Effect of Captopril first doses on Blood Pressure and Renal Function in Children with Congestive Cardiac Failure Dr Hussain Mulla, Co-Director, Centre for Therapeutic Evaluation of Drugs in Children, University Hospitals of Leicester NHS Trust

First Dose Captopril Effects on Blood Pressure and Renal Function Hussain Mulla PhD MRPharmS Senior Research Pharmacist, Paediatric Clinical Pharmacology Centre for Therapeutic Evaluation of Drugs in Children

Background ACEi doses for children with congestive cardiac failure derive from non-randomised and historical cohort studies (c.f. adults and RCT). Adverse effects of hypotension (first dose), renal dysfunction, hyperkalaemia, cough First dose hypotension 11-32% documented in adults Similar pharmacovigilance data lacking for children 1 report in children documented first dose hypotension incidence of 15%

Audit Methods Retrospective (Apr 2007 – Mar 2009) Data extracted from medical records, drug and TPR charts. No control of patient or drug related factors that could bias results Often more than one test dose administered No a priori calculation of sample size for detection of adverse event rate. Small sample size (n=48)

Results Mean (range)

Blood Pressure Effects Test dose of Captopril produced Mean peak fall in systolic blood pressure post dose of  15.6 (p<0.0005) Mean peak fall in diastolic blood pressure post dose of  12.7 (p<0.0005) 9 patients (18%) developed hypotension (drop in SBP > 25%), 1 of whom had captopril stopped No significant differences between the ages of patients who developed hypotension

Renal Effects

Conclusion / Discussion Incidence of first dose hypotension similar to adults No cases of acute renal failure Is it safe to initiate captopril in the community by GPs?

Analysis 2: PK-PD Model of SBP Response to Captopril Initiation Drug Disposition Effect Covariates Pharmacokinetics Pharmacodynamics Ka PK/PD

PK – PD Modelling Drug Concentration Response Time Response PKPD PK-PD

Why Model? 1. Modelling Quantifies the exposure-response relationship 2. Modelling provides Clarity / Insight 3. Modelling gives a Mechanistic Understanding of the drug effect 4. Modelling enables Extrapolation beyond the observed data 5. Modelling provides scientific rationale to Dose Selection

K-PD Modelling No Pharmacokinetic data available Only kinetics of response (BP) is measured Dose rate as a function of time, drives the PD (rather than traditional PK profile) A simple 1 compartmental model describes kinetics in the biophase (where drug action takes place)

The Model : Vasodilatory Effects of ACEi Indirect Response (turnover) PD Model Kout (Fractional turnover rate) Kin (turnover rate) Response (Blood Pressure) Dose (captopril) A(t) Ke Biophase Input Rate (IR)=Ke.A(t)

Model Results: Parameter Estimates Kin – zero order synthesis constant for response Kout – first order degradation rate constant for response EDK50 – dose that leads to 50% reduction in SBP ne – not estimated

Model Results: Population Mean Prediction vs Time

Model Results Peak reduction in BP estimated as 10mmHg Significant variability around the mean response Tmax of response estimated as 1.1 hrs Return to baseline estimated as between 4 – 6 hours

Simulated response with time

Conclusion / Discussion Audit suggests 0.1mg/kg associated with low incidence of asymptomatic hypotension Variability in response may be related to Diagnosis / Clinical factors Baseline BP Formulation Factors Fed/Fasted state/Ng tube/GI transit time Mobile/supine/sitting up PK/PD modelling can provide further insight into the data Prospective safety study required to determine true incidence of hypotension

Acknowledgements Eve Oualid – School of Pharmacy, University of Joseph Fourier, Grenoble, France Sarah Wheeler – Glenfield Hospital, University Hospitals of Leicester