Opioid Dose Requirements Research Articles

Length of Stay and Opioid Dose Requirement with Transversus Abdominis Plane Block vs Epidural Analgesia for Ventral Hernia Repair

Major abdominal operations often requires postoperative opioid analgesia. However, there is growing recognition of the potential for abuse. We previously reported a significant reduction in opioid consumption after implementation of an Enhanced Recovery after Surgery protocol after ventral hernia repair focusing on opioid reduction. Epidural use was routine for postoperative pain control in this protocol. Recently, we have transitioned to transversus abdominis plane (TAP) block instead of epidural analgesia. We hypothesize that this modification reduces length of stay and lowers opioid use in ventral hernia repair. All patients undergoing open ventral hernia repair were recorded prospectively in the Americas Hernia Society Quality Collaborative database. All patients receiving either TAP or epidural between February 2015 and March 2018 were identified. Additional review was performed to quantify opioid use in morphine milligram equivalents (MMEs). Primary outcomes were length of stay and opioid use. Epidural was used in 172 patients and TAP block in 74. There were no significant comorbidity differences between groups. The TAP group had a slightly higher BMI (33.6 kg/m2 vs 28.3 kg/m2) and slightly smaller hernias (8.8 cm vs 10.8 cm). There was no difference in 30-day surgical site infections. Hospital length of stay was significantly shorter with TAP block (2.4 vs 4.5 days; p < 0.001). Total MME requirements for patients receiving TAP block were lower than those with epidural during postoperative days 1 and 2 (mean 40 vs 54.1 MMEs; p= 0.033 and 36.1 vs 52.5 MMEs; p= 0.018). Use of TAP block significantly reduces length of stay and decreases opioid dose requirements in the early postoperative period compared with epidural analgesia.

Effect of cannabis use in people with chronic non-cancer pain prescribed opioids: findings from a 4-year prospective cohort study

Interest in the use of cannabis and cannabinoids to treat chronic non-cancer pain is increasing, because of their potential to reduce opioid dose requirements. We aimed to investigate cannabis use in people living with chronic non-cancer pain who had been prescribed opioids, including their reasons for use and perceived effectiveness of cannabis; associations between amount of cannabis use and pain, mental health, and opioid use; the effect of cannabis use on pain severity and interference over time; and potential opioid-sparing effects of cannabis. The Pain and Opioids IN Treatment study is a prospective, national, observational cohort of people with chronic non-cancer pain prescribed opioids. Participants were recruited through community pharmacies across Australia, completed baseline interviews, and were followed up with phone interviews or self-complete questionnaires yearly for 4 years. Recruitment took place from August 13, 2012, to April 8, 2014. Participants were asked about lifetime and past year chronic pain conditions, duration of chronic non-cancer pain, pain self-efficacy, whether pain was neuropathic, lifetime and past 12-month cannabis use, number of days cannabis was used in the past month, and current depression and generalised anxiety disorder. We also estimated daily oral morphine equivalent doses of opioids. We used logistic regression to investigate cross-sectional associations with frequency of cannabis use, and lagged mixed-effects models to examine temporal associations between cannabis use and outcomes. 1514 participants completed the baseline interview and were included in the study from Aug 20, 2012, to April 14, 2014. Cannabis use was common, and by 4-year follow-up, 295 (24%) participants had used cannabis for pain. Interest in using cannabis for pain increased from 364 (33%) participants (at baseline) to 723 (60%) participants (at 4 years). At 4-year follow-up, compared with people with no cannabis use, we found that participants who used cannabis had a greater pain severity score (risk ratio 1·14, 95% CI 1·01-1·29, for less frequent cannabis use; and 1·17, 1·03-1·32, for daily or near-daily cannabis use), greater pain interference score (1·21, 1·09-1·35; and 1·14, 1·03-1·26), lower pain self-efficacy scores (0·97, 0·96-1·00; and 0·98, 0·96-1·00), and greater generalised anxiety disorder severity scores (1·07, 1·03-1·12; and 1·10, 1·06-1·15). We found no evidence of a temporal relationship between cannabis use and pain severity or pain interference, and no evidence that cannabis use reduced prescribed opioid use or increased rates of opioid discontinuation. Cannabis use was common in people with chronic non-cancer pain who had been prescribed opioids, but we found no evidence that cannabis use improved patient outcomes. People who used cannabis had greater pain and lower self-efficacy in managing pain, and there was no evidence that cannabis use reduced pain severity or interference or exerted an opioid-sparing effect. As cannabis use for medicinal purposes increases globally, it is important that large well designed clinical trials, which include people with complex comorbidities, are conducted to determine the efficacy of cannabis for chronic non-cancer pain. National Health and Medical Research Council and the Australian Government.

