Caffeine Citrate

CAFFEINE CITRATE — caffeine citrate injection, solution
AuroMedics Pharma LLC

Caffeine Citrate Injection, USP

Rx only

DESCRIPTION

Caffeine citrate injection, USP for intravenous administration is a clear, colorless, sterile, non-pyrogenic, preservative-free, aqueous solution adjusted to pH 4.7. Each mL contains 20 mg caffeine citrate (equivalent to 10 mg of caffeine base) prepared in solution by the addition of 10 mg caffeine (anhydrous) USP to 5 mg citric acid monohydrate, 8.3 mg sodium citrate dihydrate and Water for Injection, USP.
Caffeine (anhydrous) USP, a central nervous system stimulant, is an odorless white crystalline powder or granules, with a bitter taste. It is sparingly soluble in water and ethanol at room temperature. The chemical name of caffeine is 3,7-dihydro-1,3,7-trimethyl-1H- purine-2,6-dione. In the presence of citric acid it forms caffeine citrate salt in solution. The structural formula and molecular weight of caffeine citrate follows.

CLINICAL PHARMACOLOGY

Mechanism of Action

Caffeine is structurally related to other methylxanthines, theophylline, and theobromine. It is a bronchial smooth muscle relaxant, a CNS stimulant, a cardiac muscle stimulant, and a diuretic.
Although the mechanism of action of caffeine in apnea of prematurity is not known, several mechanisms have been hypothesized. These include: (1) stimulation of the respiratory center, (2) increased minute ventilation, (3) decreased threshold to hypercapnia, (4) increased response to hypercapnia, (5) increased skeletal muscle tone, (6) decreased diaphragmatic fatigue, (7) increased metabolic rate, and (8) increased oxygen consumption. Most of these effects have been attributed to antagonism of adenosine receptors, both A₁ and A₂ subtypes, by caffeine, which has been demonstrated in receptor binding assays and observed at concentrations approximating those achieved therapeutically.

Pharmacokinetics

Absorption
After oral administration of 10 mg caffeine base/kg to preterm neonates, the peak plasma level (C_max ) for caffeine ranged from 6 to 10 mg/L and the mean time to reach peak concentration (T_max ) ranged from 30 minutes to 2 hours. The T_max was not affected by formula feeding. The absolute bioavailability, however, was not fully examined in preterm neonates.
Distribution
Caffeine is rapidly distributed into the brain. Caffeine levels in the cerebrospinal fluid of preterm neonates approximate their plasma levels. The mean volume of distribution of caffeine in infants (0.8 to 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%.
Metabolism
Hepatic cytochrome P450 1A2 (CYP1A2) is involved in caffeine biotransformation. Caffeine metabolism in preterm neonates is limited due to their immature hepatic enzyme systems.
Interconversion between caffeine and theophylline has been reported in preterm neonates; caffeine levels are approximately 25% of theophylline levels after theophylline administration and approximately 3 to 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. Mean half-life (T_1/2 ) and fraction excreted unchanged in urine (A_e ) of caffeine in infants have been shown to be inversely related to gestational/postconceptual age. In neonates, the T_1/2 is approximately 3 to 4 days and the A_e is approximately 86% (within 6 days). By 9 months of age, the metabolism of caffeine approximates that seen in adults (T_1/2 = 5 hours and A_e = 1%).

Special Populations
Studies examining the pharmacokinetics of caffeine in neonates with hepatic or renal insufficiency have not been conducted. Caffeine citrate should be administered with caution in preterm neonates with impaired renal or hepatic function. Serum concentrations of caffeine should be monitored and dose administration of caffeine citrate should be adjusted to avoid toxicity in this population.

Clinical Studies

One multicenter, randomized, double-blind trial compared caffeine citrate to placebo in eighty-five (85) preterm infants (gestational age 28 to <33 weeks) with apnea of prematurity. Apnea of prematurity was defined as having at least 6 apnea episodes of greater than 20 seconds duration in a 24-hour period with no other identifiable cause of apnea. A 1 mL/kg (20 mg/kg caffeine citrate providing 10 mg/kg as caffeine base) loading dose of caffeine citrate was administered intravenously, followed by a 0.25 mL/kg (5 mg/kg caffeine citrate providing 2.5 mg/kg of caffeine base) daily maintenance dose administered either intravenously or orally (generally through a feeding tube). The duration of treatment in this study was limited to 10 to 12 days. The protocol allowed infants to be “rescued” with open-label caffeine citrate treatment if their apnea remained uncontrolled during the double-blind phase of the trial. The percentage of patients without apnea on day 2 of treatment (24 to 48 hours after the loading dose) was significantly greater with caffeine citrate than placebo. The following table summarizes the clinically relevant endpoints evaluated in this study:

	Caffeine Citrate	Placebo	p-value
Number of patients evaluated1	45	37	–
% of patients with zero apnea events on day 2	26.7	8.1	0.03
Apnea rate on day 2 (per 24 h)	4.9	7.2	0.134
% of patients with 50% reduction in apnea events from baseline on day 2	76	57	0.07

¹ Of 85 patients who received drug, 3 were not included in the efficacy analysis because they had <6 apnea episodes/24 hours at baseline. In this 10 to 12 day trial, the mean number of days with zero apnea events was 3 in the caffeine citrate group and 1.2 in the placebo group. The mean number of days with a 50% reduction from baseline in apnea events was 6.8 in the caffeine citrate group and 4.6 in the placebo group.

INDICATIONS AND USAGE

Caffeine citrate injection, USP is indicated for the treatment of apnea of prematurity.

CONTRAINDICATIONS

Caffeine citrate injection is contraindicated in patients who have demonstrated hypersensitivity to any of its components.

WARNINGS

Necrotizing Enterocolitis
During the double-blind, placebo-controlled clinical trial, 6 cases of necrotizing enterocolitis developed among the 85 infants studied (caffeine=46, placebo=39), with 3 cases resulting in death. Five of the six patients with necrotizing enterocolitis were randomized to or had been exposed to caffeine citrate.
Reports in the published literature have raised a question regarding the possible association between the use of methylxanthines and development of necrotizing enterocolitis, although a causal relationship between methylxanthine use and necrotizing enterocolitis has not been established. In a published randomized, placebo-controlled, clinical trial that studied the use of caffeine citrate in apnea of prematurity in approximately 2,000 patients, necrotizing enterocolitis was not more common in caffeine treated patients compared to placebo. As with all preterm infants, patients being treated with caffeine citrate should be carefully monitored for the development of necrotizing enterocolitis.