found to have the lowest solubility at a pH range of 4 to 6. The relative solubility (the pH‐apparent solubility profile) of amphoteric penicillin (amoxicillin) was determined under physiological temperature conditions for amoxicillin and the results indicated U‐shaped pH‐solubility curve, with the minimum solubility at the pH near the isoelectric point26. Staniforth et al., postulated that there is increase in solubility of amoxicillin at a higher pH.