Source: Medicines & Healthcare Products Regulatory Agency (GB) Revision Year: 2013 Publisher: Viridian Pharma Ltd. Yew Tree House Hendrew Lane Llandevaud Newport Gwent NP18 2AB UK
The pharmacological actions of caffeine result from its effect as a nonspecific adenosine receptor antagonist. The desired respirogenic activity of caffeine is an expression of its central nervous system stimulation, although it may also increase the sensitivity of respiratory response to carbon dioxide levels. Caffeine increases both tidal volume and frequency of ventilation.
In the premature infant, caffeine produced increased minute ventilation, mainly due to an increase in inspiratory drive as shown by an increased mean respiratory flow (VĪ¤/T1). Caffeine regularises the breathing pattern, indicating that it stabilises the oscillation of the respiratory control system.
Caffeine also inhibits phosphodiesterase, but this effect only occurs at concentrations associated with toxicity, and not at therapeutic concentrations.
Caffeine increases metabolic rate, heart rate, cardiac contractility and output. It also increases blood flow to the kidneys, and prevents sodium and chloride from reabsorbing at the proximal tubules, so mild diuresis can occur.
Adenosine is a vasodilator and therefore caffeine, as its antagonist, can cause vasoconstriction. Hence it is a vasoconstrictor in the cerebral and splanchnic circulations. Elsewhere, it has a vasodilator effect due to an effect on vascular smooth muscle.
The stimulant effect may affect sleep patterns.
In neonates, orally administered caffeine has been shown to be rapidly and completely absorbed. Peak plasma levels and extent of absorption are comparable for oral administration and intravenous infusion. In premature infants, the volume of distribution is reported to be 0.8 to 0.9 L/kg. It is widely distributed throughout the body and passes readily into the central nervous system and into saliva.
Neonates, especially premature neonates, have a greatly reduced capacity to metabolise caffeine and it is largely excreted unchanged in the urine until hepatic metabolism becomes significantly developed, a process which is completed by about 6 months of age. Elimination half-lives may be in excess of 52-96 hours in premature neonates.
Interconversion between caffeine and theophylline has been observed in premature infants. Approximately 3% to 8% of caffeine administered is Expected to be converted to theophylline. After theophylline administration, caffeine concentrations are approximately 25% of theophylline concentrations.
The predominant caffeine metabolic process in premature infants appears to be via N7-demethylation.
Low concentrations of caffeine may be present in breast milk of the mother, and it crosses the placenta.
There is no preclinical data of relevance to the prescriber.
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