Pharmacokinetic and pharmacodynamic interactions in an outpatient maintenance therapy of intravenous heroin users with levomethadone

Smoking by people with mental illness and benefits of smoke-free mental health services

Smoking is the largest single cause of preventable illness in the UK. Those with mental health problems smoke significantly more and are therefore at greater risk. The new Health Act (2006) will require mental health facilities in England to be completely smoke-free by 1st July 2008. This article reviews the current literature regarding how smoking affects both the physical and mental well-being of people with mental health problems. It also considers the effects of smoke-free policy in mental health settings.

Review of smoking cessation treatments for people with mental illness

This article reviews the current literature regarding treatments for smoking cessation in both the general population and in those with mental health problems. The gold-standard treatment for the general population is pharmacotherapy (nicotine replacement therapy, bupropion or varenicline) coupled with individual or group psychological support. This is also effective in helping people with mental illness to reduce or quit smoking, but care must be taken to avoid adverse medication interactions and to monitor antipsychotic medication in particular as cigarette consumption reduces.

Flexible dosing of tincture of opium in the management of opioid withdrawal: pharmacokinetics and pharmacodynamics

AIMS

The aim was to evaluate the clinical effectiveness, pharmacodynamics and pharmacokinetics of a range of Tincture of Opium (TOP) doses in the management of opioid withdrawal.

METHODS

Forty-five opium-dependent Thai subjects were allocated to three dosing groups (6.66, 13.3 and 20 mg morphine equivalents, twice daily) depending on their self-reported prior opium use. On day 5 of dosing subjects underwent an interdosing interval study where blood, withdrawal scores, heart rate and blood pressure (BP) were collected at 0, 1, 3 and 8 h. Plasma morphine concentrations were quantified by high-performance liquid chromatography, and plasma morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) concentrations by LCMS.

RESULTS

Thirty-two subjects completed the study. Withdrawal scores were low for all subjects (range 9-23% of maximum response). There were dose-dependent changes in both systolic and diastolic BP (P = 0.021 and P = 0.01, respectively), but these were not considered clinically significant. There were no effects of dose on respiratory rate. Plasma morphine concentrations changed significantly across the interdosing interval (P = 0.0001), rising to a maximum at 1 h after dosing. Plasma morphine concentrations also differed according to dose (P < 0.05). The mean ratios of the morphine glucuronides were found to be: M3G/M6G = 7.7, M3G/morphine = 35.6 and M6G/morphine = 4.9, values comparable to those previously reported.

CONCLUSION

The management of opioid withdrawal can be achieved, with minimal adverse effects, by using flexible dosing of TOP.

Fluctuations in (R,S)-methadone pharmacokinetics and response among long-term methadone maintenance patients

Knowledge of how methadone disposition may fluctuate during the course of maintenance treatment is presently limited. This study investigated long-term fluctuations in methadone pharmacokinetics in five methadone maintenance patients who participated in two 24-hour testing sessions separated by at least one year. Results indicated substantial fluctuations between sessions in dose-corrected average steady-state plasma (R)-methadone concentrations (Cav), ranging from a 51% decrease to a 466% increase. These fluctuations were not consistently associated with changes in methadone dose or self-reported withdrawal status. The plasma (S)-:(R)-methadone Cav ratio increased significantly (12%, P = 0.04) between the sessions, suggesting a different pattern of long-term change in the pharmacokinetics of each enantiomer over time. The pronounced and variable fluctuations in methadone disposition evident in these patients highlight the need for an individualized approach to patient dosing and monitoring.

The effects of methadone and its role in fatalities

Methadone is a synthetic opioid, used both as an analgesic in severe pain relief and now mainly in the treatment of opiate dependence. Such use of the drug has increased as its advantages have become widely recognized. There are undesirable outcomes from its greater use, including a substantial market in diverted methadone and a high number of deaths where the drug has been implicated. It is important to understand how and why methadone causes death so that such fatalities can be minimized, and to disseminate such information. This paper presents an overview of the chief effects of methadone on the human body, considering its metabolism, drug interactions and tolerance. The principal mechanisms by which methadone causes death are discussed: respiratory depression, aspiration of vomit, pulmonary oedema, bronchopneumonia, cardiac problems and renal failure. Many such deaths are preventable, if drug interactions and polydrug use are avoided, its longer period of metabolism and individuals' tolerance levels are considered. It is hoped that this paper will (a) help guide health professionals in their management and treatment of patients participating in methadone treatment programmes, and (b) provide some basic information for those dealing with individuals who have consumed methadone.

Population pharmacokinetics of methadone in opiate users: characterization of time-dependent changes

AIMS

Although methadone is widely used to treat opiate dependence, guidelines for its dosage are poorly defined. There is increasing evidence to suggest that a strategy based on plasma drug monitoring may be useful to detect non-compliance. Therefore, we have developed a population-based pharmacokinetic (POP-PK) model that characterises adaptive changes in methadone kinetics.

METHODS

Sparse plasma rac-methadone concentrations measured in 35 opiate-users were assessed using the P-Pharm software. The final structural model comprised a biexponential function with first-order input and allowance for time-dependent change in both clearance (CL) and initial volume of distribution (V ). Values of these parameters were allowed to increase or decrease exponentially to an asymptotic value.

RESULTS

Increase in individual values of CL and increase or decrease in individual values of V with time was observed in applying the model to the experimental data.

CONCLUSIONS

A time-dependent increase in the clearance of methadone is consistent with auto-induction of CYP3A4, the enzyme responsible for much of the metabolism of the drug. The changes in V with time might reflect both up- and down-regulation of alpha1-acid glycoprotein, the major plasma binding site for methadone. By accounting for adaptive kinetic changes, the POP-PK model provides an improved basis for forecasting plasma methadone concentrations to predict and adjust dosage of the drug and to monitor compliance in opiate-users on maintenance treatment.

Plasma methadone concentrations as an indicator of opioid withdrawal symptoms and heroin use in a methadone maintenance program

Plasma methadone concentrations and its main metabolite D,L-2-ethylidiene-1,5-dimethyl-3,5-diphenylpyrrolidine (EDDP) were determined in 93 patients under methadone maintenance treatment to assess their relationship with heroin use and opioid withdrawal symptoms. Neither plasma concentrations of methadone nor EDDP were significantly different when patients that used heroin in last 3 months were compared with those testing negative for this drug (methadone, 355 +/- 217 versus 369 +/- 216 ng/ml, t = 0.29, P = NS; EDDP, 49 +/- 28 versus 54 +/- 40 ng/ml, t = 0.51, P = NS). No correlation between opioid withdrawal scale scores and plasma concentrations of methadone (r = 0.02, P = NS) and EDDP (r = -0.14, P = NS) was found. Therapeutic drug monitoring during methadone maintenance seems to be useful for assessing compliance with treatment but not for predicting heroin use and subjective withdrawal symptoms.