Human pharmacology of narcotic antagonists

Ketamine and phencyclidine: the good, the bad and the unexpected

The history of ketamine and phencyclidine from their development as potential clinical anaesthetics through drugs of abuse and animal models of schizophrenia to potential rapidly acting antidepressants is reviewed. The discovery in 1983 of the NMDA receptor antagonist property of ketamine and phencyclidine was a key step to understanding their pharmacology, including their psychotomimetic effects in man. This review describes the historical context and the course of that discovery and its expansion into other hallucinatory drugs. The relevance of these findings to modern hypotheses of schizophrenia and the implications for drug discovery are reviewed. The findings of the rapidly acting antidepressant effects of ketamine in man are discussed in relation to other glutamatergic mechanisms.

Post-marketing experience with an opioid nasal spray for migraine: lessons for the future

In 1992 a nasal spray formulation of butorphanol, an opioid medication intended for pain relief, was marketed in the USA on an unscheduled basis. Only a few years later, amid widespread reports of abuse and dependence, primarily in migraine patients, its manufacturer voluntarily requested the Food and Drug Administration to reschedule the drug as a Schedule IV narcotic. The events surrounding this episode are reviewed, and four problem areas that might have contributed are identified: (i) inadequate review of previous experience with other formulations of butorphanol; (ii) failure to consider the impact of disease state and drug formulation on the risk of adverse events; (iii) the limited scope of clinical trials prior to approval; and (iv) aggressive marketing efforts. The implications of these lessons for future drug development and post-marketing surveillance in the migraine field are considered.

Management of chronic pain. Part I

Chronic pain is associated with substantial psychosocial and economic stress, coupled with functional loss and various levels of vocational dysfunction. The role of a pain center is to focus on chronic pain in a multidisciplinary, comprehensive manner, providing the patient with the most effective opportunity to manage his or her chronic disease syndrome. This article focuses on methods to manage many types of chronic pain and describes a broad range of pharmacologic and nonpharmacologic interventions and options available to the patient. Part I of this two-part monograph describes pharmacotherapeutic interventions and regional nerve blocks. Part II focuses on psychologic assessment and treatment and physical therapy. A multimodal management strategy offers patients the greatest improvement potential for specific chronic pain syndromes. Cognitive and behavioral therapies and physical therapies are described. This combination of therapies may provide patients with the skills and knowledge needed to increase their sense of control over pain. The integration of appropriate pharmacotherapeutic regimens, neural blockades, physical therapy, and psychologic techniques maximizes a patient's effectiveness in dealing with chronic pain. Three case studies are presented in Part II.

Transnasal butorphanol. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in acute pain management

Butorphanol is a synthetic opioid agonist-antagonist analgesic with a pharmacological and therapeutic profile that has been well established since its launch as a parenteral formulation in 1978. The introduction of a transnasal formulation of butorphanol represents a new and noninvasive presentation of an analgesic for moderate to severe pain. This route of administration bypasses the gastrointestinal tract, and this is an advantage for a drug such as butorphanol that undergoes significant first-pass metabolism after oral administration. The onset of action and systemic bioavailability of butorphanol following transnasal delivery are similar to those after parenteral administration. The analgesic efficacy of transnasal butorphanol was generally superior to that of placebo in clinical trials in patients with moderate to severe postoperative pain or migraine headache. Results from single trials indicate that transnasal butorphanol provides pain relief comparable to that of intramuscular pethidine (meperidine) in postsurgical pain and comparable to or greater than intramuscular methadone in migraine headache. Moderate to severe musculoskeletal pain also appears to be responsive to transnasal butorphanol on the basis of results from 1 small noncomparative study. Tolerability of transnasal butorphanol parallels that of the injectable form, with somnolence, dizziness, nausea and/or vomiting reported most frequently. Thus, transnasal butorphanol is a novel formulation of an established analgesic which appears suitable for the short term treatment of moderate to severe pain, especially in an ambulatory setting. Transnasal butorphanol is likely to provide an alternative to oral opioid analgesics, particularly in the presence of nausea or vomiting, or to parenteral opioids when the oral route of administration is not appropriate.

