t0 = 0;
tfinal = 50;
y0 = [0 0]';
% Simulate the differential equation.
[t,y] = ode23('drugmetab',[t0 tfinal],y0);

subplot(1,2,1)
plot(t,y)
title('Time history')

subplot(1,2,2)
plot(y(:,1),y(:,2))
title('Phase plane plot')