Pharmacokinetics of metoclopramide in calves with renal dysfunction.

To clarify the effect of renal dysfunction on pharmacokinetics of the prokinetic agent metoclopramide (MCP), we administered intravenously 0.4 mg/kg MCP to healthy calves and calves subjected to right kidney vessel ligation (ligation) without or with a subsequent left nephrectomy (ligation plus removal). Plasma MCP concentration, glomerular filtration rate (GFR) and plasma prolactin level were measured by liquid chromatography-tandem mass spectrometry, simplified equation using iodixanol and enzyme-linked immunosorbent assay, respectively. Only in calves with ligation plus removal, plasma MCP concentrations were increased significantly 6, 8 and 12 hr after injection, showing that a negative correlation was observed between the plasma MCP concentrations and GFR value. A tendency to increase in plasma PRL concentration was noted also in these calves. In conclusions, plasma MCP concentrations depend on the GFR mode in calves, and its critical GFR value was estimated.

Metoclopramide (MCP) is principally a dopamine D2 antagonist, but also acts as an agonist on serotonin 5-HT4 receptors and causes weak inhibition of serotonin 5-HT3 receptors [10]. Therefore, MCP has multiple sites of pharmacological action, causing increased gastric emptying (intragastric pressure), improved antroduodenal coordination and accelerated motility via the increase in the cholinergic receptors sensitivity to acetylcholine in the upper gastrointestinal tracts [2, 10]. In humans, oral MCP is metabolized by hepatic cytochrome P450, although 10–30% of the parent compound are eliminated into urine [10]. However, when dopamine antagonists were administered at a relatively high dose to cattle [1, 6, 8] and humans [2, 10], plasma prolactin (PRL) concentration, which provoked depression and hypertonic/hypokinetic signs (extrapyramidal symptom), increased, because of its highly nonpolar, lipophilic properties. Because the PRL release from the hypothalamus is controlled (or blocked) by dopamine [1, 2, 6, 8, 10], the possibility is raised that its release is accelerated by administration of MCP having an anti-dopaminergic action. Unfortunately, few studies have examined these effects in calves, despite the fact that MCP is used extensively in the treatment of various gastrointestinal disorders, as was the case with cattle [11]. If plasma MCP concentrations increased in calves with renal dysfunction, the release of PRL to plasma would be stimulated by decreased dopaminergic tone in the hypothalamo-pituitary axis due to its D2 antagonistic action [6, 8, 10]. Although ones with renal dysfunction or aging were generally known to induce a rise in plasma drug concentration [10], little information is available on a threshold of the GFR in its event. The aim of the present study was to clarify the effect of renal dysfunction on pharmacokinetics of MCP using healthy and experimentally-induced nephropathy calves. The glomerular filtration rate (GFR), used as the overall index for precise assessment of the kidney function, was reported to equal to the sum of the filtration rates in each nephron [7, 9].

Four clinically healthy 2–3 months old male Holstein-Friesian calves, weighing 60–70 kg, were used. They were housed in free-stall barns at the Veterinary Teaching Hospital, Iwate University (Morioka, Japan). Calves were fed milk substitute (Sansan, Nippon Formula Feed Manufacturing, Yokohama, Japan), roughage harvested from a pasture and commercial concentrates supplemented with vitamins and minerals (Starter MG, Nippon Formula Feed Manufacturing). The animals used were declared healthy after clinical, hematological and plasma biochemical examinations with urinalysis. Especially, blood urea nitrogen (BUN, 15–23 mg/dl), creatinine (0.5–0.9 mg/dl) and albumin levels (3.1–3.6 g/dl) in plasma were within our background ranges. All experimental procedures were approved by the Animal Experimental Ethics Committee of Iwate University (A201027).

MCP product (10 mg/ml) was purchased from Kyoritsu Seiyaku (Tokyo, Japan), and iodixanol (320 mg I/ml) as the GFR tracer was provided by Daiichi Sankyo (Tokyo, Japan). All other chemicals and reagents were of the highest grade available from commercial sources, unless stated otherwise.

