A significant series of inadvertent intrathecal vincristine administration occurred in China in 2007 when batches of cytarabine and methotrexate (both often used intrathecally) manufactured by the company Shanghai Hualian were found to be contaminated with vincristine.The overuse of vincristine may also lead to drug resistance by overexpression of the p-glycoprotein pump (Pgp). There is an attempt to overcome resistance by the addition of derivatives and substituents to the vincristine molecule. Mechanism of action
Vincristine works partly by binding to the tubulin protein, stopping the tubulin dimers from polymerizing to form microtubules, causing the cell to be unable to separate its chromosomes during the metaphase. The cell then undergoes apoptosis. The vincristine molecule inhibits leukocyte production and maturation. A downside, however, to Vincristine is that it does not only affect the division of cancer cells. It affects all rapidly dividing cell types, making it necessary for the very specific administration of the drug. Pharmacology
The natural extraction of vincristine from Catharanthus roseus is produced at a percent yield of less than 0.0003%. For this reason, alternate methods to produce synthetic vincristine are being used. Vincristine is created through the semi-synthesis coupling of indole alkaloids vindoline and catharanthine in the vinca plant. It can also now be synthesized through a stereocontrolled total synthesis technique which retains the correct stereochemistry at C18 and C2. The absolute stereochemistry at these carbons is responsible for vincristines anticancer activity.The liposome encapsulation of vincristine enhances the efficacy of the vincristine drug while simultaneously decreasing the neurotoxicity associated with it.
The latter technique has proved to be less deleterious for the embryo, therefore it is advisable to perform the biopsy around day 5 or 6 of development. Sex selection is the attempt to control the sex of offspring to achieve a desired sex in case of X chromosome linked diseases. It can be accomplished in several ways, both pre- and post-implantation of an embryo, as well as at birth. Pre-implantation techniques include PGD, but also sperm sorting. Others
Other assisted reproduction techniques include:

Mitochondrial replacement therapy (MRT, sometimes called mitochondrial donation) is the replacement of mitochondria in one or more cells to prevent or ameliorate disease. MRT originated as a special form of IVF in which some or all of the future babys mitochondrial DNA comes from a third party. This technique is used in cases when mothers carry genes for mitochondrial diseases. The therapy is approved for use in the United Kingdom. In gamete intrafallopian transfer (GIFT) a mixture of sperm and eggs is placed directly into a womans fallopian tubes using laparoscopy following a transvaginal ovum retrieval. Reproductive surgery, treating e.g. fallopian tube obstruction and vas deferens obstruction, or reversing a vasectomy by a reverse vasectomy. In surgical sperm retrieval (SSR) the reproductive urologist obtains sperm from the vas deferens, epididymis or directly from the testis in a short outpatient procedure. By cryopreservation, eggs, sperm and reproductive tissue can be preserved for later IVF. Risks
The majority of IVF-conceived infants do not have birth defects.