Mareena Silva was six weeks pregnant when a pharmacist gave her a powerful abortion drug that can cause miscarriages and birth defects, instead of the antibiotic her doctor had prescribed.
Now, nearly a week later, the 19-year-old from Ft. Lupton, Colo., may lose her baby because of the mistake.
"I am kind of overwhelmed now," said Silva, who only just learned she was pregnant. "I don't feel like talking to anyone."
"I am so worried about myself and the baby right now," she said, crying in an interview with ABCNews.com. "They [the media] haven't stopped coming to my house."
The drug, methotrexate, is used for chemotherapy and has "very serious side effects," and "may harm the fetus," according to the National Center for Biotechnology. It is sometimes used for early-stage pregnancy termination.
"It couldn't be a worse mix up than that," said Dr. Paul Doering, professor emeritus of pharmacology at the College of Pharmacy University of Florida. "There is no excuse for them. I can't think of anything worse."
Silva went to the pharmacy because she had a bacterial infection. But when she got home, she realized there was a different name on the label.
"I just took one," she said. "But it was so much more of a big deal because I am only six weeks along and it's a very delicate time in pregnancy."
She said the pharmacist knew she was pregnant when he gave her the methotrexate. "He just asked me my name and stuff," said Silva. "The names were real similar."
"He helped my pick out my prenatal vitamins and even told me congratulations," she said. "I had just barely found out I was pregnant on the second [of February]."
Doering, who did his master's thesis on the drug, said methotrexate is the "poster child for why certain medicines shouldn't be used in pregnancy. It's such a well-known and potent cause of birth defects."
In some instances taking the drug during pregnancy warrants termination, according to Doering.
"There are downsides to that and risks," he said. "But if it were my wife or daughter, I would recommend it."
Mix-ups like this are rare, but when they happen, they can be fatal.
Some studies have shown more than 26 to 30 deaths in recent years due to methotrexate dosage errors, according to Mike Cohen, president of the Institute for Safe Medicine Practice, which operates the national medication reporting program.
"There is no question, we've have problems with that drug," said Cohen. "Unfortunately, people do have serious reactions to it and it can be fatal."
Methotrexate, which is also used to treat psoriasis and rheumatoid arthritis, is a dangerous drug, generally to be taken only once week. Antibiotics are given several times a day.
"Doctors accidentally misprescribed or the pharmacists typed in one tablet daily," said Cohen. "It's given once a week or twice a week at most."
The prescription was filled at the Ft. Lupton Safeway and was intended for a 59-year-old woman with the same last name and a similar first name. Safeway apologized for the mix-up, but now Silva's pregnancy may be at risk.
Doctors say that because Silva was so early in her pregnancy, the fetus is the most vulnerable.
"This is my first child, so it's really difficult to deal with," said the expectant mother.
Silva, said she began to feel nauseated after taking the pill.
"My doctor immediately told me to try and make myself vomit to see if I could get the medicine to come back up," she said. She was then rushed to Platte Valley Medical Center where she was administered charcoal to absorb the methotrexate.
"For all this to happen now is really overwhelming, to know that I have to come home and wait," said Silva.
It's hard to know how often pharmacies mix up drugs, according to Dr. Alasdair Conn, chief of emergency services at Massachusetts General Hospital.
"The inquiry has not yet been performed but I would not expect a member of the public to question a prescription that has been filled and is labeled 'amoxicillin,' for example," he said. "The patient would have to look at the pills and use a picture dictionary to make sure that the pills are truly amoxicillin-- all tablets and pills have identifiers on them. But I think it is a stretch for anyone to check up in a filled prescription."
Pharmacy mistakes do happen. In 2008, Terry Paul Smith, a 46-year-old roofing contractor, was given the wrong dosage instructions for a painkiller by a Jacksonville, Fla., pharmacist.
He was prescribed to take four 10-milligram tablets of methadone, twice daily. But an inexperienced pharmacist wrote the label to use it "as needed."
He died of an accidental overdose 36 hours later. The pharmacy eventually settled the family's lawsuit.
In 2007, an Atlanta woman was given the powerful antidepressant Trazadone instead of an antibiotic. A bus driver, she was so overcome by dizziness, she nearly ran off the road and had to call for a substitute driver and was hospitalized.
One person was given warfarin, a risky blood thinner, instead of a diabetes medication. Another was treated for Alzheimer's instead of getting the prescribed sleeping pills.
A report in the Atlanta Constitution indicated that about 3 percent of all prescriptions have potentially harmful errors -- the wrong medicine, the wrong dosage or the wrong directions.
In the incident last week in Colorado, Safeway admitted the prescription mistake to ABC and said they would launch a full investigation.
"When the pharmacist became aware of what happened, he worked with the patient and with her physicians to minimize any possible health consequences to the patient and her unborn child," Safeway said in a prepared statement. "We have extended our sincere apologies to the customer, and offered to pay any medical expenses incurred as a result of a prescription error.
"Safeway has pharmacy systems and processes in place to prevent this kind of occurrence," it read. "We have a well-earned reputation for reliably and safely filling prescriptions, and we will continue to work diligently to ensure our procedures and policies are being followed at each of our pharmacies."
But Silva was not happy with their response.
"Sorry's not going to cut it," she said. "I'm going to have to deal with this for a long time. My baby could have deformities. There's a lot that goes with it."
Methotrexate is a "high alert" drug, according to Cohen, and pharmacists and doctors are given a special sheet on it use and should always discuss prescriptions directly with the patient.
"Any time it is prescribed, it does warrant the pharmacist talk directly to the patient, even when the patient doesn't ask to do so," he said. "That's very critical."
Cohen just wrote an article in the Philadelphia Inquirer about checking prescriptions and questioning misspelled names.
Silva is being carefully watched by doctors, who say she could miscarry, carry to term a baby with severe birth defects or have a perfectly normal child.
The reason methtrexate works so well as a cancer and inflammatory arthritis medicine is because it attacks rapidly reproducing cells -- precisely why it is so dangerous in pregnancy.
"The effect on the baby is probably the biggest concern, because it's a drug that is used in high doses to induce abortion," said Marcel Casavant, chief of pharmacology and toxology at Nationwide Children's Hospital in Columbus, Ohio.
But even at lower doses, the drug can cause a "collection of abnormalities" to the babies exposed during pregnancy, including birth defects like throat problems, facial abnormalities and neurological problems.
Silva's unborn child had "50-50 chance" of having problems, according to Casavant. "The good news is that a lot of other women have been exposed inadvertently to the drug during pregnancy and not every baby gets a birth defect. They end up just perfectly fine."
Some of the potential abnormalities will show up on a later sonogram, but other developmental problems might not be detected until the baby is born, he said.
"The standard advice for anyone is to talk with your doctor about what your prescription is and what it is for," said Casavant. "Your pharmacist is supposed to offer counseling and it's a good idea to get it, especially if something doesn't look quite right. Double check, before you take it."
And if a patient thinks they have taken the wrong medicine, call the poison control center right away at 800-222-1222.
As for mistakes involving methotrexate during pregnancy, contact The Otis Rheumatoid Arthritis Study, which has the latest information on the drug.