Butorphanol tartrate for partial reversal of oxymorphone-induced postoperative respiratory depression in the dog

A randomized, blinded, crossover study was designed to evaluate the respiratory, cardiovascular, and behavioral effects of butorphanol given postoperatively to oxymorphone-premedicated and surgically stimulated dogs. Nine healthy adult dogs were premedicated intramuscularly with atropine (0.04 mg/kg), acepromazine (0.10 mg/kg), and oxymorphone (0.2 mg/kg). Anesthesia was induced with thiamylal (12 mg/kg) and maintained with halothane in oxygen. According to the protocol of a concurrent study, all dogs had percutaneous endoscopic gastrostomy (PEG) feeding tubes placed during the first anesthetic episode and removed during the second anesthetic episode. All dogs received postoperatively either butorphanol tartrate (0.2 mg/kg) or an isovolumetric dose of saline placebo, both given intravenously. Respiratory rate (RR), tidal volume (TV), minute ventilation (MV), end-tidal CO2 concentration (ETCO2), heart rate (HR), and indirect diastolic (DP), systolic (SP) and mean arterial (MAP) blood pressures were measured at times 0, 2, 5, 10, 20, 40, 80, and 120 minutes after injection. The time from injection of the test drug until extubation was recorded. RR, MV, HR, and DP were significantly (P < .05) increased, while ETCO2 was significantly decreased, for a minimum of 30 minutes in butorphanol-treated dogs compared with saline controls. TV, SP, and MAP were transiently (< or = 15 minutes) increased in butorphanol-treated dogs compared with saline controls. There was no significant difference between the times to extubation in the butorphanol-treated dogs versus the saline control dogs.

History of abuse liability testing in humans

Clinical testing for drug abuse liability began as part of a collaborative effort to develop non-addicting substitutes for morphine. Physical dependence capacity and euphorigenic potential were identified as the potent effects of morphine leading to abuse; quantitative measures were developed for these effects. Drugs were evaluated for morphine-like effects using principles of bioassay. In recent years, the alterations in mood, feeling, thinking, and perception induced by drugs (subjective effects) are viewed as the effects leading to reinforcement of drug-taking behavior and to abuse. The same procedures and methods developed for assessing these effects with opioids have subsequently been applied to other classes of drugs. At present, human drug abuse liability testing methods exist for opioids, stimulants, sedative hypnotics, serotonin agonist and antagonists, nicotine, alcohol, and caffeine.

Effects of the analgesic agent tramadol in normal and arthritic rats: comparison with the effects of different opioids, including tolerance and cross-tolerance to morphine

The effects of the analgesic agent tramadol (0.1-1 mg/kg i.v.) were compared to those of the mixed agonist-antagonist analgesics nalbuphine (1 mg/kg i.v.) and buprenorphine (3 micrograms/kg i.v.) in the vocalization threshold to paw pressure test. Normal and Freund's adjuvant-induced arthritic rats were used. We have shown previously that these animals used as a model of clinical pain exhibit an enhanced sensitivity to morphine (0.1-1 mg/kg i.v.), with a rapid development of tolerance after repetitive low doses, a response not observed in normal rats. In the present study, the antinociceptive effects of tramadol, buprenorphine and nalbuphine were enhanced (by 2- to 5-fold) in arthritic compared to normal rats. In this model, these effects were significantly reduced by a dose of naloxone (0.1 mg/kg i.v.) that completely antagonized the effect of morphine. In this model, the antinociceptive effect of tramadol (1 mg/kg i.v.) was comparable to that of nalbuphine (1 mg/kg i.v.), buprenorphine (3 micrograms/kg i.v.) and morphine (1 mg/kg i.v.). Repeated administration of low doses of tramadol twice daily for 4 days to arthritic rats did not induce tolerance, in contrast to nalbuphine, buprenorphine, and morphine. In addition, no cross-tolerance between tramadol and morphine was observed in these animals.

