Intravesical electromotive administration of oxybutynin in patients with detrusor hyperreflexia unresponsive to standard anticholinergic regimens

PURPOSE

About 15% to 20% of patients with detrusor hyperreflexia do not benefit from oral oxybutynin regimens, frequently because of unpleasant side effects. Several reports indicate that intravesical oxybutynin is effective in many of these patients but there are some who still fail to respond.

MATERIALS AND METHODS

A select group of 10 adults with detrusor hyperreflexia unresponsive to standard oral and intravesical oxybutynin regimens were treated at weekly intervals with 5 mg. oxybutynin orally, or 5 mg. oxybutynin in 100 ml. intravesically for 60 minutes of passive diffusion and for 30 minutes with 5 mA. electrical current. Each treatment (plus oral placebo and 2 intravesical controls) was associated with an 8-hour, full urodynamic monitoring session, and periodic blood and bladder content sampling.

RESULTS

There was no significant objective improvement with oral or intravesical passive diffusion oxybutynin. Conversely there was significant improvement in 5 of 6 objective urodynamic measurements with intravesical electromotive oxybutynin. Plasma profiles were a single peak and decay following oral oxybutynin and 2 distinct peaks with intravesical passive diffusion and electromotive oxybutynin. Area under the curve for intravesical passive diffusion were 709 ng. per 8 hours versus oral 1,485 (p <0.05) versus intravesical electromotive 2,781 (p <0.001). Bladder content samples confirmed oxybutynin absorption. Oral oxybutynin caused anticholinergic side effects in 7 of 10 patients. There were no side effects with intravesical passive diffusion or electromotive administrations.

CONCLUSIONS

Accelerated intravesical administration results in greater bioavailability and increased objective benefits without side effects in previously unresponsive patients compared with oral and intravesical passive diffusion oxybutynin administration.

Lack of effect of food on the pharmacokinetics of an extended-release oxybutynin formulation

The effect of food on the pharmacokinetics of 15 mg oxybutynin XL was evaluated in a single-dose, randomized, crossover, open-label study in healthy volunteers. A validated, stereospecific, high-performance liquid chromatography assay was used to simultaneously determine the plasma concentrations of R- and S-oxybutynin and active metabolite R- and S-desethyloxybutynin. The mean AUC and Cmax values for each of the four analytes in the fed treatment were within +/- 20% of the fasting treatment values. The 90% confidence intervals for the treatment ratios (fed/fasted) for log-transformed Cmax and AUCinf values for the drug isomers and AUCinf values for the metabolite isomers were all within the 80% to 125% range. Only the ranges for the Cmax values for R- and S-desethyloxybutynin were slightly wider but were well within the 70% to 143% criteria recommended for Cmax when comparing effect of food. Lack of effect of food on oxybutynin XL is consistent with the previous observation that the osmotically controlled formulations are nearly insensitive to the gastrointestinal environment, including food. Oxybutynin XL was well tolerated, and the safety results were comparable whether administered alone or with food. In conclusion, oxybutynin XL administration does not require any caution to be exercised regarding food.

Serum anticholinergic activity levels and delirium in the elderly

This article will briefly review the clinical studies focusing on measurement of serum levels of anticholinergic activity in delirious states. Three experimental approaches have been taken. First, to identify medications currently prescribed that have subtle anticholinergic effects. The current "list" includes 48 commonly prescribed medications. Second, to associate serum anticholinergic activity with delirium in various clinical states including postcardiotomy delirium, postelectroconvulsive delirium, delirious elderly medical inpatients, and nursing home patients. Third, to intervene in patients with elevated anticholinergic activity by reducing known anticholinergics and correlating this reduction with clinical measures of cognition and delirium. Our most recent data investigate the impact of anticholinergics on demented patients. Prevalence of delirium was significantly higher in patients receiving larger numbers of anticholinergics.

The pharmacological properties of tiotropium

Tiotropium is a long-acting anticholinergic drug. Studies with cloned human muscarinic receptors show that tiotropium binds equally well to M(1), M(2), and M(3) receptors. However, it dissociates very slowly from M(1) and M(3) receptors compared with ipratropium, and more rapidly from M(2) receptors. Binding studies with [(3)H]tiotropium in human lung show that it is approximately 10-fold more potent than ipratropium. In vitro, tiotropium has a potent inhibitory effect against cholinergic nerve-induced contraction of airways. It dissociates extremely slowly, compared with the dissociation of atropine and ipratropium. Clinical studies with single doses of inhaled tiotropium confirm that it is a potent and long-lasting bronchodilator. Furthermore, it protects against cholinergic bronchoconstriction for > 24 h. Pharmacokinetic studies show that little of the inhaled drug is absorbed, thus predicting a high margin of safety.

Extended-release oxybutynin

Extended-release oxybutynin (Ditropan XL) uses an osmotic system (OROS) to deliver a controlled amount of oxybutynin chloride into the gastrointestinal tract over a 24-hour period when taken once daily. Oxybutynin binds to M3 muscarinic receptors on the detrusor muscle of the bladder, preventing acetylcholinergic activation and relaxing the muscle. Mean peak plasma concentrations are lower with extended-release oxybutynin 15mg once daily than with conventional immediate-release oxybutynin 5mg taken 3 times daily. Relative bioavailabilities of parent drug and metabolite N-desethoxybutynin are 153 and 69%, respectively, for extended-release oxybutynin when compared with immediate-release oxybutynin. In short (< or =6 weeks) randomised, double-blind clinical trials of patients with detrusor instability, extended-release oxybutynin 5 to 30mg once daily significantly reduced the mean weekly number of urge incontinence episodes by 84 to 90%. Extended-release oxybutynin had similar efficacy to immediate-release oxybutynin. Adverse events reported by patients taking extended-release oxybutynin were dose-related anticholinergic effects, most frequently dry mouth, somnolence, constipation, blurred vision and dizziness. A large noncomparative study demonstrated that approximately two thirds of the patients prescribed extended-release oxybutynin for detrusor instability were still taking the medication 6 months later.

