Physiologic changes induced by theophylline in the treatment of apnea in preterm infants

The effect of caffeine on the ventilatory response to hypercarbia in preterm infants

BackgroundWe tested the hypotheses that caffeine therapy would increase the ventilatory response to hypercarbia in infants above the effect of maturation and those with a weaker ventilatory response to hypercarbia would be more likely to subsequently develop apnea that required treatment.MethodsInfants born at less than 34 weeks of gestation underwent a steady-state hypercarbic challenge using 0, 2, and 4% carbon dioxide soon after birth that was repeated at weekly intervals. The results of the initial study were compared between infants who did or did not subsequently develop apnea requiring treatment with caffeine.ResultsTwenty-six infants born at a median gestation of 32 (range 31-33) weeks were assessed. Caffeine administration was associated with an increase in CO₂ sensitivity, and the mean increase was 15.3 (95% CI: 1-30) ml/kg/min/% CO₂. Fourteen infants subsequently developed apnea treated with caffeine. After controlling for gestational age and birth weight, they had significantly lower carbon dioxide sensitivity at their initial study compared with those who did not require treatment.ConclusionCaffeine administration was associated with an increase in the ventilatory response to hypercarbia. An initial weaker ventilatory response to hypercarbia was associated with the subsequent development of apnea requiring treatment with caffeine.

Effects of caffeine on renal and pulmonary function in preterm newborn lambs

INTRODUCTION

Caffeine administration is associated with a reduction in bronchopulmonary dysplasia, assisted ventilation, patent ductus arteriosus (DA) and cerebral palsy in preterm infants, but the mechanisms are unknown. Our aim was to determine the effects of acute caffeine administration on renal and pulmonary function in preterm lambs.

METHODS

Lambs were delivered by caesarean section at ~126 days of gestation and ventilated with a tidal volume of 5 ml/kg, 60 breaths/min and 5 cmH(2)O positive end-expiratory pressure. After 30 minutes, lambs received 40 mg/kg caffeine i.v (n=7) or saline (controls; n=6) over 30 minutes and were ventilated for 2 hours.

RESULTS

Arterial caffeine concentrations reached 35.9 ± 7.8 mg/l. Urine output was significantly higher after caffeine treatment than in controls (5.86 ± 1.95 vs 0.76 ± 0.94 ml/kg, area under curve p=0.041). Mean heart rate was significantly higher after caffeine treatment than in controls (211 ± 8 vs 169 ± 15 beats per minute, p<0.05) and remained higher for the experimental period.

DISCUSSION

Caffeine did not affect pulmonary artery or DA blood flows or other renal, respiratory or cardiovascular parameters examined. Neonatal caffeine administration increased heart rate and urine output but had little effect on pulmonary function in ventilated preterm lambs.

Methylxanthines during pregnancy and early postnatal life

World-wide, many fetuses and infants are exposed to methylxanthines via maternal consumption of coffee and other beverages containing these substances. Methylxanthines (caffeine, theophylline and aminophylline) are also commonly used as a medication for apnea of prematurity.The metabolism of methylxanthines is impaired in pregnant women, fetuses and neonates, leading to accumulating levels thereof. Methylxanthines readily passes the placenta barrier and enters all tissues and thus may affect the fetus/newborn at any time during pregnancy or postnatal life, given that the effector systems are mature.At clinically relevant doses, the major effector system for methylxanthines is adenosine receptors. Animal studies suggest that adenosine receptors in the cardiovascular, respiratory and immune system are developed at birth, but that cerebral adenosine receptors are not fully functional. Furthermore animal studies have shown protective positive effects of methylxanthines in situations of hypoxia/ischemia in neonates. Similarly, a positive long-term effect on lung function and CNS development was found in human preterm infants treated with high doses of caffeine for apneas. There is now evidence that the overall benefits from methylxanthine therapy for apnea of prematurity outweigh potential short-term risks.On the other hand it is important to note that experimental studies have indicated that long-term effects of caffeine during pregnancy and postnatally may include altered behavior and altered respiratory control in the offspring, although there is currently no human data to support this.Some epidemiology studies have reported negative effects on pregnancy and perinatal outcomes related to maternal ingestion of high doses of caffeine, but the results are inconclusive. The evidence base for adverse effects of caffeine in first third of pregnancy are stronger than for later parts of pregnancy and there is currently insufficient evidence to advise women to restrict caffeine intake after the first trimester.

Caffeine for Apnea of Prematurity trial: benefits may vary in subgroups

OBJECTIVE

To determine whether the benefits of caffeine vary in three subgroups of 2006 participants in the Caffeine for Apnea of Prematurity (CAP) trial.

STUDY DESIGN

Post-hoc subgroup analyses were performed on the basis of: (1) indication for commencement of study drug: treat apnea, prevent apnea, or facilitate extubation; (2) positive pressure ventilation (PPV) at randomization: endotracheal tube (ETT), noninvasive ventilation, or none; and (3) timing of commencement of study drug: early or late (< or =3 versus >3 days). Outcomes assessed were those showing treatment effects in the original analyses. We investigated the consistency of caffeine effects by using regression models that incorporated treatment/subgroup factor interactions.

RESULTS

There was little evidence of a differential treatment effect of caffeine in subgroups defined by the clinical indication for starting study drug. The size and direction of the caffeine effect on death or disability differed depending on PPV at randomization (P = .03). Odds ratios (95% CI) were: no support, 1.32 (0.81-2.14); noninvasive support, 0.73 (0.52-1.03); and ETT, 0.73 (0.57-0.94). Adjustment for baseline factors strengthened this effect (P = .02). Starting caffeine early resulted in larger reductions in days of respiratory support. Postmenstrual age at time of discontinuing PPV was shorter with earlier treatment (P = .01). Mean differences (95% CI) were: early, 1.35 weeks (0.90-1.81); and late 0.55 weeks (-0.11-0.99). Adjustment for baseline factors weakened this effect (P = .03).

CONCLUSIONS

There is evidence of variable beneficial effects of caffeine. Infants receiving respiratory support appeared to derive more neurodevelopmental benefits from caffeine than infants not receiving support. Earlier initiation of caffeine may be associated with a greater reduction in time on ventilation.