In healthy calves, the GFR was first estimated before MCP injection. Three hours later, MCP was administered as a bolus intravenous injection at 0.4 mg/kg to the left jugular vein, and blood was collected via the opposite jugular vein preadministration and 0.25 (15 min), 0.5 (30 min), 0.75 (45 min), 1, 2, 4, 6, 8, 12 and 24 hr after treatment. A dose of 0.4 mg/kg MCP was selected for this study, because it is the recommended clinical dose for cattle in Japan. Five days later, the calves were subjected to right kidney vessel ligation (ligation) using the procedure reported previously [4]. At the next day, the GFR of the calves with ligation was determined, and the calves were administered intravenously MCP at 0.4 mg/kg. Blood was collected at the same scheduled time as mentioned above. Four days later, the left kidney of the calves with ligation was removed surgically to evoke severer renal dysfunction (ligation plus removal). Plasma MCP concentrations and GFR were similarly measured. In each experiment, 30 ml of 0.9% physiological saline solution were injected subcutaneously to prevent dehydration before commencement of GFR measurement. After the surgical operation, antibiotics (amoxicillin), nonsteroidal anti-inflammatory drug (flunixin meglumine) and/or nonnarcotic analgesic agent (butorphanol tartrate) were given to protect against infection and to control pain, if needed. At termination, the animal was euthanized immediately by exsanguination under sodium pentobarbital (50 mg/kg, i.v.) anesthesia, preceded by xylazine (0.2 mg/kg, i.v.).

Plasma MCP concentrations were measured with a liquid chromatography-tandem mass spectroscopy system (LC-MS/MS, Thermo Fisher Scientific INC., Waltham, MA, U.S.A.) reported previously [3]. The detection limit was 0.1 ng/ml. In the GFR measurement [5], iodixanol was administered intravenously at 40 mg iodine per kg of body weight (mg I/kg) using a 24-G indwelling catheter (Nipro, Osaka, Japan), and blood (1 ml) was collected at pre-dose and 120 min later. The blood obtained was centrifuged, and serum iodixanol concentrations were measured with reverse-phase high-performance liquid chromatography (HPLC, Waters, Milford, MA, U.S.A.). The GFR was calculated by the following equation [5]:

,

where the Ct, dose, t and Vd represent serum iodixanol concentration at 120 min, iodixanol dose (40 mg I/kg) injected, the sampling time (120 min) and estimated volume of distribution (Vd= −254.1 × In (Ct) + 1220.5), respectively [5]. BUN, creatinine and albumin concentrations in plasma were determined with an autoanalyzer (Toshiba Medical Systems, Tochigi, Japan) on the same days that the GFR was estimated. Plasma PRL concentrations before and after MCP injection were also measured using a commercially available kit (bovine PRL ELISA kit, Uscn Life Science, Houston, TX, U.S.A.).

Numerical data are expressed as the mean ± standard deviation (SD) of each group. They were compared using one-way analysis of variance (ANOVA) and Dunnett’s test. A P-value of <0.05 was considered statistically significant. As the pharmacokinetic parameters, the area under the concentration-time curve (AUC0–∞), clearance (Cl), elimination half time (t1/2), mean residence time (MRTinf) and volume of distribution at steady state (Vdss) of MCP were calculated according to the non-compartment analysis by Phoenix WinNonlin ver. 6.1 (Pharsight, Mountain View, CA, U.S.A.).

As results, increases in BUN (40–60 mg/dl) and plasma creatinine (5.0–7.0 mg/dl) concentrations and decreases in plasma albumin levels (2.3–2.8 g/dl) were observed only in calves with ligation plus removal. The mean GFR (ranges) values were 2.83 (2.31–3.49), 3.61 (2.32–5.78) and 0.37 (0.17–0.76) ml/min/kg in healthy, ligation and ligation plus removal calves, respectively, corresponding to 100, 82–204 and 6–27% of calculated kidney surviving masses. The GFR value in healthy calves measured was almost within our basal reference GFR values (2.82 ± 0.36 ml/min/kg) [4]. The relatively large fluctuation in the GFR of calves with ligation may be due to a temporarily compensatory mechanism in unilateral kidney dysfunction.

