Pralidoxime mesylate absorption and heart rate response to atropine sulphate following intramuscular administration of solution mixtures

Pharmacokinetics and efficacy of atropine sulfate/obidoxime chloride co-formulation against VX in a guinea pig model

Nerve agent exposure is generally treated by an antidote formulation composed of a muscarinic antagonist, atropine sulfate (ATR), and a reactivator of acetylcholinesterase (AChE) such as pralidoxime, obidoxime (OBI), methoxime, trimedoxime or HI-6 and an anticonvulsant. Organophosphates (OPs) irreversibly inhibit AChE, the enzyme responsible for termination of acetylcholine signal transduction. Inhibition of AChE leads to overstimulation of the central and peripheral nervous system with convulsive seizures, respiratory distress and death as result. The present study evaluated the efficacy and pharmacokinetics (PK) of ATR/OBI following exposure to two different VX dose levels. The PK of ATR and OBI administered either as a single drug, combined treatment but separately injected, or administered as the ATR/OBI co-formulation, was determined in plasma of naïve guinea pigs and found to be similar for all formulations. Following subcutaneous VX exposure, ATR/OBI-treated animals showed significant improvement in survival rate and progression of clinical signs compared to untreated animals. Moreover, AChE activity after VX exposure in both blood and brain tissue was significantly higher in ATR/OBI-treated animals compared to vehicle-treated control. In conclusion, ATR/OBI has been proven to be efficacious against exposure to VX and there were no PK interactions between ATR and OBI when administered as a co-formulation.

Pharmacokinetics of the oxime HI-6 from a mixture with atropine sulphate in dogs

The pharmacokinetics of the oxime HI-6 from an aqueous solution and from a mixture containing HI-6 and atropine (in doses similar as proposed for their combination in an automatic injector) was studied in German shepherd dogs. A standard manual injection of mixed drugs was followed by enhanced resorption of HI-6 while the elimination curves were quite similar. A comparison of the parameters describing relative bioavailability at the 80% probability level did not reveal any significant differences between the formulations of HI-6. The increase in HI-6 level in blood of animals receiving a mixture is more likely to be attributed to the local vasodilatation than to the systemic cardiovascular effects of atropine.

The effects of a single intramuscular injection of atropine sulphate on visual performance in man

The effects of a single intramuscular injection of 2 mg atropine sulphate on visual function were studied in volunteer subjects. The well-known effects of increased heart rate, dryness of the mouth, increased pupil diameter and reduced accommodative range were confirmed. Visual acuity, stereoacuity, red-green colour balance and reaction time to a visual stimulus were unaffected by atropine, while extraocular muscle balance (horizontal heterophoria and cyclophoria) underwent a transient change. There was no significant change in contrast sensitivity measurements to stationary sinusoidal grating patterns of spatial frequencies 1-30 c/deg; however contrast sensitivity to moving grating patterns of spatial frequencies 1-5 c/deg showed a sustained reduction which was still present at 6 h post-injection. It is concluded that atropine adversely affects movement detection but not stationary visual function.

The response to atropine sulfate given by aerosol and intramuscular routes to patients undergoing fiberoptic bronchoscopy

Two groups of 11 patients each were studied in their responses to intramuscular (IM) or aerosolized atropine sulfate, given in preparation for fiberoptic bronchoscopy. The patients in group 1 received 1.0 mg of atropine IM, and those in group 2 were given a prepared solution of atropine in saline (5 mg/ml) at a dosage of 0.1 mg/kg by nebulization (IPPB). Statistical analysis of the FVC, FEV1, FEF25-75%, and FEFmax showed excellent protective bronchodilatory effects of both IM and aerosolized atropine. In fact, the beneficial result was more prolonged when the drug was administered by inhalation. One possible factor to consider, however, is that atropine given by the aerosol route did not inhibit the vasovagal response in three of the 11 patients. Another factor to take into account is that atropine by IM injection is quicker to administer, more convenient, and requires less instrumentation than atropine given by aerosol.