Caffeine, a metabolite of theophylline during the treatment of apnea in the premature infant

Factors affecting the efficacy and safety of aminophylline in treatment of apnea of prematurity in neonatal intensive care unit

BACKGROUND

The factors affecting the safety and efficacy of aminophylline use in the treatment of apnea of prematurity (AOP) in the neonatal intensive care unit (NICU) are not clear. In this study, we aimed to evaluate the potential factors affecting the efficacy and safety of aminophylline in AOP treatment at standard doses and to determine appropriate patients for this therapy.

METHODS

Over a 3-year period (January 2012 to December 2014), the medical records of 206 preterm infants with apnea who were admitted to the NICU of our hospital to receive aminophylline infusions were retrospectively reviewed. These infants were subjected to routine theophylline monitoring by reversed-phase high performance liquid chromatography. The primary outcome measures were the efficacy of aminophylline treatment and adverse reactions observed upon administration.

RESULTS

One-hundred and twenty-seven (61.65%) infants were considered to have undergone effective therapy and classified accordingly. Gestational age, body weight at the initiation of aminophylline, and serum theophylline concentration were identified as protective factors of therapeutic efficacy. Receiver operating characteristic (ROC) analysis indicated cutoff values of 30.36 weeks for gestational age and 1.69 kg for body weight at initiation of aminophylline administration for ensuring high efficacy of aminophylline for AOP. Fifty-three (25.73%) infants had adverse reactions. Birth weight and serum concentration of theophylline were associated with an increased risk of adverse reactions, with odds ratios of 0.167 and 1.346, respectively. The ROC curves indicated a birth weight cutoff value of 1.48 kg.

CONCLUSION

Infants with apnea and gestational age >30.36 weeks, body weight at initiation of aminophylline treatment above 1.69 kg, and birth weight >1.48 kg are suitable for treatment with aminophylline. Monitoring of serum theophylline concentration should be implemented in the absence of clinical response or in case of suspected adverse reactions.

Caffeine use in the neonatal intensive care unit

Caffeine is the most frequently used medication in the neonatal intensive care unit. It is used for the prevention and treatment of apnea, although this has been associated with lower incidence of bronchopulmonary dysplasia (BPD) and patent ductus arteriosus as well as intact survival at 18-21 months of life. Although neurodevelopmental advantage was no longer statistically significant at age 5 years, caffeine was associated with sustained improvement in co-ordination and less gross motor impairment than placebo. The mechanism of action of caffeine on prevention of apnea and activation of breathing seems to be through central inhibition of adenosine receptors. However, its impact on BPD and neurodevelopmental outcomes might be induced through its effects as anti-inflammatory mediator, protection of white matter, and induction of surfactant protein B. Whereas long-term studies have documented the safety of caffeine as used in current practice, further studies are clearly needed to identify optimum dosing, and time of starting and discontinuing caffeine.

Predictive Factors for Efficacy and Safety of Prophylactic Theophylline for Extubation in Infants with Apnea of Prematurity

PURPOSE

This study aimed to evaluate predictive factors involved in efficacy and safety in Japanese infants who received theophylline therapy to prevent apnea of prematurity (AOP) after weaning from mechanical ventilation.

METHODS

We retrospectively reviewed the medical records of infants who were administered intravenous aminophylline (theophylline ethylenediamine) for AOP at the neonatal intensive care unit, Kagoshima University Hospital, Japan, between January 2009 and June 2013.

RESULTS

A total of 100 infants were evaluated as two separate groups in terms of efficacy and safety of theophylline. Sixty-seven (67.0%) infants had effective theophylline therapy. Multivariate logistic regression analysis showed that gestational age at birth was significant, with an odds ratio of 0.59 (p < 0.001). Receiver operating characteristic analysis showed that the cut-off value was 31.1 weeks old for predicting the efficacy of theophylline (specificity, 66.7%; sensitivity, 86.6%; p < 0.001; area under the curve, 0.750; 95% confidence interval, 0.45-0.74). Adverse reactions were identified in 21 (21.0%) infants. Multivariate logistic regression analysis showed that the number of days of theophylline administration from birth was associated with an increased risk of adverse reactions after theophylline administration (p = 0.01).

CONCLUSIONS

Physicians need to be aware of the possibility that theophylline fails to produce therapeutic effects for extubation in infants aged less than 31.1 weeks old, and adverse reactions can easily develop when theophylline is administered soon after birth.