Transient Receptor Potential Vanilloid 1 Antagonists Prevent Anesthesia-induced Hypothermia and Decrease Postincisional Opioid Dose Requirements in Rodents.

Intraoperative hypothermia and postoperative pain control are two important clinical challenges in anesthesiology. Transient receptor potential vanilloid 1 has been implicated both in thermoregulation and pain. Transient receptor potential vanilloid 1 antagonists were not advanced as analgesics in humans in part due to a side effect of hyperthermia. This study tested the hypothesis that a single, preincision injection of a transient receptor potential vanilloid 1 antagonist could prevent anesthesia-induced hypothermia and decrease the opioid requirement for postsurgical hypersensitivity. General anesthesia was induced in rats and mice with either isoflurane or ketamine, and animals were treated with transient receptor potential vanilloid 1 antagonists (AMG 517 or ABT-102). The core body temperature and oxygen consumption were monitored during anesthesia and the postanesthesia period. The effect of preincision AMG 517 on morphine-induced reversal of postincision hyperalgesia was evaluated in rats. AMG 517 and ABT-102 dose-dependently prevented general anesthesia-induced hypothermia (mean ± SD; from 1.5° ± 0.1°C to 0.1° ± 0.1°C decrease; P < 0.001) without causing hyperthermia in the postanesthesia phase. Isoflurane-induced hypothermia was prevented by AMG 517 in wild-type but not in transient receptor potential vanilloid 1 knockout mice (n = 7 to 11 per group). The prevention of anesthesia-induced hypothermia by AMG 517 involved activation of brown fat thermogenesis with a possible contribution from changes in vasomotor tone. A single preincision dose of AMG 517 decreased the morphine dose requirement for the reduction of postincision thermal (12.6 ± 3.0 vs. 15.6 ± 1.0 s) and mechanical (6.8 ± 3.0 vs. 9.5 ± 3.0 g) withdrawal latencies. These studies demonstrate that transient receptor potential vanilloid 1 antagonists prevent anesthesia-induced hypothermia and decrease opioid dose requirements for the reduction of postincisional hypersensitivity in rodents.

Opioid-Sparing Effect of Cannabinoids: A Systematic Review and Meta-Analysis.

Cannabinoids, when co-administered with opioids, may enable reduced opioid doses without loss of analgesic efficacy (ie, an opioid-sparing effect). The aim of this study was to conduct a systematic review to determine the opioid-sparing potential of cannabinoids. Eligible studies included pre-clinical and clinical studies for which the outcome was either analgesia or opioid dose requirements. Clinical studies included controlled studies and case series. We searched Scopus, Cochrane Database of Systematic Reviews, Medline, and Embase. Nineteen pre-clinical and nine clinical studies met the search criteria. Seventeen of the 19 pre-clinical studies provided evidence of synergistic effects from opioid and cannabinoid co-administration. Our meta-analysis of pre-clinical studies indicated that the median effective dose (ED50) of morphine administered in combination with delta-9-tetrahydrocannabinol (delta-9-THC) is 3.6 times lower (95% confidence interval (CI) 1.95, 6.76; n=6) than the ED50 of morphine alone. In addition, the ED50 for codeine administered in combination with delta-9-THC was 9.5 times lower (95% CI 1.6, 57.5, n=2) than the ED50 of codeine alone. One case series (n=3) provided very-low-quality evidence of a reduction in opioid requirements with cannabinoid co-administration. Larger controlled clinical studies showed some clinical benefits of cannabinoids; however, opioid dose changes were rarely reported and mixed findings were observed for analgesia. In summary, pre-clinical studies provide robust evidence of the opioid-sparing effect of cannabinoids, whereas one of the nine clinical studies identified provided very-low-quality evidence of such an effect. Prospective high-quality-controlled clinical trials are required to determine the opioid-sparing effect of cannabinoids.

Pharmacogenomics and Patient Treatment Parameters to Opioid Treatment in Chronic Pain: A Focus on Morphine, Oxycodone, Tramadol, and Fentanyl.

