a study on drug - drug interaction between sildenafil citrate and oral anti-diabetic drugs
M. PHARM DISSERTATION PROTOCOL
SUBMITTED TO THE
RAJIV GANDHI UNIVERSITY OF HEALTH
SCIENCES, KARNATAKA, BENGALURU
BY
AJAY PRATAP SINGH
B. Pharm.
UNDER THE GUIDANCE OF
Dr. S.V. RAJENDRA
M. Pharm., Ph.D.
P. G. DEPARTMENT OF PHARMACOLOGY
S. C. S. COLLEGE OF PHARMACY,
HARAPANAHALLI-583131
2010-11
Annexure – II
PROFORMA FOR REGISTRATION OF SUBJECTS FOR DISSERTATION
01 / Name and Address of the Candidate / AJAY PRATAP SINGHS/o. YOGENDRA SINGH
RAM GULAM TOLA W.N0.1, H.N0.486,
DEORIA (U.P.). (INDIA)
PIN: 274001.
02 / Name of the Institution / S.C.S. college of pharmacy
HARAPANAHALLI-583 131,
DAVANGERE DIST,
KARNATAKA (INDIA).
03 / Course of the Study
Branch / M. Pharm.,
Pharmacology
04 / Date of Admission to course / 27-05-2010
05 / Title of the Topic / a study on drug - drug interaction between sildenafil citrate and oral anti-diabetic drugs
06 /
Brief resume of the intended work
6.1. Need for the Study /Enclosure – I
6.2. Review of the Literature / Enclosure – II6.3. Objective of the Study
/ Enclosure – III07 /
Materials and Methods
7.1. Source of data /Enclosure – IV
7.2. Methods of collection of data
/ Enclosure – V7.3. Does the study require any
Investigations on animals?
If yes give details / Enclosure – VI
7.4. Has ethical clearance been
obtained form your institution
in case of 7.3. / Yes, Registration No: 157 / 1999/ CPCSEA
(Copies enclosed)
08 /
List of References (About 4 – 6)
/ Enclosure – VII09 /
Signature of the Candidate
/ (AJAY PRATAP SINGH)10 /
Remarks of the Guide
/ Enclosure – VIII11 /
Name and Designation of
(in Block Letters)11.1. Guide
11.2.Signature
11.3.Co-Guide (if any)
11.4.Signature
11.5. Head of the Department
11.6. Signature / Dr. S. V. RAJENDRA
M. Pharm, Ph.D.
Professor
P.G Department of Pharmacology
S.C.S. COLLEGE of Pharmacy,
Harapanahalli-583131, (Karnataka )
__
Prof. A. Veerana Gaud
M.Pharm.
Head of the dept. of pharmacology
S.C.S. COLLEGE OF PHARMACY
HARAPANAHALLI-583 131
DAVANGERE. (DIST.)
KARNATAKA
12 /
Remarks of the Principal
12.1. Signature / The intended work is related to drug-drug interaction. This study will be useful for clinicians while prescribing the thiazoliedinediones. The work is feasible & can be carried out in the dept. of Pharmacology, S.C.S college of pharmacy, Harapanahalli.Principal
ENCLOSURE-I
06. Brief resume of Intended Work
6.1 Need for the study.
There are several incidences that a patient may be suffering from more than one disease at a time and require simultaneous treatment for both the diseases. In such situations, multiple drugs have been prescribed by physicians to treat more than one disease. If more than one drug has been administered, there is every possibility of occurrence of drug interactions1. It is known that the incidence of ADR to drugs rise from 4.2% when five or fewer drugs are used to 45% when twenty or more drugs are used2. This may either enhance or diminish the effect of simultaneously administered drugs which results in useful or harmful effects on the patient. The useful drug interaction is illustrated by synergistic combination of drugs such as antibiotics or antihypertensives2. Harmful drug interactions are unfortunately more numerous2. During drug interactions, one drug may influence the efficacy of other drugs either pharmacokinetically or pharmacodynamically. Infact, pharmacokinetic drug interactions are more common than pharmacodynamic interactions. Pharmacokinetic interactions may be elicited at the time of absorption, distribution of drugs, metabolism and elimination. During metabolic interactions, one drug may influence the effect of another drug either by cytochrome P450 enzyme induction or inhibition. Inhibition of CYP enzymes increases the pharmacological activity while induction reduces the efficacy of co-administered drugs. Therefore it is essential to assess the statistical possibility of occurrence of drug-drug interactions so as to enhance the efficacy, safety and to reduce toxicity.
