Verapamil in the prophylaxis of bronchial asthma. Is the bronchoprotective effect related to the plasma level?

A single oral dose of verapamil 80 mg was shown significantly to inhibit histamine-induced broncho-constriction in 8 out of 16 asthmatic subjects (maximum increase in PD20FEVHi 416%). There was still significant protection (delta PD20FEV1Hi greater than 100%) in the responders 5 h after the oral dose. The relationship of the bronchoprotective effect to the plasma level of verapamil was also examined. Responders and non-responders did not differ significantly in the peak plasma level or the time course of the plasma verapamil concentration. The protective effect was not correlated with the peak plasma level of verapamil or with the baseline bronchial hyperreactivity.