Caffeine versus theophylline for apnea of prematurity: a randomised controlled trial

AIM

To compare standard doses of theophylline and caffeine for apnea of prematurity in terms of apnea frequency and assess the need for therapeutic drug monitoring.

METHODS

Seventy neonates less than 33 weeks gestation, breathing spontaneously, were randomly assigned (open-label) to receive either theophylline or caffeine for treatment or prevention of apnea. The primary outcome measure was the difference in apnea frequency between theophylline and caffeine patient groups. Methylxanthine serum levels were measured on the 1st, 3rd and 7th days of therapy and every 7 days thereafter.

RESULTS

Thirty-seven neonates received theophylline (T) and 33 caffeine (C) for treatment (8 T/10 C) or prevention of apnea (29 T/23 C). Treatment with either methylxanthine significantly decreased apnea events (T, P= 0.012; C, P= 0.005) while only C prophylaxis appeared to control apnea in infants at risk. Analysis of combined (treatment plus prophylaxis) data showed a significant decrease in apnea frequency only in those infants receiving caffeine (P= 0.001). However, there was no sustained benefit of C over T beyond the first week of therapy. T and C concentrations (2.2-13.9 mg/L; 5.5-23.7 mg/L, respectively) in the majority of cases fell within the recommended therapeutic ranges and were not significantly associated with apnea events.

CONCLUSIONS

This study shows an advantage of C over T for premature infants <33 weeks gestation during the first week of therapy. Standard regimens of both methylxanthines do not seem to require routine concentration monitoring in the first 3 weeks of treatment unless indicated by clinical effect.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

Differences in absorption, distribution, metabolism and excretion of xenobiotics between the paediatric and adult populations

In children, the therapeutic benefits and potential risks associated with drug treatment may be different from those in adults and will depend on the exposure, receptor sensitivity and relationship between effect and exposure. In this paper, key factors undergoing maturational changes accounting for differences in drug metabolism and disposition in the paediatric population compared with adults are reviewed. Gastric and duodenal pH, gastric emptying time, intestinal transit time, secretion and activity of bile and pancreatic fluid, bacterial colonisation and transporters, such as P-glycoprotein (P-gp), are important factors for drug absorption, whereas key factors explaining differences in drug distribution between the paediatric population and adults are organ size, membrane permeability, plasma protein concentration and characteristics, endogenous substances in plasma, total body and extracellular water, fat content, regional blood flow and transporters such as P-gp, which is present not only in the gut, but also in liver, kidney, brain and other tissues. As far as drug metabolism is concerned, important differences have been found in the paediatric population compared with adults both for phase I enzymes (oxidative [e.g., cytochrome P450 (CYP)1A2, and CYP3A7 versus -3A4], reductive and hydrolytic enzymes) and phase II enzymes (e.g., N-methyltransferases and glucuronosyltransferases). Generally, the major enzyme differences observed in comparison with the adult age are in newborn infants, although for some enzymes (e.g., glucuronosyltransferases and other phase II enzymes) important differences still exist between infants and toddlers and adults. Finally, key factors undergoing maturational changes accounting for differences in renal excretion in the paediatric population compared with adults are glomerular filtration and tubular secretion. The ranking of the key factors varies according to the chemical structure and physicochemical properties of the drug examined, as well as to the characteristics of its formulation. It would be important to generate additional information on the developmental aspects of renal P-gp and of other renal transporters, as has been done and is still being done with the different -isozymes involved in drug metabolism.

Caffeine Use in Sports, Pharmacokinetics in Man, and Cellular Mechanisms of Action