Opioids are one of the most commonly prescribed medicines for chronic pain. However, their use for chronic pain has been controversial. The objective of this literature review was to identify the role of genetic polymorphisms on patient treatment parameters (opioid dose requirements, response, and adverse effects) for opioids used in malignant and nonmalignant chronic pain. The opioids that this review focuses on are codeine, morphine, oxycodone, tramadol, and fentanyl. A literature search of databases Medline and Embase was carried out, and studies up to April 2016 were included in this review. Studies were included based on a combination of key words: chronic pain and related terms, pharmacogenetics and related terms, and opioids and related terms. Among the 1,408 individual papers retrieved from the search in Medline and Embase, 32 original articles were included in this review, with none related to codeine. The 32 papers reported various study designs, opioids, and polymorphisms being studied for associations with treatment outcomes. This literature review reveals that variants in ABCB1, OPRM1, and COMT have been replicated for opioid dosing and variants in ABCB1 have been replicated for both treatment response and adverse effects. Currently, there are few validated studies to form a strong evidence base to support pharmacogenomics testing when initiating opioid therapy. However, the field of pharmacogenomics in chronic pain is likely to expand over the coming years, with the increasing number of treatment options available and larger cohorts being assembled in order to identify true associations.

OHP-026 Relevance of OPRM1 gene polymorphisms on chronic opioid treatment for cancer pain

BackgroundThe mu-opioid receptor gene (OPRM1) plays a key role in pain perception, response to opioids and opioid addiction. Several gene polymorphisms on OPRM1 have been associated with higher opioid requirements,...

µ-Opioid Receptor Gene Variant OPRM1 118 A&gt;G: A Summary of its Molecular and Clinical Consequences for Pain

The human µ-opioid receptor variant 118 A>G (rs1799971) has become one of the most analyzed genetic variants in the pain field. At the molecular level, the variant reduces opioid receptor signaling efficiency and expression, the latter probably via a genetic-epigenetic interaction. In experimental settings, the variant was reproducibly associated with decreased effects of exogenous opioids. However, this translates into very small clinical effects (meta-analysis of 14 studies: Cohen's d = 0.096; p = 0.008), consisting of slightly higher opioid dosing requirements in peri- and post-operative settings. An effect can neither be maintained for chronic analgesic therapy nor for opioid side effects. It seems unlikely that further studies will reveal larger effect sizes and, therefore, further analyses appear unwarranted. Thus, due to its small effect size, the SNP is without major clinical relevance as a solitary variant, but should be regarded as a part of complex genotypes underlying pain and analgesia.

Impact of Opioid Receptor, Mu 1 (OPRM1) Polymorphisms on Pain Sensitivity and Clinical Response to Opioid Analgesic Therapy

Polymorphisms in genes involved in pain processing contribute to variation in pain sensitivity and clinical response to opioid therapy. This paper reviews the evidence on how opioid receptor, mu 1 (OPRM1) polymorphisms might influence pain sensitivity, opioid dose requirements and opioid-related effects such as analgesia and side effects. For example, it is shown that (1) individuals with AG and GG genotypes (118G variant allele carriers) exhibit lower sensitivity to pressure pain (higher pressure pain thresholds) compared with wild-type subjects (AA genotype or 118A allele carriers), and (2)individuals with GG genotypes require higher opioid doses compared with those who are AA or AG genotypes. The pain scores increase with increasing number of 118G alleles. Patients with the AA genotype have a greater analgesic effect than those with 118G allele (AG or GG genotypes). Additionally, the presence of 118G allele is associated with a reduced risk of nausea in spite of a higher morphine use, lower vomiting episodes and lower severity score for pruritus. Notably, even though many studies investigated a possible role of the OPRM1 polymorphisms in the risk for altered pain sensitivity, opioid dose and analgesia and opioid-related side effects in patients with pain, the results are conflicting. More studies to characterize the effects of other candidate genes and the combined effects of multiple genes, demography and clinical variables in predicting the clinical response and opioid-related side effects are required and these should involve larger numbers of patients in different population types.

