Oxaprost

Uses

This combination is used for treatment of the signs and symptoms of osteoarthritis or rheumatoid arthritis in patients at high risk of developing NSAID-induced gastric and duodenal ulcers and their complications.

Oxaprost is also used to associated treatment for these conditions: Actinic Keratosis (AK), Acute Arthritis, Acute Gouty Arthritis, Acute Migraine, Acute Musculoskeletal Pain, Ankylosing Spondylitis (AS), Common Cold, Fever, Gouty Arthritis, Inflammation, Inflammatory Disease of the Oral Cavity, Inflammatory Disease of the throat, Inflammatory Reaction of the Nerve, Joint Pain, Juvenile Idiopathic Arthritis (JIA), Menstrual Distress (Dysmenorrhea), Muscle Inflammation, Ocular Inflammation, Operation site inflammation, Osteoarthritis (OA), Osteoarthritis of the Knee, Pain, Pain, Nerve, Pericarditis, Photophobia, Postoperative pain, Primary Dysmenorrhoea, Radicular Pain, Rheumatic Pain, Rheumatism, Rheumatoid Arthritis, Seasonal Allergic Conjunctivitis, Soreness, Muscle, Spinal pain, Tendon pain, Vertebral column pain, Acute Musculoskeletal injury, Acute, moderate, severe Pain, Inflammatory, Localized soft tissue rheumatism, Mild to moderate joint pain, Mild to moderate pain, Minor pain, Perioperative miosisGastric Ulcer, Incomplete Abortion, Missed Abortion, Postpartum Haemorrhage (PPH), Induction of cervix ripening therapy, Medically induced abortion

How Oxaprost works

Diclofenac inhibits cyclooxygenase-1 and -2, the enzymes responsible for production of prostaglandin (PG) G₂ which is the precursor to other PGs. These molecules have broad activity in pain and inflammation and the inhibition of their production is the common mechanism linking each effect of diclofenac.

PGE₂ is the primary PG involved in modulation of nociception. It mediates peripheral sensitization through a variety of effects. PGE₂ activates the G_q-coupled EP₁ receptor leading to increased activity of the inositol trisphosphate/phospholipase C pathway. Activation of this pathway releases intracellular stores of calcium which directly reduces action potential threshold and activates protein kinase C (PKC) which contributes to several indirect mechanisms. PGE₂ also activates the EP₄ receptor, coupled to G_s, which activates the adenylyl cyclase/protein kinase A (AC/PKA) signaling pathway. PKA and PKC both contribute to the potentiation of transient receptor potential cation channel subfamily V member 1 (TRPV1) potentiation, which increases sensitivity to heat stimuli. They also activate tetrodotoxin-resistant sodium channels and inhibit inward potassium currents. PKA further contributes to the activation of the P2X3 purine receptor and sensitization of T-type calcium channels. The activation and sensitization of depolarizing ion channels and inhibition of inward potassium currents serve to reduce the intensity of stimulus necessary to generate action potentials in nociceptive sensory afferents. PGE₂ act via EP₃ to increase sensitivity to bradykinin and via EP₂ to further increase heat sensitivity. Central sensitization occurs in the dorsal horn of the spinal cord and is mediated by the EP₂ receptor which couples to G_s. Pre-synaptically, this receptor increases the release of pro-nociceptive neurotransmitters glutamate, CGRP, and substance P. Post-synaptically it increases the activity of AMPA and NMDA receptors and produces inhibition of inhibitory glycinergic neurons. Together these lead to a reduced threshold of activating, allowing low intensity stimuli to generate pain signals. PGI₂ is known to play a role via its G_s-coupled IP receptor although the magnitude of its contribution varies. It has been proposed to be of greater importance in painful inflammatory conditions such as arthritis. By limiting sensitization, both peripheral and central, via these pathways NSAIDs can effectively reduce inflammatory pain.

PGI₂ and PGE₂ contribute to acute inflammation via their IP and EP₂ receptors. Similarly to β adrenergic receptors these are G_s-coupled and mediate vasodilation through the AC/PKA pathway. PGE₂ also contributes by increasing leukocyte adhesion to the endothelium and attracts the cells to the site of injury. PGD₂ plays a role in the activation of endothelial cell release of cytokines through its DP₁ receptor. PGI₂ and PGE₂ modulate T-helper cell activation and differentiation through IP, EP₂, and EP₄ receptors which is believed to be an important activity in the pathology of arthritic conditions. By limiting the production of these PGs at the site of injury, NSAIDs can reduce inflammation.

