protamine may occur, as described in a 63-year-old female who began to develop nodular skin reactions at the injection site 12 to 24 hours after insulin injections. Intradermal testing demonstrated delayed hypersensitivity to Protamine. No specific IgE or IgG antibodies were demonstrable. She was changed to Protamine-free human delayed-action insulin. After an initial reaction-free period, red urticarial lesions, attributable to immediate hypersensitivity to human insulin, appeared at the injection sites (65).

Other unusual immune-like reactions to Protamine have been reported.
For example, a patient was described who developed a granulomatous skin reaction to injections of Protamine insulin for the treatment of her diabetes mellitus (66).

Vasectomy
Vasectomised men are reported to be at high risk for Protamine reactions. With occlusion of ejaculatory paths after a vasectomy, sperm are absorbed systemically. With the consequent disruption of the blood-testes barrier following a vasectomy, about 65% of men were found to develop hemagglutinating autoantibodies against sperm, and 22-30% were found to develop autoantibodies against nucleoprotamines (human proteins which are a normal component of human sperm cells and are similar to Protamine) (67-68). These antibodies, in turn, have been shown to cross-react with Protamine (69). Similar results have been reported from other studies (70-71).

This is of clinical significance in particular when vasectomised patients undergo cardiac surgery, as demonstrated in a report of a 63-year old vasectomised man who developed anaphylaxis to Protamine during cardiac surgery. Bradycardia and hypotension occurred 2 weeks later during heparin and Protamine infusion as part of a follow-up. A Protamine-specific IgG level of 53 mcg/ml at the time of the initial reaction was recorded, 667 at the 2nd, and 79 mcg/ml 3 months later. A subsequent evaluation of a group of 55 vasectomised men found that 16 (29%) of the men also had Protamine-specific IgG in sera, compared to none of the controls. No Protamine-specific IgE was detected in sera (71).

Characteristics of Protamine reactions
Anaphylaxis may occur during the first-ever administration of Protamine or at a second event. A 50-year-old woman, who had received Protamine previously after open-heart surgery, developed anaphylaxis in a similar operation 7 years later. Symptoms included a sudden drop of arterial blood pressure, tachycardia, and severe angioneurotic oedema of the face and trunk. Skin testing for Protamine sulphate was positive (72).

Protamine insulin use may immunologically sensitise patients to Protamine, leading to anaphylactic or anaphylactoid reactions upon subsequent exposure to Protamine sulfate during cardiac catheterisation or cardiovascular surgery (3, 73). Twenty-seven patients (diabetic and nondiabetic) who had acute reactions to intravenous Protamine and 43 diabetic patients who tolerated Protamine without a reaction during diagnostic or surgical procedures were evaluated. In diabetic patients who had received Protamine-insulin injections, the presence of serum anti-Protamine IgE antibody was a significant risk factor for acute Protamine reactions, as was anti-Protamine IgG. Eight of 27 patients (29%) with adverse reactions to Protamine had bronchospasm. In other words, patients with anti-Protamine IgE antibodies experienced severe Protamine reactions with hypotension and/or bronchospasm, suggesting that the presence of IgE antibodies is associated with more-severe reactions than those in patients without anti-Protamine IgE antibodies (74).

This is supported by a study reporting on  major anaphylactoid reactions occurring in 11 of 1,150 patients receiving Protamine; 9 of these reactions occurred in 325 insulin-dependent diabetic patients (3%), versus 2 in 825 patients not receiving insulin (0.2%). Three patients developed severe bronchospasm. Ten of these reactions occurred within 10 minutes of Protamine administration, whereas 1 reaction occurred immediately after administration of a 5 mg test dose of Protamine (75).

In a retrospective analysis of 2,996 patients, only 4 subjects experienced an adverse reaction due to Protamine. Two individuals were NPH insulin-dependent diabetics, and 2 patients had exposure to Protamine only during cardiac catheterisation. The incidence of adverse reactions was 2.9% in NPH insulin-dependent diabetics and 0.07% in non-diabetics, representing a nearly 40-fold increased risk for diabetic patients (31).