Effect of caffeine on respiratory muscle strength and lung function in prematurely born, ventilated infants

The aims of this study were to determine whether caffeine administration increased respiratory muscle function and if this was associated with lung function improvement in prematurely born infants being weaned from mechanical ventilation. Respiratory muscle function was assessed by measurement of the maximum pressures generated during occlusions at end inspiration (Pemax) and end expiration (Pimax) and lung function by measurement of lung volume (functional residual capacity (FRC)) and respiratory system compliance (CRS) and resistance (RRS) in 18 infants with a median gestational age of 28 (range 24-36) weeks. Measurements were made immediately prior to caffeine administration (baseline) and 6 h later. Six hours after caffeine administration compared to baseline, the median Pemax (p = 0.017), Pimax (p = 0.004), FRC (p < 0.001), CRS (p = 0.002) and RRS (p = 0.004) had significantly improved. Our results suggest that caffeine administration facilitates weaning of prematurely born infants from mechanical ventilation by improving respiratory muscle strength.

An adenosine A(2A) antagonist injected in the NTS reverses thermal prolongation of the LCR in decerebrate piglets

Hyperthermia prolongs the laryngeal chemoreflex (LCR). Under normothermic conditions, adenosine antagonists shorten and adenosine A(2A) (Ad-A(2A)) agonists prolong the LCR. Therefore, we tested the hypothesis that SCH-58261, an Ad-A(2A) receptor antagonist, would prevent thermal prolongation of the LCR when injected unilaterally within the nucleus of the solitary tract (NTS). We studied decerebrate piglets aged 4-13 days. We elicited the LCR by injecting 0.1ml of water into the larynx and recorded integrated phrenic nerve activity. The laryngeal chemoreflex was prolonged when the body temperature of each piglet was raised approximately 2.5 degrees C, and SCH-58261 reversed the thermal prolongation of the LCR when injected into the NTS (n=13), but not when injected in the nucleus ambiguus (n=9). Injections of vehicle alone into the NTS did not alter the thermal prolongation of the LCR (n=9). We conclude that activation of adenosine receptors, perhaps located on GABAergic neurons in the NTS, contributes to thermal prolongation of the LCR.

Adjunctive therapies in chronic lung disease: examining the evidence

Chronic lung disease (CLD) or bronchopulmonary dysplasia (BPD) is one of the most common long-term complications in very premature infants. The incidence of CLD has been increasing over the past two decades in parallel with an improvement in the survival of this population. We have witnessed a revolution in the therapies that are used, either to manage these infants' respiratory distress syndrome (RDS) with an aim to prevent CLD or to manage the established condition. Several devices and strategies have been developed to provide respiratory support with minimal risk of lung injuries. Multiple adjunctive agents have also been used either to reduce the risk of CLD or to mitigate its course. There is considerable evidence supporting the use of exogenous surfactant, but unfortunately many other therapies currently used for CLD, either preventative or as a treatment, are based on very little or no evidence. The gold standard to assess a given therapy is the randomised controlled trial (RCT), designed to look at clinically meaningful outcomes and long-term safety. In this context, we discuss the support - or lack thereof - for the adjunctive therapies used in relation to CLD. Many of the therapies have been examined as systematic reviews by the Cochrane Neonatal Review Group. These reviews are noted in the references and can be easily accessed at the following website sponsored by the National Institute of Child Health and Human Development: www.nichd.nih.gov/cochrane/default.cfm.

Measurement of the CO2 apneic threshold in newborn infants: possible relevance for periodic breathing and apnea

We measured the Pco2 apneic threshold in preterm and term infants. We hypothesized that, compared with adult subjects, the Pco2 apneic threshold in neonates is very close to the eupneic Pco2, likely facilitating the appearance of periodic breathing and apnea. In contrast with adults, who need to be artificially hyperventilated to switch from regular to periodic breathing, neonates do this spontaneously. We therefore measured the apneic threshold as the average alveolar Pco2 (PaCO2) of the last three breaths of regular breathing preceding the first apnea of an epoch of periodic breathing. We also measured the PaCO2 of the first three breaths of regular breathing after the last apnea of the same periodic breathing epoch. In preterm infants, eupneic PaCO2 was 38.6 ± 1.4 Torr, the preperiodic PaCO2 apneic threshold was 37.3 ± 1.4 Torr, and the postperiodic PaCO2 was 37.2 ± 1.4 Torr. In term infants, the eupneic PaCO2 was 39.7 ± 1.1 Torr, the preperiodic PaCO2 apneic threshold was 38.7 ± 1.0 Torr, and the postperiodic value was 37.9 ± 1.2 Torr. This means that the PaCO2 apneic thresholds were 1.3 ± 0.1 and 1.0 ± 0.2 Torr below eupneic PaCO2 in preterm and term infants, respectively. The transition from eupneic PaCO2 to PaCO2 apneic threshold preceding periodic breathing was accompanied by a minor and nonsignificant increase in ventilation, primarily related to a slight increase in frequency. The findings suggest that neonates breathe very close to their Pco2 apneic threshold, the overall average eupneic Pco2 being only 1.15 ± 0.2 Torr (0.95–1.79, 95% confidence interval) above the apneic threshold. This value is much lower than that reported for adult subjects (3.5 ± 0.4 Torr). We speculate that this closeness of eupneic and apneic Pco2 thresholds confers great vulnerability to the respiratory control system in neonates, because minor oscillations in breathing may bring eupneic Pco2 below threshold, causing apnea.

Increased peripheral chemoreceptor activity may be critical in destabilizing breathing in neonates

Periodic breathing and apnea are common in neonates, yet the physiological mechanisms involved are not clear. A low arterial PO2 might magnify peripheral chemoreceptor contribution to breathing, with its baseline variability inducing major changes in ventilation, leading to instability of the respiratory control system. We hypothesized that neonates: (1) would depend much more on the peripheral chemoreceptor contribution to breathing than adult subjects and (2) their baseline arterial PO2 would sit on the steep portion of the ventilation/arterial PO2 relationship on the adult nomogram, making breathing prone to oscillate. We analyzed data from previous polygraphic recordings in four groups of subjects: small preterm infants [SPI; postconceptional age (PCA) 33+/-2 weeks; n = 40], large preterm infants (LPI; PCA 36+/-2 weeks; n = 34), term infants (TI; PCA 42+/-1 week; n = 24), and adult subjects (AS; weight 63+/-2 kg; age 29+/-3 years, n = 16). Peripheral chemoreceptor activity was measured by: (1) the immediate decrease in ventilation and (2) apnea time during brief inhalation of 100% O2 (about 1 minute). We found that: (1) the immediate decrease in ventilation with 100% O2 was more pronounced in infants than in adult subjects (38+/-2 versus 6+/-5%), and in infants breathing periodically versus those breathing continuously; (2) the apnea time during 100% O2 was also significantly longer in periodic breathing infants; and (3) the TcPO2 was much lower in infants than in adult subjects (65+/-1 versus 93+/-1 Torr), and also lower in periodic versus continuously breathing infants. It was located significantly to the left of values for the adult subject, on the ventilation/arterial PO2 diagram. The data suggest that: (1) a substantial portion of baseline breathing activity early in life is maintained by increased peripheral chemoreceptor activity; and (2) neonates breathe irregularly with apneas due to the position of their arterial PO2 values on the ventilation/arterial PO2 diagram, in which a change in PO2 produces a more significant change in ventilation than that observed later in life.