Circadian rhythms in the pharmacokinetics and clinical effects of beta-agonist, theophylline, and anticholinergic medications in the treatment of nocturnal asthma

Published asthma consensus reports now acknowledge that asthma is a nocturnal disease in as many as 75% of those afflicted by this medical condition. Nonetheless, the treatment of this chronic obstructive pulmonary disease in the clinic continues to be based primarily on homeostatic considerations in that it relies on long-acting bronchodilator and other therapies formulated and scheduled to ensure constant or near-constant levels of medication during the 24h. The need of asthma patients prone to nighttime attacks is not the same during the day and night; the therapeutic requirements of patients who experience nocturnal asthma, especially ones with the more severe forms of the disease, are often not satisfied by conventional medications. The therapeutic response and patient tolerance to bronchodilator medications can be improved markedly when the medications are proportioned during the 24h as a chronotherapy, that is, when more medication is delivered during nighttime sleep than daytime activity, as verified by numerous studies. This article reviews how the body's circadian rhythms influence the pharmacokinetics and effects of commonly prescribed asthma therapies and addresses why and how they must be taken into consideration to increase the effectiveness of asthma treatment.

Pharmacokinetic and pharmacodynamic interactions among haloperidol, carteolol hydrochloride and biperiden hydrochloride

A beta-adrenoceptor blocker and an anticholinergic agent are often prescribed concomitantly for the treatment of neuroleptic-induced akathisia. The aim of this study was to investigate possible pharmacokinetic interactions of neuroleptic haloperidol with the beta-blocker carteolol and the anticholinergic biperiden. In a 5-step, open-labeled, oral single-dose study, eight healthy male volunteers received 2 mg haloperidol, 10 mg carteolol hydrochloride, and 2 mg biperiden hydrochloride: first each drug alone, then a combination of haloperidol and carteolol, and then all three drugs concurrently. Serum concentrations of haloperidol, carteolol, and biperiden were determined up to 24 hr postdosing, and a safety evaluation was conducted throughout the study. Carteolol increased the area under the haloperidol serum concentration-time curve (AUC0-t) 1.4-fold (P = 0.0014) and decreased the serum clearance of haloperidol up to 67% (P = 0.0127). Biperiden reduced the serum haloperidol concentrations increased by the administration of carteolol. No significant changes of the serum pharmacokinetics of carteolol and biperiden were found as a result of any drug combinations. Adverse events of the central nervous system such as sleepiness and changes in pupil size were observed, but all were mild with clinical insignificance.

Pharmacokinetic and pharmacodynamic characterization of OROS and immediate-release amitriptyline

AIMS

To characterize the pharmacokinetics of amitriptyline and its metabolite nortriptyline following OROS and IR treatments, and to correlate them with anticholinergic side-effects.

METHODS

The pharmacokinetics and safety of amitriptyline following administration of an osmotic controlled release tablet (OROS and an immediate release (IR) tablet were evaluated in 14 healthy subjects. In this randomized, open label, three-way crossover feasibility study, the subjects received a single 75 mg OROS tablet, three 25 mg IR tablets administered every 8 h, or 3x25 mg IR tablets administered at nighttime. In each treatment arm serial blood samples were collected for a period of 84 h after dosing. The plasma samples were analysed by gas chromatography for amitriptyline and its metabolite nortriptyline. Anticholinergic effects such as saliva output, visual acuity, and subject-rated drowsiness and dry mouth were measured on a continuous scale during each treatment period.

RESULTS

Following dosing with OROS (amitriptyline hydrochloride), the mean maximal plasma amitriptyline concentration Cmax (15.3 ng ml-1 ) was lower and the mean tmax (25.7 h) was longer than that associated with the equivalent IR dose administered at nighttime (26.8 ng ml-1 and 6.3 h, respectively). The bioavailability of amitriptyline following OROS dosing was 95% relative to IR every 8 h dosing, and 89% relative to IR nighttime dosing. The metabolite-to-drug ratios after the three treatment periods were similar, suggesting no change in metabolism between treatments. The relationships between plasma amitriptyline concentration and anticholinergic effects (e.g. reduced saliva weight, dry mouth, and drowsiness) were similar with all three treatments. Of the anticholinergic effects, only decreased saliva weight and dry mouth correlated well with plasma amitriptyline concentrations; drowsiness did not. There was no apparent correlation between anticholinergic effects and the plasma nortriptyline concentration.

CONCLUSIONS

The bioavailability of OROS (amitriptyline hydrochloride) was similar to that of the IR treatments and the pharmacokinetics of amitriptyline after OROS dosing may decrease the incidence of anticholinergic effects compared with that seen with nighttime dosing of the IR formulation. Therefore, this controlled-release formulation of amitriptyline may be appropriate for single daily administration.

