Pentazocine dosing

Tissue damage Severe sclerosis of skin, subcutaneous tissues, and underlying muscle has occurred at injection sites following multiple doses of pentazocine lactate. 

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 is indicated for relief of moderate pain in patients not receiving large doses of opioids. It is also used as premedication for anesthesia and as a supplement to surgical anesthesia. 

The most common side effect of pentazocine is sedation resulting from an interaction with the K-receptor. Also observed are sweating, dizziness, psychotomimetic effects, anxiety, nightmares, and headache. Nausea and vomiting are less frequent than with morphine. Respiratory depression and increased heart rate, body temperature, and blood pressure accompany overdose. Naloxone is effective in reducing the respiratory depression but requires the use of higher doses than for morphine overdose. 

Pentazocine is contraindicated in the treatment of patients with acute myocardial infarction because of cardiovascular stimulation. Psychotomimetic side effects, such as hallucinations, bizarre dreams, and sensations of depersonalisation, occur in about 6-10% of patients. They are more common in elderly patients, in those who are ambulatory, and when doses above 60 mg are given. Nausea occurs in approximately 5% of patients although vomiting is less common. Other commonly reported side effects are dizziness and drowsiness. The risk of physical dependence is low. 

Nalbuphine hydrochloride is structurally related to oxymorphone and naloxone. It is approximately equipotent with morphine. Nalbuphine is metabolised in the liver to inactive metabolites. The plasma terminal half-life is approximately 5 h. The onset of analgesia is within 2-3 min of intravenous administration and 15 min after intramuscular injection, and lasts 3-6 h with an adult dose of 10 mg. With equi-analgesic doses, similar degrees of respiratory depression to that of morphine occur up to a dose of approximately 0.45 mg-kg-1. With higher doses a ceiling effect occurs. Sedation, possibly mediated by K-receptor activation, occasionally occurs. The incidence of psychotomimetic side effects is lower than with pentazocine. The abuse potential is low, but is can cause withdrawal symptoms in opioid-dependent subjects. It has occasionally been used to reverse opioid-induced respiratory depression. 

Dosages and routes of administration Pentazocine is used as the hydrochloride or lactate in oral, parenteral and rectal formulations. Doses for the treatment of moderate to severe pain are in the range of 25-100 mg. 

The compound has a relevant abuse potential (Reed and Scholl, 1986) and high doses may produce dependence of the morphine type. Pentazocine effects can be antagonized with naloxone and combinations with naloxone are available to discourage parenteral misuse (Baum et al., 1987). 

Pentazocine is a potent analgesic of the benzo-morphan series with a 50 rag oral dose equivalent to 60 rag of codeine. It is also a weak narcotic antagonist with about one-fiftieth the activity of nalorphine. Pentazocine is indicated in the treatment of moderate to severe pain. It is also used as a preanesthetic and anesthetic supplement (1,2). 

Way and coworkers. Reviews of metabolism (51) and pharmacokinetics (97) of pentazocine have been published. The effect of route of administration on the disposition of pentazocine has been explored (27, 9,75,85,86). The metabolic pathways available to pentazocine are outlined in Figure 10. Also shown are urinary excretion data for the metabolites expressed as percent of administered dose. 

A rhesus monkey study is also included (66) which species shows the trans-alcohol metabolite excreted as well. Urinary excretion consists of unchanged pentazocine and metabolites plus phenolic glucu-ronides of each. Fecal excretion consists of less than 1% administered dose (86). 

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