Caffeine is the most widely consumed psychoactive 'drug' in the world and probably one of the most commonly used stimulants in sports. This is not surprising, since it is one of the few ergogenic aids with documented efficiency and minimal side effects. Caffeine is rapidly and completely absorbed by the gastrointestinal tract and is readily distributed throughout all tissues of the body. Peak plasma concentrations after normal consumption are usually around 50 microM, and half-lives for elimination range between 2.5-10 h. The parent compound is extensively metabolized in the liver microsomes to more than 25 derivatives, while considerably less than 5% of the ingested dose is excreted unchanged in the urine. There is, however, considerable inter-individual variability in the handling of caffeine by the body, due to both environmental and genetic factors. Evidence from in vitro studies provides a wealth of different cellular actions that could potentially contribute to the observed effects of caffeine in humans in vivo. These include potentiation of muscle contractility via induction of sarcoplasmic reticulum calcium release, inhibition of phosphodiesterase isoenzymes and concomitant cyclic monophosphate accumulation, inhibition of glycogen phosphorylase enzymes in liver and muscle, non-selective adenosine receptor antagonism, stimulation of the cellular membrane sodium/potassium pump, impairment of phosphoinositide metabolism, as well as other, less thoroughly characterized actions. Not all, however, seem to account for the observed effects in vivo, although a variable degree of contribution cannot be readily discounted on the basis of experimental data. The most physiologically relevant mechanism of action is probably the blockade of adenosine receptors, but evidence suggests that, at least under certain conditions, other biochemical mechanisms may also be operational.

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.

Drug metabolism and disposition in children

Key factors undergoing maturational changes accounting for differences in drug metabolism and disposition in the pediatric population compared with adults are reviewed. Gastric and duodenal pH, gastric emptying time, intestinal transit time, bacterial colonization and probably P-glycoprotein are important factors for drug absorption, whereas key factors explaining differences in drug distribution between the pediatric population and adults are membrane permeability, plasma protein concentration and plasma protein characteristics, endogenous substances in plasma, total body and extracellular water, fat content, regional blood flow and probably P-glycoprotein, mainly that present in the gut, liver and brain. As far as drug metabolism is concerned, important differences have been found in the pediatric population compared with adults both for phase I enzymes [oxidative (e.g. cytochrome CYP3A7 vs. CYP3A4 and CYP1A2), reductive and hydrolytic enzymes] and phase II enzymes (e.g. N-methyltransferases and glucuronosyltransferases). Finally, key factors undergoing maturational changes accounting for differences in renal excretion in the pediatric population compared with adults are glomerular filtration and tubular secretion. It would be important to generate information on the developmental aspects of renal P-glycoprotein and of other renal transporters as done and still being done with the different isozymes involved in drug metabolism.

Caffeine citrate: a review of its use in apnoea of prematurity

Apnoea of prematurity is a common condition in neonates born at less than 37 weeks' gestational age; it affects approximately 90% of premature neonates weighing under 1000 g at birth, and 25% of infants with a birthweight of less than 2500 g. Caffeine, a methylxanthine which occurs naturally in many plants, has been used for over 20 years to treat apnoea of prematurity. In a recent double-blind, placebo-controlled trial, apnoea was eliminated or reduced by at least 50% in significantly more neonates receiving caffeine citrate as first-line treatment than those receiving placebo. In a nonblind trial, caffeine citrate was more effective at reducing apnoeic episodes when compared with neonates receiving no treatment. Caffeine as first-line treatment demonstrated similar efficacy to theophylline or aminophylline (theophylline ethylenediamine) in 4 small randomised studies. Caffeine citrate was generally well tolerated in short term clinical trials, with very few adverse events reported. Caffeine was associated with fewer adverse events than theophylline in randomised trials. No differences in the incidence of individual adverse events were reported between caffeine citrate and placebo in a double-blind, randomised trial. Long term tolerability data are not yet available.

CONCLUSIONS

Caffeine citrate was generally well tolerated by neonates in clinical trials and it decreased the incidence of apnoea of prematurity compared with placebo. It has demonstrated similar efficacy to theophylline, but is generally better tolerated and has a wider therapeutic index. Caffeine citrate should, therefore, be considered the drug of choice when pharmacological treatment of apnoea of prematurity is required.

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.

Caffeine-induced increases in the brain and plasma concentrations of neuroactive steroids in the rat

The effects of caffeine, a naturally occurring stimulant, on the brain and plasma concentrations of neuroactive steroids were examined in the rat. A single intraperitoneal injection of caffeine induced dose- and time-dependent increases in the concentrations of pregnenolone, progesterone, and 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) in the cerebral cortex. The increases were significant at a caffeine dose of 25 mg/kg and greatest (+188, +388, and +71%, respectively) at a dose of 100 mg/kg in rats killed 30 min after caffeine administration. Caffeine also increased the plasma concentrations of pregnenolone and progesterone with a dose-response relation similar to that observed in the brain, whereas the caffeine-induced increase in the plasma concentration of allopregnanolone was maximal at a dose of 50 mg/kg. Caffeine increased the plasma concentration of corticosterone, but it had no effect on the brain or plasma concentrations of 3alpha, 21-dihydroxy-5alpha-pregnan-20-one and dehydroepiandrosterone. Moreover, the brain and plasma concentrations of pregnenolone, progesterone, and allopregnanolone were not affected by caffeine in adrenalectomized-orchiectomized rats. These results suggest that neuroactive steroids may modulate the stimulant and anxiogenic effects of caffeine.

