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Prodine

Prodine is a synthetic of the phenylpiperidine class, structurally analogous to meperidine, distinguished by its rapid and short duration of effect lasting approximately two hours. The compound, with the C16H23NO2, exists primarily as two stereoisomers—alphaprodine (cis isomer) and betaprodine (trans isomer)—both of which bind to receptors to produce analgesia but with alphaprodine exhibiting greater potency. Developed in during the late , prodine was investigated for short-term pain relief in surgical, , and obstetric applications due to its pharmacokinetic profile allowing for precise . Alphaprodine, marketed under the trade name Nisentil, was administered intravenously or subcutaneously for procedures requiring brief narcotic intervention, offering effects similar to or meperidine but with quicker recovery. Its metabolism occurs primarily in the liver, contributing to the limited accumulation risk compared to longer-acting opioids. Despite these attributes, clinical adoption was constrained by adverse effects including respiratory depression, , and potential for overdose given the narrow , leading to its obsolescence in favor of safer alternatives. Prodine remains classified as a Schedule II controlled substance in the United States, reflecting its high abuse potential akin to other potent opioids.

Chemistry

Chemical Structure and Properties

Prodine refers to the stereoisomers alpha-prodine and beta-prodine, both sharing the molecular formula C_{16}H_{23}NO_{2} and a molecular weight of 261.36 g/. The core structure is 1,3-dimethyl-4-phenylpiperidin-4-yl propanoate, featuring a ring substituted at position 1 with a , at position 3 with a , and at position 4 with both a and a propanoyloxy group (-OC(O)CH_{2}CH_{3}). The alpha- and beta- isomers differ in stereochemistry at the 3- and 4-positions, with alpha-prodine possessing the configuration and beta-prodine the configuration. This diastereomeric distinction arises from the chiral centers introduced by the substituents on the ring. Alpha-prodine constitutes the major active component in pharmaceutical preparations. In comparison to meperidine (), which features a 4-(ethoxycarbonyl) group directly linked via the carbonyl to the carbon 4, prodine exhibits a reversed orientation where the oxygen of the propanoate attaches to the ring carbon 4, alongside the phenyl at the same position. This structural modification, combined with the additional 3-methyl group, alters the spatial arrangement and electronic properties relative to the parent phenylpiperidine scaffold. Specific physical properties such as and values for prodine remain sparsely documented in available chemical literature.

Synthesis and Analogs

Alphaprodine, the primary of prodine, was first synthesized in 1947 by Albert Ziering and John W. Lee at Hoffmann-La Roche laboratories through a multi-step route beginning with the formation of 1,3-dimethylpiperidin-4-one via a modified Mannich condensation involving N-methylamine, , and acetone derivatives, followed by Grignard addition of to yield the tertiary alcohol intermediate 1,3-dimethyl-4-phenylpiperidin-4-ol, and concluding with esterification using or to introduce the propanoyloxy group at the 4-position. This esterification step produces a mixture of diastereomers, with the alpha isomer (trans between the 3-methyl and 4-substituents) isolated via fractional of the salts due to differences in . Betaprodine, the cis diastereomer, arises from the same synthetic sequence but is separated as the less soluble fraction during purification; its structure features the propanoyloxy and phenyl groups oriented cis to the 3-methyl substituent, influencing its conformational flexibility as later explored in quantum chemical models. Desmethylprodine, an N-demethylated analog lacking the 1-methyl group, is prepared analogously starting from unsubstituted or protected 3-methylpiperidin-4-one precursors, followed by phenyl Grignard addition and propionylation, yielding a compound with retained piperidine core but altered basicity and lipophilicity due to the secondary amine. Structural variations in prodine analogs, such as ethyl or allyl at the 3-position or modifications to the ester chain length, were investigated in extensions of the Ziering-Lee route during the late and , often employing the same intermediate esterified with alternative acyl chlorides to probe steric and effects on . Quantum chemical computations in the , using extended Hückel theory on desmethyl-, alpha-, and betaprodine conformers, revealed that equatorial preferences for the 4-phenyl and propanoyloxy groups in the alpha stabilize a bioactive chair conformation, causally linking axial/equatorial orientations to differential ring puckering and substituent interactions.

