Objective

Ibuprofen might have advantages over indomethacin, when used to effectuate closure of a neonate's patent ductus arteriosus (PDA). Several previous studies indicate that platelet plug formation is impaired after administration of indomethacin, but it is not clear whether a similar impairment occurs following ibuprofen dosing.

Study Design

We performed template bleeding times and PFA-100 tests (platelet function analyzer) on 20 neonates who had a PDA, before and again at various preset intervals following ibuprofen dosing.

Result

Patients ranged from 23 to 40 weeks gestation and weighed 511 to 2566 g. Their first dose of ibuprofen was administered at 72 h (18 to 363 h) after birth (median, range). None of the subjects had clinical bleeding problems noted during the days they received ibuprofen dosing. The template bleeding times before dosing ranged from 135 to 450 s. Repeat tests were performed in groups of four, at 2 h, 4 to 6 h, 12 to 18 h, 24 h after the first dose, and at 2 h after the third dose of ibuprofen. No changes in bleeding times were detected. (P=0.299) A PFA-100 time was performed on all 20 patients before and again after the ibuprofen administration. However, 3 of the 40 tests were unsuccessful, because of microclots in the blood sample (n=1) or failure of the analyzer for an unspecified reason (n=2). Before the dosing the PFA-100 time ranged from 52 to 300 s. A paired t-test showed a slight but statistically significant lengthening in PFA-100 time after the ibuprofen administration (P=0.019). The correlation between the bleeding time and the PFA-100 was poor (R²=0.212, P=0.576).

Conclusion

On the basis of our present studies, we speculate that ibuprofen lysine administration to neonates with a PDA, when used according to the manufacturer's recommendations, has little adverse effect on platelet plug formation. This information might be a factor to consider when deciding whether to select indomethacin or ibuprofen for PDA closure.

Introduction

A symptomatic patent ductus arteriosus (PDA) places a neonate at risk for hemorrhagic complications, including intracranial, pulmonary, mucosal and gastrointestinal bleeding.¹ Forming an effective platelet plug is an essential part of hemostasis, yet platelet plug formation can be impaired by certain medications including aspirin and other nonsteroidal anti-inflammatory drugs.^{2, 3, 4} Indomethacin has been used as a pharmacological means of effectuating PDA closure in neonates, but indomethacin has well-described adverse effects on platelet plug formation.⁵ Neonates treated with indomethacin develop a prolonged bleeding time,⁶ and hemorrhagic complications have been reported following indomethacin administration.^{7, 8}

In 2006, a formulation of ibuprofen lysine was approved by the US Food and Drug Administration (FDA) for use in neonates for the purpose of closing a symptomatic PDA.⁹ However, the effect of this product on platelet function is not clear. The capacity to generate a hemostatically effective platelet plug can be assessed by in vivo methods (template bleeding time) and by in vitro methods (platelet function analyzer (PFA)-100 time).^{2, 3, 4, 10, 11, 12, 13, 14, 15, 16, 17} We obtained these tests before and at various preset intervals after ibuprofen administration to 20 neonatal intensive care unit (NICU) patients who had a PDA and herein report the results of those studies.

Methods

Patients in the NICU of the McKay-Dee Hospital Center, Ogden, Utah, were deemed eligible to participate in this study if the neonatologist ordered a course of ibuprofen lysine, dosed according to the manufacturer's recommendation (Ovation Pharmaceuticals Inc., Deerfield, IL, USA), and if the platelet count was >100 000 per l.¹⁷ Patients were considered ineligible if they had petechiae, mucocutaneous bleeding, bleeding into an endotracheal tube or gastrointestinal bleeding. A cranial ultrasound examination was not required before study entry.

A platelet count, mean platelet volume and hematocrit were measured electronically (Coulter LH 750 Hematology Analyzer, Beckman Coulter Inc., Fullerton, CA, USA). The circulating platelet mass was calculated by multiplying the platelet count (platelets per l blood) by the mean platelet volume (fl), and expressing the value as 'nl platelets per l blood'.¹⁶ A template bleeding time was performed (by MJS or RDC) using methods previously described.^{2, 3, 4, 10, 13, 17} Briefly, a blood-pressure cuff appropriate for the infant's size was placed on an upper extremity and set at a pressure equal to the last measured mean blood pressure. If no mean blood pressure had been recorded in the previous 6 h, the pressure was set at 20 mm Hg for those with a weight <1 kg, at 25 mm Hg for those weighing 1 to 2 kg, and at 30 mm Hg for those weighing >2 kg. The volar surface of the forearm was then cleaned with alcohol and air dried. The template device (Surgicutt Newborn; International Technidyne Corporation, Edison, NJ, USA) was activated, and thereafter blood was absorbed from the incision site using the Surgicutt Newborn filter paper, every 15 s until the bleeding stopped. The number of seconds between the incision and the cessation of bleeding was read as the bleeding time.