Treatment of apnea of prematurity

In the last decade, knowledge regarding the neurodevelopment and functional aspects of the respiratory centers during postnatal maturation has increased substantially. However, an increase in such knowledge has not provided a basis for change in practice. The diagnosis of apnea of prematurity (AOP) is one of exclusion. All causes of secondary apnea must be ruled out before initiating treatment for AOP. Treatment will depend on the etiology as well as effectiveness and tolerability of the treatment by the patient. The primary goal of any treatment of AOP is to prevent the frequency of apnea lasting >20 seconds, and/or those that are shorter, but associated with cyanosis and bradycardia. The clinical management of AOP is not much different today than it was two decades ago, with pharmacologic and nonpharmacologic treatment options remaining the mainstay of therapy. Methylxanthines are still the most widely used pharmacologic agents. Due to the wider therapeutic index of caffeine and ease of once daily administration, it should be the preferred agent. Doxapram, or nonpharmacologic treatment measures such as nasal continuous positive airway pressure, may be considered in infants who are unresponsive to methylxanthine treatment alone. Treatment should be continued until there is complete resolution of apnea, and for some time thereafter. The choice of method for weaning treatment remains one of individual physician preference. Discharge from hospital after apnea requires close monitoring and some infants will require home apnea monitors. The decision to provide a home apnea monitor should be individualized for each patient, depending on the effectiveness of treatment and clinical response.

Aminophylline modulation of the mouse respiratory network changes during postnatal maturation

Aminophylline is a respiratory stimulant commonly used for the treatment of central apnea. Experiences from clinical practice, however, revealed that aminophylline is not reliably effective in preterm infants, whereas it is normally effective in infants and mature patients. In an established animal model for postnatal development of respiratory control mechanisms, we therefore examined the hypothesis that the clinical observations reflect a developmental change in the sensitivity of the central respiratory network to methylxanthines. The medullary respiratory network was isolated at different postnatal ages (postnatal days 1-13; P1-P13) in a transverse mouse brain stem slice preparation. This preparation contains the pre-Bötzinger complex (PBC), a region that is critical for generation of respiratory rhythm. Spontaneous rhythmic respiratory activity was recorded from the hypoglossal (XII) rootlets and from neurons in the PBC by using the whole cell patch clamp technique. Bath-applied aminophylline [20 microM] increased the frequency (+41%) in neonatal animals (P1-P6) without affecting the amplitude of respiratory burst activity in XII rootlets. The same concentration of aminophylline did not have any significant effect on the frequency of respiratory XII bursts but increased the amplitude (+31%) in juvenile animals (P7-P13). In the same age group, aminophylline also augmented the amplitude and the duration of respiratory synaptic drive currents in respiratory PBC neurons. The data demonstrate that augmentation of the respiratory output is due to direct enhancement of central respiratory network activity and increase of synaptic drive of hypoglossal motoneurons in juvenile, but not neonatal, animals. This indicates a developmental change in the efficacy of aminophylline to reinforce central respiratory network activity. Therefore, we believe that the variable success in treating respiratory disturbances in premature infants reflects maturational changes in the expression of receptors and/or intracellular signal pathways in the central respiratory network.

Risks and benefits of therapies for apnoea in premature infants

Apnoea in infants can result from a wide range of causes, and requires thorough evaluation before deciding on appropriate treatment. Continuous monitoring of premature infants with apnoea is mandatory in order to define the pathophysiology and type of apnoea; selection of treatment involves careful assessment of aetiology, as well as efficacy and tolerability in each individual case. The objective of treatment is to prevent the deleterious consequences of apnoeas that last >20 seconds and/or are associated with bradycardia, cyanosis or pallor, and occur more often than once an hour over a 12-hour period. Apnoea management involves both pharmacological and nonpharmacological treatment. We suggest methylxanthines as first-line therapy for idiopathic apnoeas; evidence suggests that caffeine is better tolerated and as efficacious as theophylline (since it is particularly efficacious against the 'central' component of idiopathic apnoea of prematurity). If treatment fails, additional measures such as doxapram may be appropriate when hypoventilation is present, or nasal continuous positive airway pressure when upper airway instability or obstructive apnoeas are predominant. Apnoea prophylaxis is an additional reason to advocate prenatal maturation with betamethasone. Weaning from treatment is attempted 4 to 5 days after complete resolution of apnoea, beginning with the last treatment introduced. Monitoring should be maintained for 4 to 5 days to detect any relapse of recurrent and severe apnoeas, which would lead to the resumption of the most recently withdrawn treatment.

Metabolic and respiratory effects of theophylline in the preterm infant

BACKGROUND

Methylxanthines are often administered to preterm infants for the treatment of apnoea.

AIMS

To study the effects of theophylline on energy metabolism, physical activity, and lung mechanics in preterm infants.

METHODS

Indirect calorimetry was performed for six hours before and after administration of a bolus of theophylline (5 mg/kg) in 18 preterm infants while physical activity was recorded with a video camera. Lung mechanics measurements were performed at baseline and 12 and 24 hours after theophylline treatment.

RESULTS

Theophylline increased mean (SEM) energy expenditure by 15 (5) kJ/kg/day and augmented carbohydrate utilisation from 6.8 to 8.0 g/kg/day, but fat oxidation was unchanged. After theophylline treatment, preterm infants had faster respiration, lower transcutaneous CO2, and improved static respiratory compliance without increased physical activity.

CONCLUSIONS

A bolus of 5 mg/kg theophylline increased energy expenditure independently of physical activity, increased carbohydrate utilisation, and improved respiratory compliance. The increased energy expenditure could be detrimental to the growth of the preterm infant.