Pharmacology

Mechanism of Action

Prodine functions primarily as an at the μ-opioid receptor (), exhibiting higher selectivity for this subtype compared to δ- and κ-opioid receptors, which aligns with its profile among synthetic opioids. Unlike meperidine, prodine lacks significant affinity for monoamine transporters, minimizing non-opioid contributions to its effects and emphasizing classical MOR-mediated analgesia. Upon activation, prodine couples to inhibitory heterotrimeric G proteins (Gi/o), inhibiting adenylate cyclase activity and thereby reducing cyclic (cAMP) levels in target neurons. This signaling cascade also promotes opening of inwardly rectifying potassium channels and closure of voltage-gated calcium channels, resulting in neuronal hyperpolarization and decreased neurotransmitter release, particularly of and glutamate in pain pathways. Receptor binding and functional assays confirm prodine's lower potency relative to , approximately one-fifth to one-tenth, reflecting modest affinity differences at while maintaining the core inhibitory mechanism. Its structural features confer high , enabling swift penetration of the blood-brain barrier and rapid onset of central effects.

Prodine induces analgesia, , and through mu-opioid receptor activation, producing physiological responses akin to those of meperidine but with a more rapid onset. Early clinical evaluations in postoperative and obstetric settings confirmed effective short-term pain relief at intravenous doses of 20-40 mg, accompanied by that manifests as drowsiness and reduced responsiveness to stimuli. Dose-dependent adverse effects include respiratory depression, which in animal studies elicited progressive decreases in and behavioral responding proportional to administered doses, and in humans has resulted in apnea at supratherapeutic levels. Nausea and occur frequently, particularly with intravenous use, as documented in trials from the mid-20th century where these emetic responses correlated with peak plasma concentrations. The euphoric component enhances abuse potential, classifying prodine as a Schedule II controlled substance, though its brief duration of effect—typically 1-2 hours—limits cumulative exposure compared to longer-acting opioids, potentially reducing in dependency models.

Pharmacokinetics

Alphaprodine, the active form of prodine used clinically, is typically administered intravenously or subcutaneously, with intramuscular injection contraindicated owing to risks of local tissue irritation. Intravenous dosing yields onset of analgesia in 1-2 minutes, while subcutaneous administration achieves effects within 10 minutes (ranging 2-30 minutes), reflecting rapid absorption and distribution facilitated by the drug's lipophilicity. Peak plasma concentrations occur shortly after intravenous injection, generally within 5 minutes, supporting its application in brief procedures requiring prompt relief. The drug distributes quickly to tissues, including the , due to its physicochemical properties akin to other phenylpiperidine opioids. occurs primarily in the liver via ester hydrolysis and possibly N-demethylation, yielding inactive metabolites that reduce the risk of prolonged effects or accumulation even with repeated doses. Studies from the 1950s and later confirm this hepatic predominates, with likely integrated into the process. Elimination follows a of approximately 2 hours (131 minutes post-intravenous dose), with levels declining more rapidly than those of meperidine, consistent with alphaprodine's shorter clinical . Clearance is efficient, primarily through urinary of metabolites, with minimal unchanged recovered in urine or feces, as evidenced by radiolabeled studies in animals and pharmacokinetic profiling in human volunteers. This profile, derived from mid-20th-century empirical data, underscores low accumulation potential, though renal impairment may prolong effects.

Medical Uses

Indications and Administration

Prodine, also known as alphaprodine, was indicated for the short-term relief of moderate to severe , particularly in settings requiring brief analgesia such as during labor, dental procedures, and minor surgical interventions.90208-7/fulltext) Its rapid (within minutes via intravenous route) and ultra-short duration (typically 30-60 minutes, extending to 1-2 hours depending on dose and route) distinguished it from longer-acting opioids, limiting its utility to procedural rather than management. Administration was parenteral, primarily via or injection, as oral was poor and not clinically emphasized. doses ranged from 30 to 60 mg or , often repeated as needed every 1-2 hours but with careful to patient response to prevent respiratory depression or overdose.90208-7/fulltext) For use in or , initial doses of 30 mg were common, with totals up to several hundred mg in monitored settings; absorption could be unpredictable, leading some guidelines to prefer for precision. Doses were adjusted downward for elderly patients, children (e.g., 0.4-0.6 mg/kg), or those with reduced body weight, and mid-20th-century formularies stressed incremental under direct supervision due to the drug's potency equivalence (40-60 mg approximating 10 mg ). It was contraindicated for prolonged use or self- outside clinical oversight.

