Responders and non-responders to post-operative pain treatment: the loading dose predicts analgesic needs

Experimental designs for small randomised clinical trials: an algorithm for choice

Background

Small clinical trials are necessary when there are difficulties in recruiting enough patients for conventional frequentist statistical analyses to provide an appropriate answer. These trials are often necessary for the study of rare diseases as well as specific study populations e.g. children. It has been estimated that there are between 6,000 and 8,000 rare diseases that cover a broad range of diseases and patients. In the European Union these diseases affect up to 30 million people, with about 50% of those affected being children. Therapies for treating these rare diseases need their efficacy and safety evaluated but due to the small number of potential trial participants, a standard randomised controlled trial is often not feasible. There are a number of alternative trial designs to the usual parallel group design, each of which offers specific advantages, but they also have specific limitations. Thus the choice of the most appropriate design is not simple.

Methods

PubMed was searched to identify publications about the characteristics of different trial designs that can be used in randomised, comparative small clinical trials. In addition, the contents tables from 11 journals were hand-searched. An algorithm was developed using decision nodes based on the characteristics of the identified trial designs.

Results

We identified 75 publications that reported the characteristics of 12 randomised, comparative trial designs that can be used in for the evaluation of therapies in orphan diseases. The main characteristics and the advantages and limitations of these designs were summarised and used to develop an algorithm that may be used to help select an appropriate design for a given clinical situation. We used examples from publications of given disease-treatment-outcome situations, in which the investigators had used a particular trial design, to illustrate the use of the algorithm for the identification of possible alternative designs.

Conclusions

The algorithm that we propose could be a useful tool for the choice of an appropriate trial design in the development of orphan drugs for a given disease-treatment-outcome situation.

[Clinical significance of the placebo effect]

Placebo controlled studies examining clinical problems, e.g. in pain therapy, are considered the "gold standard" for evidence-based medicine. In these studies the placebo effect itself is not the main focus of interest, but serves more as a control for the specificity of the effect of a certain treatment. What physicians in this context often do not realize is that the placebo effect itself represents a true measurable correlate of an organism's psycho-neurobiological response and, thereby, influences the healing process, e.g. the pain relief. Placebo is, therefore, not equivalent to "no treatment". The number of placebo responders, the degree and the duration of the placebo effect is not fixed, but are subject to a much greater variability then hitherto believed. The myth that placebo responders have a certain personality has not been proven correct; instead, the relationships between physicians and patients as well as sociocultural factors have a considerable impact on the placebo effect. Psychological theories explain that classical conditioning, enhanced expectation and motivation of the patient determine the degree of the placebo effect. These directly influence neurobiological systems such as the endogenous opioids which according to modern brain imaging are predominantly activated in pain-relevant areas and contribute to the effect of placebo analgesia. Placebo effects that should be deliberately excluded in controlled clinical trials, can be desirable in clinical practice to optimize the total therapeutic effect. This should mean that the context effect of each therapeutic intervention is maximized towards an improved therapeutic effect, as outlined in the recent AWMF guidelines for postoperative pain therapy, but should not include the administration of an inert substance. The latter is controlled by rigorous ethical guidelines and is only permitted in the context of ethically approved controlled clinical trials. A possible alternative is suggested by Benedetti et al. in which the hidden administration of an active substance identifies the specific response in contrast to the open application of the same substance characterizing the specific plus the placebo effect, after which the pure placebo effect can be determined.

Early impact of methadone induction for heroin dependence: differential effects of two dose sequences in a randomized controlled study

The pharmacodynamic and pharmacokinetic effects of 2 methadone (METH) induction dose sequences were evaluated in this 15-day outpatient experimental protocol. Heroin-dependent, non-treatment-seeking volunteers were randomly assigned (stratified for gender, race, and route of heroin use) to 2 groups. In 1 sequence, METH doses ascended (28, 56, then 84 mg/day; stepwise, n = 18), whereas in the other sequence doses escalated, then tapered (28-84 mg on Days 1-6 to 56 mg/day; rapid, n = 16). A contingency-management intervention was common to both groups. Drug use and heroin craving and opioid withdrawal symptoms decreased, whereas agonist symptoms and positive mood increased overall across days for both groups. Plasma concentrations and the acute reinforcing effects of METH paralleled each dose sequence. Stepwise relative to rapid METH induction significantly decreased heroin craving and opioid withdrawal symptoms and increased agonist symptoms and positive mood but did not significantly improve drug use or retention. Although these specific dosing procedures would not necessarily be used in clinical settings, they provide a procedural template that might be applied safely and effectively with a broader range of treatment-seeking individuals.

