Determination of indomethacin in serum by an extractive alkylation technique and gas-liquid chromatography

Intravenous indometacin in preterm infants with symptomatic patent ductus arteriosus. A population pharmacokinetic study

AIMS

To characterize the population pharmacokinetics of indometacin in preterm infants with symptomatic patent ductus arteriosus and to investigate the influence of various factors on the response to treatment.

METHODS

Data were collected from 35 infants (gestational age 25-34 weeks; postnatal age 1-77 days) in neonatal units in Belfast and Copenhagen. Infants received an initial course of up to three doses of intravenous indometacin (0.1-0.2 mg kg(-1)) as considered appropriate by the treating physician. For those infants who did not respond to therapy or in whom the ductus reopened, a second course was sometimes given. Population analysis of the 185 plasma concentrations obtained was conducted using NONMEM and pharmacokinetic and demographic differences between responders and nonresponders were compared.

RESULTS

The concentration-time course of indometacin was best described by a one-compartment model. The final population parameter estimates of clearance (CL) and volume of distribution (V) (standardized to the median weight of 1.17 kg) were 0.00711 l h(-1) and 0.266 l, respectively. CL increased from birth by approximately 3.38% per day and V by approximately 1.47% per day. Concomitant digoxin therapy resulted in a 30% decrease in V. Interindividual variability in CL and V was 41% and 21%, respectively. Interoccasion variability for CL was 43%. Residual variability corresponded to a standard deviation of 0.148 mg l(-1). Closure occurred in 75% of infants with a plasma concentration > or = 0.4 mg l(-1) 24 h after the last dose.

CONCLUSIONS

Dosing regimens for indometacin should take into account the weight and postnatal age of the infant and any concomitant digoxin therapy. The population estimates can be used to determine typical values of CL and V allowing the prediction of individualized doses of indometacin that should increase the probability of achieving a 24 h plasma concentration > or = 0.4 mg l(-1). Although the pharmacokinetic estimates will be affected by both interindividual and within-individual variation, it is anticipated that this approach will decrease the variability of exposure and optimize treatment outcome.

Sensitive fused-silica capillary gas chromatographic assay using electron-capture detection for indomethacin in ovine fetal fluids

A sensitive gas chromatographic (GC) method with electron-capture detection (ECD) has been developed to quantitate indomethacin (IND) in plasma, urine, amniotic, and tracheal fluids obtained from the pregnant sheep model. IND and the internal standard, alpha-methylindomethacin (alpha-Me-IND) are extracted by a simple liquid-liquid extraction procedure using ethyl acetate and derivatized with N-methyl-N-(tert.-butyldimethyl-silyl)trifluoroacetamide (MTBSTFA) at 60 degrees C for 50 min. The limit of quantitation (LOQ) is 1 ng/ml with a C.V. < 10% and signal-to-noise ratio > 10. Recoveries from all fluids were greater than 80%. Calibration curves were linear over the range of 1-32 ng/ml with a coefficient of determination (r2) > 0.999. Inter- and intra-day coefficients of variation were < 10% at concentrations of 2-32 ng/ml, and < 20% at the LOQ. Applicability of the developed method is demonstrated for a pharmacokinetic study of IND samples collected following long-term infusion of IND in a chronically instrumented ovine fetus.

Fracture healing in rats inhibited by locally administered indomethacin

We studied the inhibitory effect of indomethacin on fracture healing in 135 young, male rats after oral administration compared with local application into the fracture. A closed mid-diaphyseal fracture of the left femur was performed in all the rats. The fractures were not immobilized. In one experiment, half of the animals received indomethacin via a stomach tube (2 mg/kg/day) for 10 days; the controls received only the vehicle. In another experiment, 0.5 mg of indomethacin, contained in a bioerodible polyorthoester gel, was injected into the fracture area in half the rats; in the controls, only the gel was injected. In both experiments, random animals were killed on Days 0, 5, 10, and 20. As assessed by radiographs and manual testing, the same inhibition of fracture healing was found regardless of whether indomethacin was given orally or locally. However, the amount of indomethacin that was applied locally was only one fourth of the total dose given orally; no indomethacin was detected in the serum.

