Do sex differences exist in opioid analgesia? A systematic review and meta-analysis of human experimental and clinical studies

Effects of cold pressor pain on the abuse liability of intranasal oxycodone in male and female prescription opioid abusers

BACKGROUND

Approximately 1.9 million persons in the U.S. have prescription opioid use disorders often with concomitant bodily pain, but systematic data on the impact of pain on abuse liability of opioids is lacking. The purpose of this study was to determine whether pain alters the intranasal abuse liability of oxycodone, a commonly prescribed and abused analgesic, in males and females.

METHODS

Sporadic prescription opioid abusers (10 females, 10 males) participated in this mixed (between and within-subject), randomized inpatient study. Experimental sessions (n=6) tested intranasal placebo, oxycodone 15 or 30 mg/70 kg during cold pressor testing (CPT) and a warm water control. Observer- and subject-rated drug effect measures, analgesia, physiologic and cognitive effects were assessed.

RESULTS

The CPT significantly increased blood pressure, heart rate, pain, stress, and "opiate desire" compared to the no-pain control but did not alter opioid liking, high or street value. Intranasal oxycodone produced effects within 10 min, significantly decreasing pain and significantly increasing subjective measures of abuse liability (e.g., high). Females had higher ratings of street value, high, and liking for one or both active doses.

CONCLUSIONS

The CPT was a reliably painful and stressful stimulus that did not diminish the abuse liability of intranasal oxycodone. Females were more sensitive to oxycodone on several abuse liability measures that warrant further follow-up. Snorting oxycodone rapidly produced psychoactive effects indicative of substantial abuse liability.

Epidural pain management after open lateral thoracotomy: Female patients have better pain relief and need smaller amounts of analgesics than males

Background and aims

There is an ongoing dispute whether or not there is a gender difference in epidural drug requirements. The objective of this study was to compare the effects of a triple drug epidural mixture used for postoperative pain relief on male and female patients undergoing major surgery.

Materials and methods

To avoid possible influence of different age and type of surgery only 50–70 year old patients undergoing open lateral thoracotomy were included. 253 patients were enrolled: 116 males and 137 females. All patients received a mixture of bupivacaine 0.1 mg/ml, fentanyl 2 μg/ml, and adrenaline 2 μg/ml (BFA) by continuous infusion into the thoracic epidural space for postoperative pain relief. Infusion rate of the BFA solution was recorded and pain score was evaluated by numeric rating scale (NRS, 1–10) for 48 h post operatively.

Results

Adequate postoperative pain relief (NRS ≤ 3) at rest was accomplished in 91% of male patients on day one and 92% on day two and by 94% and 100% of female patients, respectively. Females had significantly lower median pain scores than males on day two both at rest (P < 0.011) and by movement (P < 0.012). In addition females required significantly smaller amounts of BFA mixture (P < 0.01) and less frequently rescue opioids (P < 0.025) than males.

Conclusion

Female patients had significantly better pain relief both at rest and by movement, needed smaller amounts of the epidural bupivacaine, fentanyl, adrenaline mixture for postoperative pain relief and received less frequently rescue opioids than males.

Implications

The dose of thoracic epidural infusion of low-concentration bupivacaine-, fentanyl-, and adrenaline-solution should routinely be set lower for postmenopausal women than for elderly male patients during and after thoracotomy.

Pain sensitivity and opioid analgesia: a pharmacogenomic twin study

Opioids are the cornerstone medication for the management of moderate to severe pain. Unfortunately, vast inter-individual differences in dose requirements complicate their effective and safe clinical use. Mechanisms underlying such differences are incompletely understood, are likely multifactorial, and include genetic and environmental contributions. While accumulating evidence suggests that variants of several genes account for some of the observed response variance, the relative contribution of these factors remains unknown. This study used a twin paradigm to provide a global estimate of the genetic and environmental contributions to inter-individual differences in pain sensitivity and analgesic opioid effects. Eighty one monozygotic and 31 dizygotic twin pairs successfully underwent a computer-controlled infusion with the μ-opioid agonist alfentanil in a single occasion, randomized, double-blind and placebo-controlled study design. Pain sensitivity and analgesic effects were assessed with experimental heat and cold pressor pain models along with important covariates including demographic factors, depression, anxiety, and sleep quality. Significant heritability was detected for cold pressor pain tolerance and opioid-mediated elevations in heat and cold pressor pain thresholds. Genetic effects accounted for 12-60% of the observed response variance. Significant familial effects accounting for 24-32% of observed variance were detected for heat and cold pressor pain thresholds and opioid-mediated elevation in cold pressor pain tolerance. Significant covariates included age, gender, race, education, and anxiety. Results provide a strong rationale for more detailed molecular genetic studies to elucidate mechanisms underlying inter-individual differences in pain sensitivity and analgesic opioid responses. Such studies will require careful consideration of the studied pain phenotype.

