Tawfeeg A. Najjar

Role of non-selective adenosine receptor blockade and phosphodiesterase inhibition in cisplatin-induced nephrogonadal toxicity in rats

1. It is well documented that cisplatin (CDDP) treatment increases the expression of adenosine A1 receptors in both kidney and testes. However, the effect of adenosine at these receptors is controversial. Adenosine A1 receptors have been documented to be involved in either cytoprotection or aggravation of nephrotoxicity. The aim of the present study was to examine the effect of the non‐selective adenosine receptor inhibitor theophylline and the phosphodiesterase inhibitor pentoxifylline on CDDP‐induced renal and testicular toxicity.

Inhibition of Nitric Oxide Synthase Aggravates Cisplatin-Induced Nephrotoxicity: Effect of 2-Amino-4-Methylpyridine

Background: Nitric oxide (NO) has been shown to play a role in maintaining normal renal function. However, the role of NO in cisplatin (CDDP)-induced nephrotoxicity is still unclear. The aim of the present work was to examine the effect of the NO synthase (NOS) inhibitor, 2-amino-4-methylpyridine, on the severity of CDDP-induced nephrotoxicity. Methods: Male Wistar rats were divided into six groups. Three control groups received plain drinking water or water containing 1.5% L-arginine. One of the two groups receiving plain water was treated with an intraperitoneal injection of 2-amino-4-methylpyridine (1 mg/kg in normal saline), and the other two control groups were injected intraperitoneally with normal saline. Another three groups were treated in the same manner and injected with CDDP (6 mg/kg, i.p.). CDDP was injected 1 h after 2-amino-4-methylpyridine treatment. Rats were sacrificed 7 days after CDDP treatment, and serum as well as kidneys were isolated and analysed. Results: CDDP-treated rats showed increases in the kidney weight as a percentage of the total body weight and serum creatinine and urea levels and decreases in serum albumin and calcium levels. Also, CDDP treatment induced reductions in the kidney total nitrate/nitrite (NOx), reduced glutathione (GSH) and glutathione peroxidase activity (GSH-Px) levels and an increase in the kidney malondialdehyde (MDA) production level. In contrast, 2-amino-4-methylpyridine treatment 1 h prior to CDDP injection induced marked exacerbation of CDDP-induced nephrotoxicity, as manifested by severe aggravation of the indices of nephrotoxicity. Also, 2-amino-4-methylpyridine plus CDDP-treated rats showed exaggeration of the reduction in the kidney total NOx content and GSH-Px activity and elevation of the kidney platinum accumulation level with normalization of the kidney MDA production level and rebound in the kidney GSH content. Histopathologically, CDDP-treated rats showed marked interstitial nephritis, tubular atrophy and tubular necrosis. However, treatment with 2-amino-4-methylpyridine 1 h prior to CDDP injection revealed marked exacerbation of CDDP-induced histopathological changes. Conclusions: The present findings suggest that NO plays a role in CDDP-induced nephrotoxicity. Administration of 2-amino-4-methylpyridine, an NOS inhibitor, exacerbates CDDP-induced nephrotoxicity.

Liquid chromatographic assay of nifedipine in human plasma and its application to pharmacokinetic studies.

A highly sensitive, selective and reproducible reversed-phase high-performance liquid chromatographic method has been developed for the determination of nifedipine in human plasma with minimum sample preparation. The method is sensitive to 3 ng/ml in plasma, with acceptable within- and between-day reproducibilities and linearity (r2 > 0.99) over a concentration range from 10-200 ng/ml. Acidified plasma samples were extracted using diethyether containing diazepam as internal standard and chromatographic separation was accomplished on C18 column using a mobile phase consisting of acetonitrile, methanol and water (35:17:48, v/v). The within-day precision ranged from 2.22 to 4.64% and accuracy ranged from 102.4-106.4%. The day-to-day precision ranged from 2.34-7.07% and accuracy from 95.1-100.1%. The relative recoveries of nifedipine from plasma ranged from 91.0-107.3% whereas extraction recoveries were 88.6-93.3%. Following eight 6-week freeze-thaw cycles, nifedipine in plasma samples proved to be stable with accuracy ranging from 0.64 to 3.0% and precision ranging from 3.6 to 4.15%. Nifedipine was also found to be photostable for at least 120 min in plasma, 30 min in blood and for 60 min in aqueous solutions after exposure to light. The method is sensitive and reliable for pharmacokinetic studies and therapeutic drug monitoring of nifedipine in humans after the oral administration of immediate-release capsules and sustained-release tablets to five healthy subjects.