Early hemodynamic response to tibial osteotomy in rabbits: influence of indomethacin and prostaglandin E2

The hemodynamic role of prostaglandins in the inflammatory phase of bone healing was studied on day 4 after creation of a nailed midtibial osteotomy in 40 rabbits, divided into groups of 10, treated with either indomethacin (oral dosage 10 mg/kg), subcutaneous (s.c.) prostaglandin E2 (PGE2) (dosage 1 mg/kg), or PGE2 infusion into the abdominal aorta (rate 20 ng/kg/min) for a 20-min period immediately before the animals were killed. The last group served as controls. Regional blood flow was measured by means of radioactive microspheres, and plasma volume was assessed by distribution of circulating [125I]fibrinogen. Neither indomethacin nor s.c. PGE2 treatment had any hemodynamic effects in the osteotomy area. PGE2 infusion caused increased blood flow in bone, bone marrow, and muscle of the lower limbs except in the osteotomy area. Thus, the influence of prostaglandins and indomethacin on bone healing of a rabbit midtibial osteotomy does not appear to be a direct vascular effect in the early healing phase.

High-performance liquid chromatographic analysis of indomethacin in serum

A rapid high-performance liquid chromatographic (HPLC) method for quantitative determination of indomethacin in serum is described. The assay was performed after single extraction of indomethacin and itraconazole (internal standard) from serum using diethyl ether and eluted from a 4 micron C-18 reversed-phase column at ambient temperature. The mobile phase consisted of ethanol:water:glacial acetic acid (65:34:1, v/v) pumped isocratically at a flow rate of 1.3 ml/min. The effluent was monitored at 254 nm. Quantification was achieved by the measurement of the peak area ratio, and the absolute recoveries ranged from 94 to 97%. Within-day coefficients of variation (CV) ranged from 2.72 to 5.70% and between-day CV varied from 3.61 to 6.1%. Stability testing indicated that indomethacin is stable for at least 30 days in serum at -20 degrees C. The method was used to study indomethacin pharmacokinetics in rabbits.

Indomethacin and bone trauma. Effects on remodeling of rabbit bone

The influence of indomethacin on remodeling activity in normal trabecular and cortical bone and its influence on cortical bone close to a midtibial drill hole, 2 mm in diameter were histomorphometrically evaluated. Eight rabbits were treated with indomethacin (12.5 mg/kg/day), and another 8 rabbits served as controls. After 3 days, the mean plasma indomethacin level was 542 ng/mL, resulting in an almost complete inhibition of prostaglandin synthesis as reflected by the serum levels. In the control rabbits the remodeling activity after 6 weeks was increased 1 mm away from the drill hole but not at 3 and 8 mm. In conclusion, indomethacin had no effect on the activated remodeling process in cortical bone neighboring a small drill hole or on remodeling in nontraumatized cortical and cancellous bone. This suggests that the inhibitory effect of indomethacin on the remodeling process following local trauma to bone depends on the extent of the trauma.

Indomethacin and the stress response to hysterectomy

The influence of indomethacin on the surgical stress response was evaluated in a double-blind study of 20 patients, scheduled for abdominal hysterectomy. The patients were randomly allocated to treatment with either indomethacin, 0.8 mg/kg i.v. preoperatively followed by 100 mg rectally 8-hourly for 3 days (Group I), or placebo (Group P), in both cases supplemented with nicomorphine as needed. Thiopentone was used for induction of anaesthesia, followed by nitrous oxide, enflurane, suxamethonium, and pancuronium. In both groups a significant increase in blood glucose and serum cortisol was seen postoperatively. Twenty-four hours later the values had almost returned to baseline. No differences were found between the absolute increases in the two groups. In both groups the serum concentrations of C-reactive protein, haptoglobin, and orosomucoid increased after an initial small decrease. We conclude that pathways involving prostaglandin synthesis play only a minor role in eliciting the postoperative hyperglycaemic, hypercortisolaemic, and acute phase protein response.

Pharmacokinetics of postoperative intravenous indomethacin in children

The disposition of indomethacin was studied in children aged one to four years. Indomethacin 0.35 mg/kg was administered as an intravenous infusion during 15 min. Venous blood samples were collected until 24 hr after infusion. Serum indomethacin was determined with gas chromatography. Using a non-linear regression analysis, the individual data were fitted by a two-compartment open mammillary model with central elimination. Calculated pharmacokinetic parameters were (mean +/- SD); alpha half-life 25.2 +/- 11.3 min; beta half-life 366 +/- 295 min; steady-state volume of distribution 0.74 +/- 0.75 l/kg; volume during elimination phase 1.53 +/- 1.27 l/kg; total body clearance 3.2 +/- 1.7 ml/min./kg. Accordingly, with respect to the pharmacokinetics of indomethacin, children seem to mature early, not later than at the age of one year.

