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Pharmacology: Mechanism of Actions: PARACETAMOL: Analgesic action: May act predominantly by inhibiting prostaglandin synthesis in the central nervous system (CNS) and, to a lesser extent, through a peripheral action by blocking pain-impulse generation. The peripheral action may also be due to inhibition of prostaglandin synthesis or to inhibition of the synthesis or actions of other substances that sensitize pain receptors to mechanical or chemical stimulation.
HYOSCINE-N-BUTYLBROMIDE: Depending on the dose, anticholinergics may reduce the motility and secretory activity of the gastrointestinal system, and the tone of the ureter and urinary bladder and may have a slight relaxant action on the bile ducts and gallbladder.
Antiemetic: Scopolamine act primarily by reducing the excitability of the labyrinthine receptors and by depressing conduction in the vestibular cerebellar pathway.
Antivertigo: The exact mechanism by which Scopolamine exert their antimotion sickness and antivertigo effects is unknown; however, the probably act either on the cortex or more peripherally on the maculae of the utricle and saccule.
Pharmacokinetics: PARACETAMOL: Absorption: Oral: Rapid and almost complete: may be decreased if Acetaminophen is taken following a high-carbohydrate meal. Rectal- The rate and extent of absorption from the suppository dosage form may vary, depending on the composition of the base.
Distribution: In breast milk- Peak concentrations of 10 to 15 mcg per mL (66.2 to 99.3 micromoles/L) have been measured 1 to 2 hours following maternal ingestion of a single 650 mg dose. The half-life in breast milk is 1.35 to 3.5 hours.
Protein binding: Not significant with doses producing plasma concentrations below 60 mcg per mL (397.2 micromoles may reach moderate levels with high or toxic doses.
Biotransformation: Approximately 90 to 95% of a dose is metabolized in the liver, primarily by conjugation with glucuronic acid, sulfuric acid, and cystein. An intermediate metabolite, which may accumulate in overdosage after the primary metabolic pathways become saturated, is hepatotoxic and possibly nephrotoxic.
Half-life: 1 to 4 hours; does not change with renal failure but may be prolonged in acute overdosage, in some forms of hepatic disease, in the elderly, and in the neonate; may be somewhat shortened in children.
Time to peak concentration: 0.5 to 2 hours.
Peak plasma concentration: 5 to 20 mcg per mL (33. 1 to 132.4 micromoles/L), with doses up to 650 mg.
Time to peak effect: 1 to 3 hours.
Duration of action: 3 to 4 hours.
Elimination: Renal, as metabolites, primarily conjugates; 3% of a dose may be excreted unchanged. In dialysis- Hemodialysis: 120 mL per minute (for unmetabolized drug); metabolites are also cleared rapidly. Hemoperfusion: 200 mL per minute. Peritoneal dialysis: <10 mL per minute.
HYOSCINE-N-BUTYLBROMIDE: Absorption: Tertiary amines: Rapidly absorbed from gastrointestinal tract; also enter the circulation through the mucosal surfaces of the body.
Quaternary ammonium compounds: Gastrointestinal absorption is poor and irregular. Total absorption after an oral dose is about 10 to 25%.
Distribution: Exact distribution of anticholinergics has not been fully determined. However, tertiary amines appear to the distributed throughout the entire body and readily cross the blood-brain barrier and into the eye.
Biotransformation: Most anticholinergics- hepatic, by enzymatic hydrolysis.
Half-life: Elimination: 8 hours.
Time to peak effect: Elimination (% excreted unchanged): Renal.