Opioid agonist-antagonist drugs in acute and chronic pain states

The agonist-antagonist opioid analgesics are a heterogeneous group of drugs with moderate to strong analgesic activity comparable to that of the pure agonist opioids such as codeine and morphine but with a limited effective dose range. The group includes drugs which act as an agonist or partial agonist at one receptor and an antagonist at another (pentazocine, butorphanol, nalbuphine, dezocine) and drugs acting as a partial agonist at a single receptor (buprenorphine). These drugs can be classified as nalorphine-like or morphine-like. Meptazinol does not fit into either classification and occupies a separate category. Pentazocine, butorphanol and nalbuphine are weak mu-antagonists and kappa-partial-agonists. All three drugs are strong analgesics when given by injection: pentazocine is one-sixth to one-third as potent as morphine, nalbuphine is slightly less potent than morphine, and butorphanol is 3.5 to 7 times as potent. The duration of analgesia is similar to that of morphine (3 to 4 hours). Oral pentazocine is closer in analgesic efficacy to aspirin and paracetamol (acetaminophen) than the weak opioid analgesics such as codeine. Neither nalbuphine nor butorphanol is available as an oral formulation. At usual therapeutic doses nalbuphine and butorphanol have respiratory depressant effects equivalent to that of morphine (though the duration of such effects with butorphanol may be longer). Unlike morphine there appears to be a ceiling to both the respiratory depression and the analgesic action. All of these 3 drugs have a lower abuse potential than the pure agonist opioid analgesics such as morphine. However, all have been subject to abuse and misuse, and pentazocine (but not the others) is subject to Controlled Drug restrictions. Buprenorphine is a potent partial agonist at the mu-receptor, and by intramuscular injection is 30 times as potent as morphine. A ceiling to the analgesic effect of buprenorphine has been demonstrated in animals and it is also claimed in humans. However, there are no reliable data available to define the maximal dose of buprenorphine in humans. A practical ceiling exists for sublingual use in that the only available formulation is a 2 micrograms tablet and few patients will accept more than 3 or 4 of these in a single dose. The duration of analgesia is longer than that of morphine, at 6 to 9 hours. There have been suggestions that buprenorphine causes less respiratory depression than morphine, but viewed overall it appears that in equianalgesic doses the 2 drugs have similar respiratory depressant effects.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacologic interventions for the treatment of opioid dependence and withdrawal

This article discusses current pharmacologic methods in the treatment of heroin dependence and withdrawal. Methadone hydrochloride, the most commonly used opiate agonist, is used for both withdrawal and maintenance therapy. However, it produces dependence and withdrawal results upon abrupt discontinuation. Other opiate agonists including L-alpha acetyl methadyl (LAAM) and propoxyphene napsylate have been used for both withdrawal and maintenance therapy. LAAM is currently available only as an investigational agent and propoxyphene is easily accessible but has been associated with hallucinations and dysphoria at high doses. Alpha 2-adrenergic agonists decrease opiate withdrawal symptoms by decreasing the central adrenergic hyperarousal that is associated with withdrawal. Clonidine effectively attenuates but does not totally eliminate withdrawal symptoms. Other alpha 2-adrenergic agonists (e.g., lofexidine hydrochloride, guanfacine hydrochloride, and guanabenz) have undergone only preliminary investigations. Although alpha 2 agonists effectively decrease most withdrawal symptoms they often cause hypotension. Buprenorphine hydrochloride is a partial opiate agonist that shows some promise in the treatment of the heroin-dependent population. It attenuates opiate craving and causes only minimal withdrawal upon abrupt discontinuation. Because it is well accepted by the heroin-dependent population, however, it may ultimately become an abused substance. Naltrexone is a potent, orally acting opiate antagonist that blocks all opiate-agonist effects and causes no euphoria. Unfortunately, it has not been well accepted by the heroin-dependent population. Scant research has been conducted concerning the use of adjunctive medications during opioid withdrawal.

