ate moiety is rapidly metabolized on infusion or ingestion.
Absorption: The onset of action of caffeine from caffeine citrate is within minutes of commencement of infusion. After oral administration of 10 mg caffeine base/kg body weight to preterm neonates, the peak plasma caffeine concentration (Cmax) ranged from 6 to 10 mg/l and the mean time to reach peak concentration (tmax) ranged from 30 min to 2 h. The extent of absorption is not affected by formula feeding but tmax may be prolonged.
Distribution: Caffeine is rapidly distributed into the brain following caffeine citrate administration. Caffeine concentrations in the cerebrospinal fluid of preterm neonates approximate to their plasma levels. The mean volume of distribution (Vd) of caffeine in infants (0.8-0.9 l/kg) is slightly higher than that in adults (0.6 L/kg). Plasma protein binding data are not available for neonates or infants. In adults, the mean plasma protein binding in vitro is reported to be approximately 36%.
Caffeine readily crosses the placenta into the fetal circulation and is excreted into breast milk.
Biotransformation: Caffeine metabolism in preterm neonates is very limited due to their immature hepatic enzyme systems and most of the active substance is eliminated in urine. Hepatic cytochrome P450 1A2 (CYP1A2) is involved in caffeine biotransformation in older individuals.
Inter-conversion between caffeine and theophylline has been reported in preterm neonates; caffeine levels are approximately 25% of theophylline levels after theophylline administration and approximately 3-8% of caffeine administered would be expected to convert to theophylline.
Elimination: In young infants, the elimination of caffeine is much slower than that in adults due to immature hepatic and/or renal function. In neonates, caffeine clearance is almost entirely by renal excretion. Mean half-life (t1/2) and fraction excreted unchanged in urine (Ae) of caffeine in infants are inversely related to gestational / postmenstrual age. In neonates, the t1/2 is approximately 3-4 days and the Ae is approximately 86% (within 6 days). By 9 months of age, the metabolism of caffeine approximates to that seen in adults (t1/2 = 5 hours and Ae = 1%).
Studies examining the pharmacokinetics of caffeine in neonates with hepatic or renal insufficiency have not been conducted.
In the presence of significant renal impairment, considering the increased potential for accumulation, a reduced daily maintenance dose of caffeine is required and the doses should be guided by blood caffeine measurements. In premature infants with cholestatic hepatitis a prolonged caffeine elimination half-life with an increase of plasma levels above the normal limit of variation has been found suggesting a particular caution in the dosage of these patients (see sections 4.2 and 4.4).
5.3 Preclinical safety data
Preclinical data revealed no major hazard for humans based on studies of repeated dose toxicity of caffeine. However, at high doses convulsions in rodents were induced. At therapeutic doses some behavioural changes in newborn rats were induced, most likely as a consequence of increased adenosine receptor expression that persisted into adulthood. Caffeine was shown to be devoid of mutagenic and oncogenic risk. Teratogenic potential and effects on reproductive performance observed in animals are not relevant to its indication in the preterm infant population.
6. PHARMACEUTICAL PARTICULARS
6.1 List of excipient(s)
C |