Four of 15 (27%) NPH-dependent diabetic patients had anaphylaxis after Protamine administration following cardiac catherisation. A later study, of consecutive patients undergoing cardiac catheterisation over a 20-month period, found that out of 651 who had received Protamine for reversal of heparinisation, 8.5% were diabetics and 2.3% were NPH insulin-dependent diabetics. Of 7 major reactions, 4 occurred in NPH insulin-dependent diabetics, and 1 occurred in a patient with an allergy to fish. The incidence of major Protamine reactions was 27% (4/15) in the NPH insulin-dependent diabetics vs 0.5% (3/636) in those with no history of NPH insulin use. Respiratory symptoms were reported to be the significant event: all 7 patients with major reactions had dyspnoea, wheezing and cyanosis, including 1 patient who suffered respiratory arrest. Dyspnoea was also noted in 1 patient who had a minor Protamine reaction (22).

Evaluation of Protamine sensitivity
An early study reported that a history of prior Protamine exposure, fish allergy, or vasectomy suggests patients may be at greater risk for anaphylaxis to Protamine; but stressed that patients can develop anaphylaxis in the absence of such factors. This was illustrated by an anaphylactic reaction to Protamine that occurred in a patient without identifiable risk factors (76). More recently, in an evaluation of 53 Protamine-hypersensitive patients and 223 control subjects, 3 risk factors were independently associated with events (multivariable odds ratio [95% confidence interval]): NPH insulin use (8.18 [2.08, 32.2]); fish allergy (24.5 [1.24, 482.3]), and a history of non-Protamine medication allergy (2.97 [1.25, 7.07]). These risk factors were said to demonstrate an increasingly strong association with progressively more-specific case definitions (77). This is somewhat at odds with an early study that concluded that the notion that there is cross-reactivity between IgE to Salmon and Protamine sulfate was not supported, or at least in the few cases evaluated in that study (4).

A number of studies have examined the value of various tests. Neither skin tests nor serum enzyme-linked immunosorbent assay tests have been found to provide 100% specificity for Protamine allergy. A study reported that 13% of patients had positive Protamine skin-specific IgE despite having no clinical reaction (specificity of 87%). The recommended Protamine test dose concentration was 1 microgram/ml (78). Intradermal injections of Protamine with concentrations between 100 and 1,000 microgram/ml were found to induce irritative skin responses in healthy subjects (2).

In diabetic patients receiving daily Protamine-insulin injections, the presence of anti-Protamine IgE or IgG antibodies is a significant risk factor for acute, life-threatening reactions when Protamine is given intravenously. Serum anti-Protamine IgE and IgG antibody levels, in-vitro basophil histamine release and intracutaneous skin testing to Protamine were serially measured in an NPH insulin-dependent diabetic who had a severe, protracted anaphylactic reaction to Protamine. At the time of his initial Protamine reaction, his serum contained 8.5 ng/ml of anti-Protamine IgE and 1.3 micrograms/ml of anti-Protamine IgG antibody. One month following the reaction anti-Protamine IgE and IgG increased to 16 ng/ml (a 2-fold rise) and 90.5 micrograms/ml (a 70-fold rise), respectively. With time, anti-Protamine IgE and IgG antibodies both declined. But serial intradermal skin tests using Protamine sulphate did not discriminate between the Protamine reactor and 9 normal control subjects who had no prior exposure nor any demonstrable serum IgE antibody to Protamine. In-vitro basophil histamine release to Protamine sulphate was also inconclusive in discriminating between the Protamine reactor and normal control subjects. The authors postulated that Protamine may be an incomplete or univalent antigen that must first combine with a tissue macromolecule or possibly heparin to become a complete multivalent antigen capable of eliciting IgE antibody-dependent mediator release (79).

Other reactions
Adverse responses to Protamine may include non-immune-mediated responses, ranging from mild hypotension to acute heart failure to potentially fatal events such as noncardiogenic pulmonary oedema and catastrophic pulmonary vasoconstriction (13, 80-86).

Compiled by Dr Harris Steinman, harris@zingsolutions.com