The disposition of methadone was studied in eight opiate dependent subjects during detoxification. Plasma concentrations were determined by mass fragmentography of 48 hours after administration of methadone 20 mg as tablets and simultaneous intravenous injection of deuterium-labelled methadone 20 mg. Pharmacokinetic parameters were calculated for the intravenous dose assuming a two compartment of open model. Bioavailability was determined by comprising the areas under the plasma concentration versus time curves of unlabelled and labelled methadone. The beta-phase plasma half-lives varied five-fold, with a range from 8.5 to 47 h. The apparent volumes of distribution varied from 2.1 to 5.6 l/kg. Five patients had a bioavailability exceeding 90%, and three had lower bioavailabilities of between 41 and 76%. The unlabelled and labelled drug appeared to be pharmacokinetically equivalent. The data show that for a majority of these subjects the bioavailability was higher than 45%, the previously reported value. The marked individual variation in methadone pharmacodynamics and kinetics, and the possibilities both of cellular and metabolic tolerance, require an individually optimized dosage regimen.

The influence of urinary pH on the acute disposition of methadone in man was studied in five healthy volunteers. A cross-over experiment was performed in each subject. In the first experiment the subjects were treated with ammonium chloride (urinary pH approximately 5.2) and in the other the urine was made alkaline (pH approximately 7.8) by treatment with sodium hydrogen carbonate. d, l-Methadone-HCl 10 mg (M) was administered intramuscularly on each occasion and blood, saliva and urine levels of M were determined by mass fragmentography. Plasma half-lives, volumes of distribution and body clearances of M were calculated in both experiments. The plasma half-lives in the beta-phase were 19.5 +/- 3.6 h (acidic urine) and 42.1 +/- 8.8h (alkaline urine), respectively (p less than 0.001). The volumes of distribution were increased when the pretreatment was changed from ammonium chloride to sodium bicarbonate, namely from 3.51 +/- 0.41 l/kg to 5.24 +/- 0.83 l/kg (p less than 0.01). The body clearance decreased from 134 +/- 21 ml/min (acidic) to 91.9 +/- 9.1 ml/min (alkaline urine) (p less than 0.01). The ration M plasma/M RBC was about 2.3 and the elimination of M from RBCs was good agreement with the plasma kinetics of M under both experimental conditions. The salivary levels of M did not reflect the plasma kinetics and considerable variation was seen in the ratio M saliva/ M plasma (0.26-2.98). Thus, the present experiments demonstrate that pretreatment either with ammonium chloride or bicarbonate had profound effects on both the distribution and elimination kinetics of methadone.

Aim: To study the influence of food on the systemic availability of budesonide in patients with active Crohn’s disease. Methods: Eight patients with an established diagnosis of Crohn’s disease each received 9 mg budesonide controlled ileal release (CIR) capsules (Entocort capsules) orally on two separate occasions: once in a fasting state and once after a heavy breakfast. For reference, deuterium‐labelled (2H8) budesonide, 0.5 mg, was given intravenously. Plasma concentrations of budesonide and 2H8‐budesonide were determined for 12 h, and their pharmacokinetic parameters were calculated. Results: Average systemic availability of budesonide during fasting conditions was 10.7%, area under the curve was 27.5 nmol/L × h and peak plasma concentration was 4.1 nmol/L. Corresponding postprandial values were 13.2%, 27.0 nmol/L × h and 3.8 nmol/L. Food increased the mean absorption time from 4.5 to 6.8 h (P=0.0012). Body clearance of budesonide was about 25% higher after eating (P=0.0015). Conclusions: Food had little influence on systemic availability and peak plasma concentrations of budesonide administered in CIR capsules. Absorption was retarded postprandially, likely due to delayed gastric emptying. Budesonide in CIR capsules can be administered at the same dose regardless of prandial status in patients with Crohn’s disease.

Aim: To assess the systemic effect of oral budesonide, given as Entocort controlled ileal release capsules, over a dose range of 3–15 mg/day, compared with that of a moderate dose (20 mg/day) of prednisolone. Methods: Twenty four healthy subjects were given 3, 9 or 15 mg budesonide or 20 mg prednisolone once daily, or 4.5 mg budesonide b.d., or placebo for 5 days in a randomized, double‐blind crossover study. The area under the curve (AUC) of plasma cortisol concentration and the amount of cortisol excreted in the urine were monitored. Results: Both plasma and urine cortisol suppression showed a dose‐response for the daily doses of budesonide. Prednisolone, 20 mg, suppressed plasma cortisol (AUC) statistically significantly more than 15 mg budesonide (P = 0.014), and 3 mg budesonide statistically significantly more than placebo (P = 0.010). No difference in AUC was detected between 9 mg and 4.5 mg budesonide b.d. Similar results for budesonide vs. placebo were obtained from urine cortisol excretion data. However, prednisolone affected urine cortisol less than it affected plasma cortisol. Conclusion After 5 days of administration, budesonide controlled ileal release capsules, in both clinical (9 mg/day) and high doses (15 mg/day), affected plasma cortisol less than a moderate (20 mg/day) dose of prednisolone.

The multiple-dose (200 mg levodopa t.i.d.) pharmacokinetic profile of two controlled-release products of levodopa (Madopar® HBS and Sinemet® CR) was compared to conventional Madopar capsules in 18 healthy volunteers in a cross-over, randomized design. A pronounced controlled-release profile of the Madopar HBS and Sinemet CR product was demonstrated compared to conventional Madopar capsules with a significant (p < 0.001) decrease (-40 and -55%) in C_max and a significant (p < 0.001) increase (+237 and +256%) in morning C_min for the 200 mg t.i.d. dosage schedule. Almost equivalent bioavailability (85-90%) of levodopa was demonstrated for the controlled-release formulations relative to that of conventional Madopar capsules. The Madopar HBS formulation was bioequivalent with Sinemet CR with respect to levodopa, but it exhibited a moderately higher fluctuation index compared to Sinemet CR as a result of somewhat higher C_max and lower C_min values for the Madopar HBS formulation. 3-OMD (a metabolite of levodopa) levels were significantly (p < 0.05) higher for Madopar HBS and Madopar compared to Sinemet CR. The higher 3-OMD levels for the levodopa/benserazide combinations are consistent with a more potent decarboxylase inhibitory activity of benserazide as compared to carbidopa. The number of adverse events was highest for conventional Madopar (n = 18) compared to the controlled-release formulations (n = 12 for Sinemet CR and only 2 for Madopar HBS). A more efficient inhibition of dopamine formation from levodopa (resulting in higher 3-OMD levels) by Madopar HBS was consistent with the superior tolerability (especially for initial nausea) observed for the Madopar HBS formulation as compared to Sinemet CR.