Pharmacokinetics of quinine in chronic liver disease

Treatment of Muscle Cramps in Patients With Cirrhosis of Liver: A Systematic Review

BACKGROUND

Muscle cramps are witnessed in 22-88% of patients with cirrhosis of liver and frequently lead to sleep disturbance with an appalling impact on quality of life. Despite such a high prevalence, there is lack of evidence-based management protocol due to scarcity of trials on treatment options in the literature. This study aimed to review systematically the available therapeutic options for muscle cramps in patients with cirrhosis of liver.

METHODS

A systematic review of the relevant databases (PubMed, Scopus, Embase, and Web of Science) to identify treatments for muscle cramps in patients with hepatic cirrhosis was performed. Studies meeting the selection criteria were reviewed and assessed for risk of bias and analyzed.

RESULTS

Twenty-four publications were identified as eligible for inclusion in this systematic review. Seven randomized controlled trials (RCTs) and 17 prospective studies were included. Taurine, methocarbamol, baclofen, and orphenadrine are relatively safer and effective treatment option for muscle cramps in cirrhosis on the basis of recently conducted RCTs. Moreover, l-carnitine, branched-chain amino acids (BCAAs), pregabalin, zinc, and vitamin D are also safe and showed beneficial effects on muscle cramps. However, studies on vitamin E revealed contradictory results.

CONCLUSION

Taurine, BCAAs, orphenadrine, and baclofen are safe and well-tolerated treatment options for muscle cramps in cirrhosis. However, well-designed randomized controlled clinical trials are the need of the hour to determine the most suitable treatment options for skeletal muscle cramps in patients with cirrhosis of liver.

Irreversible CYP3A inhibition accompanied by plasma protein-binding displacement: a comparative analysis in subjects with normal and impaired liver function

In this study, quinine was used as a probe substrate and erythromycin as a prototypical irreversible inhibitor of CYP3A to ascertain whether, like reversible CYP inhibition, the magnitude of irreversible inhibition is also strictly dependent on the status of liver function. The effect of erythromycin on oral quinine disposition was studied in 10 healthy subjects and in 20 patients with cirrhosis of the liver who had varying degrees of liver dysfunction. This effect was shown to be the result of two types of interaction: (i) irreversible inhibition of CYP3A-mediated quinine metabolism, the extent of which proved to be independent of liver function, and (ii) displacement of quinine from plasma protein-binding sites, the magnitude of the displacement increasing dramatically as liver function worsened. Such an interaction causes limited increases in the total concentration of the displaced drug but disproportionate increases in its free concentration; the latter increases are magnified by liver dysfunction, thereby requiring that the monitoring of free drug concentrations be made mandatory.

Pharmacokinetic interactions of antimalarial agents

Combination of antimalarial agents has been introduced as a response to widespread drug resistance. The higher number of mutations required to express complete resistance against combinations may retard the further development of resistance. Combination of drugs, especially with the artemisinin drugs, may also offer complete and rapid eradication of the parasite load in symptomatic patients and thus reduce the chance of survival of resistant strains. The advantages of combination therapy should be balanced against the increased chance of drug interactions. During the last decade, much of the pharmacokinetics and metabolic pathways of antimalarial drugs have been elucidated, including the role of the cytochrome P450 (CYP) enzyme complex. Change in protein binding is not a significant cause of interactions between antimalarial agents. CYP3A4 and CYP2C19 are frequently involved in the metabolism of antimalarial agents. Quinidine is a potent inhibitor of CYP2D6, but it appears that this enzyme does not mediate the metabolism of any other antimalarial agent. The new combinations proguanil-atovaquone and chlorproguanil-dapsone do not show significant interactions. CYP2B6 and CYP3A4 are involved in the metabolism of artemisinin and derivatives, but further studies may reveal involvement of more enzymes. Artemisinin may induce CYP2C19. Several artemisinin drugs suffer from auto-induction of the first-pass effect, resulting in a decline of bioavailability after repeated doses. The mechanism of this effect is not yet clear, but induction by other agents cannot be excluded. The combination of artemisinin drugs with mefloquine and the fixed combination artemether-lumefantrine have been studied widely, and no significant drug interactions have been found. The artemisinin drugs will be used at an increasing rate, particularly in combination with other agents. Although clinical studies have so far not shown any significant interactions, drug interactions should be given appropriate attention when other combinations are used.

Single-dose pharmacokinetics of repaglinide in subjects with chronic liver disease

Repaglinide is a novel insulin secretagogue developed in response to the need for a fast-acting, oral prandial glucose regulator for the treatment of type 2 (non-insulin-dependent) diabetes mellitus. Repaglinide is metabolized mainly in the liver; its pharmacokinetics may therefore be altered by hepatic dysfunction. This open, parallel-group study compared the pharmacokinetics and tolerability of a single 4 mg dose of repaglinide in healthy subjects (n = 12) and patients with chronic liver disease (CLD) (n = 12). Values for AUC and Cmax were significantly higher in CLD patients compared with healthy subjects, and the MRT was prolonged in CLD patients. Values for tmax did not differ between the groups, but t1/2 was significantly prolonged in CLD patients compared with previously determined values in healthy subjects. AUC was inversely correlated with caffeine clearance in CLD patients but not in healthy subjects. Blood glucose profiles were similar in both groups. Adverse events (principally hypoglycemia) were similar in the two groups; none was serious. Repaglinide clearance is significantly reduced in patients with hepatic impairment; the agent should be used with caution in this group.

Pharmacokinetics of quinine in patients with chronic renal failure

METHODS. We investigated the pharmacokinetics of quinine (Qn) following administration of a single oral dose of 600 mg Qn sulphate in six male Thai patients with a moderate degree of chronic renal failure (CRF), and six male Thai subjects with normal renal function. RESULTS. The drug was well tolerated in both groups of subjects; no major adverse reactions were observed. A marked alteration in the pharmacokinetics of Qn was found in patients with CRF compared to healthy subjects; there were six significant changes in the pharmacokinetic parameters. Absorption was delayed, but increased in CRF (tmax 4.5 vs 1.6 h, Cmax 6.17 vs 3.45 micrograms.ml-1). Total clearance was significantly reduced (0.94 vs 2.84 ml.min-1.kg-1, whereas Vz/f remained unchanged (1.82 vs 2.78 l. kg-1). This resulted in the increased values of AUC and prolongation of the t1/2z and MRT in the patients (AUC 181.5 vs 61.8 micrograms.min-1.ml-1, t1/2z 26 vs 9.7 h, MRT 36.4 vs 11.3 h). Median concentrations of plasma unbound fraction of Qn collected at 4 h after drug administration in patients and healthy subjects were 7.3 vs 9.8%, respectively.