Abstract:
A method of controlling preeclampsia includes the steps of providing a supply of digoxin immune Fab (ovine), calculating an appropriate dosage of the digoxin immune Fab (ovine) based on a patient&#39;s weight and using an assumed endogenous digitalis-like factor level, administering the appropriate dosage as an intravenous bolus, and repeating the administration of the appropriate dosage on a fixed schedule.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates generally to the field of medicine and, more particularly, to a method of controlling preeclampsia and eclampsia. 
     DESCRIPTION OF THE RELATED ART 
     Preeclampsia is a rapidly progressive condition occurring during pregnancy characterized by high blood pressure, swelling and protein in the urine. It is specifically defined as the presence of hypertension or pregnancy-induced hypertension (“PIH”) accompanied by proteinuria, edema, or both after 20 weeks gestation. Preeclampsia occurs in 5 to 10 percent of all pregnancies and is most common in first-time pregnancies or in first pregnancies with a new partner or husband. Typically, preeclampsia occurs in the late second or third trimesters of pregnancy. Complications of preeclampsia include eclamptic seizures, hemolysis, elevated liver function tests, low platelet count (HELLP) syndrome, hepatic rupture, DIC pulmonary edema, acute renal failure, placental abruption, intrauterine fetal demise (IUFD), cerebral hemorrhage, cortical blindness, and retinal detachment. 
     Preeclampsia causes vasospasm, which constricts and damages the smooth lining of the blood vessels. This leads to the accumulation of platelets in the damaged blood vessels, which form small clots along the blood vessel wall and further narrow the blood vessel. This damage to blood vessels can also lead to edema, including cerebral edema. Vasospasm can occur throughout the body, damaging the heart, kidneys and liver. Vasospasm can also develop in the placenta, decreasing the blood supply to the fetus. 
     Preeclampsia is divided into mild and severe forms. Mild preeclampsia is indicated where the patient exhibits hypertension, a proteinuria level of greater than 300 mg per 24 hour period, mild edema signaled by weight gain of greater than 2 pounds per week or 6 pounds per month, and urine output of less than 500 ml per 24 hour period. Severe preeclampsia is indicated where the patient&#39;s blood pressure is greater than 160/110 on two occasions at least six hours apart while on bed rest or a systolic blood pressure increase of greater than 60 over a baseline value or a diastolic increase of greater than 30. In addition, a proteinuria level of greater than 5 g per 24 hour period or a reading of 31 or 41 on a urine dipstick, massive edema, oliguria (less than 400 ml per 24 hour period), presence of fetal growth retardation (IUGR), or systemic symptoms including pulmonary edema, headaches, visual changes, right upper quadrant pain, elevated liver enzymes or thrombocytopenia. 
     After a diagnosis of preeclampsia, the baby is generally induced and delivered if it is near term, i.e., after 36 weeks. However, if preeclampsia occurs earlier in the pregnancy, its impact is more profound. The only “cure” for the disease is delivery of the baby, which is generally contrary to the best interests of the baby if it is not near term. However, if the condition does not respond to traditional management options, early delivery may be the only option remaining. Traditional management includes bed rest, antihypertensive therapy, including methyldopa (Aldomet®), atenolol, and labetalol. If pregnancy from the diagnosis of preeclampsia to delivery could be extended relatively safely for both the fetus and mother, then significant improvement in perinatal outcomes may be achieved. 
     While the cause of preeclampsia and eclampsia remains unknown, several theories have been propounded. One theory proposes that elevated serum digoxin-like immune factors, a sodium/potassium ATPase enzyme inhibitor, play a central role in the increased peripheral vasoconstriction. This is thought to be mediated through ion exchange pumps resulting in increased intracellular calcium which promotes vasoconstriction and resultant hypertension. Based on this theory, it has been suggested that the use of digoxin immune Fab (ovine) may be productive in controlling preeclampsia and eclampsia and extending pregnancy. 