Pain Evaluation in Patients Receiving Intravenous Patient-Controlled Analgesia After Surgery

STUDY OBJECTIVE

To evaluate the effectiveness of intravenous patient-controlled analgesia (PCA) in patients after surgery.

DESIGN

Prospective, observational study.

SETTING

University teaching hospital.

PATIENTS

Sixty patients with American Society of Anesthesiologists physical status I-III receiving intravenous PCA for postoperative pain. The PCA was programmed to deliver morphine 1 mg or hydromorphone 0.1-0.2 mg, with a lockout interval of 10 and 6 minutes for 80% and 20% of the patients, respectively.

MEASUREMENTS AND MAIN RESULTS

Patients were asked, up to 4 times during PCA use and once within 4 hours after PCA use, to describe and rate their intensity of pain at rest and after activity. During the first 12 hours of intravenous PCA use, 75% of the patients reported moderate-to-severe pain > or = 5 on a verbal numeric rating scale) at rest, 80% after activity. Corresponding values, respectively, were 33% and 72% for the 12-24-hour period, 43% and 76% for the 24-36-hour period, and 36% and 64% for the 36-48-hour period of intravenous PCA use. Within 4 hours of stopping PCA, 30% and 58% of the patients had moderate-to-severe pain at rest and after activity, respectively. In approximately 50% of patients, presence of pain was described with words signifying sensory and affective dimensions of pain. Pain control was rated as good or very good by 54% of patients during the first 12 hours of intravenous PCA. Ratings of pain control tended to improve with time.

CONCLUSION

Successful postoperative pain management using PCA is difficult to achieve on a consistent basis unless treatment is individualized. Our data support the hypothesis that small fixed doses fail to achieve adequate relief in many patients.

Postoperative Care of the Chronic Opioid-Consuming Patient

Recently, there has been a significant increase in the use of opioid analgesics for chronic pain in the outpatient setting. As a result, anesthesiologists are commonly presented with the dilemma of treating acute postoperative pain in patients who do not receive adequate analgesia with conventional doses of opioid. This article presents a practical approach to treating postoperative pain in the chronic opioid-consuming patient. Specifically, a technique based on pharmacokinetic modeling is described that predicts safe and therapeutic opioid dosing in these patients.

