Drug delivery using the various OROS products can result in an improved safety profile, stable drug concentrations, uniform drug effects, and reduced dosing frequency. OROS technology has also enabled the use of an effective starting dose, without the need for dose titration, which allows the achievement of symptom control much earlier than that observed with immediate-release preparations. Such attributes can enhance patient compliance and convenience, thereby ensuring efficacy and improving patient outcomes.
Aims Dry mouth is a common side-effect seen with immediate-release oxybutynin (IR-Oxy). Ditropan XL 1 [(Oxy-XL), a controlled-release formulation of oxybutynin chloride, is a once-daily oral dosage form that incorporates the OROS 1 technology. Dry mouth as the pharmacodynamic measure was compared between Oxy-XL and IR-Oxy administration. The steady state stereospeci®c pharmacokinetics were also established for the two formulations and the kinetic-dynamic relationship of oxybutynin was examined. Methods This was a randomized, repeated-dose, double-blind, two-treatment, twoperiod, crossover study. After a baseline assessment day, volunteers were randomly assigned to one of two treatment sequences and received 4 days of each treatment with a washout period of 7 days between treatments. The treatments were: 1) Oxy-XL 10 mg in the morning and placebo 8 h later, and 2) IR-Oxy 5 mg in the morning and again 8 h later. Volunteers assessed dry mouth severity subjectively using a 100 mm visual analogue scale, VAS (Baseline, treatment days 1 and 4) and objectively by collecting saliva (Baseline and treatment day 4) before dosing and every hour after the morning dose for y16 h. Several blood samples were collected during each treatment, with frequent sampling on day 4 to analyse for plasma R-and S-oxybutynin and R-and S-desethyloxybutynin concentrations. Results Relatively constant plasma concentrations of oxybutynin and its metabolite were seen over 24 h following Oxy-XL administration with the degree of¯uctuation being much lower (P=0.001; 66% to 81% reduction for the various analytes) than IR-Oxy. Compared with IR-Oxy, Oxy-XL yielded higher (131% and 158% for the R-and S-isomer, respectively) oxybutynin and lower (62% and 78% for the R-and S-isomer, respectively) desethyloxybutynin bioavailability, suggesting reduced ®rst-pass metabolism. Saliva output (area under the effect curve) was signi®cantly higher [P=0.001; 37% (95% con®dence interval: 24, 51%)] with Oxy-XL than with IR-Oxy and, accordingly, dry mouth severity (VAS) integrated over the day was signi®cantly lower with Oxy-XL. The decrease in saliva output and the consequent increase in dry mouth severity correlated with the metabolite R-desethyloxybutynin concentration, and no apparent relationship was observed with the R-oxybutynin concentration. This suggests that the metabolite may contribute to the dry mouth. Therefore, the reduction in metabolite exposure with Oxy-XL may be a possible explanation for the observed decrease in dry mouth severity with OXY-XL compared with IR-Oxy. Conclusions Oxy-XL maintains relatively constant plasma drug and metabolite concentrations and minimizes ®rst-pass metabolism of oxybutynin. The metabolite appears to contribute to dry mouth associated with oxybutynin, and following Oxy-XL metabolite exposure is reduced compared with IR-Oxy. Consequently less dry mouth was observed with Oxy-XL as compared with IR-Oxy.
The urge urinary incontinence episodes declined log-linearly, and no significant difference was observed between the two formulations. However, there was a trend toward higher efficacy with oxybutynin XL than with immediate-release oxybutynin at the same dose in one study. Dose-dry mouth analysis showed that the probability of dry mouth with an increasing dose was significantly lower with oxybutynin XL than with immediate-release oxybutynin in the second study, and a similar trend was observed in the first study. By combining the dose-urge urinary incontinence and dose-dry mouth relationship, a wider therapeutic index was predicted for oxybutynin XL than for immediate-release oxybutynin.
Immediate release (IR) hydromorphone has experienced significant misuse and abuse. An extended release (ER) hydromorphone formulation has been developed to provide sustained pain relief and may reduce the likelihood for abuse by delaying absorption. In this double-blind, placebo-controlled, randomized, 2-part crossover study, the abuse potential of single oral doses of hydromorphone ER (intact: 16-, 32-, and 64-mg; milled: 8-mg) was compared with 8-mg hydromorphone IR and placebo. After drug administration, subjects with a history of recreational opioid use completed a series of assessments, including subjective effects visual analog scales (eg, drug liking) and Addiction Research Center Inventory With Cole Modification, at several timepoints up to 48 hours postdose. Independent of formulation, maximum at-the-moment drug liking was higher for hydromorphone versus placebo. Maximum drug liking occurred earlier and was higher for 8-mg IR versus 16-mg ER but similar to 32- and 64-mg ER. Most positive effects were lower after 16-mg ER compared with other doses, including 8-mg IR. Bad drug effects were higher for hydromorphone ER, particularly the 64-mg dose. Milled 8-mg ER produced similar subjective effects to 8-mg IR. Comparison of scores after administration of 8-mg IR on 2 separate occasions showed that most assessments exhibited good test-retest reliability, although some scores declined marginally between test and retest. Delayed onset of good drug effects and prominent bad drug effects of hydromorphone ER suggest that, when administered intact, this formulation may have lower abuse potential than hydromorphone IR.
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