Pentazocine action

Naltrexone completely blocks the effects of IV opiates, as well as drugp with agonist-antagonist actions (butorphanol, nalbuphine, and pentazocine). The mechanism of action appears to be the same as that for naloxone... 

Uses Obesity Action Blocks uptake of norepinephrine, serotonin, dopamine Dose 10 mg/d PO, may to 5 mg after 4 wk Caution [C, -] w/ SSRIs, Li, dextromethorphan, opioids Contra MAOI w/in 14 d, uncontrolled HTN, arrhythmias Disp Caps SE HA, insomnia, xerostomia, constipation, rhinitis, tach, HTN Interactions T Risk of serotonin synd W/ dextromethorphan, ergots, fentanyl, Li, meperidine, MAOIs, naratriptan, pentazocine, rizatriptan, sumatriptan, SSRIs, tryptophan, zolmitriptan, St. John s wort effects W/ cimetidine, erythromycin, ketoconazole T CNS depression W/ EtOH EMS Use fentanyl w/ caution, may T risk of serotonin synd concurrent EtOH use can T CNS depression OD May cause tach, HTN, diaphoresis, HA, fever, agitation, muscle tremors, and Szs symptomatic and supportive... 

Pentazocine (Talwin) (see also page 252) Street Names Crackers, poor man s h oin, T s and R s> Ts and Rits (all refer to combinations w/ Ritalin) (brands Talwin, Talwin Nx [CIV]) Use Medically used as opioid analgesic euphoria similar to heroin when mixed w/antihistamines combined w/ methylphenidate (Ritalin) is new abuse combination Actions Agonist-antagonist narcotic naloxone, a narcotic antagonist added to Talwin (Talwin NX) has reduced incidence of abuse Effects Euphoria, hallucinations, skin necrosis w/ illicit injection route... 

Absorption of pentazocine following oral administration is rapid. The onset of action occurs within approximately 15 minutes, and the half-life is 2 to 3 hours. Pentazocine is extensively metabolized in the liver and thus has a high first-pass effect following oral administration its half-life differs considerably from patient to patient. Oxidation of the methyl groups followed by conjugation to glucuronides in the liver terminates the effects of pentazocine. Excretion occurs through the kidney. 

Butorphanol is a morphinan congener with a profile of actions similar to that of pentazocine. 

Naloxone (Narcan) and naltrexone hydrochloride (Trexan) reverse the respiratory depressant action of narcotics related to morphine, meperidine, and methadone. They differ from other narcotic analgesics in several respects. Naloxone does not cause respiratory depression, pupillary constriction, sedation, or analgesia. However, it does antagonize the actions of pentazocine. Naloxone neither antagonizes the respiratory depressant effects of barbiturates and other hypnotics nor aggravates their depressant effects on respiration. Similar to nalorphine, naloxone precipitates an abstinence syndrome when administered to patients addicted to opiate-like drugs. 

Dezocine is a compound structurally related to pentazocine. It has its highest affinity for receptors and less interaction with receptors. Although it is said to be equivalent in efficacy to morphine, its use is associated with the same problems observed with all opioids that have mixed receptor actions. 

Correct choice = D. Pentazocine (a mixed agonist-antagonist) should not be used with agonists such as morphine, because it can block their actions. (Pentazocine acts as an agonist on k receptors, but is an antagonist at p and 5 receptors.)... 

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