Sex and gender in adverse drug events, addiction, and placebo

Sex-gender-based differences in response to pharmaceutical treatments are still under evaluation but evidence already exists regarding the impact of sex-gender-related differences on drug safety profile, drug abuse/addiction, and placebo effects. For a number of drugs it is well recognized that a sex-gender dimorphic profile in terms of drug adverse effects exists and appears to be more frequent and severe in women than in men. However, it is not well known whether this is due to pharmacodynamic or pharmacokinetic differences. Indeed the optimization of therapy requires that attention is paid to single sex-gender. Numerous pharmacokinetic, pharmacodynamic, and sociocultural differences between women and men in drug abuse have been described. Here we focus on sex-gender differences in alcoholism and nicotine addiction. The relevance of sex and gender differences in addiction appear to be relevant. Specific programs aimed to address addicted women's specific needs (child care, pregnancy, housing, and violence and others) are recommended. Finally, this article discusses the possible effect of sex-gender on placebo response in the light of the more significant recent literature evidencing that studies are urgently required in order to better understand the role of sex-gender on placebo mechanism and its impact on randomized clinical trials outcomes.

Sex-related differences of patient-controlled epidural analgesia for postoperative pain

Gender differences in pain modulation are evident but data are rare with regard to perioperative regional analgesia. The aim of the present analysis was to assess gender-related differences in pain ratings, analgesic consumption, and adverse events in a large group of patients treated with patient-controlled epidural analgesia (PCEA) after major surgery. Data from 14,988 adult patients (6506 women; 8482 men) receiving a PCEA between January 1998 and December 2009 were examined. Demographic data and postoperative measurements assessed by the Acute Pain Service, including total PCEA consumption, pain scores, and complications, were analyzed by using PASW Statistics (18.0; SPSS Inc, Chicago, IL, USA). Beyond standard descriptive analyses, gender-related differences were investigated using a stepwise multivariate analysis of variances. Postoperative pain scores during rest and movement were almost equal between men and women. However, women showed lower total PCEA consumption consistently throughout the 5-day observation period (relative reduction by 1.7%-10.2% compared to men; P=0.00). Total PCEA consumption did not interact with surgical site (abdomen, thorax, extremity) (P=0.379) or age (<50, 50-75, >75 years; P=0.330), but was influenced by body mass index (P=0.017) and vomiting (P=0.011). Furthermore, motor blockade was greater in females compared to males (P=0.000). In patients treated with PCEA, gender differences in numeric rating scale scores exist but are not clinically relevant. However, reduced total PCEA consumption in women might be a consequence of an increased incidence of motor blockade and vomiting; the latter point towards an opioid-free PCEA solution in female patients at high risk for vomiting.

Individual differences in morphine and butorphanol analgesia: a laboratory pain study

OBJECTIVE

Responses to opioid analgesics are highly variable, and the understanding of contributing factors is limited. This laboratory study was designed to examine the contributions of sex and race to inter-individual variability in response to opioids.

DESIGN

A randomized, double-blind, mixed design was implemented in the evaluation of analgesic response to a µ-opioid agonist and mixed agonist-antagonist, using three well-validated experimental pain assays (thermal, pressure, and ischemic).

SUBJECTS

Participants included a total of 142 healthy subjects (76 men/66 women), 119 non-Hispanic whites and 23 African Americans.

INTERVENTION

Three sessions of pain testing were completed prior to and following an intravenous administration of morphine (0.08 mg/kg), butorphanol (0.016 mg/kg), and placebo (saline) in counterbalanced order.