Opiate dependence alters central reward of nalbuphine or pentazocine plus tripelennamine

The threshold lowering effects of the coadministration of tripelennamine plus nalbuphine or tripelennamine plus pentazocine on the threshold for rewarding electrical intracranial stimulation, a model of drug-induced euphoria, was determined in rats physically dependent to morphine. Although tripelennamine plus nalbuphine had threshold-lowering effects similar to tripelennamine plus pentazocine in non-opiate-dependent subjects, tripelennamine plus nalbuphine failed to lower the threshold for rewarding stimulation in morphine-dependent animals. To the extent that these data may be applied to human addicts, it suggests that opiate-dependent addicts are unlikely to use the combination of tripelennamine plus nalbuphine but are likely to use tripelennamine plus pentazocine.

Dezocine. A preliminary review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy

Dezocine is an analgesic agent with opioid agonist and antagonist activity. After parenteral administration of therapeutic doses it is approximately equipotent with morphine, and has proved at least as effective an analgesic as morphine, pethidine (meperidine) and butorphanol in moderate to severe postoperative pain. However, preliminary pharmacodynamic data indicate that the ceiling of analgesic activity of dezocine occurs at a higher level of analgesia than that of reference agonist/antagonist agents. Also, the drug exhibited a morphine-like degree of anaesthetic-sparing activity in animals. Although long term data are very limited, single doses of dezocine are well tolerated, with mild and transient sedation and gastrointestinal upset the principal adverse effects. As with some other agonist/antagonist analgesics, a 'ceiling' effect to dezocine-induced respiratory depression occurs with increasing dosage, beyond which further depression has not been observed. In single analgesic doses, however, dezocine is a slightly more potent respiratory depressant than morphine. Clinically important haemodynamic changes have not been observed with usual analgesic doses of dezocine. As an agonist/antagonist opioid, the dependence liability of dezocine would be expected to be lower than that of pure agonist opioids, but extended clinical use is required before more definitive conclusions can be drawn in this regard. Unlike older drugs of its type, dezocine produced opiate-like subjective effects and was identified as morphine-like by drug abusers. Thus, provided the promising conclusions of currently available clinical studies are confirmed with its wider use, dezocine should be a useful additional agent for the treatment of moderate to severe postoperative pain.

Interactions between pentazocine and tripelennamine on autonomic and nociceptive measures in the dog

Pentazocine and tripelennamine, which have been abused in combination by humans, were evaluated for pharmacologic interactions on autonomic, behavioral, and antinociceptive measures in chronic spinal dogs. Pentazocine (0.31-5 mg/kg, IV) produced miosis, hypothermia and antinociception which was mediated by spinal and supraspinal reflexes; these effects were antagonized by naltrexone. Tripelennamine (0.63-2.5 mg/kg, IV) elicited mydriasis, hyperthermia and antinociception; these effects were not blocked by naltrexone. Tripelennamine produced antinociception only on the supraspinally-mediated skin twitch reflex. Interactions between pentazocine and tripelennamine varied depending on the response measured. Effects of both drugs on pupils were additive. Temperature effects were infra-additive, with the hyperthermic effects of tripelennamine predominating over the pentazocine hypothermia, resulting in a complete physiologic antagonism of pentazocine hypothermia. Antinociception, measured by flexor reflex depression, represented only the effect of pentazocine, whereas skin twitch reflex antinociception reflected either infra-additive or additive properties. The coadministration of nonconvulsive doses of pentazocine and tripelennamine produced seizures indicating a potentiated adverse interaction. In summary, the patterns of the pentazocine-triplennamine interactions were complex and the effects of tripelennamine could not be attributed to opioid activity.

