Pharmacokinetics of dextropropoxyphene and nordextropropoxyphene in young and elderly volunteers after single and multiple dextropropoxyphene dosage

Perceptions of French general practitioners and patients regarding dextropropoxyphene withdrawal: a qualitative study

OBJECTIVES

Dextropropoxyphene (DXP), a step 2 analgesic commonly prescribed in France, was withdrawn from the French market in 2011 following a European decision due to its poor risk-benefit ratio. The purpose of this study was to explore the perceptions of French general practitioners (GPs) and patients regarding DXP withdrawal.

DESIGN

Qualitative study based on 26 individual semi-structured interviews.

SETTING

Rhône-Alpes region of France.

PARTICIPANTS

Thirteen patients and 13 GPs.

METHODS

Interviews were conducted to collect data concerning the status of DXP, its efficacy and safety, the conditions of DXP's withdrawal and its potential impact. The transcripts were analysed using NVivo software.

RESULTS

DXP was a very popular drug among both patients and GPs. Its withdrawal was a bad experience for patients and many GPs; these misunderstood the reasons for its withdrawal and several contested them. They generally recognised more benefits than risks of DXP and considered alternative drugs unsatisfactory. In the same period, a French court case regarding another drug led to distrust towards the pharmaceutical industry and healthcare institutions, which contributed to the negative feelings reported. However, the experience was positive for the GPs who had been alerted to the poor DXP risk-benefit ratio well before its withdrawal.

CONCLUSIONS

Apart from physicians who were previously informed of its poor risk-benefit ratio, DXP withdrawal was not a good experience for patients and GPs. Better anticipation by the health authorities, in terms of pharmacoepidemiological surveillance and communication to healthcare professionals as well as the general public, should provide better acceptance of such a decision in the future.

Analysis of the variability of the pharmacokinetics of multiple drugs in young adult and elderly subjects and its implications for acceptable daily exposures and cleaning validation limits

The elderly constitute a significant, potentially sensitive, subpopulation within the general population, which must be taken into account when performing risk assessments including determining an acceptable daily exposure (ADE) for the purpose of a cleaning validation. Known differences in the pharmacokinetics of drugs between young adults (who are typically the subjects recruited into clinical trials) and the elderly are potential contributors affecting the interindividual uncertainty factor (UF_H) component of the ADE calculation. The UF_H values were calculated for 206 drugs for young adult and elderly groups separately and combined (with the elderly assumed to be a sensitive subpopulation) from published studies where the pharmacokinetics of the young adult and elderly groups were directly compared. Based on the analysis presented here, it is recommended to use a default UF_H value of 10 for worker populations (which are assumed to be approximately equivalent to the young adult groups) where no supporting pharmacokinetic data exist, while it is recommended to use a default UF_H value of 15 for the general population, to take the elderly into consideration when calculating ADE values. The underlying reasons for the large differences between the exposures in the young adult and elderly subjects for the 10 compounds which show the greatest separation are different in almost every case, involving the OCT2 transporter, glucuronidation, hydrolysis, CYP1A2, CYP2A6, CYP2C19, CYP2D6, CYP3A4 or CYP3A5. Therefore, there is no consistent underlying mechanism which appears responsible for the largest differences in pharmacokinetic parameters between young adult and elderly subjects.

