Oxycontin 80 mg

Descripción Del Producto

1. Classification and Chemical Overview

OxyContin 80mg is the original innovator oral prolonged-release pharmaceutical preparation containing clorhidrato de oxicodona (developed by Purdue Pharma and marketed in the United Kingdom and internationally by Napp Pharmaceuticals / Mundipharma). Chemically designated as $(5R,9R,13S,14S)\text{-4,5}\alpha\text{-epoxy-14-hydroxy-3-methoxy-17-methylmorphinan-6-one hydrochloride}$, oxycodone is a semi-synthetic phenanthrene alkaloid derived from the opium poppy constituent thebaine. Structurally, it features a morphinan skeleton with a carbon-4 to carbon-5 ether linkage, a methoxy moiety at carbon-3, a tertiary hydroxyl substitution at carbon-14, and an aliphatic ketone functional group at carbon-6. Its empirical molecular formula as the hydrochloride salt is $\text{C}_{18}\text{H}_{21}\text{NO}_4\cdot\text{HCl}$, yielding an average molecular weight of $351.82\text{ g/mol}$ (unconjugated active base: $315.36\text{ g/mol}$).

Standard solid oral presentations of OxyContin 80mg in the United Kingdom consist of round, biconvex, green-colored film-coated prolonged-release tablets debossed with “OC” on one face and “80” on the reverse (or “OP” in tamper-resistant, abuse-deterrent polymer formulations deployed in select jurisdictions). The core prolonged-release delivery system utilizes the proprietary Contin dual-matrix technology (incorporating hydrophobic and hydrophilic polymers, notably ammonio methacrylate copolymer, hydroxypropyl cellulose, stearyl alcohol, magnesium stearate, and polyethylene glycol) coated with a film layer containing colorants such as indigo carmine (E132), iron oxide yellow (E172), and titanium dioxide (E171). This dual-matrix is engineered to release the substantial $80\text{ mg}$ opioid payload in a steady, biphasic profile over a 12-hour period.

Within the United Kingdom regulatory framework:

• Medicinal Classification: Categorized as a Prescription Only Medicine (POM) governed by the Human Medicines Regulations 2012.

• Controlled Drug Scheduling: Under the Misuse of Drugs Act 1971, oxycodone is scheduled as a Class A controlled substance. Under the Misuse of Drugs Regulations 2001, OxyContin 80mg sits within Schedule 2 (CD POM). Prescriptions are subject to strict statutory requirements:

  • Maximum legal prescription validity of 28 days from the date of signature.

  • Mandatory declaration of the formulation, strength, dosing instructions, and total quantity written in both words and figures.

  • Subject to Safe Custody requirements (must be stored in a locked Controlled Drugs cupboard conforming to BS 2881 standards within hospital wards and pharmacies) and mandatory logging in the statutory Controlled Drugs Register.

• NHS Formulary Positioning: Catalogued in the British National Formulary (BNF) and listed on the NHS Drug Tariff for severe Step 3 opioid analgesia.

Because a single 80mg tablet delivers an equianalgesic dose equivalent to approximately $120\text{ to }160\text{ mg}$ of oral morphine sulphate, OxyContin 80mg carries high street-level recognition and commercial diversion value (“Oxy 80s”, “Green OCs”). Bypassing the matrix by crushing, chewing, or aqueous extraction triggers immediate dose-dumping, causing rapid systemic absorption capable of inducing fatal respiratory depression, particularly in opioid-naive or partially tolerant individuals. Furthermore, illicit drug markets are extensively contaminated with counterfeit tablets pressed with lethal concentrations of illicit fentanyl or high-potency synthetic nitazene analogues (e.g., protonitazene, metonitazene, isotonitazene).

2. Mechanism of Action and Pharmacodynamics

The pharmacodynamic profile of oxycodone is characterized by potent, high-affinity agonism at central and peripheral opioid receptors:

• $\mu$-Opioid (MOP) Receptor Agonism: Oxycodone functions as a pure, high-efficacy agonist at human $\mu$-opioid receptors distributed across the laminae I and II of the spinal dorsal horn, periaqueductal gray (PAG), thalamus, and cortical sensory processing areas:

  • Receptor binding activates coupled heterotrimeric inhibitory $G_{\alpha i/o}$ proteins, which inhibit adenylyl cyclase, lowering intracellular cyclic adenosine monophosphate (cAMP).

  • Presynaptically, it inhibits voltage-gated N-type calcium ($Ca^{2+}$) channels, arresting the vesicular exocytosis of primary nociceptive neurotransmitters (substance P, calcitonin gene-related peptide [CGRP], and L-glutamate).