Comparison of the effects of theophylline and caffeine on serum erythropoietin concentration in premature infants

Theophylline administration has been shown to attenuate erythropoietin (EP) production in adults; the effect of caffeine is not known. Our aim was to determine whether caffeine and theophylline had similar effects on EP production in the premature newborn. If caffeine was found to have a greater effect, this would influence prescribing habits. Fifty preterm infants (mean gestational age 28 weeks) who had clinically significant apnoea were randomized to receive theophylline (4 mg/kg then 2 mg/kg twice daily) or caffeine (10 mg/kg then 2.5 mg/kg once daily). The methylxanthines were continued at least until discharge from the NICU and the dosage altered to keep the levels within the therapeutic range. As an assessment of EP production, serum EP concentrations were measured. Blood for EP, haemoglobin, reticulocyte count, theophylline and caffeine levels was obtained prior to treatment and at least during weeks 3 and 7. There was no significant difference in the mean EP level in the two groups taken prior to treatment at a median age of 2 days of life. There were similar falls in haematocrit and haemoglobin in the two groups during the study period compared to pre-treatment values. At that time, however, the median reticulocyte count was higher in the caffeine compared to the theophylline treated infants (P < 0.05). This was associated with a rise compared to baseline (median 10.0-0.2 mU/ml) in the mean EP levels in the caffeine group and a decrease from a median of 10.1 to 8.3 mU/ml in the theophylline group, but the EP levels in the two groups at week 7 did not differ significantly.

CONCLUSION

These results suggest that caffeine does not have a greater impact than theophylline on EP production.

Comparative effects of theophylline and caffeine on respiratory function of prematurely born infants

The aim of this study was to determine the relative effects of theophylline and caffeine on neonatal respiratory function. Fifty-three preterm infants (45 infants with a median gestational age of 28 weeks, range 24-34 weeks completed the protocol) were randomized to receive either theophylline (loading dose 4 mg/kg followed by 4 mg/kg/day) or caffeine (loading dose 10 mg/kg followed by 5 mg/kg/day). Compliance of the respiratory system (CRS), strength of Hering Breuer reflex and the inspired oxygen concentration requirement were measured immediately prior to, 24 h and 7 days after commencing therapy. There was no statistically significant difference in the patient characteristics of the two groups, but only the theophylline group contained immature infants (i.e. < 26 weeks gestational age (n = 7)). At 24 h, there was a significant improvement in CRS and reduction in supplementary oxygen requirements in the caffeine group (p < 0.01), in the theophylline group no such significant effects were seen. In the study population overall, after 7 days of treatment in both the theophylline and caffeine groups there was an improvement in CRS (p < 0.05 and p < 0.01 respectively) and a reduction in the inspired oxygen concentration (p < 0.05 and p < 0.01 respectively). There was, however, a significant reduction in the strength of the Hering Breuer reflex only in the caffeine group (p < 0.05) and this was a decrease which related to the change in CRS (p < 0.05). The only statistically significant difference in the magnitude of change in CRS, reflex strength or supplementary oxygen requirements between the two groups was that the reduction in inspired oxygen requirement in the caffeine group was greater than that in the theophylline treated infants at 24 h (p < 0.05). We conclude theophylline and caffeine have similar effects on neonatal respiratory function, but our results suggest caffeine administration may be associated with an earlier onset of action.

Aminophylline and Doppler time-averaged mean velocity in the middle cerebral artery in preterm neonates

OBJECTIVE

The purpose of this study was to assess the effect of an intravenous loading dose of aminophylline (6 mg/kg) on Doppler time-averaged mean velocity in the middle cerebral artery in ventilated preterm neonates.

METHODOLOGY

Twenty infants were studied by colour/duplex Doppler technique prior to and at 5, 10, 30 and 60 min after the administration of aminophylline.

RESULTS

Aminophylline treatment was associated with a statistically significant reduction in time-averaged mean velocity from baseline (P < 0.001) and an increase in heart rate (P < 0.001) at all timepoints. The largest reduction in time-averaged mean velocity of 19% (95% confidence interval -10 to -28%) occurred at 10 min post-dose. There were no statistically significant changes in transcutaneous PCO2 or mean arterial blood pressure.

CONCLUSIONS

The observed reduction of 19% from baseline in time-averaged mean velocity following treatment with aminophylline alone is unlikely to be of clinical importance. Whether aminophylline in combination with other drugs that decrease central blood flow velocity such as indomethacin and/or dexamethasone could result in a clinically significant reduction deserves further study.

Comparison of the effects of acetazolamide and aminophylline on apnea incidence and on ventilatory response to CO2 in preterm infants

Acetazolamide (ACTZ) reduces sleep apnea in adults exposed to high altitude and augments the ventilatory response to CO2. In order to determine the effect of ACTZ on the ventilatory response to CO2 and the incidence of apnea in preterm infants, 7 infants (BW, 1070 +/- 191 g; postnatal age, 9 +/- 7 days) were randomized to receive ACTZ (5 mg/kg/dose Q6h for 36 hr) and 7 infants (BW, 1092 +/- 292 g; post-natal age, 5 +/- 2 days) received aminophylline (AMINO; 8 mg/kg bolus then 2.5 mg/kg Q12h for 36 hr). Minute ventilation (VE), end-tidal CO2 (PETCO2), ventilatory response to CO2, number of apneic episodes (> or = 15 sec duration), and arterial blood gases were measured before and 24-36 hr after starting therapy. In the AMINO group there was a significant decrease in apnea frequency from 6 +/- 1 to 2 +/- 2 episodes over an 8 hr epoch (P < 0.05), while no significant change was observed in the ACTZ group. The end-tidal CO2 decreased significantly from 44 +/- 7 to 38 +/- 6 mmHg in the AMINO group and from 47 +/- 5 to 36 +/- 5 mmHg in the ACTZ (P < 0.05), which lead to a shift to the left of the CO2-response curve in both groups. The slope of the CO2 response curve did not change significantly in the AMINO group and decreased in the ACTZ group. There was a significant decrease of pH from 7.43 to 7.26 in the ACTZ group, whereas in the AMINO group pH increased from 7.38 to 7.44.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of aminophylline on cerebral haemodynamics and oxidative metabolism in premature infants