The pharmacokinetic profiles of MCP are shown in Table 1. The calves with ligation exhibited the increased AUC0–∞ with decreased Cl. Meanwhile, the calves with ligation plus removal elicited a significant rise in plasma MCP concentrations at 6, 8 and 12 hr later with decreased Vdss, although no significant difference was noted in AUC0–∞ and Cl, because of being a large fluctuation. The change in Vdss may be at least in part due to alterations in colloid osmotic pressure related to hypoalbuminemia and reductions in GFR. When the relationship between the GFR and plasma MCP concentrations at 6, 8 and 12 hr later, which had increased significantly (P<0.01), was examined using a least-squares regression (scatter plot), negative correlations (r=0.61, 0.79 and 0.67, respectively) were observed (Fig. 1). However, there was no relationship between the GFR and AUC0–∞ of MCP. Taken together, plasma MCP concentrations seemed to increase when the kidney surviving mass decreased to approximately 27% (see above GFR data).

Table 1.

Pharmacokinetic parameters after a single intravenous administration of metoclopramide (MCP) in healthy Holstein calves and calves with ligation or ligation plus removal

Parameters	Healthy control			Ligation			Ligation plus removal
n	4			4			4
AUC0–∞ (hr·ng/ml)	108.1	±	74.4	160.4	±	17.0*	180.8	±	62.5
Cl (l/hr/kg)	5.01	±	2.80	2.52	±	0.28*	2.44	±	0.89
Plasma MCP (ng/ml) after the injection
15 min	61.7	±	9.2	102.8	±	7.3	89.6	±	24.2
30 min	41.8	±	29.9	59.3	±	9.9	64.9	±	23.3
45 min	34.7	±	49.3	47.1	±	6.6	44.5	±	15.5
1 hr	26.0	±	15.6	33.7	±	6.5	36.3	±	12.3
2 hr	10.8	±	6.86	15.7	±	2.5	19.0	±	9.7
4 hr	4.6	±	3.2	5.6	±	0.9	7.6	±	3.0
6 hr	1.8	±	1.0	2.8	±	0.4	4.8	±	2.2**
8 hr	1.1	±	0.6	1.4	±	0.3	3.4	±	1.5**
12 hr	0.7	±	0.6	1.0	±	0.4	2.1	±	1.1**
24 hr	0.3	±	0.4	0.7	±	0.7	1.4	±	1.6
MRTinf (hr)	4.0	±	2.1	4.4	±	2.6	4.8	±	1.1
t1/2 (hr)	9.6	±	5.7	8.4	±	4.7	5.8	±	1.0
Vdss (l/kg)	16.8	±	7.1	10.8	±	6.1	12.1	±	5.9**

Data represent the mean ± SD, *P<0.05, **P<0.01 vs. healthy control.

Fig. 1.

Plots between plasma metoclopramide (MCP) concentration and glomerular filtration rate (GFR) in healthy calves (open circles) and calves subjected to right kidney vessel ligation (ligation, closed circles) without or with a subsequent left nephrectomy (ligation plus removal, closed squares). Plasma MCP concentrations 6, 8 and 12 hr after MCP injection were used, and the GFR was estimated before MCP injection. One calf with ligation plus removal was deleted from the analysis, because of an iodixanol injection error (sample number: 11, where the number elicits the sum of the individual data collected from different models on different days).

Healthy calves given intravenously 0.4 mg/kg MCP showed no change in maximum plasma PRL concentrations (11.6 ± 3.5 ng/ml), relative to the basal level at pre-dose (11.1 ± 5.3 ng/ml). Likewise, no significant change in plasma PRL concentration was observed between the healthy calves and calves with ligation (10.5 ± 12.3 ng/ml) after MCP injection. However, a tendency to increase in plasma PRL concentration was noted in calves with ligation plus removal (15.3 to 31.9 ng/ml, n=3), although there was no significantly difference from the healthy calves, because the level of one animal deviated largely from those of 3 other animals. In yearling Angus steers (182 to 232 kg) given intravenously 0.1 or 1 mg/kg MCP, significantly increased plasma PRL concentrations (21.3 to 28.7 ng/ml)) were found [8], although plasma MCP concentration was not determined in this trial. Based on these data, the PRL release from the hypothalamus may be dependent of the plasma MCP concentration rather than AUC0–∞ of MCP. However, further studies are necessary to collect the background data of MCP pharmacokinetics with plasma PRL concentrations in calves with various types of nephropathy.

In conclusion, plasma MCP concentrations depended on the GFR mode in calves, namely, plasma MCP concentration became elevated when the GFR decreased to approximately 73% of the basal reference value.