Role of active metabolites in the use of opioids

The opioid class of drugs, a large group, is mainly used for the treatment of acute and chronic persistent pain. All are eliminated from the body via metabolism involving principally CYP3A4 and the highly polymorphic CYP2D6, which markedly affects the drug's function, and by conjugation reactions mainly by UGT2B7. In many cases, the resultant metabolites have the same pharmacological activity as the parent opioid; however in many cases, plasma metabolite concentrations are too low to make a meaningful contribution to the overall clinical effects of the parent drug. These metabolites are invariably more water soluble and require renal clearance as an important overall elimination pathway. Such metabolites have the potential to accumulate in the elderly and in those with declining renal function with resultant accumulation to a much greater extent than the parent opioid. The best known example is the accumulation of morphine-6-glucuronide from morphine. Some opioids have active metabolites but at different target sites. These are norpethidine, a neurotoxic agent, and nordextropropoxyphene, a cardiotoxic agent. Clinicians need to be aware that many opioids have active metabolites that will become therapeutically important, for example in cases of altered pathology, drug interactions and genetic polymorphisms of drug-metabolizing enzymes. Thus, dose individualisation and the avoidance of adverse effects of opioids due to the accumulation of active metabolites or lack of formation of active metabolites are important considerations when opioids are used.

CYP3A4 mediates dextropropoxyphene N-demethylation to nordextropropoxyphene: humanin vitroandin vivostudies and lack of CYP2D6 involvement

The individual cytochrome P450 isoforms in dextropropoxyphene N-demethylation to nordextropropoxyphene were determined and the pharmacokinetics of dextropropoxyphene and nordextropropoxyphene in cytochrome P4502D6 (CYP2D6) extensive (EM) and poor (PM) subjects were characterized. Microsomes from six CYP2D6 extensive metabolizers and one CYP2D6 poor metabolizer were used with isoform specific chemical and antibody inhibitors and expressed recombinant CYP enzymes. Groups of three CYP2D6 EM and PM subjects received a single 65-mg oral dose of dextropropoxyphene, and blood and urine were collected for 168 and 96 h, respectively. Nordextropropoxyphene formation in vitro was not different between the CYP2D6 extensive metabolizers (Km = 179 +/- 74 microM, Cl(int) = 0.41 +/- 0.26 ml mg(-1)h(-1)) and the PM subject (K = 225 microM, Cl(int) = 0.19 ml mg(-1) h(-1)) and was catalysed predominantly by CYP3A4. There was no apparent difference in the pharmacokinetics of dextropropoxyphene and nordextropropoxyphene in CYP2D6 EM and PM subjects. CYP3A4 is the major CYP enzyme catalysing the major metabolic pathway of dextropropoxyphene metabolism. Hence variability in the pharmacodynamic effects of dextropropoxyphene are likely due to intersubject variability in hepatic CYP3A4 expression and/or drug-drug interactions. Reported CYP2D6 phenocopying is not due to dextropropoxyphene being a CYP2D6 substrate.

Cholestasis and endogenous opioids: liver disease and exogenous opioid pharmacokinetics

A class of endogenous opioids is upregulated in liver disease particular to cholestasis, which contributes to symptoms in liver disease such as pruritus, hypotension and encephalopathy. Symptoms associated with cholestasis are reversed or at least ameliorated by mu opioid receptor antagonists. Palliation of symptoms related to cholestatic liver disease also involves bile acid binding agents. Opioid receptor antagonists, unlike bile acid binding agents, have been reported to relieve multiple symptoms, except for pruritus, and improve liver function as demonstrated in experimental cholestasis. Exogenous opioid pharmacology is altered by liver disease. Dose reduction or prolongation of dose intervals is necessary depending on the severity of liver disease.