Mode of potentiating action of cocaine in morphine analgesia

The mechanism of antinociceptive interactions among morphine, cocaine and alcohol was studied in mice, guinea pigs and rabbits. In the tail-pressure test in mice, cocaine and alcohol alone showed almost no antinociceptive effects at doses up to 8 mg/kg, s.c., and 4 g/kg, respectively. Alcohol at 2 g/kg, i.g., also did not influence the effect of morphine, while cocaine at 4 mg/kg, s.c., significantly potentiated the antinociceptive effects of not only morphine but also pentazocine. In an analysis of serum and brain concentration levels of morphine in mice, when morphine and cocaine were simultaneously administered at 2 mg/kg, s.c., and 4 mg/kg, s.c., respectively, both serum and brain levels of morphine showed neither increase nor decrease in comparison with the levels in mice administered morphine alone. In myenteric plexus-longitudinal muscle preparations of isolated guinea pig ileum, 1 microM cocaine enhanced the agonistic effects of both pentazocine and ethylketocyclazocine. Furthermore, cocaine as well as ethylketocyclazocine showed naloxone-reversible agonistic effects in isolated rabbit vas deferens. These results indicate that cocaine may potentiate the antinociceptive effects of morphine and pentazocine by acting on the kappa-opioid receptors as an agonist.

Effects of buprenorphine in heroin addicts

Twelve heroin addicts on the 8th day after withdrawal, and 8 healthy volunteers were given a single i.m. injection of buprenorphine 0.6 mg and their subjective response rated on 10 psychological variables. Pre-injection rating differed significantly between addicts and controls on 7 variables out of 10. Following buprenorphine more subjective changes were noted in the control group which became more calm, depressed, more aware of the environment, sleepy, tired, intoxicated, dizzy and nauseated. The drug addicts reported changes only in 2 variables (less tense and dysphoric) but otherwise showed no significant changes. These findings support the notion that buprenorphine induces low or normalizing effects in heroin addicts. This drug might thus be suitable for maintenance therapy in opiate addiction.

The pharmacokinetics of intravenous, intramuscular, and subcutaneous nalbuphine in healthy subjects

The pharmacokinetics of intravenously, intramuscularly, and subcutaneously administered nalbuphine were studied in three parallel groups of 12 healthy volunteers each. The subjects received single doses of 10 mg and 20 mg of nalbuphine separated by a one week washout period. Blood specimens were obtained up to 15 h after dosing for determination of nalbuphine. Mean plasma nalbuphine concentrations 5 min after intravenous administration of 10 or 20 mg were 39 and 73 ng/ml, respectively. The mean maximum plasma concentrations (Cmax) after intramuscular or subcutaneous administration of nalbuphine 10 mg were 29 and 31 ng/ml, respectively. Mean Cmax values after 20 mg doses were 60 and 56 ng/ml. Mean Cmax occurred 30 to 40 min after nalbuphine administration. The mean elimination half-lives of parenterally administered nalbuphine ranged between 2.2 and 2.6 h, regardless of dose given or route administered. The mean absolute bioavailability was 81% and 83% for the 10 and 20 mg intramuscular doses, respectively, and 79% and 76% following 10 and 20 mg of subcutaneous nalbuphine. The mean volumes of distribution (Vss) of the intravenously administered drug were 290 and 274 l and the mean systemic clearances were 1.6 and 1.5 l/min following administration of 10 and 20 mg doses, respectively. Intramuscular and subcutaneous nalbuphine appear to be interchangeable based on the similarities in Cmax, mean times until maximum concentration, mean AUC data, and absolute bioavailabilities.

The effectiveness of nalbuphine and hydroxyzine for the emergency treatment of severe headache

The present treatment for acute attacks of headache is empiric. Intramuscular nalbuphine (Nubain) and hydroxyzine (Vistaril) were assessed for pain relief in a prospective, double-blind clinical trial. Ninety-four patients were assigned randomly to treatment groups receiving nalbuphine 10 mg, nalbuphine 10 mg plus hydroxyzine 50 mg, hydroxyzine 50 mg, or placebo. The treatment groups were found to be adequately homogenous with regard to age, sex, type and duration of headaches, and history of prior narcotic use. All data were analyzed by one-way analysis of variance. Patients who had headaches diagnosed as other than classic migraine had significantly greater pain relief with nalbuphine compared to placebo (P less than .01). The combination of nalbuphine and hydroxyzine was not significantly more effective than other treatment groups. In 20 patients with classic migraine, none of the treatment regimens significantly outperformed placebo. There were no clinically significant adverse effects attributed to the study drugs. These findings are similar to others that showed a lack of efficacy of kappa receptor agonists in classic migraineurs. Nalbuphine appears to be clinically useful in other types of severe headache. This study does not support the routine addition of hydroxyzine for presumed synergistic effect.

