Jan G.R. Ufkes

Pharmacokinetics of methadone and its primary metabolite in 20 opiate addicts

In a closed metabolic ward the pharmacokinetics of methadone and its primary metabolite (EDDP) were studied in 20 long-term opiate addicts. After administration of the daily oral dose of methadone HCl (mean 60 mg, range 10–225 mg) blood samples were taken and analysed, using a newly developed high-performance liquid chromatography (HPLC) method. The steady-state plasma concentrations of the 20 subjects varied from 65–630 ng·ml−1 and from 5 to 55 ng·ml−1, whereas the peak concentrations were 124–1255 ng·ml−1 and 10 – 301 ng·ml−1 for methadone and EDDP, respectively. The calculated ratios between the area under the curve (AUC(0–24 h)) for methadone and the AUC(0–24 h) for EDDP varied from 5.9 to 44.6, indicating interindividual differences in metabolic activity. In 19 out of 20 subjects the pharmacokinetics of methadone are best described using a two-compartment model. The mean body clearance was 1.64 ml·min−1·kg−1, whereas the mean elimination rate constant (β) and plasma half-life (t1/2β) were 0.026·h−1 (range 0.013–0.053·h−1) and 31.2 h (range 13–53 h), respectively. Differences of gender were also found. A poor correlation was found between the methadone dose and the steady-state level. A much better correlation was found between the normalized steady-state level and the body clearance.

Further studies on the structure-activity relationships of bradykinin-potentiating peptides

Several pentapeptides were synthesized and tested for bradykinin-potentiating activity. From these and previous data it appeared that an (L)-aromatic amino acid residue (preferably Trp) in position 3 is essential for high activity. Position 3 represents a stereospecific pillar function, whereas the other positions and the lipophilicity/hydrophilicity balance are important for additional activity. So far, BPP5a seems to have the optimal structure for a bradykinin-potentiating pentapeptide.

The mechanism of action of two bradykinin-potentiating peptides on isolated smooth muscle

Bradykinin-induced contractions in the guinea-pig ileum were potentiated by the peptides A-VI-5 (Val-Glu-Ser-Ser-Lys) and BPP5a (Pyr-Lys-Trp-Ala-Pro), while the contractions induced by other agonists were not affected. Neither peptide added alone caused any response. Previous addition of the peptides shortened the latent period following the addition of bradykinin to a value corresponding to the contraction height with an equivalent dose of bradykinin added alone. Bradykinin in contact with a piece of ileum was inactivated at a relatively slow rate. This inactivation was not inhibited by either A-VI-5 or BPP5a in doses causing potentiation. Suppression of the cholinergic activity by cooling, atropine, morphine or tetrodotoxin did not influence the potentiating activity. Addition of the peptides at the moment a submaximal contraction due to bradykinin had been fully established, increased the contraction height within seconds. The two peptides caused a parallel shift to the left of the dose-effect curve of bradykinin, whereas the maximum bradykinin effect remained unchanged. It is concluded that sensitization of bradykinin receptors due to an increased affinity of the receptor for bradykinin is the hypothesis which best fits the experimental findings.

Structure-activity relationships of bradykinin potentiating peptides.

A number of A-VI-5 (Val-Glu-Ser-Ser-Lys) analogues and fragments were synthetized and tested on bradykinin potentiating activity so as to establish the nature of the active group(s) or structural characteristics of some bradykinin potentiating pentapeptides. It could be concluded that (1) the polar groups of the side-chains, such as the two hydroxyl groups of the serine residues, the omega-carboxyl group of the glutamic acid residue and the omega-amino group of the C-terminal lysine, are not essential for the bradykinin potentiating activity; (2) the chain length (at least 5 amino acids) and the lipophilicity of the N-terminal amino acid as well as the whole peptide are of much more importance; (3) the free N-terminal NH2-group is not essential; (4) aromatic amino acids in position 3 of the peptide chain result in highly active bradykinin potentiating peptides.

Craving despite extremely high methadone dosage

A clinical case study is presented of an opiate addict, currently under methadone maintenance treatment (MMT), who claims the need of a higher daily methadone dose. He is admitted to a closed metabolic ward, where he receives 250 mg methadone per day. During 24 h both pharmacokinetic parameters and craving levels are measured simultaneously. Results show extremely high methadone concentrations and its primary metabolite EDDP in plasma and urine. The craving level shows a distinguished peak around the methadone administration on both measured days. Withdrawal symptoms as well as self-reported craving did not correspond at all to the extremely high methadone concentration level in plasma. So we suggest that in individual cases if high methadone doses and plasma methadone levels are not able to diminish craving symptoms, dose adjustment should be accompanied by education regarding daily anticipatory increase of opiate craving.

