Pharmacokinetics and pharmacodynamics of clonidine in varying states of renal function

Population pharmacokinetics of intravenous clonidine for sedation during paediatric extracorporeal membrane oxygenation and continuous venovenous hemofiltration

AIMS

Clonidine is used for sedation in the paediatric intensive care unit. Extracorporeal membrane oxygenation (ECMO) provides temporary support if respiratory and cardiac function is threatened. ECMO influences the pharmacokinetics of drugs. Clonidine during paediatric ECMO cannot be effectively titrated as PK data are lacking. The aim of this study is to describe clonidine PK in a particular ECMO system and propose dosing guidelines for children on this particular ECMO circuit.

METHODS

All children below the age of 18 years who received clonidine during ECMO were eligible. The pharmacokinetic analysis was conducted by nonlinear mixed effect modelling, which enables to establish the separate influences of determinants on drug blood level and to provide individualized dosing.

RESULTS

Twenty-two patients, median age 1 month (IQR 6.4) and weight at inclusion 4 kg (IQR 3.1) were included of whom 90% in addition to ECMO received pre-emptive continuous venovenous hemofiltration to optimize fluid balance. The clonidine clearance rate was two-fold that measured in patients not on ECMO. Clearance increased steeply with postnatal age: at days 6, 8 and 10, respectively 30%, 50% and 70% of the adult clearance rate was reached. The use of diuretics was associated with a lower clearance. The volume of distribution increased by 55% during ECMO support.

CONCLUSION

Our findings suggest that a higher dose of clonidine may be needed during ECMO. The PK parameters on ECMO and the dosing guidelines proposed hold the potential to improve sedation practices on ECMO but need to be repeated with different ECMO systems.

Pharmacologic Issues in treating hypertension in CKD

Antihypertensive drugs are prescribed to patients with CKD to slow down the rate of loss of residual kidney function; to reduce proteinuria, when present; and to protect other target organs from damage that is mediated by elevated blood pressure (BP). In most patients, a diuretic and a renin system blocking drug, such as an angiotensin-converting enzyme inhibitor, angiotensin receptor antagonist, or an aldosterone receptor antagonist are used. Often, 3 or more drugs are needed to achieve BP goals. Many drugs are eliminated through the kidney and in some cases dosage reductions are advisable to avoid adverse effects from high levels of medication. This article will review the various classes of antihypertensive drugs used in the management of high BP in patients with CKD, with an emphasis on pitfalls that arise when kidney function is impaired.

Clonidine clearance matures rapidly during the early postnatal period: a population pharmacokinetic analysis in newborns with neonatal abstinence syndrome

The population pharmacokinetic (PK) profile of oral clonidine was characterized in newborns with neonatal abstinence syndrome, and significant covariates affecting its PK parameters were identified. Plasma clonidine concentration data were obtained from a clinical trial in which 36 newborns, aged 1 to 25 days (postnatal age, PNA) and weighing 2.1 to 3.9 kg, were enrolled to take multiple oral doses of clonidine. The population PK model of clonidine was developed by NONMEM, and significant covariates were identified, followed by nonparametric bootstraps (2000 replicates) and simulation experiments. A 1-compartment open linear PK model was chosen to describe plasma concentrations of clonidine, and body weight and PNA were significant covariates for apparent clearance (CL/F) as follows: CL/F (L/h) = 15.2 × [body weight (kg)/70](0.75) × [PNA (day)(0.441)/(4.06(0.441) + PNA (day)(0.441))]. Furthermore, CL/F of clonidine increased rapidly with PNA during the first month of life after body weight was adjusted. Any optimal dosage regimen for clonidine in term neonates should be based on infant's age and body weight, and 1.5 µg/kg every 4 hours is proposed starting the second week of life based on the simulation results.

Clinical pharmacokinetics of clonidine

Clonidine is a centrally active antihypertensive agent effective in the treatment of mild, moderate and severe hypertension, alone or in combination with other drugs. Use of oral clonidine has often been limited by side effects which include dry mouth and drowsiness. Transdermal clonidine was therefore developed as an alternative to oral therapy. Ideally, a drug administered at a constant rate into the systemic circulation should attain steady-state concentrations with less peak-to-trough fluctuation than that associated with intermittent oral dosing. In theory, transdermal administration should thus minimise the adverse effects associated with peak plasma drug concentration, while avoiding the potential for decreased efficacy associated with trough levels. Clonidine has been incorporated into a small, pliable adhesive cutaneous delivery device designed to provide therapeutically effective doses of drug at a constant rate for at least 7 days. The transdermal therapeutic system is a laminate consisting of an external film impermeable to moisture and to the drug, a thin layer of active drug dispersed within a highly drug-permeable matrix, a membrane with a controlled intrinsic permeability regulating the rate of delivery of drug to the skin, and an adhesive coating that attaches the system to the skin surface. The permeation of drug through the skin occurs primarily by diffusion. Application of the clonidine transdermal system to both normotensive and hypertensive subjects has consistently reduced systolic and diastolic blood pressures. Maximum reduction in blood pressure occurs 2 to 3 days after initial application, and is maintained for at least 7 days or until the system is removed. The rate at which clonidine is presented to the skin surface is controlled by the microporous membrane: this rate is the same for all strengths of transdermal clonidine, the amount of clonidine released being proportional to its surface area. Thus, the daily dose is regulated by the area of skin covered. Typically, steady-state plasma concentrations are reached on the fourth day after initial transdermal system application. The lack of dose dependency in half-life and renal clearance estimates emphasise that the transdermal absorption of clonidine is linear. The plasma clonidine concentration produced by a particular transdermal dose varies considerably between individuals as a result of interindividual variation in renal clearance. For this reason, it is recommended that dosages be titrated up from the smallest system (3.5 cm2) until the desired pharmacological effect has been obtained.(ABSTRACT TRUNCATED AT 400 WORDS)