Influence of piperacillin on the pharmacokinetics of methotrexate and 7-hydroxymethotrexate

Abstract The influence of concomitant administration of piperacillin (PIP) on the pharmacokinetic parameters of methotrexate (MTX) and 7-hydroxymethotrexate (7-OH-MTX) was studied in rabbits. Six rabbits received an initial i.v. bolus (0.21 mg kg−1) followed by a constant-rate i.v. infusion of the drug (5 μg min−1 kg−1) for 240 min. The PIP dose (30 mg kg−1) was repeated every 30 min until the end of the infusion period. The control group consisted of four rabbits treated the same way except for the addition of PIP. There were significant increases in the mean residence times found for MTX (MRTinf) and 7-OH-MTX (MRTm,inf) following PIP administration. Concomitant administration of PIP with MTX also produced significant 1.5- and 2.8-fold increases in the area under the curve of MTX and 7-OH-MTX, respectively. The total body clearance of MTX and the operative total body clearance of 7-OH-MTX significantly decreased, but in a less than proportional manner. The study demonstrates that the interaction between MTX and PIP is mainly due to the reduced clearance of both MTX and 7-OH-MTX combined with a slight increase in the formation clearance of the metabolite.

Cisplatin pharmacokinetics and its nephrotoxicity in diabetic rabbits

Background: This study was designed to investigate the relationship between the attenuation of cisplatin (CDDP)-induced nephrotoxicity in experimental diabetic rabbits and the plasma pharmacokinetics of the free ultrafilterable and total plasma platinum (Pt) levels. Methods: Two groups of age-matched male New Zealand white rabbits were used; the first group consisted of rabbits with streptozotocin-induced diabetes (single i.v. bolus dose of streptozotocin of 65 mg/kg in citrate buffer, pH 4.6), and the second group of nondiabetic rabbits treated with the same volume of citrate buffer. Both groups were treated with CDDP (5 mg/kg, single i.v. bolus dose) 3 days after induction of the diabetic state in the first group. The plasma Pt levels were followed for 4 h after CDDP administration, in which the free ultrafilterable and total plasma Pt concentrations were determined by atomic absorption spectrometry. The pharmacokinetic parameters of free ultrafilterable plasma Pt were determined using a noncompartment pharmacokinetic model of analysis. Results: The total plasma Pt levels declined in a biphasic manner and were adequately described by a two-compartment model. No significant change was observed in the pharmacokinetics of either the free ultrafilterable or total plasma Pt levels in the diabetic group in comparison with the control nondiabetic group (p > 0.05). However, 4 h after CDDP administration, the total plasma Pt level of the nondiabetic group was significantly higher than that of the diabetic rabbits (p < 0.001). Indices of nephrotoxicity were determined 7 days after CDDP administration. The results revealed that the diabetic state protected against CDDP-induced nephrotoxicity. The nondiabetic rabbits exhibited highly significant elevations in the serum creatinine and urea levels and a decrease in the serum albumin level (p < 0.001) in comparison with the diabetic group. Conclusions: These findings might suggest that the reduction in CDDP-induced nephrotoxicity in diabetic rabbits is not due to a change in the plasma pharmacokinetic profile within the drug follow-up period. It could be anticipated that the rapid decline in the total plasma Pt level after CDDP administration to diabetic rabbits, as well as the reduction in the terminal elimination half-life of the total plasma Pt level might be responsible for the reduction in CDDP-induced nephrotoxicity. Also, alterations in the how kidneys of diabetics deal with the renal excretion of Pt and reduction of its accumulation in kidney tissue are not excluded.

Pharmacokinetics of Methotrexate in Children with Acute Lymphocytic Leukemia

Plasma methotrexate (MTX) levels were measured in 10 children (age 3-12 years) who received a total of 43 infusions of MTX. The total dose (1,000 mg/m2) was administered as a bolus of 200 mg/m2 with 24-hour infusions of 800 mg/m2. The clearance was fast at 158 +/- 81 ml/min/m2 and the elimination half-life (t1/2 beta) 3.0 +/- 0.7 h (mean +/- SD). The inter- and intrapatient variations in the steady state were wide, up to 6 times, suggesting the need for dose adjustment during infusion. The patients were at low risk for toxicity with a predicted MTX concentration at 39 h (5 half-lives) postinfusion of 0.28 +/- 0.10 mumol/l (mean +/- SD). None of them required leucovorin rescue 72 h postinfusion. An additional assessment of the MTX level may be useful as a guide to the duration of leucovorin rescue, which may be more or less than the routine 72 h postinfusion. The time suggested for this assessment was 48 h postinfusion. The mean +/- SD concentration at this time was 0.23 +/- 0.12 mumol/l and it correlated (r = 0.841) with the level measured 36 h postinfusion (n = 10). The value of this level needs to be investigated on a larger number of infusions.

