Relationship of pentazocine plasma levels to pharmacological activity in man

Evaluation of the abuse potential of difelikefalin, a selective kappa-opioid receptor agonist, in recreational polydrug users

Difelikefalin, a selective kappa‐opioid receptor agonist with limited central nervous system penetration, is being developed for the treatment of chronic pruritic conditions. This randomized, double‐blind, active‐ and placebo‐controlled, four‐way crossover study was designed to evaluate the abuse potential of difelikefalin in healthy recreational polydrug users. Using a 4 × 4 Williams design, nondependent adult users of opioids and hallucinogens (N = 44) were randomized to receive single intravenous (i.v.) injections of difelikefalin at supratherapeutic doses (5 and 15 mcg/kg); pentazocine (0.5 mg/kg), a schedule IV mu‐opioid partial agonist and kappa‐opioid receptor agonist; and placebo. The abuse potential of difelikefalin was compared with pentazocine and placebo using the maximal score (maximum effect [E_max]) of the Drug Liking visual analog scale (VAS; primary end point), along with multiple secondary end points of subject‐rated measures and pupillometry. Difelikefalin produced significantly lower Drug Liking VAS E_max, and lower peak positive, sedative, and perceptual effects compared with pentazocine. These effects of difelikefalin were small, brief, and not dose‐dependent, although marginally greater than those observed with placebo. Neither dose of difelikefalin elicited significant negative or hallucinogenic effects. On end‐of‐session measures of overall drug liking and willingness to take the drug again, difelikefalin did not differ from placebo, indicating subjects neither liked nor disliked the effects overall and did not feel motivated to take the drug again. Consistent with its lack of mu agonist activity, difelikefalin did not induce miosis compared with pentazocine. All treatments were generally well‐tolerated. This study indicates that difelikefalin presents a low potential for abuse.

AC electrokinetic platform for iontophoretic transdermal drug delivery

Iontophoretic and electroporation transdermal delivery modes of ionic drugs have been utilized in a number of clinical and biomedical devices. However, applications of these methods have been found challenging for the delivery of many non polar and high molecular weight clinically important drugs. The main goal of the present study is to investigate whether transdermal transport of non polar macromolecular drugs such as insulin and terbinafine can be safely enhanced as a result of their polarization and activation by AC electrokinetic forces. An in vitro delivery system was developed to simulate a clinical application, where transdermal non invasive delivery of medication through a biological membrane is motivated by a combination of AC electrokinetic and AC iontophoresis protocols generated on a device located external to the membrane. The developed method resulted in an average transdermal delivery of 57% of insulin and 39% of terbinafine during several minutes long delivery cycle, which is at least an order of magnitude improvement over the results reported for these drugs in the literature for various passive and active transdermal delivery protocols. For the proposed drug delivery model quantification of the amounts of transported drugs and their relationship to experimental parameters, such as AC voltage amplitude and frequency, treatment time, and membrane thickness were investigated. Experimental results validated a computational model simulating the effects of major electrokinetic forces on drug particle in non uniform AC electric field. The presented transdermal approach overcomes many limitations of existing drug delivery technologies, providing efficient, regulated, localized, non invasive and safe delivery method for high molecular weight non polar macromolecules such as insulin.

Effect of Permeation Enhancers on the in Vitro Percutaneous Absorption of Pentazocine1)

The effect of permeation enhancers on the percutaneous absorption of pentazocine (PTZ) was investigated in excised hairless mice using Franz diffusion cells in vitro. The enhancing effect on the percutaneous absorption of PTZ from the isopropyl myristate (IPM) solution system was improved with glyceryl monocaprylate (GEFA-C(8)), which is a kind of glycerol ester of fatty acid (GEFA). The flux of PTZ through the skin was ca. 4 times higher compared with IPM alone, while a less enhancing effect of glyceryl dicaprylate (GEFA-DiC(8)) and glyceryl tricaprylate (GEFA-TriC(8)) on the skin permeation of PTZ was found. Moreover, maximum enhancement of PTZ flux was observed with glyceryl monocaproate (GEFA-C(6)) among various alkyl chains (C(2)-C(18)) of monoglycerides. These results indicated that the IPM solution system combination with GEFA may be used to develop a transdermal formulation with improved skin permeation of PTZ.

