The entirety of the plant contains alkaloids and phytochemicals including lycorine, galanthamine, tazzetine, hippeastrine and haemanthamine. These toxins are very poisonous to cats, can cause gastrointestinal upset and, in extreme cases, disrupt the central nervous system. The alkaloids affect protein synthesis, which is how cells in the body produce their various needed proteins. If this process is inhibited, serious health results may follow. 

Ridderstjerne, or Hippeastrum spp as it is scientifically known, is a member of the Amaryllidaceae family of plants. It also may be called amaryllis, lily of the palace, fire lily or Barbados lily. Ridderstjerne is native to South America, but can be grown outdoors in many United States regions that do not get a deep frost. It is a perennial that grows from a bulb. Leaves that are up to two feet in length emerge from the bulb; glossy, long and pointed in shape. The flowers of the ridderstjerne grow at the top of a large stem. They are of impressive size and come in an array of colors including oranges, reds, whites, pinks, yellows or combinations of said colors. The blooms are trumpet-shaped and have long stamens and pistils.

The most common symptoms from ridderstjerne ingestion are related to the digestive tract. Severe symptoms involving the central nervous system may manifest in extreme cases and should be treated as a medical emergency. All signs to watch for include:

This plant may be found growing outdoors in gardens or indoors in pots. It is very popular due to the colossal group of flowers that bloom at the top of stems up to two feet in height. While the whole plant is toxic, the bulb contains the most alkaloids. A large amount of plant material would need to be eaten for dangerous results to occur, which is unlikely due to the immediate upset that ridderstjerne ingestion causes.

If you witness your cat eating a ridderstjerne, or there is obvious damage to the plant, monitor the animal and take it to a veterinarian at the first signs of upset in the body. You may be asked to provide the cat's medical history to further assist the vet in determining the best treatment for the animal. During this initial interaction, you may also be asked if you allow your cat outdoors and what plants you keep both in and around your home. 

The vet will then perform a complete physical examination of the cat. During this exam, all vital functions will be measured including the cat's temperature and blood pressure. While listening to the cat's heartbeat, the vet may note abnormalities in the rhythm of the heart. A sample of the cat's blood will be drawn so that routine testing can be performed. This usually involves a complete blood count and a biochemical profile, which are used to measure levels within the bloodstream. Urinalysis may also be needed to get a better idea how the internal organs are functioning.

There is no specific antidote to treat ridderstjerne poisoning in cats. Because of this, treatment generally revolves around easing symptoms and supporting the cat's vital organ function.

Pumping the cat's stomach can help by removing all remaining plant material before it has been digested. This is only done in severe cases of poisoning.

The vet may choose to administer activated charcoal if only a short time has passed since the plant was consumed. 

If the cat has become dehydrated from a lengthened period of vomiting, intravenous fluids and electrolytes may be supplemented. The cat's blood pressure and liver function should be monitored throughout the episode. 

Most cats make a full recovery from ridderstjerne poisoning, as it is rare for large amounts of the plant to be eaten due to its bad taste. As long as the liver remained functional throughout the illness, no lasting health effects should remain after recovery.

If you keep ridderstjerne in your home, be sure to keep it in a place that is far out of your cat's reach. Some may chose not to keep this plant indoors to be on the safe side. Removing this plant for your garden may prevent outdoor cats from sampling it. The only way to fully protect your cat is by keeping it indoors where you can monitor which plants it can access. Some owners have found the getting a cat its own safe plant to nibble on helps deter it from trying other houseplants.