Oral ciramadol: a new analgesic for postoperative pain

Ciramadol, a new synthetic narcotic agonist-antagonist analgesic, was compared in 30 and 60 mg doses with pentazocine 50 mg, aspirin 650 mg, and placebo in the treatment of 153 patients with postoperative pain. All drugs were administered between six and 72 hours after surgery. Analgesic efficacy was assessed for six hours after study drug administration using verbal pain intensity, analog pain intensity, and verbal pain relief scales. Significantly (P less than .05) higher analgesic efficacy scores were seen with ciramadol 30 mg than with pentazocine 50 mg and placebo at most of the evaluation points. Doses of ciramadol 30 mg were significantly (P less than .05) more effective than aspirin 650 mg at several time periods, and ciramadol 60 mg was better than pentazocine and placebo at several evaluation times. The 30-mg dose of ciramadol was generally more effective than the 60-mg dose. The mean six-hour cumulative sum of pain intensity difference scores, total pain relief scores, and sum of pain analog intensity difference scores showed that the best analgesic response occurred in the ciramadol 30 mg group, followed by the ciramadol 60 mg, aspirin 650 mg, pentazocine 50 mg, and placebo groups. Side effects were rare and mild. There were no medically important changes in vital signs in any treatment group.

Review of domiciliary consultations for pain relief

Three hundred consecutive requests for a domiciliary visit for pain relief were reviewed to assess the type of case referred by general practitioners and what treatment was instituted. Two hundred and thirty one (77%) were requested for lumbago/sciatica. In total 179 caudal epidurals and 49 other injections were performed in the patient's home. The safety of the procedures are discussed emphasising careful history taking, physical examination and meticulous attention to injection techniques as 12 patients (7%) were wrongly diagnosed as suffering from lumbago and sciatica from the 231 referred with that diagnosis.

Buprenorphine versus morphine. A comparison of intra-operative and postoperative analgesia

A randomised double-blind trial comparing morphine and buprenorphine and postoperative analgesia combined with droperidol was conducted in 60 patients. Compared with morphine, taken as the standard analgesic, buprenorphine was shown to be a satisfactory analgesic for major surgery, with no difference in the incidence of unwanted effects.

Nalbuphine

Nalbuphine is a potent analgesic with a low side effect and dependence profile in animals and man. Nalbuphine is distinguished from other agonist/antagonist analgesics in having greater antagonist activity and fewer behavioral effects at analgesic doses than pentazocine, butorphanol or buprenorphine. At equi-analgesic doses, nalbuphine is quantitatively similar to nalorphine in regard to its large ratio of antagonist to analgetic activity. Clinical studies have confirmed this balance of strong antagonist to analgesic activity. Nalbuphine has been shown to effectively antagonize the respiratory depressant activity of narcotic analgesics while concomitantly adding to their analgetic responses. Unlike nalorphine or pentazocine, nalbuphine produces few overt behavioral or autonomic effects in animals at doses over 300 times its analgesic range. These findings are confirmed by clinical results which show that nalbuphine produces few psychotomimetic effects, even at elevated dose levels, in contrast to nalorphine or pentazocine. Nalbuphine produces limited respiratory depression in animals and in man. Significant cardiovascular effects have not been found. Nalbuphine was found to produce significantly less inhibition of gastrointestinal activity than any of the clinically useful narcotic or agonist/antagonist analgesics tested in animals. Nalbuphine's analgetic effects are reversed by naloxone doses similar to those which reverse nalorphine's agonist effects. Results in this and other tests suggest that nalbuphine is primarily a kappa-agonist/mu-antagonist analgesic. Unlike pentazocine or buprenorphine, nalbuphine does not suppress the narcotic abstinence syndrome in partly-withdrawn morphine-dependent animals or man. Rather, due to nalbuphine's strong antagonist activity, analgesic-range doses of nalbuphine severely exacerbate the withdrawal syndrome in partly-withdrawn mice, monkeys and humans. Nalbuphine also precipitates a strong abstinence response in non-withdrawn morphine-dependent animals and man. In post-addict humans, analgesic-range doses of nalbuphine are perceived as minimally morphine-like, but higher doses are judged to be progressively more nalorphine-like (i.e. dysphoric), which further limits nalbuphine's abuse potential in drug-seeking individuals. Primary dependence studies have demonstrated that physical dependence is possible at high dose levels that produce marked side effects. Other studies show that dependence is unlikely to be of significance within nalbuphine's usual analgesic range. Six-month studies in patients with chronic pain have confirmed that analgesic tolerance or physical dependence is uncommon.(ABSTRACT TRUNCATED AT 400 WORDS)

