Saw this on a Times blog (for health professionals)

[kemzero]

Toxoplasmosis is normally treated using a combination of pyrimethamine and sulfadiazine, neither of which are common stock in community pharmacy. Patients are also given folinic acid, to reduce the side effects of the treatment. I also had someone on the phone from the hospital pharmacy department a few days later wanting to check whether the prescription was for folic acid. I seriously hope it was a technician and not a pharmacist, but don't hospitals have copies of Martindale?


Any comments?

[Steve G]

Re: Saw this on a Times blog (for health professionals)

Martindale has some clear information on treatment of toxoplasmosis and explicitly states that folinic acid should be given. I'd expect a hospital pharmacist from a hospital with a large opthalmology department to know that.

Folic acid is composed of pteridine, PABA and glutamic acid. After folic acid is synthesised it must be reduced firstly to dihydrofolate and then to tetrahydrofolate. Both of these steps are catalysed by dihydrofolate reducatase. Folic acid, in the form of tetrahydrofolate is essential for DNA synthesis.

Sulphadiazine competes with PABA in the synthesis of folic acid, and pyrimethamine inhibits DHFR. The two drugs therefore work on the same pathway and are synergistic. Now although these drugs are selective for protozoans, they are not specific and so the patient suffers some side effects from lack of folic acid.

Folates are absorbed unchanged from the intestine and taken up into the liver and bone marrow by active transport. There are separate mechanisms for uptake of folic acid and reduced folates. Reduced folates are taken up more readily than folic acid, and folinic acid is a synthetic tetrahydrofolic acid. Folinic acid is therefore used as it is taken up more rapidly than folic acid and so is more effective at relieving side effects. This also explains why folinic acid is used following high dose methotrexate therapy and not folic acid.

[Steve G]

Re: Saw this on a Times blog (for health professionals)

and have you got a link?

[johnep]

Re: Saw this on a Times blog (for health professionals)

Never seen a script for folinic acid in 60 years-- or have we been giving folic acid in error?
johnep

[Linnear]

Re: Saw this on a Times blog (for health professionals)

More likely that the Rxs were written as folic acid in error.

[Steve G]

Re: Saw this on a Times blog (for health professionals)

Folinic acid is used in conjunction with high dose methotrexate therapy for cancer. Folic acid is used with the low dose RA patients we see regularly in the community.