The PFA-100 test was performed by the Intermountain Healthcare Clinical Hematology Laboratory using the manufacturer's recommendations (Dade Schering, Miami, FL, USA). Samples were drawn by central line when available, otherwise by venipuncture. Only the epinephrine cartridge (not the ADP cartridge) was used in order to limit phlebotomy losses due to the study. To maintain the recommended ratio of blood to citrate (9:1), 80 l of citrate were removed from each blood collection tube (BD Diagnostics, Franklin Lakes, NJ, USA) using a micropipetter (Finnpipettte; Thermo Fisher Scientific Inc., Waltham, MA, USA).

The study design called for 20 patients who were to receive ibuprofen lysine to be tested with a template bleeding time and a PFA-100 test within 1 h before the first dose of ibuprofen, and again at one preset time after receiving the first dose. Groups of four patients each were to receive the second set of studies 2 h after, 4 to 6 h after, 12 to 18 h after or 24 h after the first dose, or 2 h after the third dose. Descriptive statistics were calculated using Statit (Corvallis, OR, USA). Means and standard deviations were used to express values in groups that were normally distributed. Differences in categorical variables were assessed using the ²-test. A paired t-test was used to assess differences in predosing vs postdosing values in each study subject. Statistical significance was set as P<0.05. The Institutional Review Board of the Intermountain Healthcare approved the study protocol, and parents of the participants signed an informed consent document.

Results

During the 10 months this study was open for enrollment (1 April 2007 to 28 January 2008), 486 patients were admitted to the NICU. Of these, 28 (6%) were treated with ibuprofen lysine. None of the 28 were excluded from study participation on the basis of a platelet count <100 000 per l or signs of bleeding. The parents of 24 of the 28 patients were contacted by the NICU research staff and given information regarding this study. The four not contacted were on the basis of unavailability of a technician (MJS or RDC) to perform the bleeding time studies. Parents of four patients declined the study and the parents of the remaining 20 gave written informed consent for participation. All 20 patients were entered onto the study protocol and none were withdrawn from the study before completing the ibuprofen dosing and all study-related laboratory determinations.

The study patients, at birth, ranged from 23 to 40 weeks gestation and weighed 511 to 2566 g. Their first dose of ibuprofen was administered at 72 h (18 to 363 h) after birth (median, range; Table 1). None of the study subjects had clinical bleeding problems noted during the days they received ibuprofen lysine dosing. The predosing platelet counts and circulating platelet mass calculations, number of doses of ibuprofen administered and effect on the PDA are shown in the Table 1.

Table 1 - Clinical features of 20 NICU patients receiving ibuprofen lysine to close a patient ductus arteriosus.

Full table

A template bleeding time was performed on all 20 patients before and again at one preset interval after ibuprofen administration. Before the first dose was given, the bleeding time ranged from 135 to 450 s (Figure 1). Two hours after completing the ibuprofen infusion, one patient had a bleeding time of 545 s, but the remaining 19 had values similar to their predosing bleeding times. No difference was detected in the pairs of pre- vs post-ibuprofen bleeding times (P=0.299). The 10 patients with a birth weight <1000 g tended to have a shortening in bleeding time (the second value was a mean of 20 s shorter than the first), whereas the 10 with a birth weight >1000 g tended to have a prolongation in bleeding time (the second value was a mean of 41 s longer than the first).

Figure 1.

Template bleeding time before and at various intervals after ibuprofen lysine dosing of 20 neonatal intensive care unit (NICU) patients. Each bleeding time measured is shown by an 'X'. Lines connect the bleeding times performed before the first dose of ibuprofen with those performed at various preset intervals following the dose.

Full figure and legend (54K)

A PFA-100 time was performed on all 20 patients before and again after the ibuprofen administration. However, 3 of the 40 tests were unsuccessful, because of microclots in the blood sample (n=1) or failure of the analyzer for an unspecified reason (n=2). Before the administration of ibuprofen the PFA-100 time ranged from 52 to 300 s (Figure 2). A paired t-test showed a slight but statistically significant lengthening in PFA-100 time after the ibuprofen administration (median 164 s before vs 237 s after; P=0.019). The correlation between the bleeding time and the PFA-100 was poor (R²=0.212, P=0.576).

Figure 2.