Pharmacological aspects of successful long-term analgesia

Persistent pain represents a major quality-of-life burden for patients and a challenge for their physician. Chronic pain often arises from multiple tissue sources and involves multiple chemical mediators and pain transmission pathways. Successful long-term pain management requires analgesic regimens that can treat pains of multiple origin and type. Safety and tolerability are also a high priority when prescribing chronic therapy. Recent publications and regulatory developments affecting anti-inflammatory drugs have limited the options available for the management of chronic pain. Major concerns in long-term use of anti-inflammatory drugs include renal toxicity, gastrointestinal ulceration and bleeding and cardiovascular events, which can be of particular concern for elderly patients. Opioid agents avoid the end-organ toxicity seen with anti-inflammatory drugs, but their use may be limited, especially in the long term, by side effects such as constipation or sedation and by concerns about the potential for physical or psychological dependence. Paracetamol (acetaminophen) has a favourable safety and tolerability profile, although exceeding the recommended dose (up to 4 g/day) carries a risk of liver damage. It exerts simultaneous anti-nociception at both spinal and supra-spinal sites, and has shown self-synergy between these two routes of activity. Tramadol, an atypical weak opioid with a multi-modal mechanism of action, inhibits re-uptake of multiple neurotransmitters and has an improved safety and tolerability profile compared with traditional opioids. Rational combinations of analgesic drugs offer a viable approach to managing persistent pain that involves multiple sites or pathways. The combination of paracetamol plus tramadol brings together two well-known analgesics that have different but complementary mechanisms of analgesic action. Laboratory studies have demonstrated that these agents interact to produce synergistic analgesia with a desirable safety/efficacy profile.

Usage of paracetamol-containing combination analgesics remains high in primary care

AIMS

Paracetamol-containing combination analgesics are widely prescribed but the use of paracetamol/dextropropoxyphene (co-proxamol) is particularly controversial. We aim to examine the prescribing patterns of the paracetamol-containing analgesics in Ireland.

METHODS

A national primary care prescribing database was used to investigate patterns of usage. Twenty-six thousand three hundred and eighteen patients who were new to therapy with paracetamol and paracetamol-containing analgesics between January and June 2002 were identified as follows: no previous analgesic medication in the 6 months prior to enrolment into the study, and followed up for at least 12 months from the time of enrolment. Duration of therapy and the number of prescriptions received post enrolment were analyzed according to age. Odds ratios for receiving long-term (>1 month) compared with short-term (1 month) prescriptions for co-proxamol, paracetamol only or a paracetamol combination-type analgesic were calculated for women vs. men, and in those aged over 65 vs. those aged under 65 years.

RESULTS

Co-proxamol was the most commonly prescribed analgesic, accounting for 42% of all prescriptions dispensed during 2003. Long-term use of paracetamol-containing analgesic preparations was uncommon, with 56.7% receiving only 1 month's prescription during the study period. However, women (OR = 1.18, 95% CI 1.07, 1.28, P < 0.0001) and those over 65 years (OR = 1.71, 95% CI 1.57, 1.86, P < 0.0001) were more likely to receive a follow-up prescription for co-proxamol, but also for paracetamol (women, OR = 1.28, 95% CI 1.16, 1.39; over 65 year olds, OR = 2.67, 95% CI 2.44, 2.93) and the paracetamol combinations (women, OR = 1.33, 95% CI 1.20, 1.47; over 65 year olds, OR = 1.69, 95% CI 1.53, 1.87).

CONCLUSIONS

Co-proxamol was the most commonly prescribed paracetamol-containing analgesic preparation in Ireland. The results may indicate inappropriate use in primary care.

Dextropropoxyphene: safety and efficacy in older patients

Dextropropoxyphene, alone or in combination with acetaminophen (paracetamol), is among the most frequently prescribed opioid analgesics in the elderly in the US despite the American Geriatric Society recommendation that its use should be restricted. However, this recommendation is based on expert opinion in an apparent absence of data. Accordingly, we conducted a literature search which identified nine studies that reported efficacy and safety data for dextropropoxyphene in predominantly older patients (> or = 55 years of age). These studies were evaluated to assess the efficacy and safety of dextropropoxyphene compared with other opioids and to evaluate whether safety and tolerability differed in older versus younger patients. The efficacy of dextropropoxyphene appeared to be similar to that of other analgesics, and its safety was comparable to that of other opioid analgesics. Although the adverse event profile suggests that elderly patients might have more frequent gastrointestinal and CNS complaints than younger patients treated with dextropropoxyphene, the frequency of reports appears similar to that of other opioids. The incidences of dizziness and somnolence were not significantly greater in older patients (1-2% and 0-21%, respectively) than in younger patients (8% and 13%, respectively). The absence of clinical studies directly addressing the safety and tolerability of dextropropoxyphene in elderly patients (>65 years of age) versus younger patients encumbers assessment of the validity of restricting its use in the elderly. Careful outcomes research is needed to assess the effectiveness and safety of dextropropoxyphene in older patients and to develop evidence-based risk/benefit prescribing criteria for use of this drug in this age group.

