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352 CLINICAL PHARMACOLOGY OF TOLAZOLINE (Tz) IN PERSISTENT FETAL CIRCULATION (PFC)

The effect of Tz in treatment of PFC was evaluated in 14 neonates (gestational age (GA) ≤ 34 weeks, n=6) receiving maximal assisted ventilation. Intravenous Tz was administered as a loading dose of 1 to 2 mg/kg followed by a continuous intravenous infusion of 1 mg/kg/hr. The dose was increased up to 4 mg/kg/hr based on the patients clinical response. Clinical status, laboratory parameters and Tz serum concentrations were monitored throughout therapy. A positive response to Tz was observed in 70% of the patients. A curvilinear relationship was noted between Tz serum concentrations and PaO2/FiO2 ratio. The response to tolazoline was dependent on GA, serum concentration and arterial pH. A significant difference (p < 0.05) in the responsiveness to tolazoline was observed between neonates > 34 weeks and ≤ 34 weeks GA. In neonates > 34 weeks, positive therapeutic response was observed with arterial pH > 7.45 and Tz serum concentrations of 2-4 μg/ml. Neonates of ≤ 34 weeks GA, a positive therapeutic response was seen at serum concentration of 4.4 - 7.7 μg/ml and an arterial pH of 7.31 - 7.44. Systemic hypotension and GI bleeding were observed in 28.6% of the patients. This was related to high serum concentrations and arterial pH < 7.30. The rational use of Tz for the treatment of PFC requires careful monitoring of respiratory status, pH, blood pressure and serum Tz concentration.