Chronic opioid use is associated with increased DNA methylation correlating with increased clinical pain

Environmentally caused changes in chromosomes that do not alter the DNA sequence but cause phenotypic changes by altering gene transcription are summarized as epigenetics. A major epigenetic mechanism is methylation or demethylation at CpG-rich DNA islands. DNA methylation triggered by drugs has largely unexplored therapeutic consequences. Here we report increased methylation at a CpG rich island in the OPRM1 gene coding for μ-opioid receptors and at a global methylation site (LINE-1) in leukocytes of methadone-substituted former opiate addicts compared with matched healthy controls. Higher DNA methylation associated with chronic opioid exposure was reproduced in an independent cohort of opioid-treated as compared to non-opioid-treated pain patients. This suggests that opioids may stimulate DNA methylation. The OPRM1 methylation had no immediate effect on μ-opioid receptor transcription and was not associated with opioid dosing requirements. However, the global DNA methylation at LINE-1 was significantly correlated with increased chronic pain. This suggests inhibitory effects on the transcription of still unspecified nocifensive gene products. It further implies that opioids may be causally associated with increased genome-wide DNA methylation, although currently there is no direct evidence of this. This has phenotypic consequences for pain and may provide a new, epigenetics-associated mechanism of opioid-induced hyperalgesia. The results indicate a potential influence of opioid analgesics on the patients’ epigenome. They emphasize the need for reliable and cost-effective screening tools and may imply that high-throughput screening for lead compounds in artificial expression systems may not provide the best tools for identifying new pain medications.

975 COMT Genetic Variation May Influence Opioid Dosing Requirements in the Treatment of Cancer-related Pain

975 COMT Genetic Variation May Influence Opioid Dosing Requirements in the Treatment of Cancer-related Pain

Pain Management in Adults With Sickle Cell Disease in a Medical Center Emergency Department

Guidelines for pain management in adult sickle cell patients with vaso-occlusive crises suggest prompt, frequent administration of parenteral opioids. Neither the ability to implement these guidelines in a busy urban emergency department nor opioid dose requirements in uncomplicated vaso-occlusive crisis have been previously documented. Thus, a retrospective review of vaso-occlusive crisis treated in an urban medical center emergency department in 2005 was performed to define opioid requirements and barriers to guideline implementation. Fifty-seven visits by 19 patients were evaluable. Opioid treatment was not initiated for more than 2 hours during 30% of visits; the interval between the first and second opioid doses exceeded 1 hour in 26% of visits and increased with subsequent doses; and total treatment time was less than 1 hour during 21% of visits (median, 2.2 hours). Opioid doses (as intravenous morphine equivalents) ranged from 4 to 26.7 mg (0.05-0.50 mg/kg) and exceeded 10 mg during 40 visits (70%) and in 10 patients (53%). Hospitalization occurred on 25 occasions with 48% of patients admitted after 3 or fewer opioid doses and 50% of patients admitted after less than 3 hours of treatment. Moreover, return emergency department visits occurred within 3 days after 9 of 32 home discharges (28%) with treatment times uniformly less than 3 hours during the preceding visit. It is concluded that: (1) opioid dose requirements vary widely, often exceeding guideline recommendations; and (2) treatment time and timely opioid administration are often compromised, resulting in delayed pain control and premature decisions on disposition with early return visits and possibly avoidable hospital admissions.

Intravenous opioid dosing and outcomes in emergency patients: a prospective cohort analysis

Objectives Pain management in emergency department (ED) patients is variable and often inadequate. This study sought to (1) describe the variability in intravenous opioid dosing and (2) compare the outcomes that result from the most commonly prescribed opioid doses. Methods This prospective cohort study enrolled emergency patients who were prescribed intravenous morphine or hydromorphone as their initial analgesic. Subjects were interviewed at the time of opioid administration and 1 to 2 hours after opioid administration. Outcomes included the numeric pain score change (using a 0-10 scale), the proportion achieving a 50% pain score reduction, and the proportion developing side effects. Logistic regression was used to assess the effects of demographic, clinical, and treatment variables on outcomes. Results Six hundred ninety-one patients were analyzed. Initial equianalgesic dosages varied by a factor of 27 (from 1 mg morphine to 4 mg hydromorphone). Opioid dose titration occurred in only 21% of patients. Outcomes were similar across the range of opioid dosages before and after adjusting for potentially confounding variables. Among patients not taking opioids at home who received a total of 4 mg of morphine or less. 48% achieved at least a 50% pain score reduction and 60% did not want additional analgesics. Conclusions We found marked opioid dosing variability and infrequent opioid dose titration. A substantial number of ED patients with severe pain responded well to relatively low opioid dosages. Improved ability to predict opioid dose requirements and strategies that increase the use of opioid dose titration in ED patients are needed.