Sex differences in opioid analgesia: clinical and experimental findings

Sex differences in analgesic responses to opioids have received increasing attention in recent years. This article examines the literature on sex differences in opioid analgesia, including the results of studies from the authors' own laboratories. In general, nonhuman animal studies suggest more robust opioid analgesic responses in males relative to females; however, the human studies completed to date seem to indicate greater opioid analgesia among females. The most consistent evidence of sex differences in analgesia comes from studies of kappa-agonist-antagonists administered to patients following oral surgery. These data indicate more robust analgesia in females, and dose-response characteristics suggest that these agents possess both analgesic and antianalgesic properties, and the agonists may produce these effects in different proportions for women versus men. In contrast, the data from laboratory pain models in humans suggest greater analgesic effects in women in response mu-opioid agonists but not kappa-agonist-antagonists. Multiple mechanisms may explain sex differences in opioid analgesia, including gonadal hormonal effects, pharmacokinetics and pharmacodynamics, genetic influences, balance of analgesic/antianalgesic processes, and psychological factors. However, the disparity of results obtained from different pain models--animals versus humans and clinical pain versus experimental pain in humans--suggests that the models themselves are mechanistically different. Additional investigation is warranted in order to further explicate the nature of sex differences in opioid analgesia and to elucidate the underlying mechanisms.

Investigation of transport mechanism of pentazocine across the blood-brain barrier using the in situ rat brain perfusion technique

To characterize pentazocine (PTZ) transport across the blood-brain barrier (BBB), the cerebrovascular permeability-surface area product (PS(inf)) of PTZ was determined by a well-established in situ rat brain perfusion technique. The uptake kinetics of PTZ by the rat brain exhibited saturability, which indicates the simultaneous mechanisms of carrier-mediated transport and passive diffusion. The kinetic parameters were estimated as follows: maximal influx rate (V(max)), 27.2 +/- 5.2 nmol/s/g brain; apparent Michaelis constant (K(m)) for the saturable component of PTZ uptake, 2.9 +/- 0.5 mM; nonsaturable uptake rate constant (K(d)), 1.5 +/- 0.3 microL/s/g brain. BBB transport of PTZ was significantly inhibited by cationic drugs such as diphenhydramine, propranolol, and eptazocine (a narcotic-antagonist analgesic), but not by choline, suggesting that the PTZ transport system is shared by cationic drugs. Furthermore, co-perfusion of verapamil caused a significant (two-fold) increase in the BBB permeability to PTZ. This finding indicates that PTZ may be a substrate of the endogenous BBB efflux transport system, P-glycoprotein. These findings demonstrate that the primary mechanism governing the uptake of PTZ by the brain is carrier-mediated transport, not passive diffusion.

Induction of glycerol phosphate dehydrogenase gene expression during seizure and analgesia

Using mRNA differential display, we found that the gene for NAD(+)-dependent glycerol phosphate dehydrogenase (GPDH; EC 1.1.1.8) is induced in rat brain following seizure activity. Northern blot and in situ hybridization analysis confirmed the differential display results; they also showed, in a separate model of neuronal activation, that after thermal noxious stimulation of the hind-paws, a similar increase in GPDH mRNA occurs in the areas of somatotopic projection in the lumbar spinal cord. Surprisingly, administration of analgesic doses of morphine or the nonsteroidal antiinflammatory drugs aspirin, metamizol (dipyrone), and indomethacin also increased GPDH mRNA levels in rat spinal cord. The opioid receptor antagonist naloxone completely blocked morphine induction of GPDH but had no effect on GPDH induction by noxious heat stimulation or metamizol treatment, implicating different mechanisms of GPDH induction. Nevertheless, in all cases, induction of the GPDH gene requires adrenal steroids and new protein synthesis, as the induction was blocked in adrenalectomized rats and by cycloheximide treatment, respectively. Our results suggest that the induction of the GPDH gene upon peripheral noxious stimulation is related to the endogenous response to pain as it is mimicked by exogenously applied analgesic drugs.

