Absorption

The oral bioavailability of quinine is 76 to 88% in healthy adults. Quinine exposure is higher in patients with malaria than in healthy subjects. After a single oral dose of quinine sulfate, the mean quinine Tmax was longer, and mean AUC and Cmax were higher in patients with uncomplicated P. falciparum malaria than in healthy subjects, as shown in Table 1 below.

QUALAQUIN capsules may be administered without regard to meals. When a single oral 324 mg capsule of QUALAQUIN was administered to healthy subjects (N=26) with a standardized high-fat breakfast, the mean Tmax of quinine was prolonged to about 4.0 hours, but the mean Cmax and AUC0-24h were similar to those achieved when QUALAQUIN capsule was given under fasted conditions [see Dosage and Administration (2.1)].

Distribution

In patients with malaria, the volume of distribution (Vd/F) decreases in proportion to the severity of the infection. In published studies with healthy subjects who received a single oral 600 mg dose of quinine sulfate, the mean Vd/F ranged from 2.5 to 7.1 L/kg.

Quinine is moderately protein-bound in blood in healthy subjects, ranging from 69 to 92%. During active malarial infection, protein binding of quinine is increased to 78 to 95%, corresponding to the increase in α1-acid glycoprotein that occurs with malaria infection.

Intra-erythrocytic levels of quinine are approximately 30 to 50% of the plasma concentration.

Quinine penetrates relatively poorly into the cerebrospinal fluid (CSF) in patients with cerebral malaria, with CSF concentration approximately 2 to 7% of plasma concentration.

In one study, quinine concentrations in placental cord blood and breast milk were approximately 32% and 31%, respectively, of quinine concentrations in maternal plasma. The estimated total dose of quinine secreted into breast milk was less than 2 to 3 mg per day [see Use in Specific Populations (8.1, 8.3)].

Metabolism

Quinine is metabolized almost exclusively via hepatic oxidative cytochrome P450 (CYP) pathways, resulting in four primary metabolites, 3-hydroxyquinine, 2´-quinone, O-desmethylquinine, and 10,11-dihydroxydihydroquinine. Six secondary metabolites result from further biotransformation of the primary metabolites. The major metabolite, 3-hydroxyquinine, is less active than the parent drug.

In vitro studies using human liver microsomes and recombinant P450 enzymes have shown that quinine is metabolized mainly by CYP3A4. Depending on the in vitro experimental conditions, other enzymes, including CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP2E1 were shown to have some role in the metabolism of quinine.

Elimination/Excretion

Quinine is eliminated primarily via hepatic biotransformation. Approximately 20% of quinine is excreted unchanged in urine. Because quinine is reabsorbed when the urine is alkaline, renal excretion of the drug is twice as rapid when the urine is acidic than when it is alkaline.

In various published studies, healthy subjects who received a single oral 600 mg dose of quinine sulfate exhibited a mean plasma clearance ranging from 0.08 to 0.47 L/h/kg (median value: 0.17 L/h/kg) with a mean plasma elimination half-life of 9.7 to 12.5 hours.

In 15 patients with uncomplicated malaria who received a 10 mg/kg oral dose of quinine sulfate, the mean total clearance of quinine was slower (approximately 0.09 L/h/kg) during the acute phase of the infection, and faster (approximately 0.16 L/h/kg) during the recovery or convalescent phase.

Extracorporeal Elimination: Administration of multiple-dose activated charcoal (50 grams administered 4 hours after quinine dosing followed by 3 further doses over the next 12 hours) decreased the mean quinine elimination half-life from 8.2 to 4.6 hours, and increased the mean quinine clearance by 56% (from 11.8 L/h to 18.4 L/h) in 7 healthy adult subjects who received a single oral 600 mg dose of quinine sulfate. Likewise, in 5 symptomatic patients with acute quinine poisoning who received multiple-dose activated charcoal (50 grams every 4 hours), the mean quinine elimination half-life was shortened to 8.1 hours in comparison to a half-life of approximately 26 hours in patients who did not receive activated charcoal [see Overdosage (10)].

In 6 patients with quinine poisoning, forced acid diuresis did not change the half-life of quinine elimination (25.1 ± 4.6 hours vs. 26.5 ± 5.8 hours), or the amount of unchanged quinine recovered in the urine, in comparison to 8 patients not treated in this manner [see Overdosage (10)].

