A three-year-old child is brought to the emergency department having just ingested a large overdose of an antihistaminic drug. This drug is a weak base capable of entering most tissues including the brain. On physical examination the heart rate is 100/minute, blood pressure is 110/60 mm Hg and the respiratory rate is 20/minute. In this case of poisoning:

- Ionization of acidic drugs is increased in alkaline urine and vice versa. Ionized drugs cannot cross the plasma membrane easily. So is not reabsorbed into the blood from the tubules. Hence, enhanced excretion of the acidic drug through alkaline urine or basic drug through acidic urine.  - A basic drug would be ionized more in acidic pH. Plasma is alkaline. - The un-ionized form is absorbed easily. So absorption will be more in an alkaline environment in the intestine.