Clinical pharmacokinetics and pharmacodynamics of opioid analgesics in infants and children

Pain in childhood has not always been managed as actively as that in adults because of the limited amount of research available to provide guidelines for the management of paediatric pain. However, for many years now the pharmacokinetics and pharmacodynamics of opioid analgesics in infants and children have been studied intensively. Morphine is the standard for opioid analgesics and its pharmacology is the best studied in paediatric patients. During the neonatal period, the volume of distribution (Vd) appears to be smaller in neonates than in adults, but adult values are reached soon after the neonatal period. Although morphine is absorbed both orally and rectally, there is little information on the pharmacokinetics of morphine administered by these routes. The bioavailability of morphine after rectal administration appears to be highly variable. For all the opioid analgesics studied, the elimination of the opioids is slower in neonates than in adults. However, the rate of elimination usually reaches and even exceeds adult values within the first year of life. The high rate of drug metabolism means higher dosage requirements. In regard to the pharmacodynamics of opioid analgesics, infants and children do not appear to be more sensitive to the effects of opioids than adults. Thus, except for the neonatal period, the pharmacokinetics and pharmacodynamics of opioid analgesics are not markedly different from those of adults, and the risk of using opioids in infants and children is not higher.

HPLC separation of pentazocine enantiomers in serum using an ovomucoid chiral stationary phase

A stereospecific HPLC method was developed for the analysis of (-) and (+) pentazocine in human serum. Each enantiomer and the internal standard nalophine were isolated from serum using a liquid-liquid extraction procedure. Recoveries of 99.05 +/- 5.37 and 97.42 +/- 2.78% were obtained for (-) and (+) pentazocine, respectively. Resolution of the enantiomers was obtained by using an ovomucoid chiral stationary phase with a mobile phase of methanol:acetonitrile: 10 mM phosphate buffer, pH 5.8 (20:5.3:74.7 v/v/v). A resolution (Rs) value of 1.80 was obtained for the pentazocine enantiomers. Linear calibration curves were obtained in the 10-100 ng/mL range for each enantiomer in serum. The detection limit based on a signal-to-noise ratio of 3 was 5 ng/mL for each enantiomer in serum using fluorescence detection with excitation at 275 nm and emission set at 335 nm. The lowest quantifiable level was found to be 10 ng for each enantiomer. Precision and accuracy of the method were in the 3.8-4.8% and 1.3-4.2% ranges, respectively.

Pharmacokinetics and pharmacodynamics of pentazocine in children

Pharmacokinetics and ventilatory effects of a single intravenous dose of 0.5 mg/kg of pentazocine were studied in ten children aged 4 to 8 years after ophthalmic surgery. Elimination half-life (mean +/- S.D.) was 3.0 +/- 1.5 hr and clearance 21.8 +/- 5.9 ml/min./kg. The values for Vc, Vss and V beta were 0.73 +/- 0.21, 4.0 +/- 1.2 and 5.3 +/- 2.1 l/kg, respectively. The pharmacokinetic parameters were similar to those of adults. After administration of pentazocine decrease in ventilatory rate and oxygen saturation and increase in end-tidal carbon dioxide were relatively fast and steep. Oxygen saturation of four patients decreased below 90% and in one patient the decrease did not recover instantly and additional oxygen was given for 2 min. No patient needed assisted ventilation. Only clinically insignificant changes in heart rate and mean arterial pressure were observed. The duration of analgesia was 164 +/- 59 min. No serious side-effects appeared.