     Digoxin immune Fab (ovine), which is marketed in the United States as DIGIBIND® by GlaxoSmithKline and DIGIFAB™ by Protherics, Inc., is a sterile lyophilized powder of antigen binding fragments (FAB) derived from specific antidigoxin antibodies raised in sheep. Digoxin immune Fab (ovine) is indicated for treatment of digoxin or digitoxin overdose manifested by severe ventricular arrhythmias such as ventricular tachycardia or ventricular fibrillation, or progressive bradyarrhythmias such as severe sinus bradycardia or second or third degree heart block not responsive to atropine. DIGIBIND® is distributed in vials, with each vial containing 38 mg of digoxin-specific Fab fragments plus 75 mg of sorbitol as a stabilizer and 28 mg of sodium chloride and capable of binding approximately 0.5 mg of digoxin. DIGIBIND® is generally administered by intravenous injection after reconstitution with 4 mL/vial of sterile water for injection. DIGIFAB™ is distributed in 40 mg vials and contains no preservatives. DIGIFAB™ is generally administered by intravenous infusion over at least thirty minutes after reconstitution with 4 mL/vial of sterile water for injection. 
     While the use of digoxin immune Fab (ovine) in the treatment of preeclampsia and eclampsia has shown promise, a truly efficacious method of calculating suitable dosages of and administering the drug have eluded researchers in this field. 
     The present invention is directed to overcoming one or more of the problems set forth above. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is to provide a method of controlling preeclampsia and eclampsia to extend pregnancy and allow further development of the fetus. 
     In accordance with the above aspect of the invention, there is provided a method of controlling preeclampsia or eclampsia that includes the steps of providing a supply of digoxin immune Fab (ovine), calculating an appropriate dosage based on a patient&#39;s weight and using an assumed endogenous digitalis-like factor level, administering the appropriate dosage as an intravenous bolus, and repeating the administration of the appropriate dosage on a fixed schedule. 
     These aspects are merely illustrative of the innumerable aspects associated with the present invention and should not be deemed as limiting in any manner. These and other aspects, features and advantages of the present invention will become apparent from the following detailed description when taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference is now made more particularly to the drawings which illustrate the best presently known mode of carrying out the invention and wherein similar reference characters indicate the same parts throughout the views. 
         FIG. 1  is a flow chart illustrating the steps and sequence of a method for controlling preeclampsia according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     According to one embodiment, a patient is first evaluated for preeclampsia or eclampsia. Once a diagnosis of preeclampsia is confirmed, a suitable dosage of a digoxin immune Fab (ovine), such as DIGIBIND® or DIGIFAB™, is calculated. A typical manufacturer&#39;s recommended dosage formula for a known digitalis toxicity level (E) is: 
               D   ×   W     100         
where (D) is the serum digoxin concentration is ng/mL and W is the patient&#39;s weight. However, in preeclampsia and eclampsia cases there is no known digitalis toxicity level. Therefore, according to the method, an assumed endogenous digitalis factor level is required for the calculation. In one embodiment, the assumed endogenous digitalis-like factor level (E) is between approximately 3.0 and 5.0 ng/mL. In a preferred embodiment, the endogenous digitalis-like factor level is approximately 4.0 ng/mL. The endogenous digitalis-like factor level is then used in the following equation:
 
               E   ×   W     100         
where E is the endogenous digitalis-like factor level. Use of the preferred endogenous digitalis-like factor level results in an equation of:
 
               4.0   ⁢           ⁢   ng   ⁢     /     ⁢   mL   ×     (   W   )       100         
which in turn produces the suitable dosage of digoxin immune Fab (ovine).
 
     Once the dosage is calculated, it is administered to the patient via an intravenous bolus. Administration of the calculated dosage via intravenous bolus is then repeated on a fixed schedule of every five to eight hours. In a preferred embodiment, the dosage is administered every six hours. 
     In another embodiment, the administration of digoxin immune Fab (ovine) is accompanied by an administration of corticosteroids, such as betamethasone, to stimulate the cells in the lungs of the fetus in preparation for breathing air and decrease the risk of brain hemorrhage and intestinal problems in the fetus. The corticosteroids are administered once at the time of admission and again in twenty-four hours. 
     The method will now be further illustrated with reference to the following non-limiting example. 