Caffeine overdose in a premature infant: clinical course and pharmacokinetics

The elimination of caffeine was investigated in a 1860 g, 31 week gestation neonate, following the accidental administration of a 160 mg.kg-1 dose. The first serum concentration measured was 217.5 mg.l-1 at 36.5 h after dosing. Fitting of time-concentration data was performed using non-linear regression with MKMODEL. A first order elimination model was superior to a mixed order model. Parameter estimates were: clearance 0.01 l.h-1, volume of distribution 1.17 litres, elimination half-life 81 h. Toxic manifestations included hypertonia, sweating, tachycardia, cardiac failure, pulmonary oedema and metabolic disturbances (metabolic acidosis, hyperglycaemia and creatine kinase elevation). An unusual feature of this infant's illness course was gastric dilatation. These signs resolved by day 7 at a serum concentration of 60-70 mg.l-1. Caffeine clearance has traditionally been reported as either an absolute value or as directly proportional to body weight. The per kilogram model gives an erroneous impression that clearance is greatest in early childhood and then decreases with age until adult rates are reached in late adolescence. Age-related clearance values reported in the literature were reviewed using an allometric 3/4 power model. This size model demonstrates that clearance increases in infancy and reaches adult rates within the first three months of life.

In vivo age-related changes in hepatic drug-oxidizing capacity in humans

Very few studies have been carried out looking at how the effects of drugs and their toxicity in humans change during their lifespan (developing and ageing). The purpose of this study is to review the literature on the changes in probe-drug metabolism, classified by cytochrome P450 (P450 or CYP) at five stages in life: neonates < 4 weeks, infants < 12 months, children < 19 years, young/mature adults 20-64 years, and elderly adults > 65 years. The main probe drugs include caffeine and theophylline, whose metabolism is catalysed by CYP1A2, tolbutamide, phenytoin and ibuprofen, catalysed by CYP2C9, amitriptyline and nortriptyline, catalysed by CYP2C19, acetaminophen, catalysed by CYP2E1 and lidocaine, midazolam and terfenadine, catalysed by 3A3/4. From the published in vivo studies two different patterns of drug metabolism can be identified: (i) activity is low immediately after birth, increases, then peaks at the young/mature adult level and, finally, decreases in old age (drugs catalysed by CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A3/4) and (ii) activity increases rapidly after birth to reach a level equivalent to that in the young/mature adult, then gradually decreases and finally decreasing faster in old age (drugs catalysed by CYP2E1). Further study of the changes in P450 with age is warranted to help prevent adverse reactions and to guide us in tailoring therapy better for the individual patient.

Anesthesia and apnea. Perioperative considerations in the former preterm infant

Former preterm infants younger than 44 weeks postconceptual age are at increased risk for developing postoperative apnea and PB. When surgery cannot be deferred until the infant is developmentally more mature, several measures should be taken to minimize the risk of ventilatory dysfunction. First, outpatient surgery is not advisable for infants younger than 44 weeks postconceptual age. All infants should be admitted to the hospital and monitored for apnea and bradycardia for at least 12 to 18 hours after surgery. Second, we recommend the use of intravenous caffeine base 10 mg/kg in all infants at risk for postoperative apnea following general anesthesia. Preliminary studies of a small number of patients indicate that spinal anesthesia without sedation is associated with less apnea than is general anesthesia or spinal anesthesia with ketamine sedation. This option warrants further consideration. Infants with anemia of prematurity, generally a benign condition, are at increased risk for postoperative apnea. It is therefore preferable to delay elective surgery and supplement the feeds with iron until the Hct is above 30%. When surgery cannot be deferred, anemic infants must be observed and monitored carefully in the postoperative period.