  • Postsynaptically, it stimulates G-protein-coupled inwardly rectifying potassium (GIRK) channels. The resulting potassium ion efflux hyperpolarizes the postsynaptic neuronal membrane, stabilizing resting potentials below the threshold necessary for action potential generation.

• Direct Intrinsic Action vs. Active Metabolites: Unlike codeine, oxycodone does not require metabolic bioactivation to produce clinical analgesia. Parent oxycodone drives approximately $80\%$ of its total central analgesic effect. While CYP2D6 converts a fraction into oxymorphone (which has an affinity for $\mu$-receptors roughly 10-fold higher than oxycodone), circulating concentrations of oxymorphone remain minimal, meaning variations in CYP2D6 metabolizer status do not significantly alter the primary analgesic response.

• Relative Potency and Morphine Equivalence: Oxycodone is a Step 3 opioid:

  • Oral oxycodone exhibits an equianalgesic potency ratio of approximately $1.5:1\text{ to }2:1$ relative to oral morphine.

  • A single OxyContin 80mg tablet taken every 12 hours delivers analgesic exposure equivalent to $240\text{ to }320\text{ mg}$ of oral morphine sulphate over a 24-hour period.

• Respiratory and Enteric Depression: Agonism within the pontomedullary respiratory pacemakers (pre-Bötzinger complex) blunts central chemoreceptor responsiveness to arterial carbon dioxide ($\text{PaCO}_2$) and hypoxia, causing dose-dependent bradypnea. In the gastrointestinal tract, stimulation of myenteric $\mu$-receptors arrests propulsive peristalsis and increases circular sphincter tone, universally causing severe constipation.

3. Approved UK Clinical Indications and Therapeutic Scope

OxyContin 80mg is indicated strictly for patients who are already established on high-dose opioid therapy and require potent Step 3 analgesia under BNF and NICE guidelines:

• Severe Cancer-Related Pain:

  • Indicated for the control of severe, intractable chronic pain in malignant disease when non-opioids, weak opioids (Step 2), or lower-dose Step 3 opioids fail to provide adequate pain relief.

  • Dosed strictly on a 12-hourly schedule ($80\text{ mg}$ twice daily). Breakthrough pain is managed using immediate-release oral oxycodone (e.g., OxyNorm liquid or capsules), calculated at one-sixth to one-tenth of the total 24-hour baseline dose (e.g., $20\text{ to }30\text{ mg}$ immediate-release PRN for a $160\text{ mg/day}$ total prolonged-release regimen).

• Severe Non-Malignant Chronic Pain (Strictly Specialist-Initiated):

  • Short-to-medium-term management of severe chronic pain (e.g., advanced osteoarthritic joint destruction, severe neuropathic conditions, failed back surgery syndrome) refractory to multi-modal non-opioid strategies.

• Tolerance Requirements and Opioid-Naive Warning:

  • OxyContin 80mg is absolutely contraindicated in opioid-naive patients.

  • Initiation of an 80mg tablet twice daily is reserved exclusively for patients who have demonstrated tolerance by receiving stable, high-dose opioid therapy for at least one to two weeks (e.g., at least $60\text{ to }80\text{ mg}$ of oral morphine daily, $30\text{ to }40\text{ mg}$ of oral oxycodone daily, or an equianalgesic dose of another Step 3 opioid).

• NICE Guidance on Chronic Non-Cancer Pain (NG193):

  • NICE explicitly advises against initiating high-potency opioids for chronic primary pain due to lack of evidence for long-term functional recovery, high dependence liabilities, and the risk of opioid-induced hyperalgesia (OIH). Treatment must be accompanied by defined functional goals, scheduled reviews, and an agreed tapering/exit strategy.

In non-medical, illicit contexts, OxyContin 80mg is abused for euphoric intoxication, emotional blunting, and somatic sedation. Mechanical tampering (crushing to snort, or dissolving for injection) bypasses the release matrix, creating high risks of fatal overdose.

4. Pharmacokinetic Profile and Metabolic Fate

The pharmacokinetic performance of OxyContin 80mg depends on maintaining matrix integrity to ensure controlled, biphasic 12-hour dissolution:

Biotransformation Pathways

1. $N$-Demethylation via CYP3A4 (Major Route, $\sim 80\%$): Converts oxycodone into noroxycodone. Noroxycodone is a weak $\mu$-opioid agonist with poor blood-brain barrier permeability, contributing negligibly to analgesia.