     BIOLOGICAL EXAMPLE 
     A 16-year-old 70 Kg primigravida at 29 weeks 5/7 days presented with a presumed diagnosis of eclampsia. Her prenatal course had been uncomplicated until the day of admission. Her past medical history was negative for chronic illness. The patient had complaints of scotomata, persistent headache, and reported seizure activity for two episodes prior to hospital arrival and one on the labor deck. Initial evaluation revealed an alert patient with obvious postictal behavior. Her blood pressure was elevated at 160/110&#39;s and otherwise stable vital signs. Physical examination revealed A-V nicking on funduscopic exam, 4+ edema of the lower extremities and obvious facial and upper extremity edema. Deep tendon reflexes were 3 plus with 2 beats of clonus. The remainder of the exam was within normal limits. Lab evaluation of the urine noted proteinuria on qualitative analysis of 2+ and a urine specific gravity of 1.025. Serum chemistry revealed hyperuricacidemia at 8.2, elevated creatinine of 1.0, BUN of 6, and otherwise normal electrolytes and liver enzymes. The complete blood count revealed a platelet count of 429,000, white count of 10.4 and a hemoglobin/hematocrit of 12.0 and 35.6 respectively. The ammonia level was 3 and coagulation studies were normal. Urine drug screening was negative for substances of abuse including cocaine and methamphetamines. CT scanning of the maternal head failed to reveal any pathological abnormalities. 
     Ultrasound examination revealed a singleton gestation with a breech presentation. The estimated gestational age was consistent with the previously determined age of 29 weeks with an estimated fetal weight of 1331 grams. The amniotic fluid index was 5.42 cm and fetal breathing, movement, and tone were noted to be present. Doppler flow studies of the umbilical artery revealed an elevated S/D ratio of 5.6, RI of 0.82, and minimal diastolic flow. No anatomical abnormalities were noted on exam. Fetal cardiotocograph revealed a baseline of 135 with minimal beat-to-beat variability. Occasional non-repetitive decelerations were noted with good recovery. They were deemed to be non-ominous. 
     The patient was placed on intravenous magnesium sulfate. Central venous access and arterial line placement were performed. After informed discussion with the immediate family including the option to stabilize with compassionate off label use of fragmented antibody to digoxin and to administer corticosteroids for fetal benefit, the patient&#39;s mother provided consent. 
     Standard preeclampsia monitoring every hour was followed with ICU one on one nursing. Using an endogenous digitalis like factor level of 4.0 ng/mL and a dosage formula of 4.0 ng/mL×patient&#39;s body weight divided by 100 resulted in a dosage of 3 vials. This dosage was administered via an intravenous bolus and was repeated every 6 hours. 
     Intravenously administered fluids were standardized to 125 cc/hr. Urine output from admission to infusion was 300 cc over 6 hours. Over the first 6 hours post infusion the average urinary output was 100 cc with blood pressure readings of 148 to 162 systolic and 104 to 111 diastolic. At the next dosing interval the drug was doubled to 6 vials every six hours until 12 hours prior to delivery. Over the next 36 hours a diuresis followed over 5,840 cc of urine for an average hourly output of 162 cc. The total intake of intravenous fluids during the same time period was 3409 cc. The urine qualitative exam revealed negative proteinuria with a specific gravity of 1.011 and osmolality of 125, normal 500 to 800 mosm. Her creatinine decreased to 0.7 with the remainder of electrolytes remaining normal. Serial blood pressure measurements during the 36-hour period from the doubling of the dose ranged from 131 to 160 systolic (mean 140&#39;s) and diastolic 58 to 111 (mean 90&#39;s). The edema resolved in face and upper extremities with significant decreases in lower extremities as well to 1+. Deep tendon reflexes became 1+ with no clonus. 
     Fetal assessment during this time showed no changes in the cardiotocograph. Ultrasound examination every 6 hours revealed a reassuring biophysical score of 8 of 10. Doppler flow assessment of the umbilical artery every 6 hours revealed a decreasing S/D ratio with increasing diastolic component. The S/D ratio 6 hours prior to delivery was 3.7 with a RI of 0.75 suggesting improved fetal hemodynamics albeit still abnormally elevated. 
     Cesarean delivery was performed at 48 hours post administration of corticosteroids secondary to a breech presentation. The delivery was attended by NICU and resulted in a livebirth of a female child. Apgars were 7 &amp; 8 at one and five minutes respectively. The neonate did not require any oxygen support and was admitted to the NICU secondary to prematurity size of 1290 grams. 
     The maternal postoperative course was complicated by elevated blood pressures of 140 to 160&#39;s systolic and diastolic readings in the 100&#39;s. The patient was started on metoprolol 100 mg twice daily. She was discharged home on postoperative day #4 with stable blood pressures controlled with metoprolol. All follow up labs remained within normal limits. The neonate had no adverse sequelae and was discharged home on day of life #31. 
     Other objects, features and advantages of the present invention will be apparent to those skilled in the art. While preferred steps of the present invention have been illustrated and described, this has been by way of illustration and the invention should not be limited except as required by the scope of the appended claims and their equivalents.