Comparison of cyclophilin binding assay and radioimmunoassay in monitoring of blood cyclosporine.

Cyclosporine binds with cyclophilin, an abundant protein found in almost all tissues, and the resulting complex interacts with calcineurin diminishing T-cell activation. Cyclophilin can be regarded as a cellular "receptor" for cyclosporine. Measuring cyclosporine binding to cyclophilin may offer a link between pharmacokinetics and pharmacodynamics that could improve monitoring of cyclosporine therapy. The authors investigated the feasibility of the cyclophilin binding assay and compared the results with a standard specific monoclonal radioimmunoassay in 100 blood samples taken for therapeutic drug monitoring. The results obtained with these methods were related closely with each other (r = 0.96; p < 0.001) but the mean (+/-SEM) concentrations were approximately two-fold higher in cyclophilin binding assay than in radioimmunoassay (520.4 +/- 49.9 ng/ml versus 257.7 +/- 28.6 ng/ml, respectively, p < 0.001). The shapes of the cyclosporine concentration versus time curves in two patients after a liver and heart transplantation, respectively, were similar after both methods but cyclophilin binding assay gave higher values than radioimmunoassay. Before firm conclusions on the clinical value of cyclophilin binding assay can be made, comparative studies in patients linking cyclosporine concentrations measured with cyclophilin binding assay and standard methods to the therapeutic outcome are needed.

Extradural, paravertebral and intercostal nerve blocks for post-thoracotomy pain.

Forty-five patients were allocated randomly to receive either a single intrathoracic block of four intercostal nerves, a continuous thoracic extradural infusion or a continuous paravertebral infusion of bupivacaine. Patients were allowed additional i.v. boluses of morphine via a PCA device. Segmental spread of pinprick analgesia was comparable in the groups for up to 20 h. Up to 2 h after the block, plasma concentrations of bupivacaine were greater in the intercostal group and there was large interindividual variation. There were no significant differences between the groups in pain, morphine consumption, respiratory function or adverse events. Moderate to severe respiratory depression was detected in 14 patients more than 2 h after operation.

Evidence for pre-hepatic metabolism of oral cyclosporine in children.

1. The pharmacokinetics of cyclosporine were investigated before renal transplantation in 20 children aged 1.1 to 16.8 years. Cyclosporine was given as a single oral dose (10 mg kg-1) or as a 4 h i.v. infusion (3 mg kg-1). 2. The blood drug concentration was measured by both specific and nonspecific monoclonal radioimmunoassays. 3. The mean oral availability of cyclosporine was 20.6% (range 10.8-34.1%). 4. The mean ratio of AUCs measured by nonspecific and specific r.i.a. was 1.96 (range 1.4-2.7) after oral administration and 1.43 (range 1.1-2.0) after i.v. administration. The mean difference between the ratios was 38.5% (P = 0.0001). The ratio of AUCnonspecific to AUCspecific was inversely related to blood drug clearance (r = 0.57; P = 0.009). 5. The findings are suggestive of presystemic, pre-hepatic metabolism of cyclosporine which could contribute to the low, and highly variable bioavailability of this drug.

Pharmacokinetically determined cyclosporine dosage in young children.

To account for the individual variability in cyclosporine pharmacokinetics and the non-existence of dosing recommendations in young children, we studied the pharmacokinetics of cyclosporine before renal transplantation in ten children aged 1.1-2.5 years, to determine the appropriate individual dose. Our aim was to reach a steady-state cyclosporine blood level of 200-300 micrograms/l, 8 h after a dose in the first days after renal transplantation. Cyclosporine was given as a single oral dose (10 mg/kg) or as a 4-h i.v. infusion (3 mg/kg), and the blood concentration was determined for 24 h by a specific monoclonal radioimmunoassay. The mean terminal cyclosporine half-life (t1/2) was 9.3 h (range 2.8-20.4), blood clearance 10.8 ml/min per kilogram (range 6.8-22.7) and volume of distribution 2.8 l/kg (range 1.4-4.7). The bioavailability of oral cyclosporine was low; the mean amount absorbed was 21.8% of the administered dose (range 11-35). The mean calculated dose needed to attain the intended predose blood cyclosporine level of 200-300 micrograms/l at steady-state was 5 mg/kg per day for i.v. and 21 mg/kg per day for oral administration. In view of the short t1/2, we used three doses/day. The validity of the predicted doses is shown by the mean cyclosporine doses used during the first 10 days after transplantation, which were 93.5% of the calculated oral and 96.6% of the calculated i.v. doses. The observed mean cyclosporine concentration during the same period was 196 micrograms/l.

Therapeutic cyclosporine monitoring: comparison of radioimmunoassay and high-performance liquid chromatography methods in organ transplant recipients.

We have determined blood cyclosporine concentrations using three different methods in a total of 212 therapeutic monitoring specimens from heart, liver, kidney, and bone marrow, transplant recipients. The specimens were analyzed by radioimmunoassay using a polyclonal nonspecific antibody (RIA, Ciclosporin RIA-Kit), radioimmunoassay using a monoclonal specific antibody (SRIA, Sandimmun Kit), and by high-performance liquid chromatography (HPLC). When the nonspecific antibody was used, mean RIA/HPLC ratios in different patient groups ranged from 2.3 to 5.5, and the variability in this ratio was large in all groups. When the specific antibody was used, mean SRIA/HPLC ratios in different groups ranged from 1.1 to 1.5, with smaller variability. It can be concluded that radioimmunoassay using a specific monoclonal antibody is well suited for therapeutic monitoring of blood cyclosporine concentrations. However, even this method overestimates cyclosporine concentrations in certain patients.

