Biopharmaceutical Studies of Drugs. I. Effect of Salicylamide on Serum Concentration of Pentazocine after Oral Administration

Abstract

The serum concentration of unchanged pentazocine (PA) was investigated in rabbits when PA was administered concurrently with acetaminophen, salicylamide (SAM), salicylic acid, acetylsalicylic acid, or p-aminosalicylic acid. The serum concentration of unchanged PA increased when 20 mg/kg PA was administered concurrently with 80 mg/kg SAM as compared with the administration of 20 mg/kg PA alone, but no similar results were obtained with the other drugs. The co-administration of PA and SAM also decreased serum and urinary PA glucuronide. On the other hand, when 80 mg/kg SAM and 375.6 mg/kg PA were administered together, the serum and urinary concentration of unchanged SAM was increased, while SAM glucuronide was decreased. We posit that the effect noted in the simultaneous 20 mg/kg PA and 80 mg/kg SAM administration experiments is due to competitive inhibition of glucuronidation.