Lack of effect of treatment with human recombinant-tumour necrosis factor (HrTNF) on the binding of quinidine to alpha 1-acid glycoprotein (AGP)

Pharmacokinetics of quinine, chloroquine and amodiaquine. Clinical implications

Malaria is associated with a reduction in the systemic clearance and apparent volume of distribution of the cinchona alkaloids; this reduction is proportional to the disease severity. There is increased plasma protein binding, predominantly to alpha 1-acid glycoprotein, and elimination half-lives (in healthy adults quinine t1/2z = 11 hours, quinidine t1/2z = 8 hours) are prolonged by 50%. Systemic clearance is predominantly by hepatic biotransformation to more polar metabolites (quinine 80%, quinidine 65%) and the remaining drug is eliminated unchanged by the kidney. Quinine is well absorbed by mouth or following intramuscular injection even in severe cases of malaria (estimated bioavailability more than 85%). Quinine and chloroquine may cause potentially lethal hypotension if given by intravenous injection. Chloroquine is extensively distributed with an enormous total apparent volume of distribution (Vd) more than 100 L/kg, and a terminal elimination half-life of 1 to 2 months. As a consequence, distribution rather than elimination processes determine the blood concentration profile of chloroquine in patients with acute malaria. Parenteral chloroquine should be given either by continuous intravenous infusion, or by frequent intramuscular or subcutaneous injections of relatively small doses. Oral bioavailability exceeds 75%. Amodiaquine is a pro-drug for the active antimalarial metabolite desethylamodiaquine. Its pharmacokinetic properties are similar to these of chloroquine although the Vd is smaller (17 to 34 L/kg) and the terminal elimination half-life is 1 to 3 weeks.

Alpha 1-acid glycoprotein (orosomucoid) and plasma protein binding of quinine in falciparum malaria

1. Plasma concentrations of alpha 1-acid glycoprotein (AAG) and plasma protein binding of quinine were measured in 97 Thai adults with acute falciparum malaria. There was a linear relationship between log AAG and percentage quinine binding (r = 0.71, P less than 0.001) in vivo, which was similar to that observed in vitro; the slopes and intercepts of the regression lines at AAG concentrations of 1 g l-1 were -8.94 and -8.41, and 7.2% and 10.9%, respectively. 2. Hill plots from these data suggest a single high affinity quinine binding site on each molecule of AAG. 3. Plasma AAG concentrations were consistently raised in acute malaria, and were higher in patients with cerebral malaria [2.03 (0.51) g l-1, mean (s.d.)], and conscious patients with severe malaria [1.93 (0.53) g l-1] than in patients with uncomplicated infections [1.55 (0.58) g l-1], P = 0.008. Plasma protein binding of quinine was correspondingly higher and thus the proportion of free drug was lower in the severe groups; 5.5 (2.4)% compared with 7.2 (1.9)%, P = 0.03. 4. Following recovery from malaria, plasma AAG concentrations fell by an estimated 0.05 g l-1 day-1 to levels that were approximately half (median 45%) the admission value at 28 days. 5. AAG is the principal binding protein for quinine in plasma. Changes in plasma concentrations of this acute phase reactant account for the increased plasma protein binding of quinine in acute malaria.