Quantification of Analgesic Use in Children With Sickle Cell Disease

The purposes of this study were: (1) to quantify analgesic use in children with sickle cell disease who were hospitalized for a vaso-occlusive episode, using the Medication Quantification Scale (MQS) and (2) to examine the relationships between pain intensity scores, number of painful areas marked on a body outline diagram, number of word descriptors of pain quality, and amount of analgesic medications administered. Children (5 to 19 y) were asked daily to provide pain intensity ratings and describe the location and quality of their pain. The nursing flowsheets were also reviewed to determine the dose, routes, and the number of times analgesic medications were administered in the previous 24 hours. Mean worst pain intensity score on the day of admission was 84.0+/-9.9 (range 63.8 to 100) on the 0 to 100 Oucher numeric rating scale. The mean MQS score administered on the day of admission was 15.7+/-4.9 (range 6 to 24). This score decreased significantly by 1.2+/-0.5 (P<0.0001; range 0.9 to 2.5) each day of hospitalization. Significant correlations were found between various pain characteristics and total MQS scores prescribed at time of admission. The MQS was a useful and sensitive measure to quantify analgesic use in patients with sickle cell disease who were hospitalized for an acute painful episode. The MQS score accounted for variations in the types of analgesic medications, routes of administration, dosing schedules, and opioid dosing requirements.

Analgesic and antisympathetic effects of clonidine in burn patients, a randomized, double-blind, placebo-controlled clinical trial

ABSTRACT Objectives:Unlike most other Analgesic drugs, α2 adrenoceptor agonists are capable of producing analgesia. The aim of this study was to evaluate the Analgesic and antisympathetic effects of clonidine, an α2 adrenoceptor agonist in burn patients.Materials and Methods:This randomized, double-blind, placebo-controlled clinical trial performed on one hundred burn patients in Zarea Hospital, Mazandaran, Iran from august 2004 to July 2005. All patients divided in two groups. Case group (n=50) received oral clonidine, 3.3μg/kg TDS and controls (n=50) received placebo. Heart rate and systolic blood pressure and pain severity Visual analogue score (VAS), were recorded after clonidine administration. Statistical analysis was done by means of Mann Witney U test. Results:50 patients (mean age 28.96±10 years) in case group, and 50 patients (mean age 27.60±11.4 years) in control group were studied. VAS pain scores and heart rate in the clonidine group were significantly lower than the control group (P&lt; 0.0001, P&lt; 0.02).there were no significant difference in systolic blood pressure between the two groups on the first and second day but on third day the systolic blood pressure in clonidine group, was lower than controls significantly (P=0.002). Conclusion: This study demonstrates that the use of oral clonidine affects the hemodynamic response to pain in burn patients. Our study demonstrated that clonidine can produce good analgesia and decreased in sympathetic over activity in burn patients, and also reduce opioid dose requirements.

Analgesic and antisympathetic effects of clonidine in burn patients, a randomized, double-blind, placebo-controlled clinical trial

Objectives: Unlike most other Analgesic drugs, α2 adrenoceptor agonists are capable of producing analgesia. The aim of this study was to evaluate the Analgesic and antisympathetic effects of clonidine, an α2 adrenoceptor agonist in burn patients. Materials and Methods: This randomized, double-blind, placebo-controlled clinical trial performed on one hundred burn patients in Zarea Hospital, Mazandaran, Iran from august 2004 to July 2005. All patients divided in two groups. Case group (n=50) received oral clonidine, 3.3μg/kg TDS and controls (n=50) received placebo. Heart rate and systolic blood pressure and pain severity Visual analogue score (VAS), were recorded after clonidine administration. Statistical analysis was done by means of Mann Witney U test. Results: 50 patients (mean age 28.96±10 years) in case group, and 50 patients (mean age 27.60±11.4 years) in control group were studied. VAS pain scores and heart rate in the clonidine group were significantly lower than the control group (P< 0.0001, P< 0.02).there were no significant difference in systolic blood pressure between the two groups on the first and second day but on third day the systolic blood pressure in clonidine group, was lower than controls significantly (P=0.002). Conclusion: This study demonstrates that the use of oral clonidine affects the hemodynamic response to pain in burn patients. Our study demonstrated that clonidine can produce good analgesia and decreased in sympathetic over activity in burn patients, and also reduce opioid dose requirements.

