Newer analgesics: with special reference to pentazocine

Opioid-induced Hallucinations: A Review of the Literature, Pathophysiology, Diagnosis, and Treatment

Despite their association with multiple adverse effects, opioid prescription continues to increase. Opioid-induced hallucination is an uncommon yet significant adverse effect of opioid treatment. The practitioner may encounter patient reluctance to volunteer the occurrence of this phenomenon because of fears of being judged mentally unsound. The majority of the literature concerning opioid-induced hallucinations arises from treatment during end-of-life care and cancer pain. Because the rate of opioid prescriptions continues to increase in the population, the rate of opioid-associated hallucinations may also conceivably increase. With a forecasted increase in the patient-to-physician ratio, opioid therapy is predicted to be provided by practitioners of varying backgrounds and medical specialties. Hence, knowledge of the pharmacology and potential adverse effects of these agents is required. This review seeks to increase awareness of this potential complication through a discussion of the literature, potential mechanisms of action, diagnosis, and treatment strategies.

Drug Profile: Fortral Suppositories

The traditional British resistance to the rectal administration of medicines is now slowly losing ground. That the patient's attitude has been reflected in the doctor's is surprising considering the obvious advantages of this route for patients unable to swallow tablets, prone to gastric irritation or suffering distress from frequent injections.

The recent availability of suppositories containing the powerful analgesic Fortral (pentazocine) is particularly welcome as it simplifies the control of severe pain in elderly, debilitated and incapacitated patients in hospital and at home.

Eleven Continental trials testifying to the effectiveness of Fortral Suppositories have been followed this year by two British papers (de Choisy 1973 and Flavell Matts 1973), whose authors both welcome the prospect of a form of potent analgesic that can be self-administered so easily even in the absence of a qualified attendant. One author (de Choisy 1973) concludes: ‘Fortral Suppositories provided good analgesia with a low incidence of side-effects. There were no reports of local irritation. The suppositories were well accepted as a source of treatment’.

Cardiovascular effects of intravenous pentazocine and cyclazocine in conscious, curarized-conscious, and anesthetized dogs

The cardiovascular effects of intravenous pentazocine and cyclazocine in dogs were studied under conscious, curarized-conscious (paralyzed by gallamine), and anesthetized states. In the conscious state, blood pressure and heart rate were dose-dependently increased by pentazocine (1, 2, 3 mg/kg) and to a lesser extent by cyclazocine (0.3 mg/kg). In all subsequent experiments on dogs, the results were obtained using 3 mg/kg pentazocine and 0.3 mg/kg cyclazocine. Pentazocine accelerated breathing, peaking at about 10 min, whereas cyclazocine reduced breathing to a minimum in 1 min, followed by a gradual recovery thereafter. In the curarized-conscious state, the blood pressure response to pentazocine was biphasic, namely an initial decrease followed by an increase; chronotrophic activity was stimulated. Pretreatment with either ganglionic or alpha andrenergic blocking agents not only significantly antagonized the pressory responses to the drug but also potentiated the initial decreases in blood pressure and unmasked a bradycardic component, but these parameters were not altered by 0.3 mg/kg naxalone. In open-chest anesthetized dogs, blood pressure, heart rate, contractility, and mean peripheral vascular resistance were simultaneously decreased by both pentazocine and cyclazocine, initially accompanied by increases in aortic blood flow. During the later stages of drug action, only the blood pressure and contractility were increased above control levels (biphasic effect). A comparison of blood pressure and heart rate responses to pentazocine in dogs kept under differing experimental conditions revealed that conscious dogs were more sensitive than curarized conscious and anesthetized animals to pentazocine action. In isolated guinea pig atria, the effect of adrenaline (0.1, 0.3, or 1 mg/mL) on the spontaneous breathing rate was significantly augmented by 10 mg/mL pentazocine (p < 0.02 for 0.3 g/mL; p < 0.01 for 0.1 g/mL adrenaline). In dogs, however, adrenaline (1 mg/kg)-induced increases in heart contractility, aortic blood flow, and blood pressure remained almost unaltered in the presence of pentazocine. We concluded that the abovementioned cardiovascular responses to pentazocine and cyclazocine are a consequence of the sum of the two following opposing effects: (i) an indirect reflex activation of sympathetic neuromediation in the periphery, and (ii) a direct membrane effect on the heart leading to bradycardia and a depression in myocardial contractility.

Total intravenous anaesthesia. A technique based on alphaxalone/alphadolone and pentazocine

Two hundred and eight patients were anaesthetised using incremental doses of intravenous alphaxalone/alphadolone (Althesin). Analgesia was provided by supplements of pentazocine, which also helped eliminate the excessive movements associated with pure Althesin anaesthesia. This is a total intravenous technique and consequently eliminates the problem of atmospheric pollution. It provides adequate anaesthesia for most minor surgical procedures.

Droperidol/fentanyl, diazepam/pentazocine: a comparison

Anaesthesia with a combination of diazepam and pentazocine is compared with the well established technique of neuroleptanaesthesia using droperidol and fentanyl. The former compared favourably, producing similar cardiovascular stability, rapid recovery of conciousness and postoperative analgesia.