Comparison of the pharmacokinetic profiles of soluble aspirin and solid paracetamol tablets in fed and fasted volunteers

The aim oft his study was to investigate the absorption of popular preparat ions of two common analgesics - soluble aspirin and solid paracetamol table ts. An open, randomised, crossover study design was used to compare the pha rmacokinetic parameters of soluble aspirin and solid paracetamol tablets in 16 healthy, male volunteers from the University of the Witwatersrand, Sout h Africa, in both fed and fasted states. Plasma concentrations of paracetam ol, aspirin and salicylic acid were measured. It was found that the rate of absorption was significantly faster for soluble aspirin than for solid par acetamol, regardless of fed or fasting state, considering time to maximum c oncentration (p < 0.01), time to first quantifiable concentrations (p < 0.0 5) and absorption rate (p < 0.01). Absorption rate was significantly affect ed by food for both soluble aspirin (p = 0.028) and for solid paracetamol ( p = 0.0003). Time to maximum concentration was not significantly affected b y food for soluble aspirin (p = 0.17) but significantly lengthened for soli d paracetamol (p = 0.0003). The extent of absorption was affected by food i n terms of maximum concentration for both drugs (p = 0.0001), with a reduct ion of 49% in the fed stare for solid paracetamol compared to 18% for solub le aspirin, the difference between the drugs being statistically significan t (p = 0.0024). The overall bioavailability of soluble aspirin was unaffect ed by food and the bioavailability of salicylic acid was increased in the f ed state, whereas that of solid paracetamol was lowered in the fed state. G reater inter-individual variation was seen in paracetamol concentrations co mpared with aspirin or salicylic acid levels. In conclusion, these results show that the absorption of soluble aspirin is largely unaffected by food, whereas, in the same volunteers, the absorption of solid paracetamol tablet s is greatly affected. In some volunteers, maximum plasma concentrations of paracetamol following food did not reach levels previously reported to be required for effective analgesia, and this may have implications for pain r elief in some individuals. The practice in some individuals of taking aspir in tablets after food to minimise potential gastric disturbance should not affect the level of analgesia.