Rectal ropivacaine is absorbed proportionally to the dose, with low intraindividual variability

Exploring anorectal manometry as a method to study the effect of locally administered ropivacaine in patients with ulcerative colitis

The symptoms of distal ulcerative colitis have been related to changes in rectal sensitivity and capacity due to inflammation, altered gastrointestinal motility, and sensory perception. With the use of anorectal manometry, the function was measured in seven patients with active distal proctitis during local treatment with ropivacaine. Seven healthy subjects were studied in the same way for comparison with normal conditions. The anal resting pressure and squeezing pressure were similar in all groups. Significantly lower rectal distention volumes were required for rectal sensation, critical volume, and to induce rectal contractility in patients with active disease compared to controls. Rectal compliance was significantly reduced in patients with active and quiescent disease. The increased rectal sensitivity and contractility in patients with active colitis appear to be related to active mucosal inflammation and ulceration. The frequency and urgency of defecation and the fecal incontinence may be due to a hypersensitive, hyperactive, and poorly compliant rectum. The findings in our study indicate that the inflammatory damage to the rectal wall with poor compliance is unaffected by local anaesthetics such as ropivacaine. The symptomatic relief and reduction in clinical symptoms following treatment are not reflected in the anorectal manometric findings.

Within- and between- subject variability in methadone pharmacokinetics and pharmacodynamics in methadone maintenance subjects

AIMS

To investigate within- and between-subject variability of the pharmacodynamics and pharmacokinetics of (R)- and (S)-methadone in methadone maintenance subjects at steady-state.

METHODS

Six non-holder subjects were studied on three occasions at 7-16 day intervals; doses (20-170 mg/day) remained unchanged. Blood samples and pharmacodynamic data were collected 10-12 times over a 24-h inter-dosing interval. All pharmacodynamic data were expressed as the area under the end-point versus time curve. Using analyses of variance with mixed effects, best estimates were made of the ratio of between- to within-subject variation, with corresponding 95% confidence intervals (CI) for within-subject variation at the average value.

RESULTS

Subjects were relatively consistent between occasions, whereas there was much greater between-subject variability (P < 0.02) for all measures. Estimates of the ratio of between- to within-subject variation ranged from 2.2-12.8 for pharmacodynamic measures, and 1.3-7.9 for pharmacokinetic parameters. For pain, total mood disturbance, withdrawal, pupil size and respiration rate, 95% CI for within-subject measures ranged < or = 2-fold, while this was greater for subjective direct opioid effects (4.2-fold). For CL/F of the active (R)-methadone, the variance ratio was 4.9 (P < 0.0003), with 95% CI for within-subject measures ranging < or = 2-fold. (S)-methadone CL/F demonstrated greater within-subject variability (3.4-fold), possibly contributing to a smaller (2.7; P < 0.0003) ratio of between- to within-subject variance.

CONCLUSIONS

Non-holder methadone maintenance treatment participants appear to respond consistently with respect to pharmacokinetics and pharmacodynamics over a 1-2 month period. Such knowledge may help prescribers to determine whether alternative dosing regimens or treatments might be more appropriate in this population.

No volume effect on retrograde colonic spread of rectally-administered ropivacaine gel

BACKGROUND

Rectal administration of enemas, foams and suppositories is the most efficient way to deliver locally acting drugs to the distal colon. Ropivacaine, a long-acting local anaesthetic, was chosen as a candidate for a new rectal treatment of ulcerative colitis.

AIM

To determine the colonic spread of a rectal ropivacaine formulation.

METHODS

In this randomized, incomplete cross-over study, 12 male volunteers were given 200 mg ropivacaine HCl rectally in 20, 40, 60 and 80 mL hydroxypropyl methylcellulose gel. The viscosity of the gel was 1.1 Pa s. The spread of the radiolabelled (99mTc-labelled diethylenetriaminepenta-acetic acid) formulations was assessed by gamma-scintigraphy. Plasma was collected and analysed for ropivacaine base.

RESULTS

The retrograde spread was limited to the descending colon and the difference between the studied volumes was not statistically significant. Only the 80-mL volume tended to have a larger distribution, although the 20-mL volume showed the same maximal distribution in two subjects. No distinct relationship between volume, retrograde colonic spread and plasma concentrations could be found. Ropivacaine was well tolerated.

CONCLUSIONS

Rectal ropivacaine gel in all volumes between 20 and 80 mL can spread up to the descending colon. There was no relationship between either retrograde colonic spread or the administered volume and the ropivacaine plasma concentrations.