PGE₂ can cross the blood-brain barrier and act on excitatory G_q EP₃ receptors on thermoregulatory neurons in the hypothalamus. This activation triggers an increase in heat-generation and a reduction in heat-loss to produce a fever. NSAIDs prevent the generation of PGE₂ thereby reducing the activity of these neurons.

Misoprostol is a synthetic prostaglandin E1 analog that stimulates prostaglandin E1 receptors on parietal cells in the stomach to reduce gastric acid secretion. Mucus and bicarbonate secretion are also increased along with thickening of the mucosal bilayer so the mucosa can generate new cells.

Misoprostol binds to smooth muscle cells in the uterine lining to increase the strength and frequency of contractions as well as degrade collagen and reduce cervical tone.

Dosage

Oxaprost dosage

Osteoarthritis: The recommended dosage for maximal GI mucosal protection is Diclofenac Sodium 50 mg & Misoprostol 200 µg tid. For patients who experience intolerance, Diclofenac Sodium 75 mg & Misoprostol 200 µg bid or Diclofenac Sodium 50 mg p& Misoprostol 200 µg bid can be used.

Rheumatoid arthritis: The recommended dosage is Diclofenac Sodium 50 mg & Misoprostol 200 µg tid or qid. For patients who experience intolerance, Diclofenac Sodium 75 mg & Misoprostol 200 µg bid or Diclofenac Sodium 50 mg & Misoprostol 200 µg bid can be used.

Side Effects

The most common reported side effects are abdominal pain, diarrhea and other GI symptoms. Diarrhea and abdominal pain developed early in the course of therapy and were usually self-limited (resolved after 2 to 7 days). Rare instances of profound diarrhea leading to severe dehydration have been reported in patients receiving Misoprostol.

Toxicity

Symptoms of overdose include lethargy, drowsiness, nausea, vomiting, and epigastric pain, and gastrointestinal bleeding. Hypertension, acute renal failure, respiratory depression and coma occur rarely. In case of overdose, provide supportive care and consider inducing emesis and administering activated charcoal if overdose occurred less than 4 hours prior.

The oral LD₅₀ in rats is 81mg/kg and in mice is 27mg/kg. The intraperitoneal LD₅₀ in rats is 40mg/kg and in mice is 70mg/kg.

Patients experiencing an overdose may present with sedation, tremor, convulsions, dyspnea, abdominal pain, diarrhea, fever, palpitations, hypotension, and bradycardia. Hemodialysis is not expected to be useful in the treatment of misoprostol overdose but oral activated charcoal may help reduce absorption. In the event of an overdose, treat symptoms with supportive therapy. This may include removal of undissolved tablets from the vagina or buccal cavity, intravenous fluid replacement, acetaminophen, diazepam, haloperidol, or intramuscular diclofenac depending on the symptoms that present.

Precaution

Patients with an underlying condition such as inflammatory bowel disease or those in whom dehydration should be monitored carefully if Diclofenac Sodium plus Misoprostol is prescribed.

Interaction

Aspirin: Concomitant administration with aspirin is not recommended because Diclofenac Sodium is displaced from its binding sites by aspirin, resulting in lower plasma concentrations, peak plasma levels and AUC values.

Digoxin: Elevated digoxin levels have been reported in patients receiving digoxin and Diclofenac Sodium. Antihypertensives: NSAIDs can inhibit the activity of antihypertensives, including ACE inhibitors.

Warfarin: The effects of warfarin and NSAIDs on GI bleeding are synergistic, such that users of both drugs together have a risk of serious bleeding greater than users of either drug alone.

Oral hypoglycaemics: Diclofenac Sodium does not alter glucose metabolism in healthy people nor it alters the effects of oral hypoglycaemics. Diclofenac Sodium may alter diabetic patient’s response to insulin or oral hypoglycaemics.

Antacids: Antacids reduce the bioavailability of Misoprostol. Antacids may also delay absorption of Diclofenac Sodium.

Diuretics: The Diclofenac Sodium component like other NSAIDs, can inhibit the activity of diuretics. Concomitant therapy with potassium-sparing diuretics may be associated with increased serum potassium levels.

Volume of Distribution

Diclofenac has a total volume of distribution of 5-10 L or 0.1-0.2 L/kg. The volume of the central compartment is 0.04 L/kg. Diclofenac distributes to the synovial fluid reaching peak concentration 2-4h after administration. There is limited crossing of the blood brain barrier and cerebrospinal fluid concentrations only reach 8.22% of plasma concentrations. Doses of 50 mg delivered via intramuscular injection produced no detectable diclofenac concentrations in breast milk, however metabolite concentrations were not investigated. Diclofenac has been shown to cross the placenta in mice and rats but human data is unavailable.