Specific Populations

Pediatric Patients: The pharmacokinetics of quinine in children (1.5 to 12 years old) with uncomplicated P. falciparum malaria appear to be similar to that seen in adults with uncomplicated malaria. Furthermore, as seen in adults, the mean total clearance and the volume of distribution of quinine were reduced in pediatric patients with malaria as compared to the healthy pediatric controls. Table 2 below provides a comparison of the mean ± SD pharmacokinetic parameters of quinine in pediatric patients vs. healthy pediatric controls.

Geriatric Patients: Following a single oral dose of 600 mg quinine sulfate, the mean AUC was about 38% higher in 8 healthy elderly subjects (65 to 78 years old) than in 12 younger subjects (20 to 35 years old). The mean Tmax and Cmax were similar in elderly and younger subjects after a single oral dose of quinine sulfate 600 mg. The mean oral clearance of quinine was significantly decreased, and the mean elimination half-life was significantly increased in elderly subjects compared with younger subjects (0.06 vs. 0.08 L/h/kg, and 18.4 hours vs. 10.5 hours, respectively). Although there was no significant difference in the renal clearance of quinine between the two age groups, elderly subjects excreted a larger proportion of the dose in urine as unchanged drug than younger subjects (16.6% vs. 11.2%).

After a single 648 mg dose or at steady state, following quinine sulfate 648 mg given three times daily for 7 days, no difference in the rate and extent of absorption or clearance of quinine was seen between 13 elderly subjects (65 to 78 years old) and 14 young subjects (20 to 39 years old). The mean elimination half-life was 20% longer in the elderly subjects (24.0 hours) than in younger subjects (20.0 hours). The steady state Cmax (±SD) and AUC0-8 (±SD) for healthy volunteers are 6.8 ± 1.24 mcg/mL and 48.8 ± 9.15 mcg*h/mL, respectively, following 7 days of oral quinine sulfate 648 mg three times daily. The steady state pharmacokinetic parameters in healthy elderly subjects were similar to the pharmacokinetic parameters in healthy young subjects.

Renal Impairment: Following a single oral 600 mg dose of quinine sulfate in otherwise healthy subjects with severe chronic renal failure not receiving any form of dialysis (mean serum creatinine = 9.6 mg/dL), the median AUC was higher by 195% and the median Cmax was higher by 79% than in subjects with normal renal function (mean serum creatinine = 1 mg/dL). The mean plasma half-life in subjects with severe chronic renal impairment was prolonged to 26 hours compared to 9.7 hours in the healthy controls. Computer assisted modeling and simulation indicates that in patients with malaria and severe chronic renal failure, a dosage regimen consisting of one loading dose of 648 mg QUALAQUIN followed 12 hours later by a maintenance dosing regimen of 324 mg every 12 hours will provide adequate systemic exposure to quinine [see Dosage and Administration (2.2)]. The effects of mild and moderate renal impairment on the pharmacokinetics and safety of quinine sulfate are not known.

Negligible to minimal amounts of circulating quinine in the blood are removed by hemodialysis or hemofiltration. In subjects with chronic renal failure (CRF) on hemodialysis, only about 6.5% of quinine is removed in 1 hour. Plasma quinine concentrations do not change during or shortly after hemofiltration in subjects with CRF [see Overdosage (10)].

Hepatic Impairment: In otherwise healthy subjects with mild hepatic impairment (Child-Pugh A; N=10), who received a single 500 mg dose of quinine sulfate, there was no significant difference in quinine pharmacokinetic parameters or exposure to the primary metabolite, 3-hydroxyquinine as compared to healthy controls (N=10). In otherwise healthy subjects with moderate hepatic impairment (Child-Pugh B; N=9) who received a single oral 600 mg dose of quinine sulfate, the mean AUC increased by 55% without a significant change in mean Cmax, as compared to healthy volunteer controls (N=6). In subjects with hepatitis, the absorption of quinine was prolonged, the elimination half-life was increased, the apparent volume of distribution was higher, but there was no significant difference in weight-adjusted clearance. Therefore, in patients with mild to moderate hepatic impairment, dosage adjustment is not needed, but patients should be monitored closely for adverse effects of quinine [see Use in Specific Populations (8.7)].

In subjects with severe hepatic impairment (Child-Pugh C; N=10), quinine oral clearance (CL/F) was reduced as was formation of the primary 3-hydroxyquinine metabolite. Volume of distribution (Vd/F) was higher and the plasma elimination half-life was increased. Therefore, quinine is not indicated in this population and alternate therapy should be administered [see Dosage and Administration (2.3)].