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Notes: Abstract We have studied the controlled-release properties and relative systemic availabilities of two dosages of the same controlled-release (CR) diltiazem tablet formulation by comparing them at steady state with those of an immediate-release formulation. We measured 24-hour plasma concentration profiles during 4-day treatments with diltiazem 90 mg CR tablet bd diltiazem 120 mg CR tablet bd, and conventional diltiazem 60 mg immediate-release (IR) tablet tid. The study had a randomized, three-way crossover design. Twelve healthy men (38–52 y) participated. Trough plasma concentrations were determined on days 3 and 4. The 24-h plasma concentration-time profiles were assessed after the last morning dose on day 4 of each period. The following steady-state pharmacokinetic values were calculated: the minimum plasma concentration (Cmin), the maximum plasma concentration (Cmax), the time interval during which the plasma concentration exceeded 75% of Cmax (t75), the area under the plasma concentration-time curve (AUC72–96), the peak-to-trough fluctuation (PTF), and the area-under-the-curve fluctuation (AUCF). Steady state was achieved on day 3. The pharmacokinetics were comparable. For diltiazem CR 90 mg and diltiazem CR 120 mg, AUC84–96 (night) was approximately 75% of AUC72–84 (daytime). The diltiazem plasma concentration increased slowly from about 6 h after the evening dose of both CR tablets, resulting in relatively high plasma concentrations in the early morning hours. Only during treatment with diltiazem CR 120 mg were the plasma concentrations of diltiazem maintained above the minimum therapeutic plasma concentration of 50 μg·1−1 throughout the full 24 h. In conclusion, twice-daily treatment with diltiazem CR tablets can replace thrice-daily treatment with the conventional diltiazem IR tablet. The early morning rise of the diltiazem plasma concentration, which might lead to a lower incidence of ischaemic events, may be an important clinical advantage of both CR tablets. Because of the minimum therapeutic plasma concentration of 50 μg·1−1, twice-daily administration of the 120 mg CR tablet may be preferred from a therapeutic point of view. Diltiazem, a benzothiazepine, is a calcium antagonist used in the treatment of angina pectoris and hypertension. The anti-ischaemic mechanism of diltiazem seems to result from an increase of myocardial oxygen supply and a reduction in myocardial oxygen demand, respectively by coronary artery dilatation and/or direct and indirect haemodynamic effects, such as afterload reduction and heart rate decrease (Braunwald 1982). Its therapeutic effect is evident at daily dosages between 180 and 360 mg (Low et al. 1981). After oral administration it is almost completely absorbed from the gastrointestinal tract, but owing to extensive first-pass metabolism, its systemic availability is approximately 40–50% (Echizen and Eichelbaum 1986). The time to maximum plasma concentrations after oral administration of immediate-release formulations is approximately 3 to 4 h. The elimination half-life of diltiazem is 3.5–7 h, implying that frequent dosing is required to maintain effective plasma concentrations. Therefore, a controlled-release formulation of diltiazem, designed to be taken twice daily, has been developed. The aim of this crossover study was to compare the systemic availability and steady-state pharmacokinetics of a controlled-release diltiazem tablet formulation (90 and 120 mg) with those of a conventional diltiazem immediate-release tablet in healthy volunteers.

Notes: Summary Repeated exponentially decreasing influsions have been used to administer theophylline and enprofylline to show whether it would be feasible to create consecutive plasma concentration plateaus within a few hours. The infusions were carried out on two separate days in 8 stable asthmatics. Before the infusion experiments, the pharmacokinetics of the substances in the individual subjects were determined on a separate day. Plasma concentration rose to the desired level within 5 min after the start of the infusion at each dose level and a stable plasma concentration plateau was maintained during the following 90 min of the infusion. It was possible to achieve 4 subsequent concentration plateaus within a 6 h period. Use of this infusion method resulted in predictable plasma concentrations at all levels and so the method appears safe when the required plasma concentrations are below the toxic level. Apart from clinical situations where effective dosages of drugs must be administered rapidly, the method showed be useful in pharmacological dose-response studies.

Notes: Summary The pharmacokinetics and pharmacodynamics of thiazinamium (Multergan) were studied after intravenous and intramuscular administration to 7 males with chronic reversible airways obstruction. Disposition after i.v. administration was described by a clearance of 0.54 l·min−1, central compartment volume of 14.8 l, distribution rate constant 0.092 min−1, and an elimination rate constant of 0.0044 min−1. The corresponding estimates after i.m. administration were 0.324 l·min−1, 34.1 l, 0.035 min−1, and 0.0018 min−1. The bronchodilator response (expressed as % predicted FEV1) after i.v. administration was characterized by maximum increase in FEV1 of 33.9%, with an EC50 of 12.8 ng·ml−1 and an equilibration half-time of 11 min. Corresponding parameter estimates after i.m. administration were 32.2%, 18.8 ng·ml−1, and 9 min. Anticholinergic activity, measured by the change in heart rate after i.v. administration, showed maximum increase of 76 beats·min−1, with an EC50 of 176 ng·ml−1 and an equilibration half-time of 1.3 min. After i.m. administration the corresponding values were 120 beats·min−1, 250 ng·ml−1, and 3 min. The optimal plasma concentration of thiazinamium was about 100 ng·ml−1, which should give a near maximal bronchodilator response (over 80% of predicted normal) and a heart rate of about 100 beats·min−1.

Notes: Abstract In a pharmacological screen on drug-drug interactions performed in laboratory animals moclobemide potentiated at high doses the antiphlogistic/anti-inflammatory activity of ibuprofen. Therefore, a study was undertaken to determine in healthy volunteers the faecal blood loss induced by multiple doses of ibuprofen (600 mg t.i.d.) in presence and absence of steady-state concentrations of concomitantly administered moclobemide (150 mg t.i.d.). The results show that multiple doses of moclobemide do not change faecal blood loss induced by ibuprofen. Furthermore, no clinically relevant pharmacokinetic interaction between the two drugs studied was detected.

Notes: Abstract The sustained-release properties and relative bioavailability of Theolin® Retard and Pharphylline® Retard were studied in eight healthy adults after treatment for five days with twice daily 450 mg, respectively 425 mg. During the day-time dosing interval on the fourth and fifth day theophylline plasma concentrations were assayed by HPLC. After intake of Theolin® Retard, minimum theophylline plasma concentrations were significantly higher, fluctuations in theophylline plasma concentrations were significantly smaller andt 75 (the period within a dosing interval during which the plasma concentration exceeds 75% of the maximal concentration) was significantly longer than after Pharphylline® Retard. Maximal concentrations and AUC values were not significantly different. For both products the plasma concentration time-curves on day 5 were significantly lower than on day 4.In vitro dissolution tests confirmed the more sustained release of theophylline from Theolin® Retard. These results indicate an equal extent of absorption from the two products but better sustained-release properties for Theolin® Retard.