Evaluation of antihypertensive drugs

Evaluation of antihypertensive drugs

1. Evaluation of antihypertensive drugs Dr. Ashishkumar baheti Md pharmacology

2. Need for new drug Treating HT is cost effective than treating the complications Average reduction in complication after effective treatment Stroke incidence 35–40% Myocardial infarction 20–25% Heart failure 50% Various side effects of existing antihypertensive drugs Large market : industry interest

3. Pre-clinical evaluation of antihypertensive drug

4. I) Pharmacodynamic studies

5. P/D: studies related to proposed therapeutic indication In-vitro studies: - Receptor specific studies - Studies on isolated tissues In-vivo studies: Animal models of hypertension

6. In-vitro studies In-vitro studies: - Receptor specific studies - Studies on isolated tissues

7. Receptor specific studies RECEPTOR TISSUE SPECIMEN α1-adrenoreceptor binding male Wistar rat submaxillary glands α2-adrenoreceptor binding Male Wistar rats cortical tissue β- adrenoreceptor binding bovine heart ventricles consists of 75–80% β1- and 20–25% β2-adrenoceptors. β2-adrenoreceptor binding Male Wistar rats : lungs Angiotensin II receptor binding rat adrenal glands,

8. Studies on isolated tissues ACTIVITY isolated organs α- sympatholytic activity guinea pig seminal vesicle β1 sympatholytic activity isolated guinea pig atria β2 sympatholytic activity isolated guinea pig tracheal chain Angiotensin converting enzyme inhibition isolated guinea pig ileum, effects of potassium channel openers Isolated guinea pig ureter

9. In-vivo studies: Animal models of hypertension

10. Various types of animal models of hypertension Renovascular hypertension Dietary hypertension Endocrine hypertension Psychogenic hypertension Genetic hypertension Other models

11. Other models Obesity –related hypertension Angiotensin-II induced hypertension Cadmium induced hypertension Chronic nitric oxide inhibition-induced hypertension Transgenic rat (TGR) models Uterine ischemia

12. Renovascular Hypertension Very commonly used model of hypertension RAAS plays important role

13. Methods of inducing renovascular hypertension External compression of renal parenchyma Reduced renal mass Glomerular sclerosis

14. Renovascular hypertension Goldblatt method Renal artery constriction activates peripheral RAAS and sympathetic nervous system sympathetic stimulation causes renin secretion Goldblatt et al (1934) in dog Also been induced in rat, rabbit and monkey

15. ACE RAAS and Goldblatt Hypertension 2K2C

16. Advantages of Goldblatt method over genetic models : can start the hypertension process at the investigator's convenience animal costs lower can produce gradations in hypertension by adjusting clip size.

17. Dietary hypertension Higher salt intake is associated with high prevalance of hypertension Chronic ingestion of excess of salt produce hypertension in rats,rabbit and chicks by replacing drinking water with 1-2% sodium chloride for 9-12 months Accelerated HT can produced if with unilateral nephrectomy in dogs, in rats after 1kidney1ligature done (HT within 3-4wks)

18. Endocrine hypertension Mineralocorticoids causes retension of salt and water and produces hypertension Selve et al first demonstrated that deoxycorticosterone acetate (DOCA) produces hypertension in rats Rats especially female and young more prone Can also produced in dogs and pigs Also possible with other mineralocorticoids e.g.,aldosterone and glucocorticoids

19. DOCA induced HT is salt dependent Method 1: rats wt.100g kept on diet high in NaCl and drinking water replaced by 2% NaCl ad libitum. After attaining wt 250g given DOCA dissolved in sesame seed oil (10mg/kg) twice wkly for 43 days Method 2: unilateral nephrectomy is performed. After a wk DOCA is given dissolved in cotton seed oil (25mg/kg/wk) s.c. for 5wks

20. Psychogenic hypertension Stress plays important part in development of human HT Repeated stressful stimuli e.g.,emotional, pschosocial, immobilisation and electrical leads to persistent HT Borderline hypertensive rats(BHR) are useful BHRs exposed to daily sessions of either short (20 min) or long (120min) air-jet stimulation develops HT within 2 wks

21. Genetic hypertension Spontaneous hypertensive rats (SHR) : Okamoto and Aoki introduced first time in 1963 No need of physiological, pharmacololgical or surgical intervention Produced by inbreeding Six genes determine HT in these animals BP elevates max. after 12wks of age During early phase, HT due to central sympathetic outflow Later phase due to tpr and cop, gfr. Therefore more resemblance to the essential HT Develops typical complications of HT Useful to study pathogenesis, therapy and prophylaxis in essential HT and its complications

22. SHR Six different strains of SHRs - Japanese strain - New Zeland strain of Smirk - Milan strain - Dahl strain - Sabra strain (Israel) - Lyon strain (France) Variants of SHRs: - stroke prone SHRs (80% develops spontaneous CVA) - obese SHRs - anterolipidosis prone SHRs

23. Experimental models of spontaneous HT also developed in rabbit and dogs Rats are mainly used since small size, lower cost and short life span