Pharmacokinetics in older persons

BACKGROUND

Physiologic changes and disease-related alterations in organ function occur with aging. These changes can affect drug pharmacokinetics in older persons.

OBJECTIVE

This article reviews age-related changes in pharmacokinetics and their clinical relevance.

METHODS

A PubMed search was conducted using the terms elderly and pharmacokinetics. Other reviews were also included for literature searching. The review includes literature in particular from 1990 through April 2004. Some articles from before 1990 were included to help illustrate principles of age-related pharmacokinetics.

RESULTS

There are minor changes in drug absorption with aging. The effect of aging on small-bowel transporter systems is not yet fully established. Bioavailability of highly extracted drugs often is increased with age. Transdermal absorption may be delayed, especially in the case of water-soluble compounds. Fat-soluble drugs may distribute more widely and water-soluble drugs less extensively in older persons. Hepatic drug metabolism shows wide interindividual variation, and in many cases, there is an age-related decline in elimination of metabolized drugs, particularly those eliminated by the cytochrome enzyme system. Any decrement in cytochrome enzyme metabolism appears nonselective. Synthetic conjugation metabolism is less affected by age. Pseudocapillarization of the sinusoidal endothelium in the liver, restricting oxygen diffusion, and the decline in liver size and liver blood flow may influence age-related changes in rate of hepatic metabolism. Frailty, physiological stress, and illness are important predictors of drug metabolism in older individuals. Inhibition of drug metabolism is not altered with aging, but induction is reduced in a minority of studies. Renal drug elimination typically declines with age, commensurate with the fall in creatinine clearance. Renal tubular organic acid transport may decline with age, while the function of the organic base transporter is preserved but may be less responsive to stimulation.

CONCLUSION

Changes in pharmacokinetics occur due to age-related physiologic perturbations. These changes contribute to altered dose requirements in older persons, particularly in the case of drugs eliminated by the kidney. Interindividual variation, disease, frailty, and stress may overshadow age-related changes.

Simultaneous determination of paracetamol and dextropropoxyphene in human plasma by liquid chromatography/tandem mass spectrometry: application to clinical bioequivalence studies

A liquid chromatography/mass spectrometry method for simultaneous determination of paracetamol and dextropropoxyphene in human plasma is described. Paracetamol and dextropropoxyphene, together with their internal standards (tolbutamide and pyrroliphene), were extracted from 0.5 mL of plasma using solid-phase extraction. The chromatography was performed using a Thermo Hypersil APS-2 Amino column (250 mm x 4.6 mm, 5 microm) with a mobile phase consisting of acetonitrile and 0.4% glacial acetic acid in water (20:80). The total run time was 6 min for each sample. The triple-quadrupole mass spectrometer was operated in both positive (for detection of dextropropoxyphene and its IS pyrroliphene) and negative (for detection of paracetamol and its IS tolbutamide) modes using a polarity-switching technique. Multiple reaction monitoring was used for quantification. The method was linear over the concentration range of 0.1-20 microg/mL for paracetamol and 0.5-80 ng/mL for dextropropoxyphene. The intra- and inter-day precision were less than 10%, and the accuracy ranged from 92.2-110.9%. The lower limits of quantification were 0.1 microg/mL for paracetamol and 0.5 ng/mL for dextropropoxyphene. The present method provides a robust, fast and sensitive analytical tool for both paracetamol and dextropropoxyphene, and has been successfully applied to a clinical bioequivalence study in 14 subjects.