The effect of aminophylline on cerebral blood volume and oxidative metabolism in newborn infants was investigated with near infrared spectroscopy (NIRS). Thirteen mechanically ventilated premature infants who received aminophylline to facilitate weaning from the respirator were selected. Gestational age ranged between 26 and 34 weeks, postnatal age between 1 and 7 days and birth weight between 760 and 2300 g. A bolus of 6 mg aminophylline/kg body weight was infused within 2 min. NIRS was performed continuously across the head to monitor changes in cerebral blood volume and cytochrome c oxidase. Heart rate, transcutaneous carbon dioxide tension (tcpCO2) and arterial haemoglobin oxygen saturation (SO2) were recorded simultaneously. The infusion of aminophylline was associated with an increase in heart rate (median 12, interquartile range 5-20 beats per min, P = 0.0004) and a drop in tcpCO2 (median -0.4, interquartile range -0.1 to -0.5 kPa, P = 0.015). Oxygen saturation remained stable (+/- 3%). A decrease in cerebral blood volume was measured with NIRS in 9/13 patients (median -0.15 ml/100g brain tissue, interquartile range +0.08 to -0.28, P = 0.10). Oxidized cytochrome c oxidase decreased in 11/13 patients (median -0.27 mumol/l, interquartile range -0.19 to -0.44, P = 0.01). Our findings demonstrate an immediate step-response of heart rate and tcpCO2 to aminophylline in premature infants. The simultaneous reduction of cytochrome c oxidase in the brain cannot be explained as a consequence of changes in tcpCO2 or changes in cerebral blood volume. We therefore speculate that aminophylline interferes directly with cerebral metabolism.

Response to added dead space in ventilated preterm neonates and outcome of trial of extubation

The ventilatory response to an added external dead space was assessed in preterm babies, recovering from respiratory distress syndrome, immediately prior to extubation. All babies were ready for extubation as defined by routine clinical criteria. Baseline measurements of respiratory rate, tidal volume, and minute ventilation were made over a 2 min period using a computerized system consisting of a pneumotachometer connected directly to the proximal end of the endotracheal tube. The measurements were repeated after addition of an external dead space equivalent to 2 anatomical dead spaces (4.4 mL/kg body weight). Thirty-four babies were studied on 40 occasions. Twenty-four infants (60%) were successfully extubated and 16 (40%) required reintubation. Infants in the success and failure groups were matched for gestation at birth, postconceptional age and weight at the time of study, maximum ventilatory requirements, and treatment with methylxanthines. The added external dead space resulted in an increase in minute ventilation in 38 out of the 40 studies. Extubation success and failure groups were compared by expressing the minute ventilation after addition of the external dead space as a percentage of the baseline minute ventilation (%MV1). Successful extubation was associated with a higher median %MV1 compared with babies who failed extubation (156; range, 89.3 to 230; compared to 131; range, 75.2 to 165; P = 0.006). This test may be useful in deciding which babies could be successfully extubated.

Influence of prolonged adenosine receptor blockade on fetal sleep and breathing patterns

Chronically prepared fetal sheep were subjected to 48 h infusions of theophylline, an adenosine antagonist, enprofylline, a xanthine without adenosine antagonism, or saline. Theophylline increased mean (+/- SD) incidence of REM sleep from 49.3 +/- 8.3% to 57.3 +/- 6.7% (p < 0.02) and wakefulness from 1.3 +/- 1.4% to 8.1 +/- 7.1% (p < 0.01). On the first day of theophylline infusion incidence of fetal breathing (FB) increased from 37.9 +/- 8.1% to 53.7 +/- 11.6% of total time (p < 0.002) and from 76.4 +/- 10.2% to 87.6 +/- 10.3% of REM sleep (p < 0.02). Diaphragmatic EMG/min increased from 6.9 +/- 4.0 to 17.3 +/- 13 arbitrary units (p < 0.02). By the second day of infusion, FB had returned to baseline value. Enprofylline and saline had no effect. 125 micrograms phenyl isopropyl adenosine (PIA) i.v. caused fetal apnea that was reduced from 143 +/- 45.5 min on the control day to 39.8 +/- 34.7 min (p < 0.001) during theophylline infusion. Enprofylline and saline had no effect, suggesting that the observed theophylline effect was due to its adenosine antagonism rather than to non-specific xanthine action. We conclude that endogenous adenosine suppresses FB, but since theophylline did not alter the basic relationship between FB and REM sleep it is not primarily responsible for apnea during NREM sleep.

Intravenous aminophylline and cerebral blood flow in preterm infants

The effect of aminophylline on cerebral blood flow (CBF) was studied in 10 preterm infants who were receiving 6.2 mg/kg intravenously over 20 minutes followed by a maintenance infusion. CBF was measured intermittently using near infrared spectroscopy. Heart rate, blood pressure, oxygen saturation, and transcutaneously measured carbon dioxide tension (TcPCO2) were recorded continuously. Aminophylline administration was associated with a fall in CBF from a median of 15.9 ml/100 g/min to 11.2 ml/100 g/min. Median fall in CBF was 4.1 ml/100 g/min (95% confidence interval 1.7 to 6.5). Heart rate rose and TcPCO2 fell in all infants, median fall being 0.66 kPa. The reduction in CBF was greater than would be expected on the basis of the modest fall in TcPCO2.

Cutaneous metabolism of theophylline by the human skin

Percutaneous absorption of theophylline in human skin from five sources was examined by use of a flow-through in vitro diffusion system. The metabolites and unchanged drug were estimated by thin-layer chromatography. Correlation was evident in the percentage of the applied dose that diffused through the five skin samples (range 2.8 +/- 0.5%-7.7 +/- 0.8%); however, the percentage of applied dose absorbed varied between different skin samples (range 3.6 +/- 0.9%-33.4 +/- 2.4%). Between 0.2 +/- 0.1%-4.6 +/- 0.2% of the doses applied were metabolized, and over 60% of the total metabolites formed diffused through the skin. The uptake and metabolism of theophylline by microsomes obtained from four of the human skin samples were measured. All preparations showed detectable activities for the metabolism of theophylline. Microsomal preparations from skin sources A, B, and E, and B, C, and E biotransformed theophylline to 1,3,7-trimethyluric acid and 1,3-dimethyluric acid, respectively. The activities of microsomes from skin samples C and E on the drug produced the pharmacologically active metabolite 3-methylxanthine. The specific activities of the microsomes from skin sources A-E for the formation of 1,3-dimethyluric acid and 3-methylxanthine varied fivefold. However, the variation in specific activities of the microsomes for the formation of 1,3,7-trimethyluric acid was twofold (range 2.8 +/- 0.1-6.2 +/- 0.5 pmol/min per mg protein). These metabolic data may be of value in the development of transdermal theophylline systems. The results indicate that a high level of absorption enhancement will be required before transdermal theophylline preparations could produce therapeutic plasma concentrations.