Anticholinergic drugs used in Parkinson's disease: An overlooked class of drugs from a pharmacokinetic perspective

Anticholinergic drugs were the first pharmacological agents used in the treatment of Parkinson"s disease. Although levodopa and other centrally acting dopaminergic agonists have largely supplanted their use, they still have a place in treatment of the disease. As a therapeutic class, there is little pharmacokinetic information available for these drugs, which is inclusive of benztropine, biperiden, diphenhydramine, ethopropazine, orphenadrine, procyclidine and trihexyphenidyl. Pharmacokinetic information is largely restricted to studies involving young health volunteers given single doses. In general, this class of drugs is rapidly absorbed after oral administration to humans. Oral bioavailability is variable between the different drugs, ranging from 30% to over 70%. Each of the drugs appears to possess a large Vd in humans and animals, and distribution to tissues is rapid. The drugs are all characterized by relatively low clearance relative to hepatic blood flow, and appear to be extensively metabolized, primarily to N-dealkylated and hydroxylated metabolites. The available information suggests that excretion of parent drug and metabolite is via the urine and bile. Although the existence of a plasma concentration vs. therapeutic effect relationship has not been explored, there is some evidence suggesting a relationship between concentration and peripheral side effects. Elderly tolerate the drugs less well than do younger patients. There is a notable lack of pharmacokinetic information for these drugs in the elderly. The lack of pharmacokinetic information for multiple dose administration and in the elderly may be a possible hindrance in the safe and effective use of these drugs in patients with Parkinson"s disease.

An extended-release formulation of oxybutynin chloride for the treatment of overactive urinary bladder

Detrusor instability, or urinary incontinence, is common in elderly patients, particularly elderly women. The clinical symptoms of overactive, or unstable, urinary bladder include urge urinary incontinence, urgency, and frequency. Mixed urinary incontinence, which comprises urge urinary incontinence and stress incontinence, is manifested by increased intraabdominal pressure on coughing or sneezing. The detrusor muscle of the bladder is under the control of the parasympathetic, or muscarinic, nervous system. The drug of choice in this condition is oxybutynin chloride, which has the ability to block acetylcholine released from parasympathetic nerves in the urinary bladder, preventing contractions of the muscle and exerting a direct spasmolytic effect on the bladder. A new extended-release oral tablet formulation, OROS oxybutynin, uses osmotic pressure to deliver the drug at a controlled rate over approximately 24 hours. It resembles a conventional tablet but has a two-part core consisting of a drug layer and below it, a "push" layer containing osmotically active components, the whole surrounded by a semipermeable membrane with a laser-drilled opening in the drug side. Water in the gastrointestinal tract enters the tablet and mixes with the drug to form a suspension. The "push" layer expands and pushes the suspended drug out of the orifice and into the gastrointestinal tract for eventual absorption. Pharmacokinetic studies have indicated a slow rise in mean plasma concentration of the isomer R-oxybutynin for 4 to 6 hours after a single dose of OROS oxybutynin, followed by maintenance of steady concentrations for up to 24 hours, minimizing the fluctuations between peak and trough associated with TID dosing of 5-mg immediate-release oxybutynin tablets. Efficacy and safety studies comparing the extended-release with the immediate-release formulation of oxybutynin demonstrated equivalent efficacy in patients with overactive urinary bladder. The adverse-event profile of oxybutynin is similar to that of a typical anticholinergic agent such as atropine--dry mouth, constipation, somnolence, blurred vision, headache, and gastrointestinal pain--although in 2 clinical studies, the incidence of dry mouth was less with the extended-release formulation. Once-daily dosing with OROS oxybutynin appears to be well tolerated and effective, as well as convenient, for the treatment of overactive bladder, particularly for elderly patients using multiple medications.

Spectral analysis of heart rate variability as a quantitative measure of parasympatholytic effect--integrated pharmacokinetics and pharmacodynamics of three anticholinergic drugs

The time course and concentration-effect relationship of parasympatholytic effects of three anticholinergic drugs were investigated using spectral analysis of heart rate (HR) variability. Single intravenous (i.v.) doses of atropine (10 microg/kg), glycopyrrolate (5 microg/kg), scopolamine (5 microg/kg), and placebo were given to eight healthy volunteers in a double-blind, randomized cross-over study. Electrocardiogram (ECG) was recorded at baseline and 2.5, 5, 10, 20, and 30 minutes, and 1, 1.5, 2, 3, 4, 5, and 6 hours after drug administration, while the subjects breathed at a fixed 0.25 Hz frequency. The powers of two frequency bands (low frequency [LF] = 0.07-0.15 Hz and high frequency [HF] = 0.15-0.40 Hz) were calculated using stationary time series of R-R intervals (RRI) free from ectopic beats. To perform pharmacokinetic-pharmacodynamic (PK-PD) modeling, venous plasma drug concentrations were measured. Atropine and glycopyrrolate, and, to a lesser extent, scopolamine induced decreases in HF power and increases in LF/HF ratio of HR variability, indicating parasympatholytic activity and corresponding changes in sympathovagal balance. Maximal average decreases in HF power were 99%, 94%, and 82%, respectively, but in two scopolamine subjects, a parasympathomimetic effect was dominant. Interindividual variability was least for the Hayano index of HF power (square root (RRI HF-power)/RRI*100), and profound and consistent decreases were seen after atropine and glycopyrrolate. Pharmacokinetics were best fitted to a two-compartment open model, and effect compartment link modeling using the Hayano index was performed with the atropine and glycopyrrolate data. The best description of the PK-PD relationship for both drugs was achieved using the sigmoidal Emax model. Mean (+/-SD) EC50, sigmoidicity factor (gamma), and equilibration rate constant (k(e0)) estimates were 1.35 (+/-0.27) ng/mL, 6.07 (+/-1.98) and 11.0 (+/-5.28) l/h for atropine and 1.35 (+/-0.49) ng/mL, 4.34 (+/-1.55) and 2.26 (+/-0.81) l/h for glycopyrrolate. Spectral analysis of HR variability appears to be a powerful tool in monitoring parasympatholytic drug activity. A sigmoidal Emax model with an extremely steep concentration-response relationship was revealed for atropine and glycopyrrolate. The effects of scopolamine were more incongruous.