Pentazocine (Talwin) intoxication: report of 57 cases

Overdose of pentazocine (Talwin), an agonist/antagonist opioid analgesic, is relatively uncommon. Fifty-seven cases occurring over ten years are reported. Twenty-three patients (40%) had ingested only pentazocine and did not have the classic opioid toxidrome of CNS and respiratory depression with miosis. Most patients were awake, and no patient had a respiratory rate below 12/minute. Other findings included: grand mal seizures, hypertension, hypotonia, dysphoria, hallucinations, delusions, and agitation. Eleven of 23 patients received IV naloxone (0.4-2.4 mg), but only two showed improvement. Thirty-four patients (60%) had coingested pentazocine with one to five additional substances. Patients who had ingested pentazocine with alcohol, a sedative/hypnotic drug, or an antihistamine, showed increased toxicity, including apnea, deep coma, and recurrent seizures. One patient developed opioid pulmonary edema. One patient died. Three of five patients with coma and inadequate respirations responded to IV naloxone in doses of 0.4 to 1.2 mg.

Parenteral pentazocine: effects on psychomotor skills and respiration, and interactions with amitriptyline

The combined effects on performance and respiration of pentazocine (PZ) and amitriptyline (AMI) were evaluated in a double-blind cross-over study in 11 healthy students. After pretreatment for 1 week with AMI or placebo, on Day 8 the subjects received placebo or 50 mg p.o. AMI and 30 mg PZ or saline i.m. so that the final treatments were 1) placebo, 2) acute AMI 50 mg, 3) acute PZ, 4) subchronic AMI + acute PZ and 5) subchronic AMI. The subacute treatments were started at two-week intervals. Objective and subjective performance tests and respiratory function (minute volume, ETCO2) were measured. Parenteral PZ impaired sensory processing (digit symbol substitution, choice reactions) and extraocular muscle balance (Maddox wing) but left motor skills (tracking, tapping speed) unaffected. A single oral dose of AMI 50 mg affected both sensory and motor performance. The psychomotor effects of PZ were clearest at 1.5 h, and those of AMI at 3.5 h. Both drugs rendered the subjects drowsy, clumsy, and muzzy on visual analogue scales, but PZ also induced positive feelings, like contentedness and friendliness. PZ depressed respiration in terms of lowered minute volume and elevated ETCO2, and subchronic AMI increased this depression. The chemically assayed plasma concentrations of AMI and PZ were as expected; radioreceptor assay revealed low or negligible mu-opiate activity in plasma after PZ. The results suggest that AMI does not enhance the moderate psychomotor decrement produced by PZ. However, respiratory depression may be increased by their concomitant use.

Pentazocine

Published clinical studies and extensive experience has shown that pentazocine, the first of the practical agonist/antagonist analgesics, is a potent analgesic with wide application in clinical medicine. It has been shown to have a spectrum of pharmacological activity which has qualitative differences from pure opiate agonists and these have important implications in clinical medicine. Pentazocine can provide analgesia as great as the opiates including morphine and meperidine, but does not have the same effect on mood. It is, therefore, less effective than the opiates in those situations where an anxiolytic effect is desired. Conversely, it produces less CNS depression in particular with regard to respiratory depression and nausea and vomiting. It also does not have the same potential for producing hypotension. The parenteral administration of pentazocine produces rapid strong analgesia which is of less duration than with morphine or meperidine. The oral administration of pentazocine is less predictable with regard to response but in appropriate patients it is capable of providing a similar degree of analgesia to that achieved with parenteral pentazocine. The dependence liability of pentazocine is substantially less than that with the opiates, and where abuse of parenteral pentazocine alone has taken place, it has usually been in medical and paramedical personnel seeking a support for inadequate personalities. Though physical and psychic dependence to parenteral pentazocine is undoubtedly possible, its incidence is extremely low with regard to the extent of the therapeutic use of pentazocine.