Mechanism and implication of cephalosporin penetration into oropharyngeal mucosa.

The aim of this study was to explore the mechanism(s) by which oral cephalosporins penetrate into human oropharyngeal mucosa, and thus, the availability of sufficient concentrations at the site of infection. Two oral cephalosporin prototypes, cephalexin (first generation) and cefixime (third generation), were administered to five healthy subjects at two different visits with a 1-week washout period. Plasma and saliva samples were collected and drug concentrations were measured using an appropriate HPLC method. The maximum plasma concentrations (Cmax) of cefixime and cephalexin were 2.97 ± 0.24 μg ml−1 and 77.65 ± 18.91 μg ml−1, respectively. These concentrations were associated with a maximum salivary concentration (CSmax) of 0.56 μg ml−1 for cefixime and 3.34 μg ml−1 for cephalexin. Such levels exceed the reported minimal inhibitory concentration (MIC) for Streptococcus pyogenes and Streptococcus pneumoniae. The average concentration of cefixime in saliva corresponded to its plasma free fraction (saliva/plasma [S/P] ratio; 0.34). However, this observation was not true for cephalexin, for which antibiotic concentrations in the saliva did not appear to correspond to its plasma free fraction (0.8–0.85), with an S/P ratio of only 0.092. Our findings indicate that an active transport mechanism exists for cefixime excretion into human oropharyngeal mucosa, whereas cephalexin is passively diffused, although to a limited extent, as measured by its salivary concentrations.

Effect of cefoperazone on the pharmacokinetics of methotrexate in the rabbit

Abstract The effect of cefoperazone (CPZ) on the pharmacokinetics of methotrexate (MTX) was studied in 10 rabbits. MTX was administered as a bolus dose of 2 mg kg −1 , followed by a constant infusion of 50 μg kg −1 min −1 for 120 min. A group of 5 rabbits received, concomitantly, 20 mg kg −1 CPZ every 30 min, begining at MTX administration. Blood samples were serially collected for a total period of 320 min post infusion, and plasma was analyzed for MTX using high performance liquid chromatography (HPLC). The mean (± SD) values of the pharmacokinetic parameters were as follows: total area under the curve (AUC) 967 ± 704, 1801 ± 778 μg min 1 −1 ; steady state MTX concentration C ss , 6.2 ± 4.1, 9.9 ± 3.6 μg ml −1 ; and maximum plasma concentration (C p max ) 7.5 ± 4.5, 24.2 ± 11.2μg ml −1 for the single and drug combination groups, respectively. The differences in these parameters were statistically significant ( p t 1 2 ) were 60 ± 21.6 and 53.3 ± 8.5 min, and the difference in the value of this parameter between the treatment groups did not reach statistical significance ( p > 0.05). These results suggest that CPZ may influence the distribution phase, rather than the elimination stage, of MTX disposition in rabbits. The results of the present study may have relevance to a potential interaction that can exist between these drugs when administered concurrently in humans. However, further studies in appropriate subjects are needed to verify and characterize the clinical significance of such an interaction.

Theophylline inhibits the elimination of flumazenil in rabbits

Abstract The effect of theophylline on the elimination of flumazenil during constant infusion of l mg/kg per h over 240 min was investigated in 10 rabbits. Theophylline was introduced as a single intravenous (i.v.) dose of 5 mg/kg (5 rabbits) and 15 mg/kg (5 rabbits), 100 min postinfusion. The addition of theophylline was associated with a new steady state which is approx. 32 and 46% higher for the 5 and 15mg/kg doses, respectively. The elimination half-life of the drug was also increased from 18 and 12 min to about 28 and 42 min, respectively, for the two doses. Despite the relatively wide margin of safety for flumazenil the changes observed in plasma concentration during concomitant administration of theophylline may be clinically important. The pharmacokinetic parameters obtained prior to theophylline injection in the 10 rabbits were 406 mg/ml and 15 min for the steady state and elimination half-life, respectively. The variations between subjects in these parameters were as much as 2-fold. A simple and sensitive HPLC procedure to measure flumazenil in plasma is also described.