Atropine Sulphate 0.5 mg / ml · Liquid injectables

Atropine is an antimuscarinic agent since it antagonizes the muscarine-like actions of acetylcholine and other choline esters.

Atropine inhibits the muscarinic actions of acetylcholine on structures innervated by postganglionic cholinergic nerves, and on smooth muscles which respond to endogenous acetylcholine but are not so innervated. As with other antimuscarinic agents, the major action of atropine is a competitive or surmountable antagonism which can be overcome by increasing the concentration of acetylcholine at receptor sites of the effector organ (e.g., by using anticholinesterase agents which inhibit the enzymatic destruction of acetylcholine). The receptors antagonized by atropine are the peripheral structures that are stimulated or inhibited by muscarine (i.e., exocrine glands and smooth and cardiac muscle). Responses to postganglionic cholinergic nerve stimulation also may be inhibited by atropine but this occurs less readily than with responses to injected (exogenous) choline esters.

Absorption — After intramuscular administration, atropine is absorbed with peak concentration occurring at 30 min following injection.

Effects of exercise: — Exercise following intramuscular administration of atropine significantly increases the absorption of atropine due to increased perfusion in the muscle, with an increase in AUC by approximately 20% and C maxby approximately 80%.

Distribution — Atropine is distributed throughout the body. Atropine’s plasma protein binding is about 44% and saturable in the 2 to 20 mcg/mL concentration range.

Elimination — The pharmacokinetics of atropine is nonlinear after intravenous administration of 0.5 to 4 mg. Atropine disappears from the blood following injection with a plasma half-life of about 2 to 4 hours. Much of the drug is destroyed by enzymatic hydrolysis, particularly in the liver, with 13 to 50% is excreted unchanged in the urine.

Metabolism — The major metabolites of atropine are noratropine, atropin-n-oxide, tropine, and tropic acid. The metabolism of atropine is inhibited by organophosphate pesticides.

Pregnant Women — Atropine readily crosses the placental barrier and enters the fetal circulation, but is not found in amniotic fluid.

Nursing Mother — Traces are found in various secretions, including milk.

Pediatric and Geriatric Patients — The elimination half-life of atropine is more than doubled in children under two years, and the elderly (> 65 years old) compared to other age groups.