Indomethacin and bone remodeling. Effect on cortical bone after osteotomy in rabbits

Remodeling in cortical bone close to a plated tibial midshaft osteotomy was histomorphometrically evaluated in 32 rabbits. The animals were divided into two groups, one being treated with indomethacin (10 mg/kg per day) and the other receiving placebo. In the placebo-treated group, the remodeling activity was higher in the osteotomized leg compared with the intact leg. Two and 6 weeks after osteotomy, the number of resorptive and formative foci was reduced in the indomethacin-treated group compared with the placebo group. Porosity did not differ between the groups after 2 weeks; but after 6 weeks, it was reduced in the indomethacin-treated animals. Throughout the study, the bone formation rate did not differ between the two groups. This study demonstrates that indomethacin inhibits the remodeling of traumatized bone.

Elevated urinary prostaglandin excretion and the effect of indomethacin on renal function in incipient diabetic nephropathy

We investigated whether the glomerular synthesis of prostaglandins modulates the glomerular filtration rate and urinary albumin excretion in incipient diabetic nephropathy (defined as urinary albumin excretion between 30 and 300 mg/24 h (microalbuminuria) in two out of three sterile ketone-free 24-h urine collections in patients having insulin-dependent diabetes mellitus (IDDM) without hypertension or other kidney disease). The urinary excretion of prostaglandin E2 was significantly elevated in 8 insulin-dependent diabetic patients with incipient nephropathy as compared with 9 normoalbuminuric IDDM patients and 11 healthy controls: 317 (182-1273); 95 (67-225); 132 (54-263) pg/min, respectively (2p less than 0.01). Glomerular filtration rate (single bolus 51Cr-EDTA technique) and albuminuria (radioimmunoassay) were measured twice within 2 weeks in 8 females having IDDM with incipient nephropathy. The study design was a randomized double-blind trial with the patients receiving either indomethacin (150 mg/day) or placebo for 3 days prior to the kidney function studies. Indomethacin treatment induced a significant reduction in urinary prostaglandin E2 excretion (73%) (2p less than 0.01), urinary albumin excretion rate diminished from 207 (63-253) to 87 (49-147) mg/24 h (2p less than 0.01), fractional clearance of albumin declined (70%) (2p less than 0.01). Glomerular filtration rate remained stable (108 (88-133) versus 110 (95-142) ml/min). Blood glucose and blood pressure were comparable during the placebo and indomethacin treatment (12.6 +/- 3 versus 13.4 +/- 5 mmol/l and 122/79 +/- 3/9 versus 122/82 +/- 4/10 mmHg, respectively). Our results suggest that enhanced glomerular synthesis of vasodilating prostaglandins may accelerate microalbuminuria in incipient diabetic nephropathy.

In vivo effects of orally administered prednisolone on prostaglandin and leucotriene production in ulcerative colitis

It has been proposed that anti-inflammatory actions of corticosteroids rely on promotion of a natural peptide phospholipase A2 inhibitor, lipocortin, but in vivo effects on arachidonic acid metabolism have not been shown. Equilibrium dialysis of the rectum in patients with ulcerative colitis was used to determine whether cyclooxygenase and lipoxygenase products released from the inflamed rectal mucosa could be differentially inhibited by systemic treatment with prednisolone and indomethacin, respectively. In 10 patients with severe disease luminal concentrations of prostaglandin E2, prostaglandin F2 alpha, and leucotriene B4 were markedly raised (p less than 0.05) on comparison with 10 healthy controls, and they decreased significantly (p less than 0.05) within 72 hours after administration of prednisolone 1.5 mg/kg/day orally. In contrast prostaglandin, but not leucotriene B4 concentrations decreased (p less than 0.05) within 72 hours after administration of indomethacin 150 mg/day in another 10 patients with distal disease. These prompt reductions in concentrations of arachidonic acid metabolites more likely are caused by direct drug actions, rather than being secondary to decreased tissue damage. The data accord with the theory explaining anti-inflammatory effects of corticosteroids through lipocortin activity and support the belief that leucotrienes are more important than prostaglandins as mediators of inflammation in ulcerative colitis.