Theophylline toxicity in a premature neonate--elimination kinetics of exchange transfusion

Exchange transfusion was utilized in the treatment of a 1871 gram female, 32 weeks gestational age, who received an IV bolus of aminophylline at 11 h for the treatment of apnea, with subsequent tachycardia and hypotension. At 22 h, plasma theophylline was 369.29 mumol/L (67 mg/L). During a single volume exchange transfusion at 33 h, the plasma theophylline decreased 19% and the estimated removal of theophylline was 13.5% of the whole body theophylline. The theophylline apparent half-times before, during, and after the exchange were 52.5, 6.6, and 53.3 h respectively.

Caffeine and the central nervous system: mechanisms of action, biochemical, metabolic and psychostimulant effects

Caffeine is the most widely consumed central-nervous-system stimulant. Three main mechanisms of action of caffeine on the central nervous system have been described. Mobilization of intracellular calcium and inhibition of specific phosphodiesterases only occur at high non-physiological concentrations of caffeine. The only likely mechanism of action of the methylxanthine is the antagonism at the level of adenosine receptors. Caffeine increases energy metabolism throughout the brain but decreases at the same time cerebral blood flow, inducing a relative brain hypoperfusion. Caffeine activates noradrenaline neurons and seems to affect the local release of dopamine. Many of the alerting effects of caffeine may be related to the action of the methylxanthine on serotonin neurons. The methylxanthine induces dose-response increases in locomotor activity in animals. Its psychostimulant action on man is, however, often subtle and not very easy to detect. The effects of caffeine on learning, memory, performance and coordination are rather related to the methylxanthine action on arousal, vigilance and fatigue. Caffeine exerts obvious effects on anxiety and sleep which vary according to individual sensitivity to the methylxanthine. However, children in general do not appear more sensitive to methylxanthine effects than adults. The central nervous system does not seem to develop a great tolerance to the effects of caffeine although dependence and withdrawal symptoms are reported.

Caffeine or theophylline for neonatal apnoea?

Caffeine, in the dose usually recommended (12.5 mg/kg loading dose and 3 mg/kg daily maintenance), and a higher dose regimen (25 mg/kg loading and 6 mg/kg daily maintenance), was compared with theophylline (7.5 mg/kg loading and 3 mg/kg thrice daily maintenance). The study was a randomised controlled trial in the treatment of a group of 44 infants of less than 31 weeks' gestation (mean gestational age 28.3 weeks) who were suffering from frequent apnoeic attacks. All three regimens produced a significant reduction in apnoeic attacks within 24 hours, but only the higher dose caffeine and theophylline groups showed a significant improvement in apnoea within eight hours. The use of caffeine for the treatment of neonatal apnoea is recommended, because a once daily dose is more easily administered, and because it was found that plasma concentrations were more predictable than those of theophylline. If used in very preterm infants, however, its is suggested that a higher dose regimen than that previously recommended be used to achieve a faster response.

Methylxanthines: toxicity to humans. 3. Theobromine, paraxanthine and the combined effects of methylxanthines

This review provides a brief overview of known information on the human toxicity of theobromine and paraxanthine. Theobromine has some pharmacological effects, although these activities are considerably weaker than those of theophylline and/or caffeine, described in parts 1 and 2 of this series (Stavric, Fd Chem. Toxic. 1988, 26, 541 & 645). Paraxanthine, which is not found in plants or foods, is the major metabolite of caffeine in humans, in whom its toxicological potency appears to be very low. This paper gives a brief retrospective view of possible toxicological effects when methylxanthines are taken simultaneously or are present in combination as a result of metabolic transformation. Critical review of toxic manifestations due to exposure to relatively large doses of caffeine and theophylline indicates that such combined exposure may potentiate the toxic effects of either drug.

Methylxanthines: toxicity to humans. 2. Caffeine

While there are several comprehensive reviews on the toxic effects of methylxanthines in animals, data on the toxicity of these chemicals in humans has not been extensively reviewed in one document. In a previous paper (Stavric, Fd Chem. Toxic. 1988, 26, 541), the toxicity of theophylline was reviewed. This paper, the second of three, is intended to provide an overview of the human toxicity of caffeine. Only pertinent and recent information on caffeine toxicity is summarized. In addition, some information regarding the benefits of caffeine and the mechanism of its effects is also provided. The use, effects and toxicity of caffeine intake are reviewed separately for different segments of the population. Controversy concerning the possible association of caffeine with fibrocystic disease of the breast and over the behavioural effects of the drug is presented briefly.