Pharmacokinetics of an oral once-a-day controlled-release oxybutynin formulation compared with immediate-release oxybutynin

Oxybutynin is used for the treatment of urge urinary incontinence. In this randomized, open-label, two-way crossover, multiple-dose study, the pharmacokinetics of a once-daily, controlled-release formulation, OROS oxybutynin chloride, was compared with that of immediate-release (IR) oxybutynin (Ditropan). Thirteen healthy female volunteers received three 5 mg OROS oxybutynin chloride tablets once daily for 4 days or IR oxybutynin 5 mg administered every 8 hours for 4 days. On day 1, with OROS oxybutynin chloride, mean plasma concentrations rose slowly over approximately 6 hours following dosing (mean Cmax 4.2 ng/mL) and remained fairly constant over the 24-hour dosing interval, whereas with IR oxybutynin, mean plasma concentrations rose rapidly within the first hour after dosing (mean Cmax 12.0 ng/mL), then declined. The mean oxybutynin degree of fluctuation was much lower for OROS oxybutynin chloride (78%) than for IR oxybutynin (371%). For both formulations, the plasma concentration-time profiles for the metabolite N-desethyloxybutynin paralleled those of oxybutynin but at higher concentrations. Steady-state oxybutynin concentrations were achieved by day 3 for both formulations. Mean area under the concentration-time curve (AUC) values for both oxybutynin and its metabolite were similar between day 1 and day 4 for each treatment, suggesting time-invariant pharmacokinetics. With OROS oxybutynin chloride, mean relative bioavailability was higher (153%) for oxybutynin and lower (69%) for N-desethyloxybutynin compared with IR oxybutynin. This increased bioavailability may be due to reduced first-pass metabolism; within 3 to 5 hours after dosing, OROS systems are thought to reach the colon, where cytochrome P450-mediated oxidation (oxybutynin's primary metabolic pathway) may be less extensive than in the small intestine. Fewer subjects reported any adverse event with OROS oxybutynin chloride than with IR oxybutynin (including dry mouth, oxybutynin's most frequently reported anticholinergic adverse effect).

Disposition of ethopropazine enantiomers in the rat: tissue distribution and plasma protein binding

PURPOSE

To determine the in vitro plasma protein binding, and the in vivo brain, heart and plasma concentrations of ethopropazine (ET) enantiomers in the rat after iv doses.

METHODS

For in vivo assessment of ET enantiomer concentrations, rats with implanted jugular vein cannulae were injected with 10 mg/kg of (+/-)-ET HCl. At selected times after dosing, rats were sacrificed and heart, brain, and plasma were collected. Equilibrium dialysis was used to determine the unbound fraction of ET in rat plasma over a concentration range of 150 to 4000 ng/mL of each enantiomer. A stereospecific assay was used to measure concentrations of ET enantiomer.

RESULTS

No stereoselectivity was observed in plasma or tissues after iv dosing. Area under the concentration vs. time curves indicated that highest uptake of ET occurred in brain tissue, followed by heart tissues, then plasma. There was no noticeable difference between concentrations of ET enantiomers in different parts of brain (substantia nigra, cortex, or striatum). There was no observed stereoselectivity in plasma protein binding of ET enantiomers in rat plasma. Saturation of binding to plasma proteins was observed between 500 and 2000 ng/mL of each ET enantiomer, but unbound fraction was constant at concentrations below and above that range.

CONCLUSION

Ethopropazine displays nonstereoselectivity in its pharmacokinetics. The drug shares distribution features similar to those of other phenothiazine derivatives. Based on the in vitro plasma protein binding results, there appears to be saturation of some, but not all, plasma binding proteins of ET within the range of concentrations studied.

Tolterodine

Tolterodine is a competitive muscarinic receptor antagonist which has recently been launched for the treatment of overactive bladder. Tolterodine shows functional selectivity for the bladder over the salivary glands in vivo, which is not attributable to muscarinic receptor subtype selectivity. It is as potent as oxybutynin in inhibiting bladder contraction, but is much less potent in inhibiting salivation, suggesting that it may have less propensity to cause dry mouth in clinical use. In patients with overactive bladder, toleterodine significantly reduces the frequency of micturition and number of incontinence episodes, while increasing the average volume voided. The onset of pharmacological action of tolterodine is < 1 hour and therapeutic efficacy is maintained during long term treatment. In comparative trials, tolterodine and oxybutynin are equivalent in terms of efficacy. However, tolterodine is significantly better tolerated than oxybutynin, particularly with respect to the incidence and severity of dry mouth. No clinically relevant ECG changes have been noted with tolterodine.