Bone repair inhibited by indomethacin. Effects on bone metabolism and strength of rabbit osteotomies

We measured mineral content, maximum bending strength, and regional blood flow after tibial osteotomy fixed with a small metal plate in 38 rabbits. Half of the animals were treated with indomethacin (10 mg/kg/day) while the other half served as controls. After 2 and 6 weeks, the bone mineral content and maximum bending strength were lower in the indomethacin group when compared with the controls. Compared with the controls, the blood flow at the osteotomy site was decreased after 2 weeks and increased after 6 weeks in the indomethacin-treated animals. Inhibition of blood flow increase by indomethacin medication in the early period following osteotomy, as well as retarded bone healing, are probably caused by inhibition of the inflammatory reaction.

A high performance liquid chromatography method for the analysis of total and free indomethacin in serum

A simple rapid and sensitive HPLC technique for the analysis of total and free plasma indomethacin concentrations in neonates is described. The advantages of the technique are small sample volumes (50 microL) enabling the use of capillary samples, direct extraction, low limits of detection (20 ng/mL) and good precision (CV less than 7% between-batch). Indomethacin and the internal standard (flufenamic acid) eluted within 12 min and the peaks were unaffected by indomethacin metabolites or by a number of commonly used drugs. The technique is suitable for the investigation into the pharmacokinetics of total and free indomethacin, in neonates with patent ductus arteriosus, and could be used to define a therapeutic window for free indomethacin levels to enable therapeutic drug monitoring to occur in this condition.

Effects of indomethacin on kidney function in type 1 (insulin-dependent) diabetic patients with nephropathy

We investigated whether the glomerular synthesis of prostaglandins modulates the glomerular filtration rate and albuminuria in diabetic nephropathy. The urinary excretion of immunoreactive prostaglandin E2 (253 pg/min) was significantly elevated in eight Type 1 (insulin-dependent) diabetic women with nephropathy as compared with nine normoalbuminuric Type 1 diabetic women (95 pg/min) and 11 non-diabetic women (132 pg/min), respectively (p less than 0.01). Glomerular filtration rate (single bolus 51Cr-EDTA technique) and albuminuria (radioimmunoassay) were measured twice within two weeks in the eight Type 1 diabetic women with nephropathy. All eight patients were on a diabetic diet without sodium restriction. The study was performed as a randomized double-blind trial, with the patients receiving either indomethacin (150 mg/day) or placebo for three days prior to the kidney function studies. Indomethacin treatment induced a significant reduction in urinary prostaglandin E2 excretion (73%, p less than 0.01), glomerular filtration rate diminished from 120 +/- 18 to 106 +/- 17 ml/min/1.73 m2 (p less than 0.05), albuminuria declined from 148 to 69 micrograms/min (median and range) (p less than 0.05) and fractional clearance of albumin diminished 42% (p less than 0.05). Blood glucose concentrations were comparable during the placebo and indomethacin treatment, 13.4 +/- 4 versus 14.2 +/- 3 mmol/l, respectively. Our results suggest that glomerular filtration rate in early diabetic nephropathy is dependent on the enhanced glomerular synthesis of vasodilating prostaglandins.

Time-dependent inhibition of platelet cyclooxygenase by indomethacin is slowly reversible

Indomethacin has been characterized in vitro as a time-dependent, irreversible inhibitor of cyclo-oxygenase, yet its effects on human platelets have been found to be reversible in vivo. To understand this apparent contradiction, we have investigated the kinetics of recovery of platelet thromboxane production after a single dose of indomethacin. The inhibition of platelet thromboxane production was greater than would be expected from the levels of indomethacin found in the plasma suggesting that the time-dependent inhibition occurs in vivo. Yet recovery of platelet thromboxane production was faster than expected for an irreversible inhibitor, with 50% of control values being regained within 24 hours after ingestion of the drug. When platelets were isolated and resuspended in homologous drug-free plasma, slow recovery of thromboxane production was seen to occur with 50% of control activity regained in 100 minutes. This recovery was much slower than that seen from a competitive inhibitor of cyclo-oxygenase, ibuprofen. Ibuprofen-treated platelets recovered nearly completely immediately on being resuspended in drug-free plasma. When microsomes were isolated from platelets, then treated with indomethacin, no time-dependent recovery of activity was seen. The recovery of cyclo-oxygenase after indomethacin inhibition appears to be limited to the unperturbed enzyme in its natural milieu.

