Design, development and performance of a novel multidose dry-powder inhaler.

The authors describe the design and development of a breath-actuated multidose dry-powder inhaler and summarize the in vitro and in vivo data demonstrating its robustness and performance in the laboratory and during clinical use. Drugs for the treatment of asthma--including budesonide, beclomethasone dipropionate and salbutamol--when formulated with lactose powder as a carrier and dispensed via this device, have exhibited clinical efficacy and safety profiles comparable with standard pressurized metered-dose inhalers and dry-powder formulations.

An ab initio approach to the understanding of cytochrome P450-ligand interactions.

1. We describe the application of novel ab initio quantum mechanical methods to the study of ligand interactions with cytochrome P450cam (CYP101). 2. We find that our techniques accurately describe the transition from a low-spin state to a high-spin state of the haem Fe3+ on binding of a substrate. Furthermore, our methods correctly predict that a large fraction of low-spin character is retained on binding of an inhibitor. 3. We demonstrate the use of 'computational experiments' to elucidate key features of the mechanism of interaction. This leads us to identify a new mechanism for the suppression of the low- to high-spin transition on binding of an inhibitor, namely the shortening of the bond between the Fe atom and the coordinated S atom of the cysteine axial ligand.

Ab initio molecular modeling in the study of drug metabolism.

We discuss the use of ab initio quantum mechanical methods in drug metabolism studies. These methods require only the positions and atomic numbers of the atoms to be specified and offer greater transferability than conventional molecular modeling techniques. This fact, coupled with the accuracy of our approach, permits 'computational experiments' to be performed, allowing details of reaction mechanisms to be understood. We review the application of these methods to the cytochrome P450 superfamily of enzymes. There is much interest in understanding the mechanisms of these enzymes due to their participation in a wide range of metabolic processes including drug activation/deactivation. We find that our methods accurately reproduce the low- to high-spin transition of the haem Fe on binding of a substrate. Furthermore, we identify a new mechanism for the suppression of this spin transition, namely the shortening of the bond between the Fe atom and the coordinated S atom of the cysteine axial ligand. These results indicate that ab initio molecular modeling may be usefully applied in the study of drug metabolism and that further study of intermediate states in the P450 reaction cycle would be beneficial, particularly those which are not accessible using conventional experimental approaches.

Haemodynamic effects of prenalterol in patients with coronary heart disease.

The haemodynamic effects of prenalterol, a new selective beta-1 adrenoreceptor agonist, have been studied in patients with coronary heart disease. The drug was administered intravenously in a dosage of 0.5 to 2.5 micrograms/kg body weight to 20 patients undergoing coronary angiography and to 10 patients with a recent myocardial infarction, who had clinical evidence of left ventricular dysfunction. Left ventricular performance was enhanced in both groups of patients--left ventricular dP/dt (max) increased by 33 per cent and the systolic time intervals, pre-ejection period, and the ratio of pre-ejection period and left ventricular ejection shortened by 28 and 21 per cent, respectively. Cardiac output and stroke volume increased with no change in heart rate nor in left ventricular filling pressure. These results indicate that prenalterol enhances the contractile state of the myocardium without altering heart rate, and suggest that prenalterol could be of value in the management of patients with coronary heart disease, who have impaired left ventricular function.

New antiarrhythmic agents. 1. Primary alpha-amino anilides.

Thirty-two alpha-amino anilides with various substituents in the aromatic ring and in the alpha position are described. Their abilities to protect mice against chloroform-induced fibrillation and to elicit toxicity were determined. Substitution of an alkyl or aryl group in the alpha position enhanced the antifibrillatory activity. In most cases, increased potency was accompanied by increased toxicity. Eleven compounds were tested in dogs with surgically induced myocardial infarction; most showed antiarrhythmic activity. 2-Aminopropiono-2',6'-xylidide, tocainide, was chosen for clinical investigation.

Pharmacokinetic and clinical pharmacological studies with mepivacaine and prilocaine.

The tolerance and pharmacokinetic properties of mepivacaine and prilocaine were compared following i.v. infusion of 250 mg (0.88 and 0.97 mmol respectively) of each drug in five healthy volunteers. Side-effects were minor and occurred in only two subjects during the infusion of mepivacaine. Plasma concentrations of mepivacaine were greater in each subject than the corresponding values for prilocaine. The elimination half-life of mepivacaine was generally longer than that for prilocaine, whereas the total body clearance of prilocaine was consistently greater than the corresponding value for mepivacaine. For each subject the clearance of prilocaine substantially exceeded normal heptic blood flow and therefore an extra-hepatic site of metabolism of prilocaine has been postulated.

Cardiovascular effects of prenalterol (H133/22) in normal man.

1 Prenalterol, (S-(-)-1-(4 hydroxyphenoxy)-3-isopropylaminopropanol-2 hydrochloride) a cardio-selective beta-adrenergic receptor agonist, was infused intravenously into six normal male volunteers to determine the cardiovascular effects of this drug. 2 On different occasions, each volunteer received a placebo infusion, an infusion of 0.5 mg prenalterol and an infusion of 1 mg prenalterol. Cardiac output (impedance cardiography), arterial pressure (sphygmomanometry), heart rate and ECG were measured throughout. 3 Prenalterol produced a statistically significant increase in cardiac output and at the end of the infusion this increase was 24% with 0.5 mg and 29% with 1 mg, mainly due to an increase in stroke volume (18% and 17%) with a lesser change in heart rate (+2 and +7 beats/min). Pulse pressure increased but mean arterial pressure showed little change. Peripheral resistance fell by 18% and 20%. As indicated by systolic time indices myocardial contractility increased. 4 Prenalterol at plasma concentrations in excess of 20 nmol l-1 produced significant inotropic effects but did not markedly increase heart rate at concentrations of 60 nmol l-1.

A review of the metabolism of amide local anaesthetic agents.

(1) Amide local anaesthetics are almost completely metabolized before excretion in both animals and man. (2) Considerable interspecies variability occurs in the quantitative excretion of local anaesthetic metabolites; however, qualitative similarities often exist. (3) The secondary amine metabolite of lignocaine, MEGX, is capable of reacting in vivo with acetaldehyde, formed as a metabolite of ethyl alcohol, to produce a cyclic condensation product. (4) Although hydrolysis in man of the secondary amine metabolite of lignocaine, MEGX, appears extensive, the same is not true for the metabolic analogue produced from mepivacaine, PPX. (5) Metabolism of mepivacaine by the neonate is impaired, but the excretion process in the newborn is capable of eliminating the drug within 24 hr after birth. (6) Metabolic data on bupivacaine and etidocaine are incomplete. The latter compound appears to have a more rapid plasma clearance.