Another type of drug that's had some attention in DMD is the calcium blocker. In muscles lacking dystrophin, the membrane of the muscle fiber (cell) becomes permeable; that is, it lets in things it normally wouldn't let in and leaks out things it normally would keep inside.
Calcium, always present in the fluid surrounding cells, can be a deadly substance if it gets into the cell in an unregulated manner. That's why many types of cells, including muscle cells, have special "gates" for calcium. These are known as calcium channels, and they open and close to regulate the flow of calcium from the outside to the inside of the cells.
There are drugs that can block these calcium channels, and some have been tried in DMD. Unfortunately, calcium is probably leaking into the muscle fibers of boys with DMD because there are tears in the membrane, so blocking the calcium channels may be like sticking a finger in a dike that has arm-size holes in it.
Some names of calcium channel blocking drugs are verapramil (Calan, Isoptin), diltiazem (Cardizem) and nifedipine (Adalat, Procardia). The antibiotic gentamicin (Garamycin, Jenamicin), which also blocks calcium channels, has been recently tried and found not effective in a pilot study.
Dantrolene (Dantrium) is another type of calcium-blocking drug. Instead of blocking calcium channels on the outside of the cell, it blocks the release of calcium from storage areas inside the cell. Although useful in other disorders, dantrolene hasn't been found helpful in DMD.
Do not stop your child from taking in calcium, in the form of milk or any other dietary product or supplement. In fact, if he's taking prednisone, calcium supplements may be prescribed for him. The calcium taken in orally doesn't change the concentration of calcium in the blood or the fluid surrounding cells (related to the blood calcium level). These concentrations are tightly regulated by the body so that they remain constant under all conditions. If a person doesn't take in enough calcium, the body will take it from the bones to bring the blood calcium level back to normal. This leaching of bone-stored calcium can lead to osteoporosis and fractures.
