BOX 6.1
Drug Interactions

  • Beta-adrenergic blockers (beta blockers): PB might interact with non-selective beta-blockers, potentially precipitating bronchospasm.

  • Alpha-adrenergic agonists: Epinephrine and norepinephrine act additively to increase PB lethality in mice when given prior to PB.

  • Other cardiac drugs: PB may interact with calcium channel antagonists or other direct-acting vasodilators which might intensify orthostatic hypotension (IOM 1996, Health consequences).

  • Quinidine: PB might accentuate atrioventricular block, resulting in hypotension.

  • Anti-malarials drugs (e.g., quinine, quinidine, and chloroquine): Might potentiate gastrointestinal effects including diarrhea associated with PB.

  • Quinolone antibiotics have been associated with diffuse weakness and dyspnea in patients with myasthenia gravis treated with PB.

  • Acetazolamide: may cause exacerbations of muscle weakness in patients with myasthenia gravis, an interaction which might be of concern given the potential use of acetazolamide by troops to prevent altitude-related symptoms.

  • Hormones: Oral contraceptive pills and corticosteroids may decrease plasma cholinesterase levels by up to 50 percent. This effect might be of importance in PB-treated patients also treated with succinylcholine and ester local anesthetics which depend upon plasma cholinesterase for metabolism.

  • Thiopental (Pentothal): Because thiopental can induce bronchospasm and reduce blood pressure, careful monitoring of troops with asthma or hemorrhage (hypovolemia) if previously treated with PB has been suggested.

  • Opioids might interact with PB to enhance bradycardia. The vasodilatory effect of morphine could also augment any hypotensive effects of PB.

  • Neuromuscular blocking agents: Non-depolarizing (curariform) agents such as Pavulon, which compete for acetylcholine, could be antagonized by pre-treatment with PB. Depolarizing agents such as succinylcholine, which cause tonic stimulation of nicotinic receptors, would be augmented by pretreatment with PB.

  • Local anesthetics: PB could interact with the ester or procaine-like compounds such as cocaine and tetracaine by inhibiting plasma cholinesterase which is necessary for their metabolism. Such inhibition could result in high serum concentrations of these drugs, potentially leading to cardiac arrhythmias or central nervous system toxicity.

SOURCE: Madsen (1998).

Clinical Studies of PB and Respiratory Effects

The respiratory effects of PB have been studied in clinical investigations of normal subjects, asthmatics, and individuals with myasthenia gravis. All of the

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