A three year old child is brought to the emergency depament 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 hea rate is 100/ minute, blood pressure is 110/60 mm Hg and the respiratory rate is 20/ minute. In this case of poisoning:
This question can be solved by the knowledge that basic drugs are ionized in the acidic medium and vice-a-versa. This antihistaminic drug is a weak base and will be highly ionized in the acidic urine. As ionized drugs cannot be reabsorbed in the nephron, urinary acidifying agents like NH4Cl will accelerate the excretion of this agent. On the other hand, NaHCO3 will decrease its excretion by increasing the unionized form. Blood pH is slightly alkaline (7.4) whereas gastric pH is highly acidic. Basic drugs are ionized more in the acidic pH, therefore option (c) is false. Only unionized molecules can cross the membranes, therefore more drug will be absorbed by the small intestine (alkaline pH).
Urinary excretion would be accelerated by administration of NH4Cl, an acidifying agent
Urinary excretion would be accelerated by administration of NaHCO 3, an alkalinizing agent
More of the drug would be ionized at blood pH than at stomach pH
Absorption of the drug would be faster from the stomach than from the small intestine.
Histamine, 5-HT and PGs