Pethidine clinical studies

In the earliest clinical studies, in 1970, vertigo was the side effect most commonly observed, being seen in some 5% of cases. Since then the incidence of this side effect, which is more prone to occur in the erect position, has been variously reported to be between S% and 20% in a comparative study against pethidine, 2 of 10 conscious patients complained of dizziness after receiving 1.5 mg/kg of tilidine parenter-ally (70 ). Other acute side effects have been found to be less marked than with pethidine nausea and vomiting occur occasionally, but there is apparently little or no... 

Pentazocine has been successfully used to relieve labour pain [201] and its obstetric use in place of pethidine is favoured by,its apparent inferior ability to pass the placental barrier [206]. A clinical trial of (+)- and (-)-pentazocine adds to the rare number of examples in which optical enantiomorphs have been evaluated [207]. In post-operative patients, response to 60 mg of the dextro isomer was less than that to 5 mg of morphine, while 25—29 mg of (-)-pentazocine was as effective as 10 mg of morphine. Hence most of the activity of the race-mate resides in the laevo isomer, as anticipated from results in animals [208]. Several studies of the distribution, excretion and metabolism of pentazocine have been made. Peak levels of the tritium-labelled drug (and its c/s-3-chloroallyl analogue) were present in the C.N.S. of a cat within 40 minutes of intramuscular administration [209], the comparable figure for morphine being 2 hours [210]. 

Clinically and statistically significant respiratory depression can occur within 1 minute of the start of a meptazinol infusion 1 mg/kg. Respiratory depression was less than after pethidine 1 mg/kg, but more than after 0.5 mg/kg (2). Other studies have confirmed these effects. In 49 patients who received either PCA with meptazinol (20 mg bolus, maximum 120 mg/hour) or morphine (2 mg bolus, maximum 12 mg/hour) after major orthopedic surgery, there was a tendency for more patients receiving meptazinol to have obstructive apnea and central apnea. 

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