Clinical Efficacy

Prodine, primarily administered as alphaprodine hydrochloride (Nisentil), demonstrated rapid-onset analgesia in clinical settings, particularly for acute procedural pain. In obstetric applications during the 1950s, studies reported effective labor pain relief with intravenous doses achieving onset within 1-2 minutes, contrasting with morphine's slower peak effect around 20 minutes and associated prolonged sedation. A 1953 evaluation of 1,000 obstetrical cases found alphaprodine provided satisfactory analgesia in the majority, facilitating quicker maternal recovery without extended respiratory depression typical of longer-acting opioids. Comparative trials positioned alphaprodine as equivalent to meperidine for obstetric . A double-blind matching doses for potency equivalence showed no significant differences in duration or maternal satisfaction between the two agents during labor. In dental extractions, particularly pediatric procedures, alphaprodine achieved high ratings, averaging 2.8-2.9 on a 3-point (where 3 indicated very effective) across retrospective analyses of uncombined administrations, supporting its utility for short procedures requiring minimal post-operative impairment. Early formulations of prodine, as a of alphaprodine and betaprodine isomers, exhibited inconsistent potency due to betaprodine's approximately fivefold greater mu-opioid receptor yet faster , leading to variable clinical outcomes in initial reports before purification to alphaprodine alone. This isomer disparity contributed to dosing uncertainties and reduced reliability in some acute pain trials, though isolated alphaprodine later stabilized efficacy profiles in targeted uses like and minor .

Adverse Effects and Safety

Common Side Effects

The most frequently reported common side effects of alphaprodine (prodine) in clinical use include , , , and pruritus (itching). In a compilation of 7372 pediatric dental sedation cases involving alphaprodine , occurred in 277 instances (approximately 3.8%), in 10 (0.1%), and —often described as sleepiness—in 2381 (32.3%), though the high sedation rate was predominantly associated with concurrent administration of . was infrequently noted, with only 2 reports in the same dataset. In a smaller series of 128 obstetric patients receiving alphaprodine for analgesia, affected 4 individuals (3.1%) and postoperative 2 (1.6%), with the overall profile indicating relative infrequency of these gastrointestinal effects compared to expectations for opioids. Pruritus and are recognized dermatologic reactions, though specific incidence rates from controlled studies remain undocumented. Alphaprodine shares a profile pharmacologically akin to meperidine, with gastrointestinal disturbances like dry mouth and potential also listed among adverse reactions, but without differentiated incidence from longer-acting s in available data. is noted as a possible effect, consistent with class actions, though its short duration of action ( approximately 2 hours) may limit cumulative gastrointestinal impact relative to agents like .

Risks of Overdose and Dependence

Overdose with prodine (primarily alphaprodine) primarily manifests as severe respiratory depression due to saturation of mu-opioid receptors, which suppresses respiratory centers and can progress to apnea, , and cardiorespiratory . This risk is heightened in vulnerable populations, such as obstetric patients or children, where even low doses (e.g., 30 mg subcutaneous alphaprodine) have caused prolonged respiratory depression lasting hours, necessitating . In pediatric dental , serious sequelae including respiratory depression occurred in only 8 of 7,372 documented cases, indicating low incidence under controlled dosing but emphasizing the potential for rapid onset in sensitive individuals. A reported pediatric fatality involved irreversible cardiorespiratory approximately six hours post-alphaprodine administration during dental analgesia, likely attributable to delayed cumulative effects. Prodine exhibits dependence potential akin to morphine-type opioids, with capacity for both psychological and physical reliance, development, and symptoms upon cessation. Its short duration of action (typically 1-2 hours) may curtail reinforcing effects and habitual use compared to longer-acting opioids, though from mu-receptor activation confers abuse liability, classified under high-potential schedules in lists. Clinical monitoring is essential to mitigate risks, as with other opioids, but documented reports remain sparse relative to extended-release alternatives, consistent with its historical niche in brief procedural analgesia rather than management.