Direct derivatization of drugs in untreated biological samples for gas chromatographic analysis

The possibilities to derivatize an analyte directly in the biological sample are reviewed with examples from our own experiences and from the literature. Techniques, such as extractive acylation, alkylation and benzoylation, are frequently used. Improvement of the extractability of the drug from the matrix is a common feature, especially with hydrophilic compounds, where sometimes cyclizing reactions can be employed. Several analytes are reactive or labile in the sample and can be trapped in derivatization reactions in situ. In many cases, two-phase reactions lead to milder derivatization conditions (e.g. dealkylation of tertiary amines), which is favourable from a clean-up point of view.

Bioavailability of indomethacin after intramuscular injection and rectal administration of solution and suppositories

The pharmacokinetics of indomethacin was studied after intravenous and intramuscular injection of 50 mg and administration of rectal solution and suppositories of 100 mg to 8 volunteers. Peak plasma concentrations of indomethacin occurred 20 min. after administration of the rectal solution (3.7 micrograms X ml-1), 40 min. after intramuscular injection (2.7 micrograms X ml-1), and 60 min. after suppositories (3.7 micrograms X ml-1). The bioavailability after the two rectal forms was found to be almost the same, about 80%. After intramuscular injection the bioavailability was calculated to be complete. These results suggest that indomethacin administered as a rectal solution or as intramuscular injection may be an alternative to intravenous administration when an early plasma peak of the drug is required.

The osteo-inductive properties of bone matrix from rats pretreated with indomethacin

Decalcified bone matrix pieces were prepared from growing rats treated for 3 weeks with subcutaneous injections of indomethacin 2 mg/kg/day or saline, and implanted into growing rats. Of the 16 recipients with 'saline implants', 8 received saline and another 8 indomethacin 2 mg/kg/day in subcutaneous injections. In another 16 recipients with 'indomethacin implants', 8 received saline and 8 indomethacin. As in previous studies, it was found that indomethacin exerted a mild inhibition of new bone formation expressed as decreased amount of ash weight in implants. The amount of ash weight and 45Ca specific activity of implants in recipients with implants from indomethacin-treated donor animals was not altered. These findings indicate that indomethacin is unable to modify the osteo-inductive properties of bone matrix.

Arachidonic acid-induced platelet aggregation and prostanoid formation in whole blood in relation to plasma concentration of indomethacin

A single oral dose of indomethacin 1 mg/kg was given to 6 male and 6 female volunteers. The formation of thromboxane B2 (TXB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) in clotting whole blood was measured by radioimmunoassay, and platelet aggregation induced by arachidonic acid (AA) was measured with a plasma aggregometer. The results were related to the concomitant plasma concentration of indomethacin. The maximum plasma concentration ranged between 3.24 and 8.11 micrograms/ml and the elimination half-life between 4 and 11 h. Formation of the prostanoids was reversibly inhibited, with maximum suppression when the drug concentration in plasma exceeded 0.5-1.0 microgram/ml; the IC50 was approximately 0.1 microgram/ml. Platelet aggregation was also reversibly inhibited. The correlation between the formation of prostanoids and the different phases of the aggregatory response to exogenous AA is discussed.

Short-term inhibition of prostaglandin synthesis has no effect on the elevated glomerular filtration rate of early insulin-dependent diabetes

Glomerular filtration rate and renal plasma flow (constant infusion technique using 125I-iothalamate and 131I-hippuran) were measured twice within a 1-week interval in nine young males with insulin-dependent diabetes of short duration (2-5 years). The study was performed in a randomized double-blind design, with the patients receiving either indomethacin (150 mg/day) or placebo for 3 days before the study. Measures of metabolic control did not change. No differences were found in glomerular filtration rate (144 +/- 9 versus 144 +/- 9 ml/min X 1.73 m2, mean +/- S.E.M.) or renal plasma flow (579 +/- 43 versus 560 +/- 52 ml/min X 1.73 m2), when measured during placebo or indomethacin treatment, respectively. It is concluded that the steady-state enhancement of glomerular filtration rate and renal plasma flow found in early insulin-dependent diabetes is not due to an excessive activity of the prostaglandin system.