Antipsychotic drugs which elicit little or no parkinsonism bind more loosely than dopamine to brain D2 receptors, yet occupy high levels of these receptors

This review addresses two questions. First, why does clozapine apparently occupy low levels of dopamine D2 receptors in patients, in contrast to all other antipsychotic drugs which occupy 70-80% of brain dopamine D2 receptors? Second, what is the receptor basis of action of antipsychotic drugs which elicit low levels of Parkinsonism? Antipsychotic doses of clozapine occupy between 0% and 50% of D2 receptors, as measured in patients by a variety of radioligands. It has recently been found, however, that the percent occupancy of a receptor by a drug depends on the radioligand used to measure that receptor. Based on this new finding, this review concludes that clozapine clinically occupies high levels of D2 receptors in the absence of any radioligand. This occupancy is estimated to be of the order of 70-80% in the dopamine-rich region of the human striatum, and even higher in the limbic D2-containing regions which are low in endogenous synaptic dopamine. This conclusion arises from two different approaches. One approach is to relate the reported clozapine occupancies in the human striatum with the dissociation constants of the various radioligands at the D2 receptor. This relation extrapolates to approximately 70-80% occupancy by clozapine when clozapine competes with endogenous dopamine at the D2 receptor. The second approach is to calculate the D2 occupancy of each antipsychotic drug, using the average spinal fluid concentration and the correct dissociation constant of the antipsychotic, thereby revealing that all antipsychotic drugs, including clozapine, occupy approximately 70-80% of dopamine D2 receptors in the human striatum, and possibly higher in the limbic regions. As determined by the new dissociation constants, antipsychotic drugs which elicit Parkinsonism (trifluperazine, chlorpromazine, raclopride, haloperidol, fluphenazine, risperidone) bind more tightly than dopamine to D2, while those antipsychotic drugs which elicit little or no Parkinsonism (melperone, seroquel, perlapine, clozapine, remoxipride, molindone, sulpiride, olanzapine, sertindole) bind more loosely than dopamine to D2 receptors. Compared to the tightly bound antipsychotic drugs, the more loosely bound antipsychotics generally require higher clinical doses, require fewer days for clinical adjustment, but may dissociate from the D2 receptor more rapidly and could lead to clinical relapse somewhat earlier than that found with the traditional tightly bound antipsychotic drugs.

Effect of sequence of administration on the pharmacokinetic interaction between the anticholinergic drug biperiden and [3H]quinuclidinyl benzylate or [3H]N-methylscopolamine in rats

In rats the pharmacokinetic interactions between the anticholinergic drug biperiden and [3H]quinuclidinyl benzylate ([3H]QNB) or [3H]N-methylscopolamine ([3H]NMS) is affected by the sequence in which the drugs are administered. Drug concentrations in various tissues were determined after intravenous administration of [3H]QNB or [3H]NMS (325 ng kg(-1)). Biperiden (6.4 mg kg(-1)) was administered either 5 min before, concomitantly with or 20 min after injection of [3H]QNB or [3H]NMS. When biperiden was administered concomitantly with or before [3H]QNB, distribution of [3H]QNB among the regions of the brain and other tissues was reduced; at 4 h the ratio of the distribution of [3H]QNB for experimental animals to that for control animals ranged from 0.15 to 0.9. When biperiden was administered after [3H]QNB, the distribution of [3H]QNB in the brain and other tissues was significantly higher than for the other two treatments (P < 0.01). However, for [3H]NMS the sequence of administration had no effect on the distribution of the drug in the brain and other tissues except for the kidney. In-vitro, in crude synaptosomal membranes, the amount of [3H]QNB at 2 h relative to the control concentration at equilibrium was 87% when biperiden was added before [3H]QNB and 56% when biperiden was added after [3H]QNB. In both instances the concentration of [3H]NMS reached equilibrium within 30 min. These findings suggest that the difference between the rate constant of association and dissociation at the possible site of action gives rise to the effect of the sequence of administration on the pharmacokinetic interaction.

The pharmacokinetics of oxybutynin is unaffected by gender and contraceptive steroids

OBJECTIVE AND METHODS

The effect of gender and concomitant use of contraceptive steroids on the absorption and metabolism of oxybutynin was investigated in 49 healthy volunteers, 24 females and 25 males. Serum concentrations of oxybutynin and its active metabolite, N-desethyloxybutynin, were measured for up to 48 h after ingestion of a single dose of 10 mg oxybutynin.

RESULTS

Intake of oral contraceptive steroids had no significant effect on the pharmacokinetic parameters of oxybutynin or its metabolite. Both in males and females, the mean area under the curve (AUC0-t) of N-desethyloxybutynin was about 13 times higher and the peak concentration (Cmax) 15 to 19 times higher than the AUC0-t and Cmax of the parent oxybutynin, with no significant differences between males and females.

CONCLUSIONS

The pharmacokinetics of orally administered oxybutynin shows a considerable interindividual variability, but is unaffected by gender and use of contraceptive steroids.

Anticholinergic and calcium antagonistic activities of NS-21 contribute to the inhibition of rat urinary bladder contractions

1. Pharmacological characteristics of NS-21 and its main metabolite, RCC-36, in the inhibition of rat urinary bladder contractions were investigated both in vitro and in vivo. 2. NS-21 and RCC-36 inhibited muscarinic receptor bindings to rat bladder membranes with [3H]3-quinuclidinyl bezilate (pKi 6.19 and 7.24, respectively), whereas they failed to inhibit the following receptor bindings: adrenergic (alpha 1, alpha 2 and beta), dopaminergic (D1 and D2), adenosine (A1 and A2), histaminergic (H1) and opioid (mu, delta and kappa) receptors. 3. NS-21 and RCC-36 suppressed carbachol-induced contractions of isolated rat detrusor strips in competitive (pA2 6.80 and 7.93, respectively) and noncompetitive (pD'2 5.93 and 5.77, respectively) manners. 4. NS-21 and RCC-36 inhibited CaCl2-induced contractions of rat detrusor strips in the presence of 100 mM K+ (pIC50 6.54 and 5.76, respectively), as well as the 100 mM K(+)-induced 45Ca influx into the isolated bladder strips at > or = 1 microM. 5. Electrical stimulation of the peripheral end of the pelvic nerve in anesthetized rats induced bladder contractions composed of two phases: an initial phasic contraction that was weakly suppressed by atropine, and a tonic contraction that was strongly suppressed by atropine. NS-21 suppressed both contractions to the same degree (ID50 2.65 and 2.19 mg/kg, i.v., respectively). RCC-36 suppressed the tonic contraction (ID50 1.20 mg/kg, i.v.) more markedly than the initial contraction (ID50 7.43 mg/kg, i.v.). 6. These results suggest that NS-21 and RCC-36 suppressed bladder contractions owing to their anticholinergic and calcium antagonistic activities.