Erectile dysfunction (ED) is defined as the consistence or recurrent inability of a man to attain and/or maintain penile erection sufficient for sexual activity3. Erectile dysfunction is a highly prevalent health problem4. Erectile dysfunction (ED) is a common complication of diabetes and an important cause of decreased quality of life in men with diabetes. The prevalence of ED is observed in many people throughout the world5. The prevalence of diabetes mellitus is also increasing with non-insulin-dependent (type 2) accounting for 90–95% of the diagnosed diabetic patients6. Erectile dysfunction frequently represents a neurovascular complication of diabetic mellitus, and it has been calculated that almost 50% of diabetic men will have erectile dysfunction within 6 years after diagnosis7. ED in diabetic men has been associated with diabetic neuropathy, peripheral vascular disease, poor glycemic control, use of specific types of medications and increased age8.
There are many instances that a patient may be suffering with diabetes mellitus associated with erectile dysfunction. Then the patient has to be treated simultaneously with antidiabetic drugs and sildenafil citrate. In the current study, it is planned to observe the influence of sildenafil citrate [a selective inhibitor of cyclic guanosine monophosphate (cGMP) - specific phosphodiesterase type 5 (PDE5)] 9, more commonly prescribed drug in erectile dysfunction on the commonly used antidiabetic drugs like pioglitazone and rosiglitazone (thiazoliedinedione class). Since, sildenafil citrate is known to inhibit multiple cytochrome P-450 enzyme system; there is a possibility of occurrence of pharmacokinetic type of drug interactions with concomitantly used antidiabetic drugs like pioglitazone and rosiglitazone. The study drugs (thiazoliedinedione like pioglitazone and rosiglitazone) are metabolized by cytochrome P-450 enzyme system, while sildenafil citrate is an inhibitor of cytochrome P-450 enzymes. When such combinations are being employed, there may be occurrence of drug interactions between them. Further, maintenance of blood glucose levels is very much required in diabetic patients. The interaction could result in severe hypoglycemia or there may be reduction in the effectiveness of the one or either of the administered drugs. Since there are no reports of drug interactions between the study drugs, it is planned to undertake the influence of sildenafil citrate on the hypoglycemic activity of some selected thiazoliedinedione like pioglitazone and rosiglitazone in various experimental models. Further the outcome may be useful to the physician to adjust the dose and frequency of administration of thiazoliedinediones when concurrently administered with sildenafil citrate. Hence the study is needed and the work is justifiable.
ENCLOSURE-II
6.2 Review of literature:
Sildenafil citrate is a popular drug in the treatment of erectile dysfunction and is a selective inhibitor of cyclic guanosine monophosphate (cGMP) - specific phosphodiesterase type 5 (PDE5)9. It is approved for the treatment of erectile dysfunction10, pulmonary arterial hypertension (PAH)11, useful for the prevention and treatment of high-altitude pulmonary edema associated with altitude sickness (such as that suffered by mountain climbers)12, 13. Sildenafil is also a weak inhibitor of CYP enzymes such as CYP 3A4, 2C9, 2C19, 1A2, 2D6 and 2E114. ED in diabetic patients is principally related to organic causes such as vasculogenic and neurogenic abnormalities15.
Antidiabetic drugs like rosiglitazone is a substrate for the CYP2C8 and to a lesser extent CYP2C9 pathways, and pioglitazone is a substrate for CYP2C8 (39%) and CYP3A4 (17%), as well as several other CYP450 pathways17, 18. Rosiglitazone and pioglitazone metabolism in vivo may be affected by inhibitors or inducers of CYP2C9 and CYP3A4, but no significant drug-drug interactions have been reported with sildenafil citrate which weakly inhibits the cytochrome P-450 isoenzyme CYP 3A4 and CYP 2C9 which is involved in the metabolism of pioglitazone17,18,25 and rosiglitazone17,18. There are reports that sildenafil citrate can interact with drugs such as atazanavir, indinavir, saquinavir, and ritonavir etc16. Sildenafil also interacts with azole antifungals, erythromycin, cimetidine (causes symptomatic hypotension) 22, grapefruit juice, rifampicin23, adrenergic blockers like doxazocin24. But there are no reports of drug interactions between sildenafil citrate and oral antidiabetic agents such as pioglitazone and rosiglitazone. Further sildenafil citrate is a weak inhibitor of many CYP enzymes which are involved in the metabolism of thiazoliedinediones under study14, 17, 18, 25. Therefore the present study is planned to investigate the influence of sildenafil citrate on the hypoglycemic effect of some selected thiazoliedinedione like pioglitazone and rosiglitazone in normal as well as diabetic animals.
.
ENCLOSURE – III
6.3 Objectives of the study:
Since there are several reports that sildenafil citrate interfere with cytochrome P-450 enzyme system and there by alter the pharmacokinetics of various drugs that are metabolized by this enzyme system when they are used concomitantly. Even sildenafil citrate is likely to alter the pharmacokinetic properties of orally administered anti-diabetic agents like pioglitazone and rosiglitazone. Hence, the present study is planned with the following objectives.