Human pharmacokinetics of analgesics and methods for their determination in biological fluids

The main pharmacokinetic data of analgesics--biological half-lives, apparent volumes of distribution, total body clearances--obtained in humans, and their clinical relevance are summarized. Special emphasis has been given to the analytical methods used for the quantitative determination of these drugs in biological fluids.

A collection of therapeutic, toxic and fatal blood drug concentrations in man

In order to assess the significance of drug concentrations measured in clinical and toxicological investigations, it is essential that good collections of data are readily available. As a guide to interpreting findings, the present work provides a compilation of therapeutic, toxic and fatal blood concentration ranges of 298 drugs of interest to clinical pharmacologists, clinical toxicologists, and forensic toxicologists. Wherever possible, ranges are expressed concisely in terms of the maximum blood concentrations which account for 10, 50 and 90% of the data collected. They provide easy access to the most reliable information which relates the blood drug concentration to the biological response it produces. Where appropriate, the different toxic effects of a drug and/or the different degrees of severity of toxic symptoms associated with different drug levels are clearly defined. The original sources of all data used are provided to allow the analyst to obtain further analytical, pharmacokinetic and toxicological information should this be necessary. Those factors (e.g. age, capacity for drug metabolism, drug interactions, etc) which can modify the relationship between a drug concentration and the response it produces are briefly discussed.

Toxicological findings in deaths due to ingestion of pentazocine: a report of two cases

Two cases of fatal suicidal ingestion of pentazocine are presented. Toxicological findings in these deaths are compared to those of twelve similar pentazocine fatalities gleaned from various compilation of toxicology data. Pentazocine blood and liver concentrations in the presented cases were 3.3 and 9.2 mg/l, and 34 and 43 mg/kg, respectively. Blood and liver concentrations in references cases ranged from 0.8 - 38 mg/l and 3 - 197 mg/kg, respectively. The interpretation of toxicology findings following the ingestion of pentazocine is discussed.

Determination of pentazocine and tripelennamine in blood of T's and Blue addicts by gas-liquid chromatography with a nitrogen detector

A procedure for the quantitative determination of pentazocine (T's) and tripelennamine (Blues) in blood obtained from T's and Blues addicts is described. The underivatized drugs were analyzed by gas-liquid chromatography with a nitrogen detector. The retention times relative to mepivicaine (internal standard) on OV-17 at 220 degrees C were: tripelennamine 0.69 and pentazocine 1.77. The linear ranges of blood standards were: tripelennamine, 0.10-1.00 microgram/ml; pentazocine, 0.50-5.0 microgram/ml. For simultaneous analysis, the within-run and between-run CVs of tripelennamine were 5.6% (n = 23) and 13% (n = 12); and for pentazocine 5.2% (n = 23) and 9.9% (n = 12). Mean recoveries over the range of standards were: tripelennamine, 103% +/- 2.5% (n = 12); pentazocine 77.8% +/- 3.6% (n = 12).

Pharmacokinetics and mechanisms of action of analgesics in clinical pain

Due to recent interest in the development of drug assay techniques, the pharmacokinetics of many analgesics have been defined. In addition, mechanisms of action of the commonly used analgesics have been partly delineated, and currently accepted analgesic regimens and usages are being questioned. By considering both the pharmacokinetics and the mechanism of action of each of these analgesics, it would appear that only a few of the currently available agents are needed for the treatment of acute and chronic pain. Newer agents with reduced toxicity have been introduced but have resulted in little expansion of novel ways to interfere with pain. The recent discovery of the beta-endorphin system, the reevaluation of older agents, and the development of new agents that work at pain pathways other than the classical sites hold out the promise of alternative means of control of certain types of pain. An agent that has analgesic efficacy equivalent to morphine but with reduced toxicity is especially exciting in the development of new analgesics. An agent that, in addition, does not lead to intolerable psychomimetic reactions but instead addresses multiple aspects of treating the fear, pain, and tension triad of pain will be beneficial in acute pain but will especially enhance the spectrum of the control of chronic pain such as cancer, neuralgia and arthralgia.