2. $O$-Demethylation via CYP2D6 (Minor Route, $\sim 10\%$): Converts oxycodone into oxymorphone, a potent $\mu$-opioid agonist. Although oxymorphone has high receptor affinity, its circulating plasma concentrations are low, meaning that genetic CYP2D6 variations do not meaningfully alter the overall analgesic response.

3. Phase II Conjugation: Unchanged drug and Phase I metabolites undergo glucuronidation via UDP-glucuronosyltransferases into polar glucuronide conjugates for renal excretion.

4. Renal Clearance Dynamics: Less than $10\%$ is excreted unchanged in the urine. In patients with severe renal impairment (eGFR $<30\text{ mL/min/1.73 m}^2$), total drug exposure ($AUC$) increases by $40\text{ to }60\%$, requiring conservative dose titration and extended dosing intervals.

5. Physiological Effects and Adverse Event Spectrum

Therapeutic administration produces potent analgesia and suppression of pain-associated autonomic distress. However, extensive $\mu$-opioid receptor engagement across multiple organ systems produces a characteristic spectrum of adverse effects:

• Gastrointestinal Disturbances (Very Common, $\ge 1/10$):

  • Constipation: Occurs in up to $80\%$ of treated individuals. Opioid receptor binding in the myenteric plexus inhibits propulsive peristalsis and arrests secretomotor fluid transport. Tolerance does not develop; co-prescribing a prophylactic laxative regimen is clinically mandatory.

  • Nausea and vomiting: Triggered by direct stimulation of the chemoreceptor trigger zone (CTZ) in the area postrema.

  • Xerostomia (dry mouth), dyspepsia, and biliary spasm (constriction of the Sphincter of Oddi).

• Central Nervous System and Neuropsychiatric Toxicity (Common, $1/100$ to $<1/10$):

  • Somnolence, daytime sedation, dizziness, headache, and cognitive clouding.

  • Euphoria or paradoxical restlessness, dysphoria, and confusion (more frequent in elderly patients).

  • Muscle fasciculations, myoclonus, and hyperalgesia (associated with high-dose accumulation).

• Cutaneous Reactions:

  • Pruritus, flushing, and diaphoresis. Oxycodone induces significantly less mast-cell degranulation than morphine, but pruritus remains common due to central $\mu$-receptor mechanisms.

• Severe, Emergent and Life-Threatening Hazards (Overdose & Dependence):

  • Catastrophic Central Respiratory Depression: The primary cause of fatal poisoning. Suppression of the medullary pre-Bötzinger complex produces severe bradypnea ($<8\text{ breaths/min}$), progressive cyanosis, stupor advancing to coma, hypercapnic acidosis, and fatal cardiac arrest.

  • Dose-Dumping Toxicity: If an OxyContin 80mg tablet is chewed, crushed, or dissolved, the entire $80\text{ mg}$ payload is released immediately ($C_{max}$ occurs within 30 to 45 minutes rather than 6 to 8 hours), predisposing even opioid-tolerant individuals to acute, potentially fatal respiratory failure.

  • Synergistic Depressant Collapse: Co-ingestion with alcohol, benzodiazepines, or gabapentinoids (pregabalin, gabapentin) dramatically amplifies medullary depression, causing rapid loss of consciousness, airway compromise, and fatal asphyxiation.

  • Physical Dependence and Acute Opioid Withdrawal: Continuous use beyond 2 to 4 weeks drives neuroadaptation. Abrupt discontinuation precipitates a severe withdrawal syndrome: autonomic hyperactivity (tachycardia, hypertension, diaphoresis), gastrointestinal cramping, diarrhea, piloerection (“cold turkey”), pupil dilation (mydriasis), myalgias, and severe insomnia.

  • Counterfeit Nitazene Poisoning: Black-market tablets sold as “Oxy 80” frequently contain synthetic nitazene opioids (e.g., protonitazene, metonitazene), which exhibit potencies tens to hundreds of times higher than morphine, causing rapid, severe respiratory arrest that requires massive, escalated doses of naloxone.

6. Contraindications, Drug Interactions, and Clinical Precautions

Prescribing, titrating, and monitoring OxyContin 80mg mandates strict adherence to safety exclusions, metabolic drug-interaction screening, and Controlled Drugs governance:

• Contraindications:

  • Opioid-Naive Patients: Absolute, Life-Threatening Contraindication. Ingestion of $80\text{ mg}$ of oxycodone without pre-existing tolerance frequently precipitates fatal respiratory arrest.

  • Severe Respiratory Depression: Absolute contraindication in acute respiratory failure, severe chronic obstructive pulmonary disease (COPD), respiratory arrest, or acute severe asthma.