24. Other models Obesity related HT: Wistar fatty rats (WFR)- persitent hyperinsulinemia and HT after 16 wks of age Angiotesin-II induced HT: s.c. infusion 0.7mg/kg/day develops HT in 4-8 wks Cadmium induced HT: Cd ion may mimic Ca ion and produce vascular smooth muscle contracion 1mg/kg/day i.p. for 2wks

25. Chronic nitric oxide inhibition induced HT: - SHRs given nonselective nitric oxide synthetase inhibitor, N ω -nitro-L- argininemethyl ester (L-NAME) for 4 wks - develops time and dose dependent HT Transgenic rat (TGR): - transgenic rats expressing candidate gene for HT - TGR(mREN2)27 – introduction of murine REN2, renin gene into germline of rats develops hypertesion with overexpession of renin

26. Uterine ischemia: - preeclampsia can be induced in rats and monkeys - in monkey at 116 ± 7days of gestation, lower aortic pressure reduced by 24 ± 11mmHg by stricture on the aorta just below the renal arteries , develops sustained HT

27. Comparison of animal models with human hypertension Experimental HT Clinical HT Spontaneous HT Essential HT Renal a.stenosis HT Renal a. stenosis Overdosage of glucocorticoids Cushings syndrome Overdosage of mineralocorticoids Primary hyperaldosteronism Overdosage of salt Chronic high salt intake Obesity related hypertension Obese hypertension Uterine ischemia Preeclampsia Reduced renal mass Renal disease

28. Effect of antihypertensive drugs New drug studied in more than one model More than one species Fixed dose schedule Interval monitoring of BP Drug given after development of HT

29. Antihypertensive drugs according to their mode of action affect only certain type of experimental hypertension Diuretics : - Endocrine HT preferred model - mineralocortiocoid and salt induced HT - ineffective in renovascular HT

30. β blockers : - SHR in late stage - not useful in endocrine and renal HT ACE inhibitors, ARBs and renin blockers : - highly effective in renovascular HT - effective in salt induced HT in reduced renal mass and TGR(mREN2)27 - negligible effect in DOCA-salt HT rat, low renin models - decreases complications in SHR - effective in the initial phase of 2K1C,1K1C - in 5/6 nephroctemised SHR

31. Vasodilators (minoxidil, hydralazine, diazoxide) : - Renal hypertensive rats Calcium channel blockers : - in 5/6 nephroctemised SHR, also reduces injury α blockers, α methyldopa, guanethedine, clonidine : - Endocrine HT - Neurogenic HT

32. Clinical evaluation of anti-hypertensive drugs Phase I Phase II Phase III Phase IV

33. Phase I and phase II Phase I: Study population: healthy volunteers Gender Age Race Drugs : alcolhol,smoking, caffine marijuhana, OTC drugs (sympathomimetics,NSAIDS)

34. Safety consideration: Adequate sample size Recording of - hemodynamic changes (postural hypotension, HR,vasodilatation , fluid retention) - ECG changes - Subjective changes like mood,alertness (using VAS) - renal or heart failure - CNS effects - Sexual dysfunctions - changes in the serum lipid, glucose, electolytes

35. General trial design Diet : food and bioavailibility, salt intake First into man studies: - starting dose - single dose - BP, HR, continuous ECG monitoring, COP and pvr measurement Ascending dose – single dose studies (1x, 3x, 10x, 30x) Ascending multiple dose studies Both placebo controlled studies Phase I : objective is to find the safe dose range

36. Dose range relationship By end of phase II : min effective dose and max. tolerated dose of drug calculated Dose ranging trials : models - classic parallel group, fixed dose design - parallel group, forced titration - parallel group, optional titration - Randomized cross over

37. P/K issues: - Phase I main objective to get P/K data - oral and i.v. dosing: propranolol P/D issues: - phase I objective is to establish hemodynamic reponse and in-vitro effects observed in pre-clinical studies - Principal concern : an adequate blood pressure control late in the dose interval, without an excessive fall in blood pressure at peak - trough: peak ratio: 50-60%

38. Hemodynamic studies: measurement of BP - supine or sitting (efficacy) - erect and supine ( saftey ) COP, tpr , ECG Arterial or venous selectivity of drug- large artery pulse wave

39. Patient studies : selection criteria randomised according to severity of HT and presence or absence of LV hypertrophy secondary HT cause excluded parallel group design more commonly used

40. Surrogate marker for cardiovascular morbidity and mortility : BP reduction Dose ranging studies: primary end point decrease in DBP and SBP

41. Phase III Conformation of efficacy in larger population Exclusion criteria little relaxed Elderly and different ethnic groups included Placebo controlled primary efficacy outcome measure was the proportion of subjects with SeDBP < 90 mmHg Safety measurements included the frequency of treatment discontinuations due to adverse events (AEs), the frequencies of hypotension,etc

42. Phase IV Post marketing surveillance For marketing purpose For potential new use For ADR monitoring

43. Thank You!