The relative analgesic efficacy of propiram fumarate, codeine, aspirin, and placebo in post-impaction dental pain

To evaluate the analgesic efficacy of orally administered 50 mg propiram fumarate, 650 mg aspirin, 60 mg codeine phosphate, and placebo in acute post-impaction dental pain, 159 patients with moderate or severe pain were randomly allocated to the four treatments in this single-dose double-blind, stratified, parallel-group study. A research nurse questioned the patients at 1/2 hour and hourly for 6 hours after medicating. A standard format was used to question subjects about their pain intensity and relief from the starting pain. Propiram, 50 mg, produced a level of analgesia approaching that of 650 mg aspirin in peak effect, total effect, and duration of action and was statistically superior to 60 mg codeine and placebo for every measure of analgesic efficacy. Several mild adverse effects were observed; however, they appeared to be evenly distributed among the active treatments.

Nalbuphine. A preliminary review of its pharmacological properties and therapeutic efficacy

Nalbuphine is an agonist/antagonist analgesic. After parenteral administration of 'usual' doses it is approximately equipotent in analgesic activity to morphine on a weight basis. In studies in patients with moderate to severe pain, usually following surgery, the characteristics of analgesia with nalbuphine were comparable to those seen with equianalgesic doses of morphine or pentazocine. It also appears to produce satisfactory anaesthesia when used as a component of a 'balanced' anaesthesia technique, although a relatively low 'ceiling' effect for reduction of anaesthetic requirements with nalbuphine may limit its usefulness in this regard. As with other agonist/antagonist analgesics, a 'ceiling' effect to nalbuphine-induced respiratory depression is also seen, beyond which further depression does not readily occur. However, with usual analgesic doses, respiratory depression seen with nalbuphine is comparable to that with morphine. Important haemodynamic changes have not occurred after usual doses of nalbuphine, even in patients with cardiac disease. Like other agonist/antagonist analgesic drugs, the abuse potential of nalbuphine seems relatively low, but only wider clinical use for longer periods can establish this with certainty. Thus, nalbuphine appears to offer a useful alternative to morphine in patients with moderate to severe pain.

Analgesic effects of oral propiram fumarate, codeine sulfate and placebo in postoperative pain

Our purpose was to evaluate the analgesic efficacy and safety of single oral doses of propiram fumarate 50 mg, codeine sulfate 60 mg and placebo in the relief of moderate to severe postoperative pain. One hundred and twenty patients completed a randomized, double-blind, single-dose, stratified, parallel-groups trial and were observed for either 4 or 6 hours. Based upon each of the summary efficacy measures--SPID, % SPID and TOTAL--propiram and codeine were approximately equally effective and both were statistically superior to placebo. Propiram was significantly more effective than codeine at hour 5 for Pain Intensity Difference. Two adverse effects were attributed to propiram. Propiram fumarate 50 mg is an effective oral analgesic similar to codeine sulfate 60 mg, with the possibility of a longer duration of action.