[In vivo and in vitro metabolism of tricyclopinate hydrochloride in the rat]

The metabolism of tricyclopinate hydrochloride(TCPN), a new anticholinergic agent, was studied by in situ perfused rat liver preparation. Two metabolites were isolated by HPLC. Metabolite I was identified as an N-demethylation product, while metabolite II was shown to be an arylhydroxylation product. Metabolite I and metabolite II were also isolated from the urine of the rat given TCPN i.g. This result shows that the two metabolites from the perfused rat liver are just the final metabolites produced in vivo. The metabolites in rat liver microsomes were also identified as those just described. These results suggest that the biotransformation reaction of TCPN is mainly catalyzed by the enzyme in rat liver microsomes. The results of experiment on receptor activity indicate that the action potency with mAChR of metabolite I and metabolite II was only 1/20 and 1/50, respectively, of that of TCPN.

[The pharmacokinetic interaction of cholinolytics and cholinesterase reactivators as a reflection of the modulation of their binding in blood plasma and in brain tissue]

Radioligand assay showed that the cholinesterase (ChE) reactivators dipiroxime and benzyxime, but not carboxime, modulate selective absorption of some cholinolytics (tributam, pediphen, aprophen) in rat brain. Significant suppression of the specific binding of muscarine antagonists was recorded after chlorophos (2.LD50) intoxication. Under such conditions, the ChE reactivators induce increase in the number of binding sites and in the parameters of the constant of cholinolytic absorption on the brain membranes. It was also established by equilibrium dialysis that the binding of cholinolytics in blood plasma under the effect of ChE reactivators is reduced, leading to redistribution of their free and bound fractures, which is most favorable for tissue sorption.

Electromotive administration of oxybutynin into the human bladder wall

PURPOSE

To compare concentrations of oxybutynin in the human bladder wall after either passive delivery (PD) or electromotive administration (EMDA).

MATERIALS AND METHODS

Tissue sections of human bladder were inserted into a diffusion cell with urothelium exposed to the donor compartment containing oxybutynin (4.5 mg. in 100 ml. NaCl 0.45%) and an anode. Twelve paired experiments, "current 5 mA/no current", were conducted over 15 minutes. Oxybutynin tissue contents were measured and tissue viability, morphology and oxybutynin stability were assessed.

RESULTS

Mean oxybutynin tissue concentrations were 3.84 micrograms./gm. in samples exposed to EMDA and 0.87 microgram./gm. in samples exposed to PD (p = 0.0006). The mean coefficients of variation were 57.85% in EMDA experiments and 89.78% in PD experiments. Tissues were viable and undamaged histologically and no oxybutynin structural modification was observed.

CONCLUSIONS

EMDA enhances oxybutynin administration into viable bladder wall and reduces the variability in drug delivery rate.

Effect of time interval between food and drug ingestion on the absorption of oxybutynin from a controlled-release tablet

The effect of time interval between food and drug ingestion on the bioavailability of oxybutynin was investigated in a randomized, three-phase cross-over study in 31 healthy volunteers. The serum concentrations of oxybutynin and the metabolite, N-desethyloxybutynin were measured up to 48 hr after ingestion of a controlled-release 10 mg oxybutynin tablet either in fasting state, 2 hr after breakfast or 1 hr before. The Cmax of both oxybutynin (P < 0.0001) and N-desethyloxybutynin (P < 0.0001) and the AUC0-1 of N-desethyloxybutynin (P < 0.05) were significantly larger when oxybutynin was ingested 2 hr after breakfast, than during the fasting, but the AUC0-1 of oxybutynin remained unchanged. Breakfast ingested 1 hr after oxybutynin did not affect the pharmacokinetic parameters of oxybutynin or N-desethyloxybutynin. The saliva secretion rate decreased slightly more (P < 0.05), when oxybutynin was administered 2 hr after breakfast than during fasting. The effect of food ingestion on the serum concentrations of oxybutynin and N-desethyloxybutynin is expected to have minor clinical significance only. However, ingestion of the controlled-release tablet 1 hr before meal increases the likelihood of obtaining constant drug levels with lower peak concentrations during the dosage interval, and thus ingestion of the controlled-release tablet 0.5-1 hr before food may well improve tolerability and compliance in patients who suffer from adverse reactions.