Can NSAIDs Reduce Morphine Dose and Side Effects

Concomitant use of nonsteroidal antiinflammatory drugs (NSAIDs) can reduce opioid dosing requirements, but previous studies have been too small to

A RETROSPECTIVE STUDY OF LENGTH OF HOSPITAL STAY IN INFANTS TREATED FOR NEONATAL ABSTINENCE SYNDROME WITH METHADONE VERSUS ORAL MORPHINE PREPARATIONS

Length of hospital stay (LOS) of infants treated for neonatal abstinence syndrome (NAS) with methadone was compared to LOS of those treated with an oral morphine preparation (OMP, neonatal morphine solution, or deodorized tincture of opium). A retrospective review of medical records of infants treated for NAS due to in utero exposure to methadone and/or illicit drugs such as heroin or morphine was performed for birthweight, neonatal abstinence scores, infant and maternal illicit drug exposure history, maternal methadone dose (if any), and details of treatment. Length of stay was the primary outcome measure. Forty-six infants met the inclusion criteria. The median LOS of infants treated with methadone versus OMP was not significant (P > 0.05). Prolonged LOS was associated with larger pharmacological treatment doses required to control withdrawal symptoms, larger maternal methadone dose, and increased birthweight. After adjusting for these factors, exposure to opioids in utero, maternal nicotine use, hospital of treatment, severity of withdrawal symptoms, and foster care placement were not significantly associated with LOS in univariate or multivariate analyses. These results suggest that infants treated with OMP or methadone have similar LOS. Longer LOS is associated with both higher maternal methadone doses and higher opioid treatment dose requirements after birth. The potential effect of maternal methadone dose on neonatal LOS should be considered when treating expectant mothers on methadone maintenance therapy.

The Patient Requiring High-Dose Opiates: A Case Study Involving Dependence, Tolerance, and Pseudo-Addiction

Historically, the patient experiencing pain has had to convince clinicians that his or her pain is a real phenomenon and that the pain should be treated. On many occasions, health care professionals have overestimated the risk of true addiction to opioid analgesics and have been reluctant to prescribe adequate doses of opioids. Patients with undertreated pain who seek appropriate doses of opioid analgesics have, at times, been labeled as addicts. However, far more patients remain undertreated for pain as opposed to those who have become addicted to opioid analgesics. It is within this background that the patient with very high opioid dose requirements continues to present as an important topic to pain practitioners at every level.

Pain management after major orthopaedic surgery: current strategies and new concepts.

Several recently developed analgesic techniques effectively control pain after major orthopaedic surgery. Neuraxial analgesia provided by epidural and spinal administration of local anesthetics and opioids provides the highest level of pain control; however, such therapy is highly invasive and labor intensive. Neuraxial analgesia is contraindicated in patients receiving low-molecular-weight heparin. Continuous plexus and peripheral neural blockades offer excellent analgesia without the side effects associated with neuraxial and parenteral opioids. Intravenous patient-controlled analgesia allows patients to titrate analgesics in amounts proportional to perceived pain stimulus and provide improved analgesic uniformity. Oral sustained-release opioids offer superior pain control and greater convenience than short-duration agents provide. Opioid dose requirements may be reduced by coadministration of COX-2-type nonsteroidal analgesics.

Patient-Specific Factors Affecting Patient-Controlled Analgesia Dosing

A study was conducted to evaluate the effect of characteristics patients' gender, age, weight, height, and body surface area, as well as the concurrent or recent use of opioids, ethanol and tobacco, on opioid dose requirements during administration of patient-controlled analgesia (PCA). Data were collected retrospectively from the medical records of 150 patients who underwent open cholecystectomies during an 18 month period at one institution. Demonstrable inter-patient variability in patterns of PCA use was observed. The results of the study demonstrate that during the first 48 hours of PCA therapy, patient age, height, weight, body surface area, gender, smoking, alcohol use, and preoperative opioid use may have significant influence on opioid analgesic use (p < 0.05). The data support the hypothesis that patient-specific factors may contribute to the variability observed in patients' PCA analgesic dose requirements, and these factors should be considered when selecting a proper demand (bolus) dose for PCA therapy.