Absorption, distribution, metabolism, and excretion (ADME) are important selection tools in deciding which drug candidates should be pursued for further development.It evaluates the factors that differentiate a drug from an interesting compound, including: determination of approximate lethal dose, in vivo safety pharmacology, pharmacokinetics to match an intended dosing regimen, and development of an appropriate formulation.
Pharmacokinetics has been broadly divided into two categories of study: absorption and disposition. Once a drug is administered as a dose, these processes begin simultaneously.The process of absorption can be seen as increasing the amount of a compound or dose x introduced into a system.Disposition is further subdivided into the study of the distribution, metabolism and excretion of a drug. The latter two processes are also know as elimination. Thus, pharmacokinetics is sometimes referred to as ADME.
In practice, pharmacokinetics is applied mainly to drug substances, though in principle it concerns itself with all manner of compounds residing within an organism or system, such as nutrients, metabolites, endogenous hormones, toxins, etc. So, in basic terms, while pharmacodynamics explores what a drug does to the body, pharmacokinetics explores what the body does to the drug.
Pharmacokinetic profiling including: study design and protocol development, management of in-life dosing, bioanalytical method development, sample analysis, and data analysis. The goal of these studies is to identify compounds for our clients that have desirable pharmaceutical properties and pharmacokinetic profiles. Compounds that meet these goals are most likely to be successful in supporting the intended indication, and such data assist with predicting the clinical and pre-clinical dosing regimen.
So, it plays an important role in safety evaluation of drugs. In this presentation various kinds of pharmacokinetic studies have been discussed with specific examples of the studies that should be conducted in support of safety evaluation of new drugs. The design and evaluation of toxicologic and pathologic studies in animals, as well as of safety and efficacy studies in man, should take into consideration the pharmacokinetic characteristics of drugs.
U.S. officials are notifying pharmaceutical companies about more than 1,100 generic and brand-name drugs that might have been approved or are awaiting approval based on faulty testing.
In letters sent by the U.S. Food and Drug Administration, companies are being asked to identify any pharmacokinetic studies conducted by MDS Inc. between 2000 and 2004 so that FDA officials can decide whether audits, new analyses or retesting might be required. The studies measure the level of a drug in a person's blood, and can be used to support approval of a drug.
Officials stressed, however, that individuals taking any of the drugs in question were not believed to be at any extra risk.
"Patients who use the products are not believed to be at any increased safety risk," said Joseph Famulare, deputy director of the Office of Compliance at the Center for Drug Evaluation and Research (CDER) of the FDA. "We are requesting confirmation of these analyses of bioequivalency studies simply as a precaution because of a pattern of irregularities at two MDS sites. FDA believes that all of the drugs involved continue to be safe and effective."
Famulare, who spoke at a news conference, would not reveal the names of any of the drugs, citing confidentiality issues.
The Associated Press reported that FDA officials have identified all 217 generic drugs that either have won or are seeking federal approval and that included MDS studies in their applications. For brand-name drugs, the FDA isn't sure which companies relied on testing done by MDS. As a result, the agency is notifying all brand-name drug makers that submitted the more than 900 applications received since 2000 to review their files to find out.
The FDA has been concerned with the quality of tests performed at MDS for years. The company is known as a contract company, hired by various pharmaceutical firms to conduct testing on drugs. It is one of the larger players in the field, Famulare said.
Regular on-site inspections of two MDS facilities in Canada revealed potential problems with laboratory analyses used for pharmacokinetic studies. Further inspections narrowed it down to laboratory analyses completed from 2000 to 2004 and submitted to the FDA to support generic and new drug applications.
"A number of unexpected results in tests conducted during that time period prompted concerns that all laboratory tests were accurate," Famulare said.
To date, the FDA has conducted four inspections and issued three letters to the company; the most recent was dated Aug. 31, 2006. MDS committed to a five-year retrospective audit of the time period 2000 to 2004 but that was considered inadequate, Famulare said.
"We did not receive enough assurances through that audit that all the issues we had brought up were addressed," Famulare said. "The issues involved a variety of issues, such as reporting inaccurate drug level data, not investigating unexpected values, and lack of reproducibility."
So, FDA officials have identified all of the approved generic and brand-name drugs that were submitted for approval from 2000 to the present day, and is notifying those companies about the potential for faulty testing. More than 900 brand-name drugs and 217 generic drugs were identified.
The actual number of affected drugs is likely to be much lower, however.
"It's a very broad net we're casting," said Dr. John Jenkins, director of the Office of New Drugs at CDER. "It's a very comprehensive search strategy we're taking to make sure we're touching the entire universe of potentially affected products, but it's much broader than the actual universe that included MDS studies."
Once companies have identified any studies conducted by MDS, the FDA "will determine what actions are needed," Famulare said. This may include validating the data through audits, new analyses or repeating the tests.
Companies have six months to get the information to the FDA. Drugs which are currently pending approval may take longer to be approved, said Gary Buehler, director of CDER's Office of Generic Drugs.
Potential deficiencies that were identified and reevaluated have turned out not to be problems after all, Buehler added.
In a company statement released , Stephen P. DeFalco, president and CEO of MDS Inc., said, "While we are disappointed in the time and effort that it has taken to get to this course of action, we believe that it will benefit everyone involved to have a crisp path forward to resolve this issue. We will fully support our clients with data and information from their studies to help bring this issue to a rapid and complete resolution."
The statement also noted that the company has ended its retrospective review of the tests in question, and will instead support its clients with independent audits.
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