Case Studies of Complications

One documented case involved a pregnant who experienced and prolonged respiratory depression following a single low subcutaneous dose of alphaprodine (20 mg) administered for obstetric analgesia during labor. The patient, otherwise healthy, developed apnea requiring for over 12 hours, with recovery after supportive care including reversal, underscoring individual variability in sensitivity even at therapeutic doses. In pediatric dental procedures, a 4-year-old received alphaprodine intravenously as part of analgesia for tooth extraction, followed by multiple doses totaling approximately 1.5 mg/kg over several hours. Approximately six hours after the initial administration, the suffered sudden irreversible cardiorespiratory arrest, attributed to cumulative effects leading to and respiratory depression, despite monitoring. This incident highlights risks associated with repeated dosing in young patients with potentially immature metabolic pathways. Rapid intravenous administration of alphaprodine has been linked to complications such as muscle rigidity and convulsions in case reports from surgical and dental settings. For instance, a undergoing minor developed acute muscle rigidity and shortly after a bolus dose exceeding 0.5 mg/kg, necessitating immediate airway intervention; animal studies corroborate that supratherapeutic doses can induce clonic convulsions due to the drug's excitatory metabolites. These events emphasize the need for slow , continuous monitoring of respiratory status, and avoidance in with compromised pulmonary function or concurrent CNS depressants.

History

Development and Early Research

Prodine, encompassing the diastereoisomers alphaprodine and betaprodine, emerged from systematic modifications to the scaffold of (meperidine), a synthetic first reported in 1939. In 1947, chemists Albert Ziering and John Lee at Hoffmann-La Roche Laboratories synthesized these compounds through esterification of 1,3-dimethyl-4-piperidinol with , yielding the trans diastereomers as racemic mixtures. This approach targeted potent, short-acting analgesics by altering the ester substituent on the 4-position phenylpiperidine core, with preclinical evaluations confirming μ-opioid receptor agonism akin to pethidine but with accelerated onset due to structural rigidity in the trans configuration. Early pharmacological assessments in highlighted alphaprodine's viability, demonstrating subcutaneous analgesic potency at approximately 97% of morphine's equipotent dose in tail-flick assays, alongside rapid that limited duration to 30-60 minutes. Betaprodine exhibited even greater potency—up to 5 times that of alphaprodine—but faster clearance, prompting focus on the alpha for further development. These findings validated the ester modifications for enhancing and receptor , informing subsequent claims on piperidine derivatives as antagonists and analgesics. U.S. Patent No. 2,686,784, filed by John Lee and assigned to Hoffmann-La Roche, detailed the synthesis and utility of these esters in 1951 (issued August 17, 1954), emphasizing their role in addressing the demand for synthetic alternatives to natural opiates amid the 1940s surge in opioid chemistry spurred by wartime medical needs. Initial animal data underscored low respiratory depression relative to potency in mice, though addiction liability mirrored other phenylpiperidines, challenging early hopes for non-habit-forming variants. This preclinical foundation established prodine's scaffold as a template for iterative opioid design, preceding human trials.

Introduction and Clinical Adoption

Alphaprodine hydrochloride, marketed under the brand name Nisentil by Hoffmann-La Roche, was introduced to clinical practice in the United States in 1951 as a short-acting synthetic opioid analgesic. Developed as a meperidine analog with a more rapid onset and briefer duration of action—typically 30-60 minutes following intravenous administration—it targeted applications requiring transient pain control, including obstetrics, dentistry, and minor surgical procedures. Initial adoption occurred swiftly in U.S. hospitals and dental practices during the early , driven by endorsements in for its pharmacokinetic advantages over longer-acting opioids like meperidine, which often caused extended postoperative . Clinical reports highlighted its efficacy; for instance, a of 1,000 obstetrical cases reported effective labor analgesia with low rates of neonatal respiratory depression when administered judiciously, typically in 20-40 mg intravenous doses. In , Nisentil facilitated analgesia for extractions and pediatric , often combined with barbiturates like thiopental for rapid and in procedures lasting under an hour, as documented in early trials involving over 100 patients. By the mid-1950s, Nisentil achieved widespread use for these indications, reflecting professional preference for its profile in time-sensitive settings, though quantitative prescription data from the era remains limited in public archives. Its reception emphasized the balance of potent mu-opioid agonism with reduced accumulation risk compared to alternatives, positioning it as a preferred agent for and delivery-room analgesia until the emergence of newer synthetics with refined safety margins in subsequent decades.

