DESCRIPTION
Aminocaproic Acid is 6-aminohexanoic acid, which acts as an inhibitor of fibrinolysis. The structural formula is:
The molecular formula is: C6H13NO2
Aminocaproic Acid is soluble in water, acid and alkaline solutions; it is sparingly soluble in methanol and practically insoluble in chloroform.
Aminocaproic Acid Injection, USP, for intravenous administration, is a sterile pyrogen-free solution containing 250 mg/mL of Aminocaproic Acid with Benzyl Alcohol 0.9%, as a preservative, and Water for Injection q.s. The pH is adjusted to approximately 6.8 with Hydrochloric Acid and/or Sodium Hydroxide.
CLINICAL PHARMACOLOGY
The fibrinolysis-inhibitory effects of aminocaproic acid appear to be exerted principally via inhibition of plasminogen activators and to a lesser degree through antiplasmin activity.
In adults, oral absorption appears to be a zero-order process with an absorption rate of 5.2 g/hr. The mean lag time in absorption is 10 minutes. After a single oral dose of 5 g, absorption was complete (F=1). Mean ± SD peak plasma concentrations (164 ± 28 mcg/mL) were reached within 1.2 ± 0.45 hours.
After oral administration, the apparent volume of distribution was estimated to be 23.1 ± 6.6 L (mean ± SD). Correspondingly, the volume of distribution after intravenous administration has been reported to be 30.0 ± 8.2 L. After prolonged administration, aminocaproic acid has been found to distribute throughout extravascular and intravascular compartments of the body, penetrating human red blood cells as well as other tissue cells.
Renal excretion is the primary route of elimination, whether aminocaproic acid is administered orally or intravenously. Sixty-five percent of the dose is recovered in the urine as unchanged drug and 11% of the dose appears as the metabolite adipic acid. Renal clearance (116 mL/min) approximates endogenous creatinine clearance. The total body clearance is 169 mL/min. The terminal elimination half-life for aminocaproic acid is approximately 2 hours.
INDICATIONS AND USAGE
Aminocaproic acid is useful in enhancing hemostasis when fibrinolysis contributes to bleeding. In life-threatening situations, transfusion of appropriate blood products and other emergency measures may be required.
Fibrinolytic bleeding may frequently be associated with surgical complications following heart surgery (with or without cardiac bypass procedures) and portacaval shunt; hematological disorders such as amegakaryocytic thrombocytopenia (accompanying aplastic anemia); acute and life-threatening abruptio placentae; hepatic cirrhosis; and neoplastic disease such as carcinoma of the prostate, lung, stomach, and cervix.
Urinary fibrinolysis, usually a normal physiological phenomenon, may contribute to excessive urinary tract fibrinolytic bleeding associated with surgical hematuria (following prostatectomy and nephrectomy) or nonsurgical hematuria (accompanying polycystic or neoplastic diseases of the genitourinary system). (See WARNINGS.)
CONTRAINDICATIONS
Aminocaproic acid should not be used when there is evidence of an active intravascular clotting process.
When there is uncertainty as to whether the cause of bleeding is primary fibrinolysis or disseminated intravascular coagulation (DIC), this distinction must be made before administering aminocaproic acid.
The following tests can be applied to differentiate the two conditions:
•Platelet count is usually decreased in DIC but normal in primary fibrinolysis.
•Protamine paracoagulation test is positive in DIC; a precipitate forms when protamine sulfate is dropped into citrated plasma. The test is negative in the presence of primary fibrinolysis.
•The euglobulin clot lysis test is abnormal in primary fibrinolysis but normal in DIC.
Aminocaproic acid must not be used in the presence of DIC without concomitant heparin.
WARNINGS
Aminocaproic Acid Injection, USP contains benzyl alcohol as a preservative. The administration of medications containing benzyl alcohol as a preservative to premature neonates has been associated with a fatal "Gasping Syndrome". (See PRECAUTIONS, Pediatric Use).
In patients with upper urinary tract bleeding, aminocaproic acid administration has been known to cause intrarenal obstruction in the form of glomerular capillary thrombosis or clots in the renal pelvis and ureters. For this reason, aminocaproic acid should not be used in hematuria of upper urinary tract origin, unless the possible benefits outweigh the risk.
Subendocardial hemorrhages have been observed in dogs given intravenous infusions of 0.2 times the maximum human therapeutic dose of aminocaproic acid and in monkeys given 8 times the maximum human therapeutic dose of aminocaproic acid.