Response to tube breathing in preterm infants with apnea

In order to analyze the effects of maturity and apnea frequency on the respiratory control of preterm infants, we studied their responses to tube breathing using tubes equivalent to two anatomical dead spaces. Ventilation during tube breathing was expressed as a percentage above baseline and compared to an "expected" value calculated from the volume of the added tube. Twenty-seven preterm infants (median birthweight, 1.14 kg.; and gestational age, 29 weeks) were studied on 86 occasions. The percentage of "expected" ventilation increased with post-conceptional age (r = 0.48, slope = 3.12, P less than 0.0005), from a mean of 73% at 26 weeks up to 104% at 36 weeks. Using multiple regression analysis, neither postnatal age nor apnea frequency had any effect once allowance had been made for post-conceptional age. Although the respiratory adaptation of the most immature infants was poor, this study suggests that infants with apnea show no gross deficit in respiratory control, compared to those without apnea.

Drug therapy for bronchopulmonary dysplasia

With improved survival of critically ill premature infants, BPD has become an important sequela of neonatal intensive care. A variety of medications are used in the management of BPD. In this article we have attempted to summarize clinical efficacy, pharmacokinetics, and side effects of many of these medications. Longer-term studies on the efficacy of drug therapy are needed and may be facilitated by the development of accurate and reproducible computerized techniques for the measurement of pulmonary mechanics in neonates. Ultimately, new pharmacologic agents or other strategies that will prevent lung injury from hyperoxia and mechanical ventilation or accelerate tissue repair once injury occurs will play a major role in the prevention and treatment of infants with BPD.

Physiological approaches to respiratory control mechanisms in infants. Assessing the risk for SIDS

We have examined in a group of normal infants and in an "at-risk" group with clinical sleep apnea syndrome the duration and frequency distribution of apneas during sleep. In order to improve the estimation of an apnea factor, we introduced a weighting function which is based on the expected frequency distribution of apnea durations of normal infants. We were able to observe a good agreement between clinical rating, based on anamnestic symptoms, and numerical scoring. All infants of the at-risk group were treated with aminophylline, and the respiratory state improved significantly in nearly all cases. Breathing hypoxic gas mixtures tended to depress respiration, especially in the at-risk group, with a pronounced drop of pO2-values. Investigations on the coordination of respiration, sucking, and swallowing during nutritive sucking demonstrated a correspondence between disturbed coordination ability and the sleep apnea syndrome (SAS). This relationship is interpreted to be a result of an immaturity of the autonomic nervous system. In order to evaluate possible hereditary components in conjunction with respiratory disorders and, possibly, SIDS, we studied siblings of SIDS victims, of near-miss infants, and of infants with SAS. Only siblings of SAS and near-miss infants showed clinical signs of respiratory disorders with a rather high prevalence, whereas most of the siblings of SIDS victims were completely lacking conspicuous respiratory symptoms. Our results suggest that not all infants with sleep apnea syndrome are necessarily at increased risk for SIDS.

The dose response of theophylline in the treatment of apnea of prematurity

In an effort to establish the minimum effective dose of theophylline in the treatment of idiopathic apnea of prematurity, a prospective trial of 22 infants with at least 0.33 episodes of apnea per hour were studied. Apnea was diagnosed exclusively by continuous recording of heart rate, respiratory impedance, end-tidal CO2, and either or both transcutaneous oxygen and pulse oximetry. Four discrete serum concentrations of theophylline (23 mumol/l or 4.2 mg/L, 47 mumol/L or 8.5 mg/L, 70 mumol/L or 12.7 mg/L, and 84 mumol/L or 15.3 mg/L) were attained by using repeated loading doses of 4 mg/kg and increasing the maintenance dose from 1 to 1.5 mg/kg to 2 to 2.5 mg/kg, given every 8 hours. Before treatment and 24 hours after each loading dose, airway occlusions and measures of tidal volume, minute ventilation, and respiratory timing were performed. The effectiveness of therapy was assessed by either a continuous computer data-acquisition system or paper recording for the duration of the study. Of the 22 infants, three responded at level 1, three at level 2, and 10 at level 3. One of the four infants loaded to the fourth level had a sustained response for a total cumulative response of 77%. The five remaining infants required additional treatment with doxapram or continuous positive airway pressure. There was a significant increase in inspiratory pressure 100 msec after airway occlusion, maximum inspiratory pressure during airway occlusion, tidal volume, ratio of tidal volume to inspiratory time (mean inspiratory flow), and minute ventilation from the pretreatment measurements to those at the maximum dose of theophylline. The apnea response did not correlate with these improvements in ventilation measures.

Use of caffeine in infants unresponsive to theophylline in apnea of prematurity

Eleven premature infants with severe apnea unresponsive to therapeutic theophylline levels were studied to determine if caffeine is an effective treatment in such cases. Apnea was documented and quantitated with thermistor-pneumocardiograms measuring heart rate, thoracic impedance, and nasal air flow. Infants with prolonged central or mixed apnea were then treated with caffeine and restudied. Caffeine reduced the total number of apneic episodes of greater than 10 sec duration by 80% (P less than 0.01) and prolonged episodes of apnea (greater than 20 sec) by 88% (P less than 0.05). These data suggest that caffeine may be effective in the management of apnea of prematurity, particularly the prolonged type, unresponsive to theophylline.

Effect of aminophylline on the respiratory depressant action of intravenous adenosine in neonatal rabbits

We administered intravenous adenosine to 11 neonatal rabbits. Adenosine depressed respiration in 10 of 11 rabbits. For the group as a whole the adenosine-induced respiratory depression was highly significant (p less than 0.001). After aminophylline administration to the same animals the respiratory effect of intravenous adenosine was abolished in 3 animals. In 7 animals the effect of adenosine was reversed and respiratory stimulation was observed. After aminophylline adenosine produced a significant (p less than 0.001) increase in respiration in the group studied. The alteration of responses to intravenous adenosine by aminophylline in neonatal rabbits is similar to the effect of aminophylline on respiratory responses to hypoxia in neonates. Such an effect of aminophylline and other methylxanthines on adenosine actions, possibly central in site may explain their beneficial effect in the treatment of apnoea in the human neonate.

