A Pharmacokinetic and Pharmacodynamic Study of Intravenous Pilocarpine in Humans

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Abstract
Pilocarpine (P) is of potential utility in the treatment of xerostomia. Because optimal development of P dosage forms for humans requires that its pharmacokinetics and pharmacodynamics be defined, this intravenous study of its disposition and associated salivary responses was performed. In a hospital setting, two healthy female subjects were given a series of graded doses of intravenous P or placebo to stimulate salivary secretion. Plasma levels of P, heart rate, blood pressure, and respiratory rate were simultaneously monitored. Other objective and subjective physiological parameters were assessed. Plasma concentrations of P declined either mono- or bi-exponentially with time, and brisk initial salivation was followed by prolonged salivation at doses ≥ 1 mg. At doses between 0.5 and 3.5 mg, dose-independent pharmacokinetic parameters included a small steady-state volume of distribution (2.4 to 3.0 L/kg), a high plasma clearance (0.026 to 0.03 L/kg/min), and a mean residence time of approximately 100 min. The cumulative volume of whole saliva secreted during the first 3 h post-dose was linearly related to the area under the plasma concentration-time curve. Plasma concentrations from 1 to 42 ng/mL were associated with significant levels of salivation. The pharmacokinetic linearity of the system and proportionality between the area under plasma concentration-time curves and overall salivary response have important implications for the design and utilization of pilocarpine dosage forms.