Methylxanthines: toxicity to humans. 1. Theophylline

While there are several comprehensive reviews on the toxic effects of theophylline, caffeine and theobromine in animals, data on the toxicity of these methylxanthines in humans have not been extensively reviewed in one document. This question will be addressed in a series of three papers. This paper provides an overview of the human toxicity of theophylline. Only pertinent and recent information on theophylline toxicity is summarized. In addition, some information regarding the use and benefits of theophylline, the mechanism of its effects and factors that affect variability in its clearance and half-life is also provided. Some problems in the analytical methodology of theophylline, problems that may be responsible for the controversy in the reported dose-response effects, are critically reviewed.

Pharmacokinetics of caffeine in breast milk and plasma after single oral administration of caffeine to lactating mothers

Six healthy lactating women ranging in age from 28 to 35 years were selected to participate in the study. The women had been nursing their infants from 3 1/2 weeks up to 17 weeks. On the morning of the study each participant received 100 mg dose of caffeine. The oral dose of caffeine was taken with a glass of water on an empty stomach. Blood samples were collected from zero time to 24 h after caffeine administration. Each subject aseptically collected breast milk from the right and left breasts by manual expression or using a mechanical breast pump, from zero time to 24 h after caffeine administration. Caffeine in plasma and breast milk was determined by gas liquid chromatography using nitrogen phosphorous detection. Caffeine was rapidly absorbed producing plasma time to peaks ranging from 0.50 to 1.00 h, with values for peak concentrations between 3.60 and 6.15 micrograms ml-1 in plasma. In breast milk, time to peak ranged from 0.75 to 2.00 h and concentration values between 1.98 and 4.30 micrograms ml-1. No significant differences were found between attainment of the time of the peak in plasma and breast milk, p greater than 0.05. In addition, peak concentration for the right and left breast were not statistically different, p greater than 0.05. However, significant differences, p less than 0.05, between plasma and both breasts in regards to the peak concentrations were found. The overall breast milk/plasma ratio obtained from the respective area under the curves were 0.815 +/- 0.0521 and 0.809 +/- 0.202 for the right and left breast, respectively, and no statistical differences were observed between the right and left breasts, p greater than 0.05. In summary, caffeine is rapidly transferred to breast milk. Multiple dose studies are needed to provide more information about caffeine concentration in breast milk of women who receive multiple doses of caffeine or who chronically consume caffeine.

A rapid HPLC method for monitoring plasma levels of caffeine and theophylline using solid phase extraction columns

A simple HPLC method for the determination of caffeine and theophylline in plasma is described. Separation of theobromine, paraxanthine, theophylline, beta-hydroxyethyltheophylline and caffeine is obtained using a mobile phase of 1% acetic acid/methanol (83:17, v/v) and a Waters Associates NOVA-PAK C18 column protected by a Guard-PAK precolumn module containing a Guard-PAK CN cartridge. Rapid sample preparation is achieved by solid-phase extraction columns (Bond-Elut C18, 1 mL capacity) which provide excellent recovery values for both drugs. The cost per sample using this approach can be minimised by column regeneration and re-use. Results obtained for theophylline are in good agreement with values determined by other techniques.

Improved high-performance liquid chromatographic method for the simultaneous determination of caffeine and its N-demethylated metabolites in plasma using solid-phase extraction

An improved high-performance liquid chromatographic method for the simultaneous determination of caffeine and its N-demethylated metabolites in plasma is described. Excellent resolution of all components is provided by reversed-phase chromatography using a mobile phase consisting of 1% acetic acid-methanol (83:17) at a flow-rate of 2.7 ml/min, in conjunction with a Waters Assoc. Nova-Pak C18 column which was protected by a Waters Assoc. Guard-Pak precolumn module containing a Guard-Pak CN cartridge. Rapid extraction of caffeine and the dimethylxanthines from plasma was achieved using reversed-phase octadecylsilane bonded-silica columns (Bond-Elut C18). With only 100 microliters of sample, plasma levels in the region of 50 ng/ml for the dimethylxanthines and 100 ng/ml for caffeine can be determined using ultraviolet detection at 273 nm. The method has been used for measuring umbilical cord plasma samples to provide information regarding foetal exposure to caffeine and its metabolites and is also suitable for therapeutic drug monitoring of caffeine and theophylline levels in the treatment of neonatal apnoea.