Pharmacokinetics of (+/-)-4-diethylamino-1,1-dimethylbut-2-yn-1-yl 2-cyclohexyl-2-hydroxy-2-phenylacetate monohydrochloride monohydrate. 1st communication: absorption, distribution and excretion after single administration of 14C-labeled compound to rats and dogs

The absorption, distribution and excretion of radioactivity were studied in rats and dogs after intravenous or oral administration of NS-21 ((+/-)-4-diethylamino-1, 1-dimethylbut-2-yn-1-yl 2-cyclohexyl-2-hydroxy-2-phenylacetate monohydrochloride monohydrate, CAS 129927-33-4). 14C-NS-21 was rapidly absorbed from the gastrointestinal tract after oral administration to rats and dogs. NS-21 was absorbed throughout the whole area of the small intestine. NS-21 entered the systemic circulation via the portal vein because the transfer of radioactivity into the lymph was negligible. The presence of food did not affect the absorption ratio of NS-21. There was no difference in the plasma concentrations of radioactivity after intravenous and oral administrations of 14C-NS-21 to male and female rats. After oral administration of 3, 30 or 100 mg/kg of 14C-NS-21 to rats, the area under the plasma concentration-time curve increased in a dose-dependent manner. After oral administration of 14C-NS-21 to rats, radioactivity was distributed throughout the whole body. The concentrations of radioactivity in most tissues reached their maximums within 2 h, and then declined as the plasma concentration decreased. No radioactivity was detected in most tissues 168 h after administration. In vitro serum binding of 14C-NS-21 was more than 98% in all the animal species tested. NS-21 bound to both human serum albumin and alpha 1-acid glycoprotein. Radioactivity was mainly excreted into the feces via bile in rats, and evenly excreted into the urine and feces in dogs. No differences were observed in the excretion of radioactivity between male and female rats.

Itraconazole moderately increases serum concentrations of oxybutynin but does not affect those of the active metabolite

OBJECTIVE

Oxybutynin has low oral bioavailability due to an extensive presystemic metabolism. It has been suggested that the biotransformation of oxybutynin is dependent on CYP3A. Because itraconazole, a widely used mycotic, is a potent inhibitor of CYP3A4, we wanted to study a possible interaction between oxybutynin and itraconazole.

METHODS

In this double-blind, randomized, two-phase cross-over study, ten healthy volunteers received either 200 mg itraconazole or placebo for 4 days. On day 4, each volunteer ingested a single dose of 5 mg oxybutynin. Serum concentrations of oxybutynin, its active metabolite N-desethyloxybutynin, and itraconazole were monitored over 24 h.

RESULTS

Itraconazole significantly increased both the area under the serum drug concentration-time curve (AUC0-t) and the peak concentration of oxybutynin twofold. The AUC0-t and the peak concentration of N-desethyloxybutynin were not significantly affected by itraconazole. Itraconazole did not change the peak time or the elimination half-life of either oxybutynin or N-desethyloxybutynin. The occurrence of adverse events after oxybutynin administration was not increased by itraconazole.

CONCLUSIONS

Itraconazole moderately increases serum concentrations of oxybutynin, probably by inhibiting the CYP3A-mediated metabolism. However, the concentrations of N-desethyloxybutynin were practically unchanged. Since about 90% of the antimuscarinic activity of oxybutynin is attributable to N-desethyloxybutynin, any interaction of oxybutynin with CYP3A4 inhibiting drugs has only minor clinical significance.

Bioavailability of intranasal scopolamine in normal subjects

The bioavailability of scopolamine in three dosage forms was compared in 12 healthy nonsmoking male volunteers. Subjects received 0.4-mg doses of scopolamine bromide in intravenous (i.v.), intranasal (i.n.), or oral (p.o.) dosage forms on three occasions, with at least 2 weeks separating the doses. Scopolamine concentrations in plasma were determined with a combined reverse-phase liquid chromatographic-radioreceptor binding assay. Saliva volume and flow rate and percent suppression of control flow rate were determined from each sample. Absorption after i.n. and po scopolamine administration was rapid; plasma concentrations [1680 (i.n.) and 164 pg/mL (p.o.)] peaked within 1 h of dosing [0.37 (i.n.) and 0.78 h (p.o.)], respectively. i.n. and i.v. scopolamine suppressed salivary flow rate to similar extents (95% and 99.7%), respectively. Times to reach maximum effect were 1.05 and 0.27 h after i.n. and i.v. dosage, respectively. Absolute intranasal bioavailability, calculated from the area under the drug concentration vs time curve, was found to be significantly greater than that of p.o. scopolamine (83% vs 3.7%, p < 0.05). The i.n. route may provide a noninvasive, reliable, fast, and effective route for administering scopolamine.

Effect of food on the bioavailability of oxybutynin from a controlled release tablet

OBJECTIVE

The effect of food on the bioavailability of oxybutynin was assessed in a randomised cross-over study in 23 healthy volunteers. A single oral 10 mg dose of a controlled release oxybutynin tablet was administered after a high fat breakfast and to fasting subjects. The AUC, Cmax, tmax, t1/2 and MRT of oxybutynin and its active metabolite N-desethyloxybutynin were determined.

RESULTS

Breakfast did not change the AUC of oxybutynin but increased the AUC of N-desethyloxybutynin by about 20%. The Cmax of oxybutynin and N-desethyloxybutynin were two-fold higher when the drug was administered after breakfast compared to the fasting state.

CONCLUSION

Breakfast significantly reduced the MRT of oxybutynin and N-desethyloxybutynin.