  • Paralytic Ileus or Obstructive Bowel Disease: Absolute contraindication due to the risk of precipitating toxic megacolon or bowel perforation.

  • Raised Intracranial Pressure (ICP) and Severe Head Injury: Opioid-induced $\text{CO}_2$ retention promotes cerebral vasodilation, dangerously spiking intracranial pressure.

  • Severe Hepatic Cirrhosis (Child-Pugh Class C): Clearance of parent drug is severely blunted, leading to massive, uncontrolled drug accumulation.

  • Concurrent Monoamine Oxidase Inhibitors (MAOIs): Absolute contraindication during or within 14 days of MAOI therapy.

  • Pregnancy and Breastfeeding: Avoided during pregnancy unless essential (risks neonatal respiratory depression and neonatal opioid withdrawal syndrome [NOWS]); contraindicated in nursing mothers (oxycodone concentrates in breast milk, causing fatal infant sedation).

• Drug Interactions:

  • Potent Cytochrome P450 3A4 Inhibitors (e.g., Ketoconazole, Itraconazole, Clarithromycin, Erythromycin, Ritonavir, Grapefruit Juice): High-Level Hazard. Inhibiting CYP3A4 shuts down the primary clearance pathway of oxycodone, increasing plasma $AUC$ by $100\text{ to }200\%$ and doubling its elimination half-life, transforming a standard maintenance dose into a dangerous overdose.

  • CYP3A4 Inducers (e.g., Rifampicin, Carbamazepine, Phenytoin, St John’s Wort): Accelerates clearance, dropping plasma oxycodone concentrations by up to $50\text{ to }80\%$, risking acute breakthrough pain crises or opioid withdrawal.

  • Central Nervous System Depressants (Benzodiazepines, Alcohol, Gabapentinoids, Sedating Antihistamines): Highest-Tier Mortality Risk. Concomitant use multiplies the risk of fatal respiratory depression, profound coma, and brain damage.

  • Anticholinergic Agents (e.g., TCAs, Antimuscarinics): Compounded paralytic burden on the bowel, drastically elevating the risk of severe obstipation and paralytic ileus.

• Clinical Precautions and Emergency Overdose Management (“Red Flags”):

  • Administration Mandate:

    • Tablets must be swallowed completely whole. They must never be broken, crushed, chewed, or dissolved, as doing so destroys the sustained-release matrix, resulting in rapid dose-dumping and fatal poisoning.

  • Acute Overdose Resuscitation Protocol: Patients presenting to emergency departments (999/A&E) with the classic opioid triad (respiratory depression $<8\text{ breaths/min}$, pinpoint pupils [miosis], and coma):

    • Airway and Oxygenation: Prioritize airway patency, position in the recovery position, deliver high-flow oxygen, and provide bag-valve-mask or mechanical ventilation immediately.

    • Targeted Naloxone Administration: Administer intravenous naloxone ($400\text{ mcg}$ IV initially, titrating up to $800\text{ mcg}$ to $2\text{ mg}$ every 2 to 3 minutes, up to $10\text{ mg}$ as clinically indicated to restore adequate spontaneous ventilation).

    • Extended Monitoring Window for Prolonged-Release Overdose: Because OxyContin 80mg slowly releases active drug from its matrix over 12 hours, naloxone (which has a short half-life of $30\text{ to }60\text{ minutes}$) will wear off long before the tablet has finished absorbing.

    • Once initial resuscitation is achieved, patients must be observed under continuous intensive care / telemetry monitoring for a minimum of 24 to 48 hours (or initiated on a continuous intravenous naloxone infusion) to prevent fatal “re-narcotization.”

  • Laxative Co-Prescribing Mandate: Prescribing standards dictate that all patients initiated on OxyContin 80mg must be concurrently co-prescribed a prophylactic laxative regimen (combining an osmotic agent like macrogol with a stimulant laxative like senna) to prevent severe fecal impaction.

  • Structured Discontinuation Protocols: OxyContin 80mg must never be stopped abruptly in dependent individuals. Doses must be tapered down systematically (e.g., reducing the total daily dose by $10\text{ to }20\%$ every 1 to 2 weeks) under close medical supervision to prevent severe autonomic withdrawal and acute pain flares.

  • Driving Regulations: Under Section 5A of the Road Traffic Act 1988, driving with specified controlled drugs in the blood above statutory limits is an offence. While a statutory medical defense applies when the medicine is taken strictly in accordance with prescription instructions, patients must be warned that driving while impaired remains an offence under Section 4 of the Act.

Información Adicional