Pharmacokinetics of parenteral paracetamol and its analgesic effects in post-operative dental pain

A double-blind, randomised, crossover trial was undertaken to compare the analgesic effects of a single dose of paracetamol (1000 mg i.v.) with placebo in the immediate post-operative period following removal of impacted lower third molars. There was no significant difference in the pain relief between paracetamol and placebo in the first hour following injection. Thereafter, there was significantly less pain (P less than 0.05) after treatment with paracetamol than after placebo. Plasma concentrations of paracetamol were measured and pharmacokinetic variables were determined. Over the four hour period of investigation there was no clear relationship between analgesia and paracetamol concentration in either central or peripheral compartments.

Pentazocine-blocked myogenesis in human foetal muscle cultures

A critical review of the published cases reports suggests that the muscle changes could be induced by Pentazocine by mechanisms other than local myotoxicity. The mechanism of myotoxicity in Pentazocine-myopathy remains uncertain and for this reason a tissue culture study was performed in order to investigate the close relationship between myopathy and Pentazocine. The effects of Pentazocine on the extent of myogenesis in human foetal muscle cultures were investigated. The phase contrast study, the light microscopy the quantitative assessment of myogenesis (the number of nuclei incorporated into myotubes were counted and expressed as a percentage of the total number of nuclei) showed a complete block of myogenesis in Pentazocine treated culture and a delayed fusion process was present in D-arabinofuranosylcytosine (Ara-C)-Pentazocine-treated cultures. The present preliminary data, however, suggest that muscle stem cells could participate in the replacement of skeletal muscle by fibrous tissue in neuromuscular syndrome induced by Pentazocine.

Plasma pentazocine radioimmunoassay

A sensitive and specific radioimmunoassay of dog and human plasma pentazocine is described. Rabbit antiserum and the second antibody method separated bound from free pentazocine. The radioimmunoassay employed an 125I-labeled radioligand and required extraction from the sample prior to quantitation. The method had a detection limit of approximately 200 pg/assay tube (1 ng/ml). The assay was used successfully to measure pentazocine in the plasma of beagle hounds given 0.3 mg of pentazocine/kg iv. The decline in plasma levels fitted a two-compartment body model with a 100-min mean overall half-life and a 3.2-liters/hr mean plasma clearance rate.

Kinetics of analgesic response in man; an example with two non-steroidal anti-inflammatory analgesic drugs

A double-blind, controlled trial is described in which a total of forty hospital in-patients suffering from severe post-operative pain were randomly allocated to treatment with one of two non-steroidal anti-inflammatory drugs, namely, either indoprofen which has a short half-life (two-hours) or naproxen which has a long half-life (thirteen hours). The drugs were administered orally on a single-dose basis. The doses used in this way were 300 mg of indoprofen or 250 mg of naproxen. Patients scored the severity of their pain on a five-point scale and these scores were recorded prior to and at fixed time intervals up to eight hours following administration of medication. No significant differences emerged between the two test drugs and the duration of the response was also found to be similar for the two compounds despite their very different plasma half-life values.