Clinical pharmacology of tramadol

Tramadol, a centrally acting analgesic structurally related to codeine and morphine, consists of two enantiomers, both of which contribute to analgesic activity via different mechanisms. (+)-Tramadol and the metabolite (+)-O-desmethyl-tramadol (M1) are agonists of the mu opioid receptor. (+)-Tramadol inhibits serotonin reuptake and (-)-tramadol inhibits norepinephrine reuptake, enhancing inhibitory effects on pain transmission in the spinal cord. The complementary and synergistic actions of the two enantiomers improve the analgesic efficacy and tolerability profile of the racemate. Tramadol is available as drops, capsules and sustained-release formulations for oral use, suppositories for rectal use and solution for intramuscular, intravenous and subcutaneous injection. After oral administration, tramadol is rapidly and almost completely absorbed. Sustained-release tablets release the active ingredient over a period of 12 hours, reach peak concentrations after 4.9 hours and have a bioavailability of 87-95% compared with capsules. Tramadol is rapidly distributed in the body; plasma protein binding is about 20%. Tramadol is mainly metabolised by O- and N-demethylation and by conjugation reactions forming glucuronides and sulfates. Tramadol and its metabolites are mainly excreted via the kidneys. The mean elimination half-life is about 6 hours. The O-demethylation of tramadol to M1, the main analgesic effective metabolite, is catalysed by cytochrome P450 (CYP) 2D6, whereas N-demethylation to M2 is catalysed by CYP2B6 and CYP3A4. The wide variability in the pharmacokinetic properties of tramadol can partly be ascribed to CYP polymorphism. O- and N-demethylation of tramadol as well as renal elimination are stereoselective. Pharmacokinetic-pharmacodynamic characterisation of tramadol is difficult because of differences between tramadol concentrations in plasma and at the site of action, and because of pharmacodynamic interactions between the two enantiomers of tramadol and its active metabolites. The analgesic potency of tramadol is about 10% of that of morphine following parenteral administration. Tramadol provides postoperative pain relief comparable with that of pethidine, and the analgesic efficacy of tramadol can further be improved by combination with a non-opioid analgesic. Tramadol may prove particularly useful in patients with a risk of poor cardiopulmonary function, after surgery of the thorax or upper abdomen and when non-opioid analgesics are contraindicated. Tramadol is an effective and well tolerated agent to reduce pain resulting from trauma, renal or biliary colic and labour, and also for the management of chronic pain of malignant or nonmalignant origin, particularly neuropathic pain. Tramadol appears to produce less constipation and dependence than equianalgesic doses of strong opioids.

Analgesic and Hemodynamic Effects of a Single 7.5-mg Intravenous Dose of Morphine in Patients with Moderate-to-Severe Postoperative Pain

STUDY OBJECTIVES

To evaluate the analgesic and hemodynamic effects of a single dose of intravenous morphine 7.5 mg in patients experiencing moderate-to-severe postoperative pain, and to determine any gender differences in analgesic response.

DESIGN

Randomized, double-blind, parallel-group, multicenter study.

SETTING

Postanesthesia care unit of a university teaching hospital.

PATIENTS

Eighty-eight patients who underwent total abdominal hysterectomy or prostatectomy.

INTERVENTION

Thirty-seven patients received a single dose of morphine sulfate 7.5 mg and 51 patients received placebo, both administered intravenously for 1 minute.

MEASUREMENTS AND MAIN RESULTS

Overall, morphine had no significant effect on systolic or diastolic blood pressure, heart rate, oxygen saturation, or respiratory rate. Compared with baseline, morphine significantly reduced pain intensity at 2, 5, and 10 minutes after administration (p<0.05). The difference in pain intensity between patients who received morphine and those who received placebo, however, was significant only at the 5-minute time point (p<0.02). Patients receiving morphine also reported mild pain relief at 2 and 5 minutes after its administration. Peak analgesic effect was reported 2 minutes after its administration in three quarters of the patients. Significant gender differences also were observed in response to analgesic effect. In women, no significant differences in pain intensity were seen at any time between the morphine and placebo groups, whereas in men receiving morphine, pain intensity was significantly less at 2, 5, and 10 minutes compared with baseline and that seen in the placebo group. Women were generally more satisfied with their pain treatment than were men.

CONCLUSION

A single 7.5-mg intravenous bolus dose of morphine did not appear to provide adequate reduction in perceived pain intensity in patients with moderate-to-severe postoperative pain. In addition, in contrast to the findings of other experimental pain studies, our data suggest that women are more tolerant of postoperative pain than are men.

Opioid Dose Titration for Severe Cancer Pain: A Systematic Evidence-Based Review

Dosing strategies to achieve rapid analgesia in patients with severe or crescendo cancer pain are important. A systematic review of research trials for treatment of severe or crescendo cancer pain was conducted; nine studies were identified. Eight trials were prospective; two were randomized between different dosing strategies. Dosing frequency predicted onset to analgesia regardless of baseline opioid dose. None of the trials were associated with evidence of respiratory depression. The studies all suffered significant methodological problems limiting broad conclusions. Until better data exist, opioid dose titration for severe/crescendo pain will be guided by expert opinion and experience.