Lack of effect of indomethacin on mesenchymal limb-bud cells in vitro

Stimulated by reports of an inhibitory effect of non-steroid anti-inflammatory drugs on fracture healing and heterotopic bone formation in clinical and experimental studies, this investigation was performed to study the effect of indomethacin on chondrogenesis and mineralization in vitro by chicken mesenchymal limb-bud cells. Limb-bud cell cultures were treated with indomethacin and, in order to study a possible effect of metabolites, with serum from indomethacin-treated rats. No effects of the drug on chondrogenesis, as estimated by staining with alcian blue, could be detected. This was also the case when mineralization in the cultures induced by high phosphate concentrations was studied. It is concluded that indomethacin probably exerts its effect on bone metabolism through mechanisms other than modulation of cell differentiation or cell proliferation.

Local application of indomethacin in healthy eyes and in post-operative cataract patients

The effects of locally applied Indomethacin were studied. Ten healthy subjects received 1 drop of a 1% watery solution 4 times a day in their left eye during 2 weeks, the right eye serving as control. Neither changes in visual acuity and refraction nor in the appearance and function of the external and anterior segment of the eye were found during this period. Sixty-four patients underwent surgery for simple senile cataract. Half of the patients, by random selection, received Indomethacin solution locally during the first week. The remaining half received routine treatment with a compound preparation of antibiotics and corticosteroid from the third post-operative day. An inflammatory score was calculated and was found to be significantly reduced in the Indomethacin group during the first week.

Derivatization reactions in the gas—liquid chromatographic analysis of drugs in biological fluids

Alkylation, acylation, silylation and other derivatization reactions applied to the gas chromatographic analysis of drugs in biological matrices are reviewed. Reaction conditions are discussed in relation to reaction mechanisms. Detector-oriented labelling of drugs, and derivatization with chiral reagents for the separation of enantiomers are surveyed. Data on the sample clean-up, derivatization and GLC analysis of more than 300 drugs and related compounds are listed.

Plasma indomethacin assay by reversed-phase ion pair high pressure liquid chromatography

A new rapid, selective and sensitive high pressure liquid chromatographic (HPLC) assay for indomethacin in plasma is described. The method involves precipitation of proteins with perchloric acid, followed by dichloromethane extraction using flurbiprofen as an internal standard. The organic solvent was evaporated and the residue dissolved in a water-methanol (2 + 3) phosphate buffer mixture with an apparent pH of 6.8. Aliquots of 100 microliters were injected automatically into the chromatograph. The separation of indomethacin was achieved on a reversed phase (C18, 10 micron) column with a mobile phase consisting of 65% (vol/vol) methanol in water solution of apparent pH 6.8 containing tetrabutylammonium hydrogensulfate as an ion pairing agent. Quantitation of indomethacin was performed by UV detection at 235 nm. At a 2.0 mg X l-1 concentration of indomethacin in plasma the analytical recovery was 82.9 +/- 3.4% (n = 7), the intra-day variability (CV) was 3.6% (n = 7) and the inter-day variability (CV) was 11.0% (n = 7). The calibration curve was linear (typical r-values greater than 0.990) in the range of plasma concentrations as usually found during indomethacin therapy (up to 6 mg X l-1). The limit of sensitivity is 0.025 mg X l-1. The metabolites O-desmethylindomethacin and O-desmethyldeschlorobenzoylindomethacin did not interfere with the method. The capacity of an analyst using this method with automated injection and peak integration is about forty samples in duplicate per day. The applicability of the method for pharmacokinetic studies is demonstrated.

The renin-aldosterone system in nephrogenic diabetes insipidus and the influence of hydrochlorothiazide and indomethacin

Three generations of a family with nephrogenic diabetes insipidus were studied. Treatment of a male infant patient with hydrochlorothiazide normalized the serum sodium concentration and improved the clinical condition, but did not influence the polyuria. Although indomethacin alone was without long-term effect, combined therapy with hydrochlorothiazide and indomethacin regulated serum sodium better than hydrochlorothiazide alone. The renin-aldosterone system was not activated in healthy carriers or patients with nephrogenic diabetes insipidus neither in infancy during severe hypernatremic dehydration nor in adult patients.

High-performance liquid chromatographic assay of indomethacin and its application in pharmacokinetics in healthy volunteers

A new sensitive high-performance liquid chromatographic method for indomethacin from plasma on a reversed-phase column (C18) has been developed. The method involves precipitation of plasma with perchloric acid followed by diethyl ether extraction. The assay is quantitative down to 0.25 microgram ml-1 from a 200-microliters aliquot of plasma with a detection limit of 0.1 microgram ml-1 and a recovery of approximately 90%. The method was applied to single-dose studies with volunteers under various dietary restrictions. The results of these studies indicated that intrasubject variability within these regimens may be as important a factor as the intersubject variability already documented for this drug. These results have important implications in the determination of bioavailability and pharmacokinetic parameters of this drug.