01. To study the influence of repeated administration of sildenafil citrate per se on the blood glucose levels in experimental animals.(rats and rabbits)
02. To study the influence of single and multiple doses of sildenafil citrate on the hypoglycemic activity of pioglitazone and rosiglitazone in experimental animals. (rats and rabbits)
03. To study the influence of single and multiple doses of sildenafil citrate on the anti-diabetic activity of pioglitazone and rosiglitazone in the experimentally induced diabetes in rats (alloxan induced diabetic rats).
04. It is also planned to investigate the effects of sildenafil citrate on the insulin levels in experimental animals
05. To suggest the alteration in the dose and frequency of administration of hypoglycemic agents like pioglitazone and rosiglitazone when they are used along with sildenafil citrate.
ENCLOSURE – IV
7. Material & methods
7.1 Source of data
This study is planned to generate data by conducting laboratory-based research in animals. It is also planned to use rats, rabbits and diabetic rats in the experiments. Estimation of blood glucose levels at a regular interval after the administration of hypoglycemic agents to normal/diabetic animals with or without pre treatment of sildenafil citrate is important criteria for generating required data. This study is also intended to generate data by using certain pharmacological tools. In addition it is also planned to take some data from the available literature.
ENCLOSURE – V
7.2 Method of collection of data:
The whole study is divided into three phases to generate data. Following are the four phases.
Phase-I: It is planned to study the influence of sildenafil citrate per se on the blood glucose levels in rats, rabbits and alloxan induced diabetic rats. It is also planned to investigate the effect of single and multiple doses of sildenafil citrate on the hypoglycemic activity of anti-diabetic drugs (pioglitazone and rosiglitazone) in normal albino rats.
Phase II: In this phase, the experiments of previous phase will be repeated in the normal albino rabbits (It is mandatory to establish drug interactions in two dissimilar species). Further, there are reports that the carnivorous animals (rats) and herbivorous animals (rabbits) responds differentially to insulin variations, i.e. rats are more sensitive to insulin lack than rabbits19. In the present study, there is a possibility of occurrence of insulin variations during interaction. Therefore in the II phase of study, rabbits have been selected.
Phase III: In this phase, it is planned to estimate the insulin concentrations in experimental animals before and after pretreatment with sildenafil citrate.
Phase IV: In this phase, diabetic rats (alloxan induced diabetic rats) will be used to study the possible drug-drug interaction of sildenafil citrate and oral anti-diabetic drugs (pioglitazone and rosiglitazone) when they are used concomitantly in the patho-physiological conditions.
I) Study Subjects and groups: Normal rats, normal rabbits and alloxan induced diabetic rats will be used. Six rats and rabbits will be used in each group. Groups are made for single/ multiple dose/doses study in various experimental animals.
For single dose study: Sildenafil citrate is given one hour prior to thiazoliedinediones and then the blood samples will be collected at frequent intervals on the same day.
Doses are converted to animals doses from human doses.
Human doses for sildenafil citrate are 25mg and 100 mg. Then the two lower and higher subsequent doses in animals will be 2.5mg/kg and 10 mg/kg.
For multiple dose study: Sildenafil citrate is administered for 7 consecutive days and on 8th day, one hour after sildenafil citrate, thiazoliedinediones are administered and the blood samples will be collected. However, same doses of sildenafil citrate are considered for the current investigation.
II) Inclusion criteria:
Normal rats: Albino Wistar rats of either sex, weight range 200-250 G.
Normal rabbits: Albino rabbits of either sex, weight range 1.5-2.0 kg.
Diabetic rats: Alloxan induced diabetic rats of either sex; weigh between 200-250G. The diabetic rates with more than 200 mg/dl of blood glucose levels will be selected for study.
Exclusion Criteria: Any animal which do not comply with the above criteria are excluded from the study.
III) Study sampling & design:
A. Estimation of plasma glucose- GOD-POD method20.
It is one such evolved method by Trinder in 1969. This method is simple, single, stepped, rapid & reliable and there is precision. Hence, this method is adopted in the present investigation. Trinders method (1969) utilizes two enzymes glucose oxidase (GOD) and peroxidase (POD) along with the chromogen L-amino antipyrine and phenol. This method is for in vitro quantitative determination of glucose in serum / plasma or cerebrospinal fluid. Hemoglobin or bilirubin upon 10 mg % does not affect the test.
Principle
Glucose is determined after enzymatic oxidation in the presence of oxidase. The hydrogen peroxide so formed reacts under catalysis of peroxidase with phenol and 4-amino antipyrine (4 AAP) to form red colored quinoneimine compound that is measured at 505nm and the intensity is directly proportional to glucose concentration.
Glucose + O2 + H2O GOD Gluconic acid + H2O2
H2O2 + 4AAP + Phenol POD Red quinoneimine complex + H2O