Protein binding and kinetics of drugs in liver diseases

Although the liver is the major site for drug biotransformation, the effect of hepatic dysfunction on drug disposition has not been consistent or predictable. Most early studies of drug kinetics in liver disease measured only half-life. Only in the past few years has it been realised that liver diseases can affect drug absorption, hepatic metabolism, tissue distribution, and protein binding, which complicate interpretation of any change, or lack of change in drug half-life. Furthermore, it is now apparent that the efficiency with which a drug is metabolised by the liver, the extent of binding to blood constituents, and the aetiology and stage of the hepatic disorder are each important in determining whether significant alterations in drug disposition will occur. A pharmacokinetic perfusion model which takes into account many of the above factors has been proposed, and appears to be useful for predicting changes in the disposition of rapidly metabolised compounds. Nevertheless, the state of knowledge about those factors which limit the rate of metabolism of individual drugs or classes of drugs in inadequate, and no general model or guidelines which are useful clinically have been developed. Patients with hepatic disorders may show increases or decreases in sensitivity independent of alterations in drug disposition. The clinician caring for such patients must be cautious about the use of any drugs, and rely heavily on careful patient observation to determine efficacy or toxicity.

The influence of smoking on the intersubject variation in pentazocine elimination

The cumulative urinary excretion over 24 h of pentazocine, under conditions of acidic urinary pH, has been measured in smokers and non-smokers using both male and female subjects (seventy subjects in total). A restricted urban population was studied. An overall three-fold inter-subject variation in elimination was observed. The cumulative urinary excretion of pentazocine was normally distributed in both smokers and non-smokers. Smokers metabolize 40% more pentazocine than non-smokers. It is concluded that induction is principally responsible for the observed subject variability.

Human sleep during chronic morphine intoxication

The sleep of 6 opiate addicts was studied for 11 nights during 3 phases of a chronic morphine cycle. The control phase consisted of 5 consecutive nights before morphine administration. The induction phase consisted of 1 night at 21-36 days after the onset of morphine administration, when the daily dose was 140-220 mg. The stable dose phase consisted of 5 consecutive nights after the subjects had received 240 mg of morphine daily for 8-19 weeks. No sleep could be studied during the withdrawal phase. Sleep was continuously monitored with EEG, EMG and EOG. Chronic morphine produces signs of a small but persistent sleep disturbance: delta sleep (early night) becomes less stable and shifts toward later in the night, waking state increases during the middle of the night, RME sleep (expecially its activated EEG without eye movements) decreases, the RMES cycle increases, and burst of delta activity (with mean duration of 5-6 sec) increase. Although this disturbance persists throughout the night, it is much less than that seen after single doses of morphine in a previous study. With chronic morphine, therefore, partial tolerance develops to the sleep disturbance produced by morphine. The small but persistent nocturnal arousal during chronic morphine contrasts with the sedation seen during chronic methadone. Both opioids produce an increase in delta bursts during chronic administration, which might be an EEG phenomenon specific to chronic opioid intake.

An analysis of the inter-subject variation in the metabolism of pentazocine

Significant inter-subject variation in the cumulative urinary excretion of pentazocine, following its oral administration, was observed. Individual variations in the rate of metabolic oxidation of pentazocine are responsible for the variations in the urinary excretion of pentazocine (24 h cumulative). Smoking did not affect the metabolism of the drug. Pharmacokinetic analysis of the urinary excretion rate of pentazocine, using an open three compartment model, indicated that the fractional metabolic clearance is correlated with the cumulative urinary excretion (24 h) of the drug under conditions of acidic urinary pH. A g.l.c. method for the determination of pentazocine in urine is described.

Distribution of pentazocine in blood and brain of the baboon following intravenous injection

1 In the baboon the blood levels of pentazocine between 1 and 60 min after intravenous injection of 0.5 mg/kg were measured by a gas chromatographic technique. From cerebral arteriovenous differences it was shown that the peak of the brain concentration occurred within 15 min and probably within 10 min of intravenous injection. At the time of peak concentration about 10% of the injected dose was in the brain, while the corresponding value at 60 min was 2%.2 The concentration of pentazocine in the brain was an order of magnitude greater than the concentration in cerebral venous blood both at 5 min and 60 min after injection. No major brain interregional differences were demonstrated. Cerebrospinal fluid from the cisterna magna did not yield values from which the cerebral concentration of pentazocine could be predicted.