Discontinuation and Legacy

Alphaprodine, marketed as Nisentil or , was voluntarily withdrawn from the U.S. market by its manufacturer, Laboratories, in the late 1970s following reports of severe adverse reactions, particularly in pediatric dental procedures. A notable case in 1972 involved a experiencing irreversible cardiorespiratory approximately six hours after alphaprodine administration during dental surgery, attributed to the drug's unpredictable and rapid onset of toxicity. These incidents, including respiratory and seizures, stemmed from the compound's ester linkage, which led to variable rates and inconsistent plasma levels, rather than widespread recreational or epidemics. The withdrawal was not prompted by regulatory mandates but by 's assessment of the risk-benefit profile, especially in vulnerable populations like children, where dosing errors amplified dangers. In its legacy, alphaprodine demonstrated the challenges of designing short-acting via prodrugs, influencing subsequent to prioritize more predictable metabolic pathways for ultra-short-duration agents used in . Its rapid by provided early insights into achieving quick offset for procedural analgesia, such as in and minor , but also underscored risks of instability, including sudden toxicity from incomplete or erratic breakdown. analyses indicate that while alphaprodine advanced short-acting opioid applications—offering analgesia with durations of 1-2 hours—its safety limitations, including to esterase variability, outweighed benefits, prompting refinements in compounds like with engineered stability. Usage data from the pre-1980 era show no substantive contribution to the modern opioid crisis, which escalated in the with extended-release formulations, as alphaprodine's market exit predated those trends.

Regulation and Legal Status

United States Scheduling

Alphaprodine, the primary isomer marketed as prodine and under the brand name Nisentil, is classified as a Schedule II under the federal of 1970. Schedule II placement reflects criteria for substances with high potential for abuse—comparable to other opioid analgesics—and severe risk of psychological or , yet with accepted medical applications under strict regulatory oversight, including no refills on prescriptions and requirements for secure handling by manufacturers, distributors, and prescribers. This scheduling was established upon the CSA's enactment, incorporating prior opioid classifications from the 1960s while formalizing federal authority over enforcement via the (). The (FDA) initially approved alphaprodine for clinical use as a short-acting injectable in the mid-20th century, prior to CSA implementation, for obstetric and minor surgical analgesia due to its rapid onset and brief duration of action. Subsequent market restrictions, including manufacturer withdrawal of Nisentil from U.S. distribution in 1986 amid safety profile concerns such as risks and emergence of safer alternatives, led to its effective discontinuation without subsequent FDA-approved reformulations or generic equivalents. DEA enforcement history shows no notable diversion incidents or quota adjustments specific to prodine post-discontinuation, consistent with its negligible production and prescription volume relative to contemporaries like meperidine, which faced higher scrutiny for abuse. Current aggregate production quotas for alphaprodine remain minimal, primarily allocated for or residual legitimate needs rather than , underscoring limited ongoing relevance under Schedule II controls. Violations involving prodine, such as unauthorized possession or , carry penalties aligned with Schedule II offenses, including up to 20 years imprisonment for trafficking offenses without prior convictions, though empirical enforcement data indicate rarity due to the drug's obsolescence.

International Controls and Availability

Alphaprodine, known generically as prodine, is classified under Schedule I of the of 1961, obligating signatory states to regulate its manufacture, trade, distribution, and possession through national legislation to prevent abuse and ensure medical or scientific use only. This international framework, ratified by over 180 countries, imposes reporting requirements to the (INCB) on quantities handled, with global estimated requirements remaining negligible at under 1 gram annually in recent assessments, indicating minimal legitimate demand. In the , prodine is designated a Class A substance under the , attracting severe penalties for unauthorized handling and restricting possession, supply, or production to licensed entities under Schedule 2 of the Misuse of Drugs Regulations 2001. lists it in Schedule I of the , prohibiting non-authorized activities and mandating secure storage for any permitted research stocks. categorizes it as a Schedule 8 controlled drug under state poisons schedules, with federal customs regulations barring imports absent special permits from the Office of Drug Control. European Union member states implement convention-aligned controls variably but uniformly restrict prodine to authorized scientific purposes, as exemplified by Germany's Anlage I classification under the Narcotics Act, which confines it to institutional research with no routine medical dispensing. These post-1970s national restrictions, enacted amid growing recognition of opioid dependency risks, have rendered prodine commercially unavailable worldwide for clinical or veterinary applications, with no documented production for human use since the late 20th century and no contemporary efforts to reinstate it. Regulatory emphasis in Europe often prioritizes alternatives for acute procedural pain over short-acting synthetics like prodine, contrasting with historical U.S. scheduling that theoretically allowed limited medical access prior to market withdrawal.