Inhibition of partial closure of epiphyseal plate in rabbits by indomethacin

The efficiency of indomethacin (10 mg/kg/day) in inhibiting recurrent partial closure of the epiphyseal plate was tested in rabbits. An epiphysiodesis was done laterally in the distal left femoral epiphyseal plate in 10 adolescent rabbits. This produced a valgus deformity in 14 of them. The bone bridge was then removed operatively and the rabbits were treated with either indomethacin or vehicle for 21 days postoperatively. Indomethacin plasma levels were about 180 ng/ml. The valgus deformity improved in indomethacin-treated rabbits, whereas it became worse in the controls (P = 0.004).

Lack of effect of indomethacin on ordered growth of the femur in rats

The effect of indomethacin on ordered growth in length and width of the femur was studied in 48 adolescent rats given 2 mg/kg/day of the drug, a regimen previously shown to inhibit fracture healing. The animals were given either indomethacin suspension, or the vehicle alone, orally for 6 weeks. All the animals tolerated the treatment well. During drug treatment the femur distal to the intertrochanteric crest grew about 7 mm in length. Indomethacin plasma levels were about 1 microgram/ml in the indomethacin-treated animals. Indomethacin did not inhibit ordered growth in either length or width. This indicates that indomethacin does not inhibit the normal homeostasis of the skeletal system in adolescent rats.

Alkylation with alkylhalides as a derivatization method for the gas chromatographic determination of acidic pharmaceuticals

The various types of alkylation reactions with alkyl halides and their application in the gas chromatographic analysis of acidic compounds of pharmaceutical interest are reviewed. An extensive survey of the use of these methods for the analysis of various (classes of) compounds is given, with special reference to their determination in biological matrices.

Serum indomethacin concentrations after intravenous administration to preterm infants with patent ductus arteriosus

Six preterm infants with PDA received 14 treatments with indomethacin 0.2 mg/kg intravenously. Auscultatory and echocardiographic assessment indicated closure of the duct in 2, partial closure in 2, and no effect in 2 infants. The mean serum concentration of indomethacin was: 15 min after the first injection 1 314 ng/ml, after 1 hour 970 ng/ml, after 6 hours 718 ng/ml, and after 24 hours 388 ng/ml. The mean half-life of indomethacin in the serum was 20 hours (range 9-50 hours). Side effects in all infants were hyponatraemia, decreased urinary output, decreased urinary sodium excretion, and weight gain. One infant had transient thrombocytopenia and gastrointestinal haemorrhage. By intravenous administration of indomethacin in a dose of 0.2 mg/kg to preterm infants a sufficiently high serum concentration is obtained shortly after the injection. To maintain a high serum concentration for a longer period it is recommended to give a second dose of 0.2 mg/kg after 6 hours and if necessary a third dose of 0.1 mg/kg 24 hours after the first dose.

General practitioners' evaluation of side-effects and efficacy of oxamethacin as compared with indomethacin

Sixteen general practitioners conducted a multicentre double-blind clinical trial to compare oxamethacin (100 mg t.i.d.) with indomethacin (50 mg t.i.d.) for a maximum duration of 2 weeks. Each drug was administered to 339 patients suffering from various pathological conditions requiring a non-steroidal anti-inflammatory drug. When focusing on patients without associated drug therapy, 126/259 patients (50%) presented a good response on inflammation under oxamethacin and 98/236 patients (42%) a good response under indomethacin (p less than 10(-2)); 141/250 patients (56%) presented a good response on pain under oxamethacin and 117/236 (50%) under indomethacin (p less than 5.10(-2)). Side effects and complaints were reported by 34/250 patients (14%) under oxamethacin and by 67/236 (28%) under indomethacin (p less than 5.10(-5)). Some patients stopped treatment because of side-effects: 14/250 (6%) under oxamethacin and 32/236 (14%) under indomethacin (p less than 2.10(-3)).

