Absorption
Glycopyrronium bromide is poorly absorbed from the gastrointestinal tract. Oral glycopyrronium bromide has low oral bioavailability; a mean of approximately 3% is found in plasma.
Mean absolute oral bioavailability of glycopyrronium comparing a single 50 μg/kg oral dose and a single 5 μg/kg i.v. dose was low at approximately 3% (range 1.3–13.3%) in children aged 7–14 years undergoing intraocular surgery (n = 6) due to the medicinal product's low lipid solubility. Data from sparse PK sampling in children suggests dose proportional PK.
Therapeutic doses of oral glycopyrronium bromide produce low plasma concentrations (Cmax 0.318 ± 0.190 ng/ml) lasting up to 12 hours.
Food effect data indicate that the mean Cmax under fed high-fat meal conditions is ~75% lower than the Cmax observed under fasting conditions.
Distribution
The bioavailability of oral glycopyrronium in children is between that of adults under fed and fasted conditions. Co-administration with food results in a marked decrease in systemic glycopyrronium exposure.
In adults, distribution of glycopyrronium was rapid following a single 6 μg/kg i.v. dose; distribution half-life was 2.2 ± 1.3 minutes. Following administration of 3H-labelled glycopyrronium >90% of the radiolabel disappeared from plasma in 5 minutes, and almost 100% within 30 minutes, reflecting rapid distribution. Analyses of population pharmacokinetic data from healthy adults and children with cerebral palsy-associated chronic moderate to severe drooling who received glycopyrronium (route of administration and dosages unspecified) did not demonstrate linear pharmacokinetics of the medicinal product.
The volume of distribution (Vd), 0.64 ± 0.29 L/kg in adults is similar to that of total body water. Vd is somewhat higher in the paediatric population in the range 1.31 to 1.83 L/kg.
The PK of glycopyrronium has been shown to be essentially independent of age in children 0.19-14 years administered a 5 μg/kg i.v. single-dose. In most paediatric subjects, plasma glycopyrronium vs. time plots are reported to show a triexponential curve; adults generally show a biexponential curve. Modest changes in volume of distribution (Vss) and clearance (Cl) have been observed in children between 1 and 3 years of age, leading to a statistically significantly shorter elimination half-life (t½) than that observed in younger (<1 year of age; p = 0.037) or older (>3 years of age; p = 0.042) groups.
In a study in healthy adults, a 2000 μg single dose of glycopyrronium bromide resulted in an AUC of 2.39 μg.h/L (fasted). An AUC0-6 h of 8.64 μg.h/L was observed after 6 μg/kg i.v. glycopyrronium.
Based upon theoretical physicochemical considerations, the quaternary ammonium compound glycopyrronium would be expected to have low central bioavailability. No glycopyrronium was detected in the CSF of anaesthetised surgical patients or patients undergoing caesarean section following a 6-8 μg/kg i.v. dose. In the paediatric population 5 μg/kg i.v. glycopyrronium has low central bioavailability, except in the case where the blood brain barrier has been compromised (e.g. a shunt infection).
The primary route of elimination of glycopyrronium is via renal excretion, mainly as unchanged medicinal product. Approximately 65% of an i.v. dose is renally excreted within the first 24 hours. A small proportion (~5%) is eliminated in the bile.
The elimination half-life of glycopyrronium appears to be dependent on route of administration: 0.83 ± 0.27 hours after i.v. administration, 75 minutes after i.m. administration and ~2.5-4 h after oral (solution) administration, though this was highly variable. The latter two half-lives, and especially that for oral administration, are longer than for i.v. administration probably reflecting the complex absorption and distribution of glycopyrronium by each route. It is possible that prolonged absorption after oral administration translates into elimination being faster than absorption (flipflop kinetics).
The total body clearance of the medicinal product following an i.v. dose is relatively high at between 0.54 ± 0.14 L/h/kg and 1.14 ± 0.31 L/h/kg. Since this exceeds the glomerular filtration rate and more than 50% of the dose is excreted unchanged in the urine, it is probable that the renal elimination of glycopyrronium involves both glomerular filtration and proximal tubular basal secretion.
A mean increase in total systemic exposure (AUClast) of up to 1.4 fold was seen in adult subjects with mild and moderate renal impairment (GFR ≥30mL/min/1.73m2) and up to 2.2 fold in subjects with severe renal impairment or end stage renal disease (estimated GFR <30 mL/min/1.73m2). A 30% dose reduction is required for patients with mild to moderate renal impairment. Glycopyrronium is contraindicated in patients with severe renal impairment.
Baseline characteristics (age, weight, gender and race) do not affect the pharmacokinetics of glycopyrronium.
Glycopyrronium bromide penetrates the blood-brain barrier poorly. Glycopyrronium bromide crosses the placenta to a limited extent; it is not known whether it is distributed into milk.
Biotransformation
In adult patients who underwent surgery for cholelithiasis and were given a single IV dose of tritiated glycopyrronium bromide, approximately 85% of total radioactivity was excreted in urine and < 5% was present in T-tube drainage of bile. In both urine and bile, > 80% of the radioactivity corresponded to unchanged drug. These data suggest a small proportion of i.v. glycopyrronium bromide is excreted as one or more metabolites.
Elimination
A study using intravenous 3H-glycopyrronium bromide in humans showed the disappearance of more than 90% from serum in 5 minutes and almost 100% in 30 minutes. Urinary radioactivity was highest in the first 3 h and 85% was excreted in the urine within 48 h. 80% of the radioactivity in bile and urine was unchanged glycopyrronium bromide. Following oral administration to mice, 7.6% was excreted in the urine and ~79% in the faeces.
Impaired hepatic function is not expected to affect the pharmacokinetics of glycopyrronium since the majority of the medicinal product is eliminated through the kidneys.
Co-administration with food results in a marked decrease in systemic glycopyrronium exposure (see section 4.2.).
Different formulations of glycopyrronium differ in bioavailability and should not be regarded as interchangeable (see section 4.2).