Effect of theophylline on respiratory neuromuscular drive

To investigate the possible mechanisms by which theophylline affects the control of ventilation, neuromuscular drive and ventilatory function were examined in 7 healthy men receiving an incremental intravenous aminophylline dosing schedule to achieve plasma theophylline concentrations of 5, 10, and 15 micrograms/ml. As compared with the baseline (predose) values, the 3 incremental aminophylline doses significantly (p less than 0.05 to 0.01) increased occlusion pressure (P0.1) and maximum inspiratory pressure static (MIPS) at functional residual capacity (FRC). This was not observed for ventilatory flow (V), tidal volume (VT), inspiratory time to total breathing cycle time ratio (Ti/Ttot) VT/Ti, and effective impedance [P0.1/VT/Ti)]. When maximum electrical activity of diaphragm (Edimax) and transdiaphragmatic pressure (Pdimax) were examined in 3 of the 7 subjects, Pdi/Edi tended to increase with increasing theophylline concentrations, while Edimax did not. Our results suggest that the increase in P0.1 during the increase in aminophylline dose is caused by an improvement in respiratory muscle contractility, rather than by a central effect or by an increase in neural drive.

The therapeutic actions of theophylline in preterm ventilated infants

40 preterm, ventilated infants (gestational ages 24-33 weeks) were entered into a double-blind randomised trial to assess the effect of oral theophylline on lung function and ventilator dependence. Theophylline administration was associated with a significant improvement in compliance (P less than 0.05) and hastened weaning from ventilation (P less than 0.01).

Caffeine and endurance performance

The belief among athletes that caffeine is an ergogenic aid is common, and several governing bodies of sport have barred use of the drug during competition. At the cellular level, caffeine has been implicated to affect the translocation of calcium in muscle, promote an increase in cellular levels of cyclic AMP and cause a blockade of adenosine receptors in the central nervous system. The general systemic effect of caffeine is to cause central nervous system arousal, mobilisation of free fatty acids and other metabolites, and possibly enhance the contractile status of muscle. At present, the scientific community remains divided as to whether caffeine ingestion will indeed produce an ergogenic effect upon sport performance. Some evidence suggests that caffeine may improve performance in events relying upon strength and power; however, the lack of in vivo research in humans makes it difficult to form firm conclusions. In addition, reports concerning caffeine's effect on VO2max and performance during incremental exercise are not in agreement. On the other hand, recent studies suggest that caffeine might indeed have ergogenic potential in endurance events (e.g. marathon running). It is hypothesised that the mechanism behind these findings is related to the increased availability of free fatty acids for muscle metabolism which has a glycogen-sparing effect.

Rectal aminophylline in the management of apnoea of prematurity

Rectal suppositories as an alternative to intravenous aminophylline in the management of recurrent apnoea were studied in 41 preterm infants of mean gestation 28.3 weeks and mean birthweight 1176 g. Therapeutic blood concentrations were obtained two hours after a rectal loading dose of 10 mg/kg, with steady concentrations and maximum reduction in apnoeic episodes (from a mean of 0.5 per hour to 0.09 per hour) within 24 hours on a maintenance dose of 10 mg/kg/day. There was good correlation between the rectal dose and the plasma theophylline concentration. Several infants showed a significant reduction in Pco2 when treated with aminophylline. Side effects were related to the plasma theophylline concentration and were not seen at concentrations less than 14 mg/l.

Attempted antagonism of adenosine analogue induced depression of respiration

Intracerebroventricular (ICV) administration of the stable adenosine analogue 2-chloroadenosine (2CA) to hyperoxic halothane-anesthetized rats produced a dose-dependent depression of respiration largely as a result of a decrease in tidal volume. Similar changes were noted after another adenosine analogue, phenylisopropyladenosine (PIA). Higher doses shifted the minute ventilation-PaCO2 curve to the right and decreased its slope. Bradycardia and hypotension were produced at doses which altered respiration. Neonatal destruction of brain serotonin or dopamine-containing nerve terminals did not alter the 2CA-induced respiratory depression. Naloxone significantly antagonized the respiratory and circulatory changes produced by 2CA though the changes produced by PIA were not significantly antagonized. Peripherally and intracerebroventricularly administered theophylline were largely ineffective in reversing the 2CA-induced respiratory depression. Thus, these data suggest that a major part of the respiratory depression produced by 2CA is due to indirect activation of opioid receptors. In contrast, very little of the respiratory depression after PIA is via mechanisms antagonized by naloxone. Thus, putative adenosine agonists appear to vary in the extent to which respiratory depression is provoked by interactions with opioid systems.

Clinical spectrum of neonatal apnoea in very low birthweight infants

This study quantifies apnoea and assesses the response to xanthine derivatives amongst 172 consecutively born, surviving very low birth weight (VLBW) infants, 136 appropriate weight for gestational age (AGA), 36 small for gestational age (SGA). All babies had electronic monitoring of heart and respiratory rates and nursing staff recorded episodes of apnoea (greater than 10 s), bradycardia (less than 100) and cyanosis. Only 42 (24.2%) babies had no episodes recorded. (25 AGA, 17 SGA). Sixty-four (37.2%) received active resuscitation on at least one occasion with six babies ventilated by bag and mask on more than 10 occasions. Apnoea had commenced by day 10 of life in all the babies who had apnoea and persisted beyond day 50 in only six; however four of these infants were still requiring active resuscitation. Apnoea had ceased by 37 weeks post-conceptual age in 88% and by 40 weeks in all but three babies. Risk factor analysis revealed a strong correlation (P less than 0.005) with lower gestational ages and birth weights, respiratory distress syndrome (RDS) and the problems associated with it, such as mechanical ventilation, patency of the ductus arteriosus (PDA) and chronic neonatal lung disease. A single, reversible cause for apnoea was rarely demonstrated. Care must be exercised with feeding, physiotherapy and suctioning the pharynx and trachea of 'at risk' infants. Xanthine derivatives were highly effective in decreasing the frequency of recurrent apnoea from a mean of 10.08 episodes one day before, to 1.83 two days after commencement of treatment.