Indomethacin-induced inhibition of haversian remodelling in rabbits

The effect of indomethacin on haversian remodelling in the radius was studied in 16 rabbits. An osteotomy and a saw-cut almost through the bone were made in the middle and distal parts of the right radius, respectively. In order to obtain biological osteosynthesis in the osteotomy and the saw-cut the rabbits were not treated in any way during the following 3 weeks. They were then given either indomethacin or placebo suspensions per os, 10 mg/kg/day for 2 weeks, followed by 5 mg/kg/day for 4 weeks. The extent of haversian remodelling was estimated by calcein and oxytetracycline fluorochrome labels given at the start of the indomethacin treatment and 3 weeks later, respectively. After 2 weeks of indomethacin treatment (10 mg/kg/day) the indomethacin plasma levels were about 0.18 microgram/ml 24 hours after the last dose. Indomethacin treatment significantly (2P less than 0.019) inhibited haversian remodelling as estimated by fluorochrome labelling.

Inhibition of fracture healing by indomethacin in rats

The effect of indomethacin (2 mg/kg/day) on the healing of closed unimmobilized femoral fractures was examined in rats. A standard femoral fracture was produced in 205 male adolescent rats, and three different experiments were done. In a long-term experiment, the rats were treated with either indomethacin or placebo for 29 days and fracture healing followed for a maximum of 91 days. In two short-term experiments, the rats were treated with either indomethacin or placebo for a week and followed for a maximum of 122 days. The effect of age was studied in one experiment. Indomethacin plasma levels were about 1 microgram/ml in the indomethacin-treated animals. In the long-term experiment, indomethacin inhibited fracture healing (P less than 0.006) and increased the angulation between the femur fragments. In the short-term experiments indomethacin inhibited fracture healding (P less than 0.033) and increased the interfragmentary angle as well as fracture instability. All untreated fractures healed within 10 weeks in younger rats (210 g), whereas only 44% healed in older rats (295 g).

A new anti-inflammatory derivative of imidazole which is less ulcerogenic than indomethacin in rats

The mechanism of the anti-inflammatory activity and ulcerogenicity of (2-dimethylamino-1(2)-methyl) ethyl ester of the 1-(2-carboxyethyl)-2-(p-chlorophenyl)-4,5-bis-(p-methoxyphenyl)-imidazole (A-162-ester) was compared with that of indomethacin in rats and enzymatic preparations derived from other species. A-162-ester was found to be deesterified in plasma to A-162. A-162-ester was about 3 times less anti-inflammatory and about 17 times less ulcerogenic than indomethacin. A-162-ester, when given orally, decreased prostaglandin I2 (PGI2) biosynthesis by gastric mucosa. The IC50 was close to the ulcerogenic ED50. Indomethacin--in the same test--was 37 times more potent than A-162-ester and the PGI2 inhibition and ulcerogenic dose-response curves for indomethacin were parallel. In other in vitro systems of prostaglandin (PG) biosynthesis, the inhibitory activity of A-162 was comparable to that of indomethacin. It is concluded that the ulcerogenicity of indomethacin results from a high affinity of this drug to gastric mucosal wall PG-synthetase which leads to decreased PGI3 formation at this site. The relatively low ulcerogenicity of A-162-ester most probable results from a lower affinity of this drug to the same site.

Interaction of salicylates and other non-steroidal anti-inflammatory agents in rats as shown by gastro-ulcerogenic and anti-inflammatory activities, and plasma concentrations

The interaction of salicylates and other non-steroidal anti-inflammatory drugs was studied in rats. Concurrent oral administration of sodium salicylate (SS) or salicylic acid (SA) and indomethacin (IND) significantly reduced the gastro-ulcerogenicity and the plasma concentrations of IND. Acetylsalicylic acid (ASA) failed to do so. IND had no significant influence on plasma concentrations of SA. Simultaneous administration of SS and IND intraperitoneally or subcutaneously showed the same pattern of interaction as for oral administration. Concurrent oral administration of SS and IND exerted similar anti-inflammatory activity as the single drugs. SS significantly antagonized the ulcerogenicity of ibuprofen and tended to antagonize the ulcerogenic activity of ASA, phenylbutazone, tolfenamic acid and naproxen. The results suggest that in rats SS and SA (but not ASA) interact with IND concerning both gastro-ulcerogenicity and plasma concentrations of IND (but not of SA) and that the interaction is systemic in nature. We propose that the ulcerogenic interaction might be explained partly by the reduced IND plasma concentrations and partly by a weaker inhibition by SS of the prostaglandin system in the rat stomach.