Antidepressants and cognitive impairment in the elderly

Cognitive impairment is an important consideration in the treatment of depression in the elderly because such impairment increases with age, is a symptom of depression, and is a side effect of many antidepressant drugs. Older depressed patients are more likely to suffer acute cognitive impairment from medications including antidepressants, often superimposed on the cognitive impairment of depression. Even mild cognitive impairment can contribute to increased disability in the elderly. The occurrence of severe cognitive impairment (i.e., delirium) with tricyclic antidepressants is probably related to anticholinergic effects. Since the serotonin selective reuptake inhibitors (SSRIs) and some reversible inhibitors of monoamine oxidase (RIMAs) have little if any anticholinergic activity, these agents are expected to result in less cognitive impairment. This hypothesis is supported by a variety of comparative studies. The SSRIs and some RIMAs also have fewer additive effects with other psychoactive agents. Additional evidence suggests that some SSRIs and RIMAs may even improve cognitive functions through mechanisms separate from their antidepressant effects.

Effects of 6R-L-erythro-5,6,7,8-tetrahydrobiopterin on the dopaminergic and cholinergic receptors as evaluated by positron emission tomography in the Rhesus monkey

The effects of 6R-L-erythro-5,6,7,8-tetrahydrobiopterin (R-THBP) on the central cholinergic and dopaminergic systems in the Rhesus monkey brain were investigated by positron emission tomography (PET) with the muscarinic cholinergic receptor ligands (N-[11C]methyl-benztropine) and dopaminergic receptor ligands selective for D1, D2, and D3 subtypes ([11C]SCH23390, N-[11C]methyl-spiperone, and (+)[11C]UH232, respectively). None of the doses (3, 10, and 30 mg/kg i.v.) of R-THBP used significantly affected the regional cerebral blood flow (rCBF as determined by Raichle's H(2)15O method), and 10 mg/kg of R-THBP had little effect on the regional cerebral metabolic rate of glucose (rCMRglc) in the Rhesus monkey brain, as assessed by the graphical [18F]fluoro-deoxyglucose method. The effect of R-THBP on the muscarinic cholinergic system was dose dependent; while 3 mg/kg of R-THBP did not significantly alter the uptake ratio of N-[11C]methylbenztropine in several brain regions to that in the cerebellum, 10 and 30 mg/kg of R-THBP significantly reduced the uptake ratio in the thalamus, as well as in the frontal and temporal cortices. None of the doses (3, 10, and 30 mg/kg i.v.) of R-THBP tested affected [11C]SCH23390 (dopamine D1 receptor) binding. However, the k3 value for N-[11C]methyl-spiperone (dopamine D2 receptor) binding, which represents the association rate X Bmax value, was significantly decreased in the striatum. The uptake ratio of (+)[11C]UH232 (dopamine D3 receptor) in the striatum to that in the cerebellum was also decreased by administration of R-THBP (3 and 30 mg/kg i.v.). These findings suggest that R-THBP acts on dopamine D2 and D3 receptors selectively without markedly affecting dopamine D1 receptor binding. Furthermore, the changes in cholinergic and dopamine D2 and D3 receptors in vivo can not be attributed to a change in rCBF but may depend on the action of R-THBP.

Quantitative analysis of bencynonate in human plasma using a deuterated internal standard by gas chromatography-mass spectrometry with selected-ion monitoring

A gas chromatographic-mass spectrometric method is described for the quantitative analysis of bencynonate in human plasma. Deuterated bencynonate served as the internal standard and selected-ion monitoring of the fragments of bencynonate and internal standard permitted the quantitation of bencynonate down to 25 pg/ml of plasma. The assay is linear for plasma bencynonate concentrations in the range 25 pg/ml-3 ng/ml. At 0.25 ng/ml the recovery and coefficient of variation are 54.3% and 19.1%, respectively. Application of the method to clinical studies gave data for the pharmacokinetics and relative bioavailability of bencynonate in man.

Pharmacokinetic drug interactions with gastrointestinal motility modifying agents

Drugs may affect gastrointestinal motility and, therefore, absorption of other concomitantly administered drugs. Gastrointestinal prokinetic agents increase the rate of gastric emptying and also upper intestinal motility. These effects would be expected to increase the initial rate of absorption of orally administered drugs, but reduce total bioavailability of the agents. Metoclopramide has been shown to increase the rate of absorption of several classes of drug, reflected by reduced time taken to achieve maximal plasma concentration (tmax) and increased maximal plasma concentration (Cmax). However, the effect of these agents on the area under the plasma concentration-time curve from zero to infinity (AUC0-infinity), when measured, is not consistent. Cisapride and domperidone appear to have similar effects, but there are relatively less data available regarding these products. Opioids may delay gastric emptying considerably, an effect which will often have significant clinical and therapeutic implications. Most of the data confirming this observation concern oral analgesics, but the effect should be considered when prescribing any oral medication. Drugs with anticholinergic or sympathomimetic activity are likely to have a similar effect and this is confirmed, in the main, by the limited data available. Although many effects reported in the literature are of limited clinical importance, they may be significant when prescribing a drug with a narrow therapeutic index, especially if it is absorbed poorly.

[The characteristics of the binding of M-cholinergic blockers and beta-adrenoblockers by the brain synaptosomes of 15-day-old and adult rats]

Significant difference in values of basic parameters, Bmax and Kd which characterize binding of 3H-quinuclidynylbenzylate and 3H-dihydroalprenolol, specific blockers of m-cholino- and beta-adrenoreceptors, has been established for brain synaptosomes from 15-day and adult rats. It was shown that phospholipase A2 (1 microgram/ml), a membrane active component from the venom of the cobra Naja naja oxiana, reduced Bmax and Kd for binding 3H-quinuclidynylbenzylate and 3H-dihydroalprenolol by synaptosomes. It is suggested that functional modifications in membrane during animal development or induced by phospholipase A2 result in shifts in the specific activity of adreno- and cholinoreceptors and, as a result, in disturbances of adrenergic and cholinergic responses.