Comparative effects and analgesic efficacy of the agonist-antagonist opioids

Pentazocine, butorphanol, nalbuphine, and buprenorphine are mixed agonist-antagonist opioids that are effective analgesics, with less abuse potential than the agonists morphine, propoxyphene, and codeine. The dual properties of the agonist-antagonists are largely explained by their varying actions at the postulated three types (mu, chi, and sigma) of opioid receptors. The agonist-antagonists are classified as either morphine-like or nalorphine-like, based on their acute effects and withdrawal symptoms after chronic dosing. Buprenorphine is morphine-like, while the other drugs are nalorphine-like. These agents vary in the duration of analgesia, with pentazocine having a mean action of three hours and buprenorphine greater than six hours. The hemodynamic effects of nalbuphine and buprenorphine generally resemble those of morphine, while pentazocine and butorphanol increase cardiac workload, blood pressure, and pulmonary artery pressure. The agonist-antagonists have ceilings for respiratory depression, whereas the agonists produce dose-dependent depression. Agonist-antagonists generally produce less increase in biliary ductal pressure than does morphine. The major clinical limitations are that agonist-dependent patients may experience unpleasant subjective effects, when treated with the agonist-antagonists, and the nalorphine-like agents can produce psychotomimetic effects. More clinical experience is needed to rank the abuse potential within this group of opioids. The newer agents are being studied for oral use in acute and chronic pain.

Double-blind, multiple-dose comparison of buprenorphine and morphine in postoperative pain

The analgesic profile and side-effects of buprenorphine 0.3 mg and morphine 10 mg intramuscularly were compared postoperatively in a double-blind, non-crossover, multiple-dose study. When the patient complained of moderate to severe postoperative pain after halothane-relaxant anesthesia for upper abdominal surgery, the first test dose of either drug was given. Subsequent similar doses of buprenorphine 0.3 mg or morphine 10 mg were given when required (maximum ten doses). The first dose of both drugs gave an equal decrease in pain intensity, suggesting a relative potency of 33:1 for both buprenorphine/morphine. A mean of 0.51 mg buprenorphine or 17 mg morphine had to be administered for satisfactory initial analgesia. Thereafter, the next analgesic dose was required a mean of 10.3 h after buprenorphine compared to 5.9 h after morphine (P less than 0.01). Significantly (P less than 0.01) fewer analgesic doses (mean 5.6) were needed in the buprenorphine group within the first 48 h postoperatively as compared to the morphine group (mean 7.3). A more pronounced mean decrease in the respiratory rate was observed after buprenorphine, but the mean minimum respiratory rates did not differ significantly from each other. Other effects of the two drugs on vital signs were similar. The incidence of other side-effects was fairly similar after both analgesics. The patients' subjective appraisal favoured buprenorphine.

Mixed agonist-antagonist opiates and physical dependence

1 General methods (chronic, subacute and acute) for assessing physical dependence potential, abstinence precipitating capacity and abstinence preventing activity are briefly presented. 2 Direct dependence experiments indicate that, in general, mixed agonist-antagonist analgesics have relatively lower physical dependence potentials than pure agonist analgesics. That of buprenorphine seems to be particularly low in various animal species. 3 When substitution techniques are used, the dependence potential of buprenorphine seems to be somewhat more developed than with direct dependence techniques. 4 Among various agonists (morphine, methadone and etorphine), antagonists (naloxone, naltrexone and diprenorphine) and mixed agonist-antagonists (pentazocine, butorphanol and buprenorphine), buprenorphine is the most potent and the longest acting drug in preventing precipitated abstinence in mice, rats and dogs. 5 The low physical dependence potential of buprenorphine may result in part from the very slow dissociation of the complex it forms with opiate receptors. This potential might be underestimated when precipitated abstinence methods are used, as naloxone would displace buprenorphine from its receptors only to a very limited extent. New means of evaluating dependence by more direct means need to be developed. 6 Overall, the properties of mixed agonists in general justify their use as analgesics with lower physical dependence potential than the pure opiates and further, those of buprenorphine seem to indicate its possible utility for the treatment of opiate addiction.