Theophylline improves pneumogram abnormalities in infants at risk for sudden infant death syndrome

To determine the efficacy of theophylline treatment in infants at increased risk for SIDS, we obtained 24-hour cardiorespiratory recordings (pneumograms) in 80 infants given theophylline in whom the initial pneumogram was abnormal. Fifty-three infants had a clinical diagnosis of near-SIDS, and 27 were asymptomatic siblings with a positive family history for SIDS. The initial pneumogram was obtained at a mean age of 6.9 weeks, and the repeat pneumogram 2.3 weeks later, when the mean theophylline blood concentration was 11.2 +/- 0.5 micrograms/ml. Theophylline treatment resulted in comparable and highly significant improvements in both groups. Among all 80 infants, apnea density decreased from 1.6 +/- 0.2% (SEM) to 0.3 +/- 0.1% (P less than 0.001), periodic breathing episodes/100 minutes decreased from 2.7 +/- 0.4 to 0.3 +/- 0.1 (P less than 0.001), and the longest apneic period decreased from 13.5 +/- 0.7 to 10.1 +/- 0.5 seconds (P less than 0.001). Findings on the pneumogram became completely normal with theophylline therapy in 87% of infants with near-SIDS and 81.5% of asymptomatic siblings. Pneumogram normalization was associated with absence of further symptomatic sleep apnea in the near-SIDS group and with continued absence of any clinical symptoms in the asymptomatic family history group. There were no deaths from SIDS.

Effect of caffeine on control of breathing in infantile apnea

Abnormalities in control of breathing have been associated with near-miss sudden infant death syndrome. Because caffeine is a respiratory stimulant, its effect on breathing pattern was evaluated in 12 infants with infantile apnea. Caffeine induced a significant increase in ventilation, tidal volume, and mean inspiratory flow. In contrast, no changes were noted in inspiratory time, expiratory time, or total cycle duration. These effects were observed with plasma concentrations of caffeine ranging from 8 to 20 mg/L. Caffeine increases ventilation mainly by increasing central inspiratory drive, and not be effective timing (T1/TTOT). This drug may be of value in near-miss SIDS.

Neonatal breathing control mediated via the central chemoreceptors

Respiratory changes elicited via the central chemoreceptor system have been studied in anesthetized newborn guinea pigs and newborn rabbits. Periodic breathing was induced by inhibition of the central chemoreceptors by superfusion with alkaline cerebrospinal fluid. The periodic breathing was promptly reversed to steady by increasing the oxygen or carbon dioxide concentration in the inspired air or by intravenous theophylline. Elicitation of periodic breathing simply by exposing the animals to hypoxia succeeded only when very low oxygen concentrations were given. Clearcut respiratory excitation was produced by small amounts of theophylline applied onto the ventral surface of the medulla. Not only theophylline intravenously but also theophylline topically applied on the ventral medullary surface normalized spontaneously developed periodic breathing. Application of meperidine onto the ventral medullary surface gave respiratory inhibition with dosages considerably lower than required when given intravenously. The results emphasize the importance of an adequate respiratory drive from the central chemoreceptors for the maintenance of a regular breathing pattern. The findings support a view that at least part of the respiratory effects seen in the newborn following administration of meperidine or theophylline is due to effect of the drugs on the central chemosensitive system.

Mechanism of respiratory effects of methylxanthines

Neural respiratory responses to theophylline, aminophylline and ethylenediamine were determined in paralyzed, vagotomized and glomectomized cats whose end-tidal PCO2 and brain temperature were kept constant. Intravenous theophylline and aminophylline similarly stimulated respiration, but ethylenediamine had no effect. The following did not cause the response: muscular and mechanical factors, carotid body and vagal reflexes, spinally mediated mechanisms arising below C7, changes of arterial PCO2 or medullary ECF pH, changes of whole body metabolic rate or release of substances from the adrenal glands. Absence of suprapontine brain did not prevent the response. Pretreatment with a serotonin antagonist did not affect the response but two different dopamine antagonists caused its attenuation. When administered into the third ventricle, theophylline did not stimulate respiration, but both aminophylline and ethylenediamine, due to the latter's ability to mimic the inhibitory effects on neurons of gamma-aminobutyric acid (GABA), caused significant depression of respiration. We conclude that the neural respiratory response to systemically administered theophylline is mediated at the level of the brainstem, and somehow involves the action of the neurochemical dopamine. The failure of cerebroventricularly administered theophylline to stimulate respiration must be related to its inability to reach the appropriate neurons from the cerebrospinal fluid.

Physiological and clinical aspects of respiration control in infants with relation to the sudden infant death syndrome

We have examined the behavior of several variables which are related to respiratory control in 114 infants (up to 6 months of age) in order to assess the risk for the sudden infant death syndrome (SIDS), 23 of the infants had already had demonstratable serious or life threatening apneas or respiratory problems during surgical anesthesia. These infants were assigned as a risk group, and the rest of the investigated babies was taken as a control group. We found that practically all infants of the risk group had apneas during sleep, which lasted longer than 8 s each. Only 22% of the infants of the control group had apneas of such a duration. As a statistical parameter, calculated from at least 1 hour recording of respiration, we defined the mean apnea duration (MA-value) as average value of apnea duration time in seconds per minute of recording. The MA-value proved to be significantly elevated in the infants of the risk group. The trend to hypoxia in the infants of the risk group was also indicated by the observation of lower transcutaneous PO2-values (tc-PO2) during sleep, when compared with control infants. In agreement with this observation is the increase of the 2,3-DPG concentration and the decrease of the density of erythrocytes of the infants of the risk group. Breathing hypoxic gas mixtures tended to depress respiration in all infants tested, and, especially in the risk group, to elicit irregular respiratory patterns. On the other hand, we observed that inhalation of pure oxygen markedly stimulated respiration in all infants investigated. We conclude from these observations that a risk for SIDS may be related to a particular response pattern of the respiratory center during the early postnatal life. We are able to distinguish infants with a higher risk for SIDS from other children by determination of the MA-value during sleep.

Pharmacologic considerations in the therapy of neonatal apnea

Theophylline and caffeine are both effective stimulants of the central nervous system for the therapy of neonatal apnea. Both drugs are slowly eliminated from the body, and doses should be adjusted to account for this slow elimination. Interconversion of theophylline and caffeine occurs in the newborn infant, with the methylation of theophylline to caffeine as the probable predominant pathway. Caffeine may offer advantages over theophylline: wider therapeutic index, case of administration, less need for therapeutic drug monitoring, less fluctuation in plasma concentrations, and fewer peripheral effects. A major disadvantage of caffeine is in the lack of a readily available commercial preparation. Both drugs exert many pharmacologic actions that require further evaluation in the newborn infant. Long-term effects of these drugs administered during a critical period in the developing human remains an area of concern.