β-Lactam antibiotic-induced platelet dysfunction: Evidence for irreversible inhibition of platelet activation in vitro and in Vivo after prolonged exposure to penicillin

β-Lactam antibiotics cause platelet dysfunction with bleeding complications. Previous in vitro studies documented reversible inhibition of agonist-receptor interaction. This mechanism is inadequate to explain the effect of β-lactam antibiotics in vivo. Platelet function does not return to normal immediately after drug treatment, implying irreversible inhibition of platelet function. We report here evidence of irreversible platelet functional and biochemical abnormalities after in vitro and in vivo exposure to β-lactam antibiotics. Irreversible binding of [¹⁴C]-penicillin (Pen) occurred in vitro. After 24 hours' in vitro incubation with 10 to 20 mmol/L Pen. or ex vivo after antibiotic treatment, irreversible functional impairment occurred; but no irreversible inhibition of α₂ adrenergic receptors, measured with [³H]-yohimbine, or high-affinity thromboxane A₂/prostaglandin H₂ (TXA₂/PGH₂) receptors, measured with agonist [³H]-U46619 and antagonist [³H]-SQ29548, occurred. However, low-affinity platelet TXA₂/PGH₂ receptors were decreased 40% after Pen exposure in vitro or in vivo, indicating irreversible membrane alteration. Two postreceptor biochemical events were irreversibly inhibited in platelets incubated with Pen for 24 hours in vitro or ex vivo after antibiotic treatment. Thromboxane synthesis was inhibited 28.3% to 81.7%. Agonist-induced rises in cytosolic calcium ([Ca²⁺]_i) were inhibited 40.1% to 67.5% in vitro and 26.6% to 52.2% ex vivo. Therefore, Pen binds to platelets after prolonged exposure, resulting in irreversible dysfunction attributable to inhibition of TXA₂ synthesis and impairment of the rise in [Ca²⁺]_i, The loss of low-affinity TXA₂/PGH₂ receptors suggests that the primary site of action of these drugs is on the platelet membrane.