TABLE I.

Percentile Contribution of the Different Forms of Astemizole (pK_a1 = 5.6 and pK_a2 = 8.5) at Different pH

	pH
	6.4	7.4	8.4
	%	%	%
Unprotonateda	0.7	7.3	44.2
Monoprotonatedb	85.7	91.3	55.7
Diprotonatedc	13.6	1.4	0.1

^a=100 × [H⁺]² ÷ den.

^b=100 × [H⁺] × K_a1 ÷ den.

^c=100 × K_a1 × K_a2 ÷ den, where den = [H⁺]² + [H⁺] × K_a1 + K_a1 × K_a2 (Netter, 1969).