Acceptability and efficacy of two associations of paracetamol with a central analgesic (dextropropoxyphene or codeine): comparison in osteoarthritis

A double-blind randomized parallel group trial was undertaken to compare the acceptability and efficacy of 2 forms of analgesic treatment, DI-Antalvic (Houde Laboratories, Puteaux, France) (30 mg dextropropoxyphene and 400 mg paracetamol per capsule) and Efferalgan-Codeine (UPSA Laboratories, Rueil Malmaison, France) (30 mg codeine and 500 mg paracetamol per tablet) prescribed for 1 week at doses of 6 capsules/day and 6 tablets/day, respectively, in 141 outpatients with active osteoarthritis of the knee or hip. The principal aim of the trial was concerned with acceptability, with efficacy as its secondary aim. The principal trial criterion was defined as overall assessment of acceptability by the patient at the end of the trial (success or failure) or by treatment dropouts because of an adverse effect (failure). Comparability of the groups was confirmed before any treatment regarding the physical characteristics of the patients, characteristics of osteoarthritis, and the initial level of pain and functional consequences of pain. Results show that the analgesic efficacy of the treatment was similar, but that the acceptability of Efferalgan-Codeine was significantly worse than that of DI-Antalvic: 53% failure with Efferalgan-Codeine versus 29% failure with DI-Antalvic (P = .005). Other trials of the same type would seem necessary (comparison of lower doses, other types of pain) before being able to generally extrapolate such findings.

Hepatic drug metabolism and aging

Although there is considerable variation in the effect of age on drug biotransformation, the metabolism of many drugs is impaired in the elderly. Age-related physiological changes, such as a reduction in liver mass, hepatic metabolising enzyme activity, liver blood flow and alterations in plasma drug binding may account for the decreased elimination of some metabolised drugs in the elderly. It is difficult, however, to separate an effect of aging from a background of marked variation in the rate of metabolism due to factors such as individual metabolic phenotype, environmental influences, concomitant disease states and drug intake. The prevailing data suggest that initial doses of metabolised drugs should be reduced in older patients and then modified according to the clinical response. In most studies the elderly appear as responsive as young individuals to the effects of compounds which induce or inhibit the activity of cytochrome P450 isozymes. Concurrent use of other agents, which induce or inhibit drug metabolism, mandates dose adjustment as in younger patients. Many questions remain unanswered. For instance, limitations of in vitro studies prevent any firm conclusion about changes in hepatic drug metabolising enzyme activity in the elderly. With aging, some pathways of drug metabolism may be selectively affected, but this has not been adequately scrutinised. The possibility that metabolism of stereoisomers may be altered in the elderly has not been adequately tested. The effect of aging on the distribution of polymorphic drug metabolism phenotypes is still not established, despite potential implications for disease susceptibility and survival advantage.

Adverse drug reactions. An overview of special considerations in the management of the elderly patient

The incidence of adverse drug reactions increases with aging, and the elderly are more likely to suffer serious or fatal reactions. Thus, morbidity and mortality are considerable in old patients, with 15% of those in hospital suffering a reaction, and many admitted as a consequence of one. The greater propensity of older patients for adverse drug reactions largely reflects the prescription of drugs to them, although over-the-counter purchases must also play a part. The elderly take more drugs per se (which is a reflection of multiple pathology), and more drugs with a narrow therapeutic index associated with a high risk of dangerous adverse reactions and drug interactions. They also have a reduced ability to withstand any reactions due to concomitant disease, and an altered pharmacokinetic and -dynamic response which tends to increase drug effects. The recommendation must be to use fewer drugs in older patients, perhaps trying alternative medicine first in nonacute conditions. Starting doses can often be reduced in the elderly, and clinical and therapeutic monitoring of effect is mandatory. The use of diuretics, antihypertensives, anti-Parkinsonian drugs and anticoagulants emphasise these points, and is discussed in detail together with digoxin, analgesics and nonsteroidal anti-inflammatory drugs. Clear guidelines are given for the use of each of these classes of drug.