Effects of resins and activated charcoal on the absorption of digoxin, carbamazepine and frusemide.

1. The interference of resins and activated charcoal with the absorption of digoxin, carbamazepine and frusemide was studied. 2. In a cross-over study consisting of four phases, single doses of colestipol hydrochloride (10 g), cholestyramine (8 g), activated charcoal (8 g) or water only were given to six healthy volunteers immediately after the simultaneous ingestion of digoxin (0.25 mg), carbamazepine (400 mg) and frusemide (40 mg). Plasma and urine concentrations of the test drugs and the urine volumes were determined up to 72 h. 3. The absorption of digoxin was not reduced by colestipol, moderately (30-40%, P less than 0.05) reduced by cholestyramine and greatly (96%) by charcoal. 4. The absorption of carbamazepine was not decreased by cholestyramine, slightly (10%) by colestipol and greatly (90%) by activated charcoal. 5. The absorption and the diuretic effect of frusemide were significantly diminished by all agents. The bioavailability was reduced by colestipol 80%, by cholestyramine 95% and by activated charcoal 99.5%. 6. The interference with the gastrointestinal absorption of most of the basic drugs by colestipol and cholestyramine seems to be minimal. On the other hand, the resins may seriously impair the absorption of certain acidic drugs, for example frusemide.

External quality assessment of serum drug determinations in the Nordic countries.

A system for external quality assessment of serum drug determinations in the five Nordic countries has been established, and results of several surveys of antiepileptic drug determinations are described. The work was started as a pioneer work of NORDKEM at the time when NORDKEM was founded and was carried out during the years 1977-1979. The problems concerning methodology of drug analyses and, consequently, the problem of setting up quality assessment systems differ clearly from those in connection with the common analyses of clinical chemistry. Especially the quality of control materials is very important. An expert panel of drug specialists is necessary to plan and interpret an external quality assessment program of drug analyses, but it can very well be carried out in connection with other quality assessment programs. The state of the art of antiepileptic drug determinations in the Nordic countries at the time of the surveys was very good. The level of inaccuracy was well below 5%, and the level of imprecision was mainly in the range of 15-20%, although no outliers were excluded during the statistical treatment of the data.

Effect of activated charcoal on absorption of tolbutamide and valproate in man.

The claim that activated charcoal should be ineffective or even contraindicated in intoxication due to tolbutamide is based only on limited in vitro studies. To test the claim, the effect of activated charcoal 50 g on the absorption of tolbutamide and, as a reference, of sodium valproate, was studied in 6 healthy volunteers. Each volunteer swallowed tolbutamide 500 mg and sodium valproate 300 mg with 50 ml water 1 h after a light breakfast, and within 5 min they took in randomized order either a suspension of activated charcoal or water. The absorption of tolbutamide, calculated as the peak concentration and the area under the serum drug concentration-time curve during 0-48 h, was reduced by 90% by charcoal (p less than 0.001). The absorption of valproate in these conditions was reduced on average by 65% (p less than 0.01). In each subject charcoal had a greater effect on the absorption of tolbutamide than of valproate. According to these findings and preliminary in vitro studies on other sulphonylureas high doses of activated charcoal can be recommended for the preventing the absorption of sulphonylureas in acute intoxications. The poor aqueous solubility of these substances at the gastric pH probably delays their gastrointestinal absorption, so that they may be adsorbed on to charcoal even given several hours later.

Composition of human serum sphingomyelins.

Serum sphingomyelins were analyzed by argentation chromatography of the corresponding ceramide diacetates. Six subfractions were obtained. Three of them contained 4-sphingenines in combination with saturated, trans-, or cis-monoenoic fatty acids; the remaining three contained sphingadienine, also in combination with saturated, trans-, or cis-monoenoic fatty acids. Palmitic acid was the principal fatty acid combined with 4-sphingenines, while nervonic acid was the principal fatty acid combined with sphingadienine. About 4% of the total fatty acids of sphingomyelin were trans-monoenoic. They were comprised of many positional isomers of straight-chain C(22-24) compounds. The cis-monoenoic acids made up 33% of the total acids and consisted of almost pure nervonic acid. The rest of the acids were saturated. The 4-sphingenines contained small amounts of iso-C(18) and anteiso-C(19) compounds in addition to the straight-chain C(16-18) bases.

Structure of plasma sphingadienine.

The dienic long-chain base (sphingadienine) of human plasma sphingomyelins has been identified as d-erythro-1,3-dihydroxy-2-amino-4-trans-14-cis-octadecadiene. A similar sphingosine was also detected in plasma sphingomyelins of rat, rabbit, and cat. The key reaction in the structural studies was partial reduction of sphingadienine with hydrazine to cis-14-sphingenine and 4-sphingenine.