Fatty degeneration of the myocardium has been reported in dogs given intravenous doses of aminocaproic acid at 0.8 to 3.3 times the maximum human therapeutic dose and in monkeys given intravenous doses of aminocaproic acid at 6 times the maximum human therapeutic dose.
Rarely, skeletal muscle weakness with necrosis of muscle fibers has been reported following prolonged administration. Clinical presentation may range from mild myalgias with weakness and fatigue to a severe proximal myopathy with rhabdomyolysis, myoglobinuria, and acute renal failure. Muscle enzymes, especially creatine phosphokinase (CPK) are elevated. CPK levels should be monitored in patients on long-term therapy. Aminocaproic acid administration should be stopped if a rise in CPK is noted. Resolution follows discontinuation of aminocaproic acid; however, the syndrome may recur if aminocaproic acid is restarted.
The possibility of cardiac muscle damage should also be considered when skeletal myopathy occurs. One case of cardiac and hepatic lesions observed in man has been reported. The patient received 2 g of aminocaproic acid every 6 hours for a total dose of 26 g. Death was due to continued cerebrovascular hemorrhage. Necrotic changes in the heart and liver were noted at autopsy.
PRECAUTIONS
ADVERSE REACTIONS
Aminocaproic acid is generally well tolerated. The following adverse experiences have been reported:
General: Edema, headache, malaise.
Hypersensitivity Reactions: Allergic and anaphylactoid reactions, anaphylaxis.
Local Reactions: Injection site reactions, pain and necrosis.
Cardiovascular: Bradycardia, hypotension, peripheral ischemia, thrombosis.
Gastrointestinal: Abdominal pain, diarrhea, nausea, vomiting.
Hematologic: Agranulocytosis, coagulation disorder, leukopenia, thrombocytopenia.
Musculoskeletal: CPK increased, muscle weakness, myalgia, myopathy (see WARNINGS), myositis, rhabdomyolysis.
Neurologic: Confusion, convulsions, delirium, dizziness, hallucinations, intracranial hypertension, stroke, syncope.
Respiratory: Dyspnea, nasal congestion, pulmonary embolism.
Skin: Pruritus, rash.
Special Senses: Tinnitus, vision decreased, watery eyes.
Urogenital: BUN increased, renal failure. There have been some reports of dry ejaculation during the period of aminocaproic acid treatment. These have been reported to date only in hemophilia patients who received the drug after undergoing dental surgical procedures. However, this symptom resolved in all patients within 24 to 48 hours of completion of therapy.
OVERDOSAGE
A few cases of acute overdosage with aminocaproic acid administered intravenously have been reported. The effects have ranged from no reaction to transient hypotension to severe acute renal failure leading to death. One patient with a history of brain tumor and seizures experienced seizures after receiving an 8 gram bolus injection of aminocaproic acid. The single dose of aminocaproic acid causing symptoms of overdosage or considered to be life-threatening is unknown. Patients have tolerated doses as high as 100 grams while acute renal failure has been reported following a dose of 12 grams.
The intravenous and oral LD50 of aminocaproic acid were 3.0 and 12.0 g/kg, respectively in the mouse and 3.2 and 16.4 g/kg, respectively, in the rat. An intravenous infusion dose of 2.3 g/kg was lethal in the dog. On intravenous administration, tonic-clonic convulsions were observed in dogs and mice.
No treatment for overdosage is known, although evidence exists that aminocaproic acid is removed by hemodialysis and may be removed by peritoneal dialysis. Pharmacokinetic studies have shown that total body clearance of aminocaproic acid is markedly decreased in patients with severe renal failure.
DOSAGE AND ADMINISTRATION
Aminocaproic Acid Injection, USP is administered by infusion, utilizing the usual compatible intravenous vehicles (e.g., Sterile Water for Injection, Sodium Chloride Injection 0.9%, Dextrose Injection 5% or Ringer's Injection). Although Sterile Water for Injection is compatible for intravenous injection, the resultant solution is hypo-osmolar. RAPID INJECTION OF AMINOCAPROIC ACID INJECTION, USP UNDILUTED INTO A VEIN IS NOT RECOMMENDED.
For the treatment of acute bleeding syndromes due to elevated fibrinolytic activity, it is suggested that 16 to 20 mL (4 to 5 g) of Aminocaproic Acid Injection, USP in 250 mL of diluent be administered by infusion during the first hour of treatment, followed by a continuing infusion at the rate of 4 mL (1 g) per hour in 50 mL of diluent. This method of treatment would ordinarily be continued for about 8 hours or until the bleeding situation has been controlled.