Comparison of the urinary metabolite profile of caffeine in young and elderly males

The urinary metabolite profile of caffeine was compared in a group of seven healthy young men aged 18-29 years and in a group of five healthy elderly men aged 66-71 years. All subjects were given 5 mg/kg doses of caffeine as an aqueous oral solution or an intravenous infusion on two separate occasions in a randomized crossover design. Urine samples were collected for 24 h after dosing and analysed for caffeine and eleven of its metabolites by high-performance liquid chromatography. The effects of age, route of administration, and order of administration by route on the metabolite profile of caffeine were examined. The route of administration and the order of administration by the two routes were found not to influence the urinary metabolite pattern significantly. The urinary metabolite profile did not vary substantially with age except for the observation that significantly greater amounts of 1-methyluric acid, 7-methyluric acid and 1,7-dimethyluric acid were excreted by the elderly subjects.

Apnea in newborn infants: approach to management

Approximately 25% of infants with birth weights less than 1800 g or infants of about 34 weeks gestational age have an apneic episode. This, and the known high incidence of apneas in infants who subsequently are victims of sudden infant death syndrome, has led to aggressive attempts at early identification of newborns with abnormal cardio-respiratory patterns. We have found the pneumocardiogram to be effective in detecting cardio-respiratory abnormality in the newborn, and a very useful tool in the assessment of the effectiveness of pharmacologic therapy of neonatal apnea. Infants who are discharged on a home apnea monitor should be managed, utilizing a coordinated multidisciplinary team approach, that includes 24 h availability of a physician, technician, community health nurse, social worker and, when possible, a member of a parent support group. This paper presents a review of neonatal apnea and our institutional approach to its evaluation and management.

Plasma xanthine levels in premature infants treated for apnoea with theophylline

Evidence is presented that oral theophylline doses of 3 mg per kg per 24 h in premature babies produces plasma levels of theophylline and caffeine of about 5 and 1-2 mg/l respectively in most subjects.

Gas chromatographic-mass spectrometric quantitation of theophylline and its metabolites in biological fluids

In premature infants, theophylline is converted to caffeine, and the biological half-life is prolonged. To assess the metabolic alterations of theophylline during development of premature infants, a sensitive and simple method was developed which quantitated all theophylline metabolites in plasma, urine, and red blood cells. Theophylline and its metabolites in the sample were converted to the N-propyl derivative using n-propyl iodide in dimethylformamide with potassium carbonate catalysis and were analyzed under isothermal conditions on a gas chromatograph-mass spectrometer with a 3% methylsilicone-phenylsilicone column. Deuterated caffeine (caffeine-d3) was used as the internal standard. A selected ion-monitoring technique, together with 70-eV electron impact ionization mode, was used. The ion current ratios between caffeine-d3 (m/z 197) and caffeine (m/z 194), theophylline (m/z 222), 3-methylxanthine (m/z 250), 1,3-dimethyluric acid (m/z 280), and 1-methyluric acid (m/z 308) were monitored. The total analysis time was 12 min with a detection limit ranging from 500 pg to 10 ng, depending on the metabolites. With this sensitivity, sample sizes of 50-100 microliters of plasma and 0.5 ml of urine were sufficient for the analysis of all theophylline metabolites. The coefficient of variation of this method was less than 5% for the analysis of biological samples.

Theophylline. A "state of the art" review

Theophylline is a bronchodilator and respiratory stimulant that is effective in the treatment of acute and chronic asthma, Cheyne-Stokes respirations, and apnea/bradycardia episodes in newborns. It is also used as an adjunct in the treatment of congestive heart failure and acute pulmonary edema, but it has no established efficacy in patients with chronic irreversible airways obstruction. Benefits and risks from theophylline relate directly to serum concentration, which is a function of both dose and elimination characteristics of the drug in an individual patient. When used to treat acute symptoms, an initial loading dose based on a mean volume of distribution is required to rapidly obtain maximum bronchodilator effect. Because of large interpatient differences in elimination, constant intravenous infusion rates for continued therapy must be guided by monitoring serum theophylline concentration at intervals until a steady-state serum concentration is reached within the 10-20 micrograms/ml therapeutic range. Intravenous, oral or rectal solutions and plain uncoated tablets are appropriate for acute therapy, while reliably absorbed slow-release formulations offer therapeutic advantages for the management of chronic asthma, particularly in patients with rapid elimination. Dosage for long-term therapy is determined by starting with low doses that allow virtually complete acceptance of the medication followed by gradual increases, if tolerated, at three day intervals until mean age-specific doses are reached. Subsequent adjustment in dosage regimens are then based upon serum concentration measurements. Most clinical laboratories now measure theophylline, and newer systems have been developed to provide emergency results within minutes at a reasonable cost. In cases of theophylline poisoning, the drug must be rapidly removed to prevent life-threatening toxicity. When serum concentrations are in excess of 60 micrograms/ml charcoal hemoperfusion dialysis may be indicated, even in the absence of obvious signs of toxicity.

