In this study, we investigated the effects of certain respiratory drugs, which are mainly used on human serum paraoxonase-1 (hPON1; EC 188.8.131.52). hPON1 was purified from human serum, with 354.91 fold and 45% yield by using two simple step procedures including, first, ammonium sulfate precipitation, then, Sepharose-4B-l-tyrosine-1-naphthylamine hydrophobic interaction chromatography. SDS-polyacrylamide gel electrophoresis showed a single protein band belonging to hPON1 with 43 kDa. All the pharmaceutical compounds inhibited the PON1 enzyme highly at the micromolar level. The obtained IC50 values for nine different pharmaceutics ranged from 0.219 mu M (salbutamol sulfate) to 67.205 mu M (montelukast sodium). So, all drugs could be considered as potent hPON1 inhibitors. K-i values and inhibition types were determined by Lineweaver-Burk graphs. While varenicline tartrate and moxifloxacin hydrochloride inhibited the enzyme in a noncompetitive manner, others inhibited it in a mixed manner.