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Brand Name, Dosage Format and Strength
Algesia 37.5 mg/325 mg Tablet
Tramadol is a synthetic opioid analgesic. Its exact mechanism of action is unknown but its analgesic effect appears to be produced via the following mechanisms: (1) the affinity of M1, tramadol’s major metabolite, for the μ opioid receptor (2) the inhibition of the reuptake of serotonin and noradrenaline.
Paracetamol has analgesic and antipyretic properties with weak anti-inflammatory activity. The mechanism behind its therapeutic effects has not been clearly explained although recent studies propose that paracetamol inhibits the peroxidase portion of COX, specifically targeting COX-3 enzyme, which is mainly responsible for the synthesis of prostaglandins in the brain cortex.
The tramadol + paracetamol combination presents an opportunity to improve the spectrum of analgesic activity and reduce opioid dosage. Studies have shown that tramadol given at subtherapeutic doses (25% less than the recommended dose) together with paracetamol at a fixed ratio of 1:9 can provide the same analgesic effect produced by equianalgesic doses (50 mg) of tramadol alone. The dose reduction markedly diminished the troublesome dose-related adverse effects of tramadol (nausea, dizziness, somnolence, constipation, and vomiting) and improved tolerability.
After a single oral dose of tramadol 37.5 mg + paracetamol 325 mg combination tablet, the Cmax of both tramadol enantiomers were 64.3 ng/mL [(+)-tramadol] and 55.5 ng/mL [(-)-tramadol]. These concentrations were achieved after 1.8 hrs. The Cmax of paracetamol achieved after 0.9 hr was 4.2 mcg/mL. The mean elimination t1/2 of both tramadol enantiomers were 5.1 hrs [(+)-tramadol] and 4.7 [(-)-tramadol] hrs, and 2.5 hrs for paracetamol.
Tramadol is well absorbed with mean absolute bioavailability of approximately 75% after a single oral 100 mg dose. Cmax of tramadol and the M1 metabolite occur after 2 and 3 hrs, respectively.
Paracetamol is rapidly and completely absorbed in the small intestine via passive diffusion. Cmax are achieved within 0.4 to 1 hr. A fatty meal may delay absorption but does not affect extent of absorption.
Tramadol has high tissue affinity with a Vd of 2.6 and 2.9 L/kg in male and female subjects, respectively, after oral administration. Its affinity for plasma proteins is approximately 20% and saturation occurs at doses beyond the therapeutic range.
Paracetamol is evenly distributed throughout most body fluids, but not in fatty tissue. Vd is approximately 0.9 L/kg. Its affinity for plasma proteins is low (approximately 10%-25%), and practically does not displace other drugs which are highly protein bound.
Tramadol and its metabolites undergo extensive hepatic metabolism via the CYP 2D6 and CYP 3A4 pathways and conjugation of the parent drug and its metabolites. Most of the drug is excreted in the urine as metabolites (approximately 60%) and the remaining drug fraction is excreted in its unchanged form.
Paracetamol metabolism follows first-order kinetics, and primary metabolic pathways involve conjugation with glucuronide and sulfate and oxidation via the cytochrome P-450 mixed-function oxidase pathway. In adults, most of the drug fraction is transformed into the active glucuronide salt, and the remainder is conjugated with sulfate.
Tramadol is cleared from the circulation via renal excretion. The plasma elimination t1/2 of racemic tramadol and M1 are approximately six and seven hrs, respectively. The plasma elimination t1/2 of racemic tramadol increased from approximately seven to nine hrs upon multiple dosing of tramadol + paracetamol.
Paracetamol has a plasma elimination t1/2 that ranges from two to three hrs in adults but this may be prolonged in patients with liver disease. It is mainly excreted in the urine in its glucuronide or sulfate form, and less than 9% is excreted unchanged.
Last Update: Aug 8, 2011