Data regarding the volume of distribution of misoprostol is scarce.

The apparent volume of distribution of the active metabolite of misoprostol was in subjects with normal renal function was 13.6±8.0L/kg, with mild renal impairment was 17.3±23.0L/kg, with moderate renal impairment was 14.3±6.8L/kg, and with end stage renal disease was 11.0±9.6L/kg.

Elimination Route

Diclofenac is completely absorbed from the GI tract but likely undergoes significant first pass metabolism with only 60% of the drug reaching systemic circulation unchanged . Many topical formulations are absorbed percutaneous and produce clinically significant plasma concentrations. Absorption is dose proportional over the range of 25-150 mg. Tmax varies between formulations with the oral solution reaching peak plasma concentrations in 10-40min, the enteric coated tablet in 1.5-2h, and the sustained- and extended-release formulations prolonging Tmax even further. Administration with food has no significant effects on AUC but does delay Tmax to 2.5-12h.

For an 800µg oral dose of misoprostol, the AUC was 2.0192±0.8032h*ng/mL, the C_max was 2.6830±1.2161ng/mL, and a t_max of 0.345±0.186h. For a 800µg sublingual dose of misoprostol, the AUC was 3.2094±1.0417h*ng/mL, the C_max was 2.4391±1.1567ng/mL, and a t_max of 0.712±0.415h. For a 800µg buccal dose of misoprostol, the AUC was 2.0726±0.3578h*ng/mL, the C_max was 1.3611±0.3436ng/mL, and a t_max of 1.308±0.624h.

Half Life

The terminal half-life of diclofenac is approximately 2 h, however the apparent half-life including all metabolites is 25.8-33 h.

The half life of an 800µg oral dose is 1.0401±0.5090h, for a sublingual dose is 0.8542±0.1170h, and for a buccal dose is 0.8365±0.1346h.

Clearance

Diclofenac has a plasma clearance 16 L/h.

Because of the rapid de-esterification of misoprostol before or during absorption, it is usually undetectable in plasma. Misoprostol's active metabolite, misoprostol acid, has a total body clearance of 0.286L/kg/min. Subjects with mild renal impairment had a total body clearance of 0.226±0.073L/kg/min, subjects with moderate renal impairment had a total body clearance of 0.270±0.103L/kg/min, and subjects with end stage renal disease had a total body clearance of 0.105±0.052L/kg/min.

Elimination Route

Diclofenac is mainly eliminated via metabolism. Of the total dose, 60-70% is eliminated in the urine and 30% is eliminated in the feces. No significant enterohepatic recycling occurs.

As much as 73.2±4.6% of a radiolabelled oral dose of misoprostol is recovered in the urine.

Pregnancy & Breastfeeding use

Lactation: Diclofenac Sodium has been found in the milk of nursing mothers. It is unlikely that Misoprostol is excreted into milk since the drug is rapidly metabolized throughout the body. Excretion of the active metabolite (Misoprostol acid) into milk is possible, but has not been studied. Because of the potential for serious adverse reactions in nursing infants, Diclofenac Sodium and Misoprostol combination is not recommended for use by nursing mothers.

Contraindication

This is contraindicated in patients with hypersensitivity to Diclofenac, Misoprostol or to other prostaglandins. This should not be given to patients who have experienced asthma, urticaria or other allergic-type reactions after taking aspirin or other NSAIDs. This is also contraindicated in pregnant women because of the abortifacient property of Misoprostol.

Special Warning

Paediatric use: Safety and effectiveness of Diclofenac Sodium and Misoprostol combination in paediatric patients have not been established.

Geriatric use: No overall differences in safety or effectiveness were observed between these subjects and younger subjects, and other reported clinical experience has not identified differences in responses between the elderly and younger patients, but greater sensitivity of some elderly person cannot be ruled out. As with any NSAID, the elderly are likely to tolerate adverse events less well than younger patients.

Acute Overdose

Misoprostol: Convulsions, sedation, tremor, dyspnoea, diarrhoea, abdominal pain, fever, palpitations, hypotension, bradycardia. Management: Supportive treatment.

Diclofenac: Lethargy, drowsiness, nausea, vomiting, epigastric pain, GI bleeding. HTN, acute renal failure, resp depression, anaphylactoid reactions and coma may occur rarely

Storage Condition

Store in a cool and dry place below 25º C. Protect from light.

Innovators Monograph

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