PFA-100 time before and at various intervals after ibuprofen lysine dosing of 20 neonatal intensive care unit (NICU) patients. Each PFA-100 time is shown by an 'X'. Lines connect the values obtained before the first dose of ibuprofen with those obtained at various preset intervals following the dose. The squares represent values lacking a pre-ibuprofen value (due to microclots in the sample (n=1) or failure of the analyzer for unspecified reasons (n=2)).

Full figure and legend (57K)

Discussion

Producing an effective platelet plug is an important component of hemostasis.^{2, 3, 4} Medications such as clopidogrel have been specifically developed to inhibit platelet plug formation, and these can be useful in preventing microthrombotic complications such as coronary artery thrombosis.¹⁸ However, other medications inhibit platelet plug formation not as a desired effect but as an unwanted effect. For example, in adults with rheumatoid arthritis, platelet function is inhibited by nonselective nonsteroidal anti-inflammatory drugs, such as naproxen, and this unwanted effect can lead to hemorrhagic complications such as gastrointestinal bleeding.¹⁹

It is not clear which, if any, of the medications that are commonly administered to ELBW (extremely low birth weight (<1000 g)) neonates in the first days of life significantly inhibit their platelet plug formation. Hemorrhagic complications among ELBW neonates can be significant and therefore medications that do not impair platelet function might be considered preferentially above alternative medications that do.^{17, 20} In this study we assessed platelet plug formation of 20 NICU patients where ibuprofen dosing had been ordered by the clinician in order to close a PDA. We assessed platelet plug formation using two tests: the template bleeding time and the PFA-100 closure time. We made measurements before the first dose of ibuprofen and at various intervals thereafter. The plasma half-life of i.v. ibuprofen lysine in preterm infants is generally over 30 h, much longer than that in adults.²¹ Whether any adverse effect of ibuprofen on platelets would correspond with plasma half-life is unclear. To cover a wide range of possibilities, we obtained measurements at intervals ranging from 2 to 24 h after the first i.v. infusion and 2 h after the third dose.

We found that, unlike the prolongation in bleeding time observed after indomethacin administration to neonates,⁶ no prolongation occurred in the bleeding time after ibuprofen lysine treatment. However, we did observe a statistically significant but small anti-platelet effect of ibuprofen lysine using the PFA-100 test.

We are aware of several pitfalls in our study. First, this was not a head-to-head comparison between ibuprofen and indomethacin. Therefore, our data do not permit a direct comparison between the effects of these two drugs on platelet plug formation. Following the FDA approval of ibuprofen lysine for treating symptomatic PDAs, our NICU has not used indomethacin, with the supposition that the two medications are equally effective for PDA closure, but ibuprofen may have a better safety profile.⁹ A second limitation is that the tests we selected (bleeding time and PFA-100) may not be as sensitive to platelet dysfunction as is platelet aggregometry.²² However, the volume of blood required for aggregometry precludes application to neonates, and therefore the tests we selected are the best we are aware of for this population.¹⁷ Third, operator variability reduces the reproducibility of the bleeding time, but we limited our technicians to only two (MJS and RDC). Indeed, the range in bleeding times we obtained was not more than the range in PFA-100 times. A fourth confounding variable is a developmental shortening in the bleeding time that occurs during the first week after birth, which is particularly marked among the most immature neonates. For instance, Del Vecchio reported that bleeding times of neonates (<28 weeks gestation) fell by about 50 s between day 1 and day 10.¹⁷ That shortening is in keeping with our present observation that the bleeding times tended to shorten among those weighing <1000 g. Perhaps a physiological shortening in bleeding time plus a prolongation in bleeding time from ibuprofen were offsetting in this study.

In contrast to the template bleeding time, the PFA-100 time does not seem to shorten over the first days, possibly because it is not influenced by endothelial factors, which may be susceptible to rapid maturation.^{15, 16} In fact, the PFA-100 times we measured were generally longer than those found in umbilical cord blood.^{23, 24, 25} PFA closure times measured using umbilical cord blood are generally shorter than those measured from adult blood.^{23, 24, 25}.We speculate that platelet dysfunction can be induced during the first days of NICU care by medications such as ampicillin given in high doses (100 mg kg^-1 per dose).²⁶ That theory might explain the longer baseline PFA-100 times we found, compared with cord blood. The effect of high-dose ampicillin on platelet plug formation in neonates remains to be tested.

On the basis of our present studies, we speculate that ibuprofen lysine administration to neonates with a PDA, when used according to the manufacturer's recommendations, has little adverse effect on platelet plug formation. This information might be a factor to consider when deciding whether to use indomethacin or ibuprofen for PDA closure.

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Acknowledgments

Assisted by an unrestricted educational grant from Ovation Pharmaceuticals.