The efficacy of caffeine in the treatment of recurrent idiopathic apnea in premature infants

This prospective controlled study was aimed at evaluating the efficacy of caffeine in treating recurrent idiopathic apnea in the premature infant. Eighteen preterm infants (29 to 35 weeks' gestation) were studied. Recordings during the first 24 hours and on the fifth day of caffeine treatment showed a significant decrease of severe apnea (P less than 0.01) and of mild apnea (P less than 0.001) in the treated group (group 1) as compared with the control group (group II). No treatment of apnea other than caffeine was required in group I, whereas six neonates in group II had such severe and frequent apneic episodes for more than 48 hours that withholding additional treatment was believed to be unethical. No undesirable side effects of caffeine treatment were observed.

Sleep-related breathing disorders

Disorders of breathing related to sleep are relatively newly recognized and less than fully understood. This review presents the terminology used to describe them, and describes the physiology of sleep and the control of ventilation, the pathophysiology of breathing disorders during sleep, their various clinical manifestations, current diagnostic techniques, and the treatment modalities available at present. Among the diagnostic approaches discussed are airway fluoroscopy during sleep, pneumography, and polysomnography. Approaches to medical and surgical management of these disorders are reviewed. Speculation regarding the underestimation of the prevalence of these disorders, the male predominance, and their relationship to snoring, coronary artery disease, and hypertension, which also show male predominance, are presented. Also suggested is a relationship of sleep apnea, obesity, and mental retardation in childhood-onset or congenital disorders such as Down's syndrome and Prader-Willi syndrome, and in other endocrine dysfunction diseases.

Effect of caffeine on circulating theophylline levels in beagle dogs

The pharmacokinetic interactions of caffeine with theophylline were examined in two beagle dogs by administering 100 mg of aminophylline intravenously, 3 weeks before and immediately after repeated oral doses of caffeine. Serial plasma samples were analyzed for caffeine and theophylline simultaneously by high-performance liquid chromatography. Upon multiple oral dosing, 100 mg every 12 hr for 7 days, the caffeine half-life increased slightly in one dog but decreased in the other. As predicted from single-dose data, caffeine accumulation in plasma after repeated doses was slight, while plasma levels of the N-demethylated metabolite, theophylline, rose to about three times the initial values. After rapid intravenous doses of aminophylline, the theophylline half-life was 5-7 hr, which decreased slightly when the drug was administered concomitantly with caffeine during steady state of caffeine. The theophylline volume of distribution (0.75 liter/kg) was unaffected by caffeine. On the other hand, an acute aminophylline injection prolonged the elimination half-life and increased the apparent volume of distribution of caffeine, causing little overall change in its plasma clearance. The results suggested that interactions between theophylline and caffeine may be attributed to changes in drug distribution and drug elimination characteristics.

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.

Pharmacokinetics of diuretics and methylxanthines in the neonate

The elimination of diuretics and methylxanthines is considerably slower in the neonate than in the adult. Dose guidelines, especially during long term maintenance, must be adjusted to account for this slower drug elimination. Pharmacokinetic studies and the requisite pharmacologic evaluation on diuretics such as hydrochlorothiazide, spironolactone, ethacrynic acid and others should be done. Furosemide undergoes biotransformation in the newborn producing an acid metabolite and a glucuronide conjugate. Methylxanthines are effective in the treatment of neonatal apnea. Plasma elimination of theophylline is exceedingly slow, more so with caffeine. Decreased elimination is partly explained by decreased oxidative biotransformation. Caffeine is excreted in the urine of the newborn mainly unchanged (85%) in contrast to the adult where caffeine is a minor portion of urinary excretion (2%). Theophylline is methylated to caffeine and may possibly exert additive pharmacologic effects.