L-Methadone and D,L-Methadonein Methadone Maintenance Treatment: A Comparison of Therapeutic Effectiveness and Plasma Concentrations

The clinical effectiveness of l-methadone maintenance treatment (LMMT) carried out using d,l-methadone or l-methadone have been compared with ambulatory heroin-dependent subjects. A total of 40 heroin-dependent subjects, previously maintained on l-methadone in Frankfurt am Main, were divided into two groups under randomised double-blind conditions and received either an equivalent dose of l-methadone as d,l-methadone or remained on the previous l-methadone treatment. Requests for a change in the dose of d,l-methadone and l-methadone were recorded, urine samples for determination of illicit drug use were collected and the individual level of opiate craving was determined over a 22-day observation period. There was no significant difference between the two groups in the number requests for a dose change (dose increase <10%). However, there was a significant increase in heroin use in the group which continued to receive l-methadone. Although there was less variability in opiate craving in the group receiving d,l-methadone, the mean intensity of opiate craving did not differ between the two groups. The mean l-methadone dose:l-methadone plasma concentration ratio, an index of the bioavailability of l-methadone in individual subjects, showed no significant change when the treatment was changed to d,l-methadone. The mean d-methadone:l-methadone plasma concentration ratio was 1.17. There was no significant difference between these ratios for day 15 and day 22. The mean l-methadone:EDDP plasma concentration ratio in the l-methadone group was 22.2 and the d,l-methadone:EDDP plasma concentration ratio was 18.4 . The plasma EDDP concentration in the d,l-methadone group increased 3-fold after starting treatment with d,l-methadone. These findings suggest that d,l-methadone can be used in methadone maintenance treatment of heroin-dependent subjects but that further studies are required to evaluate pharmacokinetic interactions between methadone enantiomers.

The bradykinin potentiating activity of two pentapeptides on various isolated smooth muscle preparations

Two bradykinin potentiating peptides A-VI5 (Val-Glu-Ser-Ser-Lys) and BPP5a (Pyr-Lys-Trp-Ala-Pro), were compared with respect to their potentiation of a number of different bradykinin effects on six isolated smooth muscle preparations. Apart from the considerable difference in effective concentrations, no essential qualitative difference was observed between these two peptides. Therefore the assumption of a different mechanism of action for the two peptides, which have a completely different structure, could not be substantiated.

Effect of naloxone on blood pressure and survival in different shock models in rats

The effect of naloxone on a number of experimental shock models, using the anaesthetized rat, was studied with special emphasis on mean arterial blood pressure (MABP) and chance of survival. Only a slight increase in MABP was noted in haemorrhagic shock models whereas survival was not affected. Naloxone was without effect in endotoxin shock (i.p. administration of endotoxin). In endotoxin shock (i.v. administration) naloxone increased MABP especially at a high dose of endotoxin. Although survival time was prolonged, the chance of permanent survival was not improved. Naloxone had practically no effect in anaphylactic shock and intestinal ischaemia shock. It is concluded that if naloxone has any effect it is relatively slight. However, this does not exclude the possibility that naloxone might still be considered as an adjunct to other forms of shock treatment at least in certain types of shock.

Characterization of various antiallergic agents using a new method for inducing systemic anaphylaxis in the rat

Five different types of antiallergic agents were studied using a newly developed method for inducing IgE-mediated bronchial and cardiovascular anaphylaxis in the rat. With the exception of the histamine H1 antagonist mepyramine (no activity at all), each antiallergic tested showed a different and characteristic profile of antiallergic activity. Prednisolone and the SRS-A antagonist FPL 55712 protected the rats completely against mortality, whereas cromoglycate and ketotifen offered only partial protection. The cardiovascular events were favorably influenced by FPL 55712 and cromoglycate, but ketotifen was completely ineffective in this respect. However, ketotifen showed the highest activity in suppressing the antigen-induced bronchoconstriction, followed by cromoglycate and prednisolone, whereas FPL 55712 was practically inactive. It can be concluded that the antiallergic activity of various types of antiallergics can be characterized and differentiated by means of this highly reproducible method.

A new method for inducing fatal, IgE-mediated, bronchial and cardiovascular anaphylaxis in the rat

Brown-Norway rats, sensitized with trinitrophenyl (TNP) haptenized ovalbumin and AIPO4 as adjuvant 12 days before, were challenged with trinitrophenyl haptenized bovine serum albumin intravenously, while lung function (Vt, V, Ppl, Fres, Cdyn, and Rl) and cardiovascular function (BP and Fheart) were measured continuously. This resulted in a highly reproducible, plasma IgE-antiTNP related, immediate anaphylactic response characterized by a short-lasting (8-10 min) bronchoconstriction, together with a long-lasting fall in blood pressure. All rats died in shock within 21-150 min. This method is simple and appeared to be highly reproducible and therefore suitable to screen or study antiallergic drugs in vivo.