OUTCOME MEASURES

A change score was calculated from the difference between the pre-drug and postdrug values. Three separate change scores (morphine, saline, and butorphanol) were computed for each experimental pain variable. Mixed-model analyses of covariance were performed on analgesic change scores.

RESULTS

Significant sex differences emerged for predrug pain measures with minimal differences for race. Sex differences in opioid analgesia were not demonstrated. However, significant race differences and race X drug interactions emerged for thermal, pressure, and ischemic pain measures. The pattern of results generally indicated that for pressure and ischemic pain, African American subjects showed greater analgesic responses to both medications compared with non-Hispanic whites. For thermal pain threshold, butorphanol but not morphine analgesia was greater for African American vs non-Hispanic whites.

CONCLUSIONS

Findings are among the first to demonstrate race differences in a laboratory study of opioid analgesia.

Evaluation of menstrual cycle effects on morphine and pentazocine analgesia

Studies have demonstrated menstrual cycle influences on basal pain perception, but direct evidence of menstrual cycle influences on analgesic responses has not been reported in humans. Our aim was to determine whether the magnitude of morphine and pentazocine analgesia varied across the menstrual cycle. Sixty-five healthy women, 35 taking oral contraceptives (OC) and 30 normally cycling (NOC), underwent experimental pain assessment both before and after intravenous administration morphine (0.08mg/kg) or pentazocine (0.5mg/kg) compared to saline placebo. Both active drug and placebo were administered once during the follicular phase and once during the luteal phase. Measures of heat, ischemic, and pressure pain sensitivity were obtained before and after drug administration. Change scores in pain responses were computed to determine morphine and pentazocine analgesic responses, and medication side effects were recorded. The data were analyzed using mixed-model analyses of variance. NOC women showed slightly greater heat pain sensitivity in the follicular vs luteal phase, while the reverse pattern emerged for OC women (P=0.046). Also, OC women showed lower pressure pain thresholds compared to NOC women (P<0.05). Regarding analgesic responses, NOC women showed greater morphine analgesia for ischemic pain during the follicular vs the luteal phase (P=0.004). Likewise, side effects for morphine were significantly higher in NOC women in the follicular phase than in the luteal phase (P=0.02). These findings suggest that sex hormones may influence opioid responses; however, the effects vary across medications and pain modalities and are likely to be modest in magnitude. Limited menstrual cycle effects on baseline pain responses were observed; however, morphine analgesia and side effects were greater during the follicular phase.

Opioid chronopharmacology: influence of timing of infusion on fentanyl's analgesic efficacy in healthy human volunteers

Chronopharmacology studies the effect of the timing of drug administration on drug effect. Here, we measured the influence of 4 timing moments on fentanyl-induced antinociception in healthy volunteers. Eight subjects received 2.1 μg/kg intravenous fentanyl at 2 pm and 2 am, with at least 2 weeks between occasions, and 8 others at 8 am and 8 pm. Heat pain measurements using a thermode placed on the skin were taken at regular intervals for 3 hours, and verbal analog scores (VAS) were then obtained. The data were modeled with a sinusoid function using the statistical package NONMEM. The study was registered at trialregister.nl under number NTR1254. A significant circadian sinusoidal rhythm in the antinociceptive effect of fentanyl was observed. Variations were observed for peak analgesic effect, duration of effect, and the occurrence of hyperalgesia. A peak in pain relief occurred late in the afternoon (5:30 pm) and a trough in the early morning hours (5:30 am). The difference between the peak and trough in pain relief corresponds to a difference in VAS of 1.3–2 cm. Only when given at 2 am, did fentanyl cause a small but significant period of hyperalgesia following analgesia. No significant changes were observed for baseline pain, sedation, or the increase in end-tidal CO₂. The variations in fentanyl’s antinociceptive behavior are well explained by a chronopharmacodynamic effect originating at the circadian clock in the hypothalamus. This may be a direct effect through shared pathways of the circadian and opioid systems or an indirect effect via diurnal variations in hormones or endogenous opioid peptides that rhythmically change the pain response and/or analgesic response to fentanyl.